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1

Theoretical and experimental analysis of vertical, concentric-tube ground-coupled heat exchangers

An experimental and analytical project to study the design of vertical, concentric-tube ground-coupled heat exchangers for use in heat pump applications is described. A mathematical model was developed and converted into a computer program to simulate the operation of the ground-coupled heat exchanger. The experimental apparatus consisted of a concentric configuration of two 47.2-m (155-ft) polyvinyl chloride (PVC) pipes (sealed

V. C. Mei; S. K. Fischer

1984-01-01

2

A Reference Model for Ground Coupled Heat Transfer

A recently completed extension to IEA BESTEST includes further work on tests suitable for the validation of ground coupled heat transfer modules within building energy simulation software. The model described here forms part of this work. A finite difference model was prepared and applied to ground coupled heat transfer in the environs of a building for a range of geometries

Michael Crowley

2009-01-01

3

Cooperative Heat Transfer and Ground Coupled Storage System.

National Technical Information Service (NTIS)

A cooperative heat transfer and ground coupled storage system wherein collected solar heat energy is ground stored and permitted to radiate into the adjacent ground for storage therein over an extended period of time when such heat energy is seasonally ma...

P. D. Metz

1979-01-01

4

Cooperative heat transfer and ground coupled storage system

A cooperative heat transfer and ground coupled storage system wherein collected solar heat energy is ground stored and permitted to radiate into the adjacent ground for storage therein over an extended period of time when such heat energy is seasonally maximally available. Thereafter, when said heat energy is seasonally minimally available and has propagated through the adjacent ground a substantial distance, the stored heat energy may be retrieved by a circumferentially arranged heat transfer means having a high rate of heat transfer.

Metz, Philip D. (Rocky Point, NY)

1982-01-01

5

International Energy Agency BESTEST for Ground Coupled Heat Transfer

The objective of this project is to assess the accuracy of building energy analysis tools that have incorporated detailed models for predicting ground-coupled heat transfer related to floor slab and basement constructions. An executive summary is to be found in the main report.

Joel Neymark; Ron Judkoff; Michael Crowley

2008-01-01

6

THE EFFECTIVENESS OF A GROUND-COUPLED HEATING AND COOLING SYSTEM

A municipality water reticulation R22 ground-coupled reversible heat pump, was investigated as an alternative to conventional air source systems. The investigation was conducted by developing analytical models that were used for the design of a ground-coupled reversible heat pump and a conventional, also reversible air-to-air system. The models were verified with a commercially available computer program as well as with

S. Oerder; J. P. Meyer

7

Ground-Coupled Heating-Cooling Systems in Urban Areas: How Sustainable Are They?

ERIC Educational Resources Information Center

|Ground-coupled heating-cooling systems (GCHCSs) exchange heat between the built environment and the subsurface using pipework buried in trenches or boreholes. If heat pumps in GCHCSs are powered by "green electricity," they offer genuine carbon-free heating-cooling; for this reason, there has been a surge in the technology in recent years.…

Younger, Paul L.

2008-01-01

8

A three-dimensional, finite-element, heat-transfer computer program was developed to study ground-coupled heat transfer from buildings. It was used in conjunction with the SUNREL whole-building energy simulation program to analyze ground-coupled heat transfer from buildings, and the results were compared with the simple ground-coupled heat transfer models used in whole-building energy simulation programs. The detailed model provides another method of testing

M. Deru; R. Judkoff; J. Neymark

2002-01-01

9

Analysis and field evaluation of an advanced ground-coupled heat pump system.

National Technical Information Service (NTIS)

This paper addresses the performance of a ground-coupled heat pump (GCHP) system with a water-source heat pump (WSHP) package designed expressly for such systems for a northern climate. The research objective was to minimize the life-cycle cost (LCC) of a...

V. D. Baxter M. A. Catan H. M. Hughes P. J. Hughes R. A. O'Neil

1986-01-01

10

Ground-coupled heat pumps projects Austin Independent School District

Austin Independent School District was introduced to the closed loop concept in 1985 during or after the time that Goodnight Junior High School in San Marcos geothermal heat pump system was installed. The first project was a joint effort of an equipment manufacturer, a pipe extruder, a distributor, an HVAC contractor and the school district. This was a trial for this new system. The two leading factors which contributed to the decision to go geothermal, were that the tower on the building was already at capacity and a reduced price was offered on the first installation. The school district owns every type, make, model, configuration, style and paint color of heating and cooling equipment made. They were ready for anything that would give them relief.

Cadwallader, R.A. [Loop Tech International, Huntsville, TX (United States)

1994-03-01

11

This study presents a new approach to compute the heat transfer of ground-coupled envelope quickly and correctly which is suitable for implementation into building thermal simulation software. The heat transfer process is decomposed into three processes which are controlled by ground-coupled envelope surface temperature, outdoor ground surface temperature and the temperature difference of ground-coupled envelope surfaces. The three processes are

Xiaona Xie; Yi Jiang; Jianjun Xia

2008-01-01

12

The use of serpentine earth coils in ground coupled heat pump systems

A research program at Brookhaven National Laboratory (BNL) has studied ground coupling, i.e., the use of the earth as a heat source\\/sink or storage medium for solar-assisted and stand-alone heat pump systems. As part of this research program, five serpentine earth coil experiments were operated between December 1978 and September 1981. Heat was added to or removed from the earth

P. D. Metz

1984-01-01

13

Second generation ground coupled solar assisted heat pump systems. Six month progress report

Progress is reported on an investigation of the technical and commercial viability of a novel ground coupled, solar assisted heat pump system for residential space heating and cooling applications. Specific areas of study are solar collector/heat rejector performance, flat plate earth heat exchanger performance, system performance simulations, and commercialization and marketing analysis. Collector/rejector performance, determined by various thermal experiments, is discussed. The design and construction of an experimental site to study ground coupling is discussed. Theoretical analysis is also presented. The performance of the GCSAHP system and conventional alternatives, as determined by simple computer models, is presented and discussed. Finally, the commercial viability of this unique space conditioning system is examined.

Rhodes, G W; Backlund, J C; Helm, J M

1981-01-01

14

A three-dimensional, finite-element, heat-transfer computer program was developed to study ground-coupled heat transfer from buildings. It was used in conjunction with the SUNREL whole-building energy simulation program to analyze ground-coupled heat transfer from buildings, and the results were compared with the simple ground-coupled heat transfer models used in whole-building energy simulation programs. The detailed model provides another method of testing and refining the simple models and analyzing complex problems. This work is part of an effort to improve the analysis of the ground-coupled heat transfer in building energy simulation programs. The output from this detailed model and several others will form a set of reference results for use with the BESTEST diagnostic procedure. We anticipate that the results from the work will be incorporated into ANSI/ASHRAE 140-2001, Standard Method of Test for the Evaluation of Building Energy Analysis Computer Programs.

Deru, M.; Judkoff, R.; Neymark, J.

2002-08-01

15

Performance and costs of a roof-sized PV\\/thermal array combined with a ground coupled heat pump

A photovoltaic\\/thermal (PVT) panel is a combination of photovoltaic cells with a solar thermal collector, generating solar electricity and solar heat simultaneously. Hence, PVT panels are an alternative for a combination of separate PV panels and solar thermal collectors. A promising system concept, consisting of 25m2 of PVT panels and a ground coupled heat pump, has been simulated in TRNSYS.

M. Bakker; H. A. Zondag; M. J. Elswijk; K. J. Strootman; M. J. M. Jong

2005-01-01

16

NASA Astrophysics Data System (ADS)

Ground coupling (the use of the Earth as a heat source sink or storage element) for solar assisted heat pump systems was studied. Four buried tank experiments were operated between December, 1978 and March 1981 in order to determine the feasibility of ground coupled tanks in these systems. Heat was added to or removed from the tanks according to a weekly schedule derived from computer simulations of solar heat pump systems in the local (New York) climate. Each tank was operated according to a different control strategy. Experimental results from these tank experiments for this period are presented and these results are compared to those generated by a computer model. The model is found to be valid, for the most part, using undisturbed soil thermal properties which provide the best fit to the data most of the time. Its results are very sensitive to soil thermal conductivity during periods of large heat addition to the tanks. A ground coupled tank is found to be desirable in series solar assisted heat pump systems. However, no important carry over of summer collected heat to winter was observed.

Metz, P. D.

1982-02-01

17

This study establishes the ranges of values of thermal conductivity and thermal diffusivity of the various soils and rocks in the United States and provides this information in a form that can be used in the design of ground-coupled heat pump systems. It presents a simple classification system for use in the identification of soils and rocks by persons not trained in soil mechanics or petrology. This technical document is given practical application in a companion field manual for the identification and classification of thermal conductivity of the various soils and rocks that can be encountered in the United States. The field manual, supported by EPRI, was published by the International Ground Source Heat Pump Association. The soil study provides a correlation between thermal resistivity and moisture content. It examines temporal behavior of ambient soil moisture and influence of environmental factors on soil moisture content. It cites factors known to influence soil moisture content, and the National Soil Moisture Study, which provided ambient soil moisture data for a four- to six-year period in six states. It discusses limit states of soil moisture content (field capacity and wilting point) and use of these states to define approximate extremes of ambient soil moisture levels. It proposes a new method of normalization of soil moisture content by its limit states -- the thermal moisture index -- and investigates some of its properties. It uses a mathematical simulator of soil/water hydraulics -- the EPIC model -- to illustrate effects of soil texture, precipitation, and soil temperature on soil moisture under more controlled conditions and with greater geographic coverage than is obtainable from National Soil Moisture Study data. Results of this study demonstrate that four general soil groups can be used to determine earth-loop size (pipe length) for ground-coupled heat pump systems. 48 refs., 162 figs., 26 tabs.

Salomone, L.A.; Marlowe, J.I.

1989-08-01

18

NASA Astrophysics Data System (ADS)

An increased uptake of alternative low or non-CO2 emitting energy sources is one of the key priorities for policy makers to mitigate the effects of environmental change. Relatively little work has been undertaken on the mitigation potential of Ground Coupled Heat Pumps (GCHPs) despite the fact that a GCHP could significantly reduce CO2 emissions from heating systems. It is predicted that under climate change the most probable scenario is for UK temperatures to increase and for winter rainfall to become more abundant; the latter is likely to cause a general rise in groundwater levels. Summer rainfall may reduce considerably, while vegetation type and density may change. Furthermore, recent studies underline the likelihood of an increase in the number of heat waves. Under such a scenario, GCHPs will increasingly be used for cooling as well as heating. These factors will affect long-term performance of horizontal GCHP systems and hence their economic viability and mitigation potential during their life span ( 50 years). The seasonal temperature differences encountered in soil are harnessed by GCHPs to provide heating in the winter and cooling in the summer. The performance of a GCHP system will depend on technical factors (heat exchanger (HE) type, length, depth, and spacing of pipes), but also it will be determined to a large extent by interactions between the below-ground parts of the system and the environment (atmospheric conditions, vegetation and soil characteristics). Depending on the balance between extraction and rejection of heat from and to the ground, the soil temperature in the neighbourhood of the HE may fall or rise. The GROMIT project (GROund coupled heat pumps MITigation potential), funded by the Natural Environment Research Council (UK), is a multi-disciplinary research project, in collaboration with EarthEnergy Ltd., which aims to quantify the CO2 mitigation potential of horizontal GCHPs. It considers changing environmental conditions and combines model predictions of soil moisture content and soil temperature with measurements at different GCHP locations over the UK. The combined effect of environment dynamics and horizontal GCHP technical properties on long-term GCHP performance will be assessed using a detailed land surface model (JULES: Joint UK Land Environment Simulator, Meteorological Office, UK) with additional equations embedded describing the interaction between GCHP heat exchangers and the surrounding soil. However, a number of key soil physical processes are currently not incorporated in JULES, such as groundwater flow, which, especially in lowland areas, can have an important effect on the heat flow between soil and HE. Furthermore, the interaction between HE and soil may also cause soil vapour and moisture fluxes. These will affect soil thermal conductivity and hence heat flow between the HE and the surrounding soil, which will in turn influence system performance. The project will address these issues. We propose to drive an improved version of JULES (with equations to simulate GCHP exchange embedded), with long-term gridded (1 km) atmospheric, soil and vegetation data (reflecting current and future environmental conditions) to reliably assess the mitigation potential of GCHPs over the entire domain of the UK, where uptake of GCHPs has been low traditionally. In this way we can identify areas that are most suitable for the installation of GCHPs. Only then recommendations can be made to local and regional governments, for example, on how to improve the mitigation potential in less suitable areas by adjusting GCHP configurations or design.

García González, Raquel; Verhoef, Anne; Vidale, Pier Luigi; Gan, Guohui; Wu, Yupeng; Hughes, Andrew; Mansour, Majdi; Blyth, Eleanor; Finch, Jon; Main, Bruce

2010-05-01

19

The thermal response of an infinite line of open loop wells for ground coupled heat pump systems

Ground thermal energy storage is a means of storing thermal energy underground during the summer and utilizing it during the winter. The main use of such a technology is in the heating, ventilating and air conditioning sector where the ground provides a stable temperature reservoir for a heat pump system. Heat pumps are mechanical systems that provide heating to a

Kevin Woods; Alfonso Ortega

2011-01-01

20

National Technical Information Service (NTIS)

Results from the first year of operation of the solar ground coupling research facility at Brookhaven National Laboratory (BNL) are presented. Nine experiments which are first generation ground coupled heat transfer and storage devices for a solar source ...

P. D. Meta

1979-01-01

21

Vertical integration of thermally activated heat pumps

Many thermally activated heat pump systems are being developed along technology lines, such as, engine-driven and absorption heat pumps. Their thermal performances are temperature dependent. Based on the temperature-dependent behavior of heat pump cycle performance and the energy cascading idea, the concept of vertically integrating various thermally activated heat pump technologies to maximize resources utilization is explored. Based on a preliminary analysis, it is found that integrating a desiccant dehumidification subsystem to an engine-driven heat pump could improve its cooling performance by 36% and integrating an ejector to it could improve its cooling performance by 20%. The added advantage of an ejector-coupled engine-driven heat pump is its system simplicity which should result in equipment cost savings.

Chen, F.C.

1985-01-01

22

Thermal performance of ground-coupled desert buildings

Results of a computer simulation study of ground-coupled buildings in desert regions are presented. Using finite difference models, the computer program SPICE was used to analyze two-dimensional thermal networks when various parameters of the system were varied. The 150-m/sup 2/ building's annual performance was found to be sensitive to the fenestration amount and orientation, to the depth of soil around the building, and to the insulation amount and placement. However, varying the soil's thermal properties and berming as opposed to burying the building to the same depth had little influence on the annual performance. In order to trace the performance trends in more detail, soil isotherms and monthly heat balances were computer to compare the behavior of a high-mass above-grade building that is well-insulated to a high-mass ground-coupled structure that has only roof insulation.

Bircher, T.L.

1981-07-01

23

Conjugate forced convection–conduction heat transfer analysis of a heat generating vertical cylinder

Conjugate heat transfer by forced convection over a vertical cylinder without heat generation has been a subject of many investigations in the recent past. In the present work, the radial heat conduction along with heat generation in a vertical cylinder is considered for analysis. The steady two-dimensional conduction equation for the heat generating cylinder and steady two-dimensional laminar boundary layer

G Jilani; S Jayaraj; M Adeel Ahmad

2002-01-01

24

A computational model for determining annual periodic performance of a cooling system utilizing a ground coupled chiller and a spherical underground thermal energy storage tank is developed. An analytical solution for the transient heat transfer problem outside the storage tank is obtained by the application of complex finite Fourier transform (CFFT) technique. Analytical expressions for heat gain to the space

Recep Yumruta?; Mehmet Kano?lu; Ali Bolatturk; Mehmet ?irin Bedir

2005-01-01

25

Upflow turbulent mixed convection heat transfer in vertical pipes

The present work deals with the results of an experimental investigation on heat transfer in water cooled vertical pipes, for thermal–hydraulic conditions ranging from forced convective flow to mixed convective flow. The flow of water in the pipe is upwards.Experimental data confirm the reduction in the heat transfer rate for mixed convection in upward heat flow, mainly due to the

Gian Piero Celata; Francesco Dannibale; Andrea Chiaradia; Maurizio Cumo

1998-01-01

26

Computer simulation of ground-coupled liquid desiccant air conditioner for sub-tropical regions

Computer model for a novel ground-coupled liquid desiccant air conditioner (GCLDAC) was developed in which a liquid desiccant cycle selectively operated in parallel with a conventional ground-source heat pump cycle by employing just a single compressor. Reverse cycle operation was incorporated to provide heating in winter. Dynamic simulation was carried out for a single-zone sample building at two occupancy levels

C. K. Lee; H. N. Lam

2009-01-01

27

Study of contact melting inside isothermally heated vertical cylindrical capsules

NASA Astrophysics Data System (ADS)

Close-contact melting processes of phase change material (PCM) inside vertical cylindrical capsule are studied. PCM are heated by the capsule isothermally at the bottom and side. The theoretical formulas of the melting rate and thickness of liquid layer during the heat transfer process are obtained by analysis, which are convenient for engineering predictions. Finally, the factors that affect melting are discussed, and conclusions are drawn.

Chen, Wenzhen; Cheng, Shangmo; Luo, Zhen; Gu, Wangmin

1993-09-01

28

Forced Convection Film Boiling Heat Transfer Over a Vertical Cylinder

The knowledge of subcooled film boiling heat transfer is important as the basis of understanding the reflooding phenomenon during emergency cooling in a nuclear reactor under a loss-of-coolant accident. In this study, forced convection film boiling heat transfer from a vertical cylinder in Freon-113 flowing upward along the cylinder was measured for the flow velocities ranging from 0 to 1.3

Q. S. Liu; K. Fukuda; M. Shiotsu

2011-01-01

29

Pool boiling heat transfer in vertical annular crevices

Effects of vertical annuli on nucleate pool boiling heat transfer of water at atmospheric pressure have been obtained experimentally. Experiments were performed for annuli with a height of 570 mm and gap sizes of 3.9 and 15 mm. Through the tests, tube bottom confinement (open or closed) has been investigated, too, and the whole results are compared with a single

Myeong-Gie Kang

2002-01-01

30

Single thermal plume in locally heated vertical soap films

NASA Astrophysics Data System (ADS)

A vertical soap film is maintained by injection of a soap solution from the top. The film is then locally heated. Thermal plumes may be observed to rise in the film, depending on the magnitude of the heating and injected flows. The nearly two-dimensional nature of the system allows to visualize the motion of the plumes using an infrared camera. A model is proposed to describe the growth, emergence, and stationarity of the plumes in the film by taking into account both magnitudes of the heating ?T and injected flow Q.

Adami, N.; Dorbolo, S.; Caps, H.

2011-10-01

31

Single thermal plume in locally heated vertical soap films.

A vertical soap film is maintained by injection of a soap solution from the top. The film is then locally heated. Thermal plumes may be observed to rise in the film, depending on the magnitude of the heating and injected flows. The nearly two-dimensional nature of the system allows to visualize the motion of the plumes using an infrared camera. A model is proposed to describe the growth, emergence, and stationarity of the plumes in the film by taking into account both magnitudes of the heating ?T and injected flow Q. PMID:22181270

Adami, N; Dorbolo, S; Caps, H

2011-10-19

32

Thermal plumes in locally heated vertical soap films

NASA Astrophysics Data System (ADS)

A vertical soap film is maintained by injection of a soap solution from the top. The film is then locally heated. Thermal plumes may be observed to rise in the film, depending on the magnitude of the heating and injected flows. The nearly-2D nature of the system allows to visualize the motion of the plumes using an infrared camera. A model is proposed to describe the growth, emergence, and stationarity of the plumes in the film by taking into account both magnitudes of the heating ?T and injected flow Q. Oscillatory behaviors of both the full-grown plumes size and direction with respect to the vertical direction may also be observed. Particular soap film thickness dynamics shows to be the origin of those phenomena.

Adami, Nicolas; Dorbolo, Stéphane; Caps, Hervé.

2012-02-01

33

Pr<1 intrusion flow induced by a vertical heated wall.

A horizontal flow induced by a vertical heated wall with a low Prandtl number (e.g., Pr<1 for air and liquid metals) is common in nature and industry. In this paper, a Pr<1 intrusion flow induced by a vertical heated boundary of an open sided cavity (that is, a cavity with one heated wall and open at the other end) is investigated by a scaling analysis and direct numerical simulations. The scaling analysis of the intrusion flow reveals that there are four possible flow regimes dependent on the Rayleigh and Prandtl numbers. In a typical case, the intrusion flow could travel under different dynamical and thermal processes such as unsteady (or steady) conduction-viscous, conduction-inertial, and convection-inertial dominance. Proper scaling relations have been presented to quantify these flows under different flow regimes. Furthermore, corresponding numerical simulations have verified the scaling results. PMID:20866916

Xu, Feng; Patterson, John C; Lei, Chengwang

2010-08-26

34

Natural convection heat transfer from a thermal heat source located in a vertical plate fin

A steady state conjugate conduction–convection investigation is performed on vertical plate fin in which a small heat source is located. Heat from the fin surface is transferred to the surroundings by laminar natural convection. The governing equations for the problem are the heat conduction equation for the fin and the boundary layer equations, which are continuity, momentum and energy equations,

Moghtada Mobedi; Bengt Sunden

2006-01-01

35

Critical heat flux in uniformly heated vertical tubes

Experimental investigations on critical heat flux have been performed in circular tubes of different diameters ranging from 2 to 16 mm. The model fluid Freon-12 was used as working fluid due to its low latent heat, low critical pressure and well-known properties. About 1700 data points have been obtained in a large range of parameters: pressure 1.0–3.0 MPa, mass flux

F. G. Pang

1997-01-01

36

Heat transfer analysis of boreholes in vertical ground heat exchangers

A ground heat exchanger (GHE) is devised for extraction or injection of thermal energy from\\/into the ground. Bearing strong impact on GHE performance, the borehole thermal resistance is defined by the thermal properties of the construction materials and the arrangement of flow channels of the GHEs. Taking the fluid axial convective heat transfer and thermal “short-circuiting” among U-tube legs into

Heyi Zeng; Nairen Diao; Zhaohong Fang

2003-01-01

37

Residential water heating is an important consideration in California?s building energy efficiency standard. Explicit treatment of ground-coupled hot water piping is one of several planned improvements to the standard. The properties of water, piping, insulation, backfill materials, concrete slabs, and soil, their interactions, and their variations with temperature and over time are important considerations in the required supporting analysis. Heat

J. L. Warner; J. D. Lutz

2006-01-01

38

Melting heat transfer of liquid ice in a rectangular cavity with a heated vertical wall

The melting characteristics of liquid ice in a rectangular cavity were studied experimentally. The liquid ice, mixture of ice particles and ethylene-glycol aqueous solution, was heated from one of the vertical walls of the cavity. The shape of the mush-liquid interface, melting rate, and local/mean heat-transfer coefficient at the heated vertical wall were observed and measured under a variety of conditions of heat flux and initial concentration of the aqueous binary solution. It was found that the formation of double-diffusive layers based on the thermal and solutal buoyancy forces exerted a great influence on the melting process of the liquid ice.

Fukusako, Shoichiro; Yamada, Masahiko; Kim, Myounghwan (Hokkaido Univ. (Japan). Dept. of Mechanical Engineering)

1993-12-01

39

Heat transfer during melting around an isothermal vertical cylinder

Research on alternative energy resources has intensified during the past few decades as a consequence of the alarming increase in energy cost. Effective thermal energy storage systems have become a true necessity, especially in solar energy applications. Using the phase change of some materials in thermal energy storage systems is advantageous in various ways. For example, the heat capacity of the storage reservoir is tremendously increased (on a unit volume basis), since latent heat of fusion is involved. In addition, there are advantages as far as heat transfer from and to the reservoir is concerned. Until recently, most papers on phase change dealt exclusively with conduction heat transfer, although it has been known for some time that natural convection may play a key role during melting and freezing. Lately, however, several studies (Viskanta, 1983) considering buoyancy effects on phase-change heat transfer have been reported. The present paper reports on experimental measurements undertaken to investigate outward melting around a vertical cylinder embedded in a solid initially at its fusion temperature. The cylinder is maintained at a uniform temperature that exceeds the fusion temperature. The top and bottom of the phase-change material are adiabatic, and a small air gap provides a slip boundary condition at the top. The main objective of the research reported here was to obtain experimental data for the above mentioned configuration. It is remarkable that, although the isothermal boundary condition at the heat source has been extensively studied experimentally for melting to a vertical plate (e.g., Ho and Viskanta, 1984; Okada, 1983), there are very few experimental data available for melting to an isothermal cylinder positioned vertically.

Souza Mendes, P.R.; Pinho Brasil, A.C. Jr. (Pontificia Univ. Catolica, Rio de Janeiro (Brazil))

1987-11-01

40

Continuing efforts to achieve increased circuit performance in electronic package have resulted in higher power density at\\u000a chip and module level. As a result, the thermal management of electronic package has been important in maintaining or improving\\u000a the reliability of the component. An experimental investigation of thermosyphonic boiling in vertical tube and channel made\\u000a by two parallel rectangular plates was

Jin-Seok Jeon; Jung Hee Na; Hong Chul Park; Ho-Young Kwak

2001-01-01

41

Fluid Flow and Heat Transfer of Natural Convection around Heated Vertical Cylinders

Natural convective flows of water induced around heated vertical cylinders have been investigated experimentally. Special interests were paid to the influences of cylinder diameter on the turbulent transition and also on the local heat transfer characteristics of the cylinders. The diameters of the cylinders were varied systematically from 10 to 165mm. Visualizations of the flows around the cylinder and of

Fumiyoshi Kimura; Tatsuo Tachibana; Kenzo Kitamura; Tsutomu Hosokawa

2004-01-01

42

Retrieving Latent Heat Vertical Structure Using Precipitation and Cloud Profiles

NASA Astrophysics Data System (ADS)

The latent heat (LH) released from tropical precipitation plays a critical role in driving regional and global atmosphere circulation. However, the vertical distribution of LH is one of most difficult parameters to be measured and has a large uncertainty in both residual diagnostic products and satellite retrievals. Most of current satellite LH products use limited observational information of precipitation and cloud profiles and highly depend on cloud resolving model (CRM) simulations. Our novel approach, distinguishing from existing schemes, is directly using observable precipitation and cloud profiles in combination with phase change partition parameterization of various kinds from the CRM simulations to produce the latent heating profiles. This hybrid latent heat algorithm separately deals with the condensation-evaporation heating (LHc_e), the deposition-sublimation heating (LHd_s) and the freezing-melting heating (LHf_m) for convective rain, stratiform rain, and shallow warm rain. Each component is based on physical processes, such as nucleation and auto conversion, by combining observable precipitation and cloud profiles. Although the proposed algorithm utilizes microphysical parameterizations from a specific CRM, the general LH vertical structure is primarily determined by the precipitation and cloud profiles observable from cloud and precipitation radars available at ground sites or from satellite platforms, and less sensitive to the specific CRM. The self consistency tests of this algorithm show good agreements with the CRM simulated LH at different spatial and temporal scales, even at simultaneous and pixel level. The applications of this algorithm are expected to provide new information for understanding the heating budget in the atmosphere and its impacts on the atmosphere circulations at various spatial and temporal scales.

Li, R.; Min, Q.; Wu, X.

2011-12-01

43

Heat transfer in vertically aligned phase change energy storage systems

Convection effects on heat transfer are analyzed in low temperature and vertically aligned phase change energy storage systems. This is performed by detailed temperature measurements in the phase change material (PCM) in eighteen locations forming a grid of six radial and three axial positions. The system constitutes a double pipe configuration, where commercial grade paraffin wax is stored in the annular space between the two pipes and water flows inside the inner pipe. Vertical alignment of the system allowed for reverse of the flow direction of the heat transfer fluid (HTF), which is water. Therefore, the PCM is heated from the bottom for HTF flow from bottom to top and from the top as the HTF flow direction is reversed. For the former case, natural convection affects the melting process. Collected data are used to study variations in the transient temperature distribution at axial and radial positions as well as for the two-dimensional temperature field. The data are used to calculate the PCM heat transfer coefficient and to develop correlations for the melting Fourier number. Results indicate that the PCM heat transfer coefficient is higher for the case of PCM heating from bottom to top. Nusselt number correlations are developed as a function of Rayleigh, Stefan, and Fourier numbers for the HTF flow from bottom to top and as a function of Stefan and Fourier numbers for HTF flow from top to bottom. The enhancement ratio for heat transfer caused by natural convection increases and then levels off as the inlet temperature of the HTF is increased.

El-Dessouky, H.T.; Bouhamra, W.S.; Ettouney, H.M.; Akbar, M. [Kuwait Univ., Safat (Kuwait). Dept. of Chemical Engineering

1999-05-01

44

Convective heat transfer around vertical jet fires: an experimental study.

The convection heat transfer phenomenon in vertical jet fires was experimentally analyzed. In these experiments, turbulent propane flames were generated in subsonic as well as sonic regimes. The experimental data demonstrated that the rate of convection heat transfer increases by increasing the length of the flame. Assuming the solid flame model, the convection heat transfer coefficient was calculated. Two equations in terms of adimensional numbers were developed. It was found out that the Nusselt number attains greater values for higher values of the Rayleigh and Reynolds numbers. On the other hand, the Froude number was analyzed only for the subsonic flames where the Nusselt number grows by this number and the diameter of the orifice. PMID:21962859

Kozanoglu, Bulent; Zárate, Luis; Gómez-Mares, Mercedes; Casal, Joaquim

2011-09-21

45

Experiments were done using subcooled Freon-113 sprayed vertically downward. Local and average heat transfers were investigated fro Freon-113 sprays with 40 C subcooling, droplet sizes 200-1250{mu}m, and droplet breakup velocities 5-29 m/s. Full-cone type nozzles were used to generate the spray. Test assemblies consisted of 1 to 6 7.62 cm vertical constant heat flux surfaces parallel with each other and aligned horizontally. Distance between heated surfaces was varied from 6.35 to 76.2 mm. Steady state heat fluxes as high as 13 W/cm{sup 2} were achieved. Dependence on the surface distance from axial centerline of the spray was found. For surfaces sufficiently removed from centerline, local and average heat transfers were identical and correlated by a power relation of the form seen for normal-impact sprays which involves the Weber number, a nondimensionalized temperature difference, and a mass flux parameter. For surfaces closer to centerline, the local heat transfer depended on vertical location on the surface while the average heat transfer was described by a semi-log correlation involving the same parameters. The heat transfer was independent of the distance (gap) between the heated surfaces for the gaps investigated.

Kendall, C.M. [Lawrence Livermore National Lab., CA (United States); Holman, J.P. [Southern Methodist Univ., Dallas, TX (United States). Dept. of Mechanical Engineering

1996-06-06

46

Efficient Energy Supply from Ground Coupled Heat Transfer Source

\\u000a The increasing demands of Energy for industrial production and urban facilities, asks for new strategies for Energy sources.\\u000a In recent years an important problem is to have some energy storage, energy production and energy consumption which fulfill\\u000a some environment friendly expectations. Much more attention has been recently devoted to renewable energies [1]. Among them\\u000a energy production from geothermal sources has

Maurizio Carlini; Sonia Castellucci

2010-01-01

47

The heat transfer characteristics of the natural convection regime through a vertical rectangular channel simulating a cooling channel of typical material testing reactor have been experimentally investigated. Experiments are performed on demineralized water as coolant passing under atmospheric pressure through narrow rectangular channel of 80cm length, 7cm width and 2.7mm gap thickness under different heat fluxes ranging from 2.7kW\\/m2 to

Salah El-Din El-Morshedy; Adel Alyan; Loula Shouman

48

Experimental Study of Natural Convection from Electrically Heated Vertical Cylinders Immersed in Air

An experimental study of laminar steady-state natural convection heat transfer from electrically heated vertical cylinders immersed in air has been undertaken. Three stainless steel (316 SS) test sections of different slenderness ratios were employed. Surface temperature profiles along the vertical cylinders were obtained using miniature thermocouples when the cylinders were heated with different power levels resulting in different total wall

Sad Jarall; Antonio Campo

2005-01-01

49

National Technical Information Service (NTIS)

Experimental data are presented for turbulent mixed convection in the passages formed by vertical plates. The electrically heated plates simulated the oil-filled heat exchangers of large transformers which are to be cooled by gentle upward air flows. Each...

R. Winstanley B. P. Axcell

1989-01-01

50

The similarity solution for the problem of mixed convection boundary layer flow adjacent to a stretching vertical sheet in\\u000a an incompressible electrically conducting fluid in the presence of a transverse magnetic field is presented. It is assumed\\u000a that the sheet is stretched with a power-law velocity and is subjected to a variable surface heat flux. The governing partial\\u000a differential equations

Fazlina Aman; Anuar Ishak

2010-01-01

51

The steady state heat transfer characteristics of a thin vertical strip with internal heat generation is studied in this work. The nondimensional temperature distribution in the strip is obtained as a function of the following parameters: (a) the intensity and distribution of the internal heat sources, (b) the aspect ratio of the strip, (c) the longitudinal heat conductance of the

F Méndez; C Treviño

2000-01-01

52

AN EXPERIMENTAL STUDY OF MIXED CONVECTION HEAT TRANSFER IN VERTICAL PACKED CHANNELS

The experimental results of mixed convection heat transfer in a vertical packed channel with asymmetric heating of opposing walls are reported in this paper. The experiments were carried out in the range of 2< Pe<2200 and 700

W. L. Pu; P. Cheng; T. S. Zhao

1999-01-01

53

Numerical simulations of natural convection heat transfer along a vertical cylinder

Purpose – The purpose of this paper is to present a numerical solution for the problem of steady laminar flow and heat transfer characteristics of viscous incompressible fluid. Design\\/methodology\\/approach – For this purpose a two dimensional code has been developed to simulate the natural convection heat transfer along a vertical cylinder, for four different geometries: from vertical cylinder in infinite

Muhammad Rafique; I. Ahmad; M. Abdul Basit; Romana Begum; Wajid Aziz; Muhammad Farooq; Kamran Rasheed Qureshi

2011-01-01

54

The effects of height and radius ratio with a Newtonian fluid have been investigated numerically to determine heat transfer by natural convection between the sphere and vertical cylinder with isothermal boundary conditions. The inner sphere and outer vertical cylinder were heated and cooled in a steady change of temperature. Calculations were carried out systematically for a range of the Rayleigh

Wen Ruey Chen

2007-01-01

55

Investigation on air to ground coupled waves and other geophysical studies

NASA Astrophysics Data System (ADS)

This work describes three geophysical investigations in the Western United States. The first section is an investigation regarding the amplitude of air to ground coupled waves recorded at the Nevada Seismic Array. The waves are modeled as loads propagating with sound speed velocities, and the resulting transfer functions are compared with observations. The results are also in agreement with the current held geological information obtained from shallow refraction profiles. In the second section new heat flow values for several sites in southwest are obtained and interpreted in terms of local and regional geology. The main result is that the Ouachita tectonic front represents an important thermal boundary. A cross section over the front zone suggest heat flow values of 48 mW/m2 in the Fort Worth Basin, 61 mW/m2 exactly in the front zone and then drops to 55 in the interior zone. In addition several other problems are addressed. The third section discusses heat flow patterns in the Yellowstone Lake, and the link between heat flow and structural features. Simple conductive computations suggest average heat flow of 200 mW/m2, while average measured heat flow over the entire lake is estimated at 1200 mW/m 2. Therefore the measured heat loss must be raised by convective heat and Nusselt numbers at least 6 are obtained. The implications for the natural hazard assessment are also discussed.

Negraru, Petru Teodor

56

Inverse Heat Transfer Problems (IHTP) are characterized by estimation of unknown quantities by utilizing any given information of the system. In this study, the inverse problem of estimation of heat generation in multiple two dimensional protruding heat sources on a vertical plate, a geometry frequently encountered in the cooling of electronic equipment, is carried out from the information available on

Apurv Kumar; C. Balaji

2011-01-01

57

Prediction of critical heat flux for annular flow in vertical pipes

A semiempirical model for adiabatic two phase annular flow is extended to predict critical heat flux in a vertical pipe for conditions of interest to boiling water reactors. The model exhibits a sharply declining curve of critical heat flux versus steam quality at low steam qualities where it is relatively independent of heat flux distribution. In this region, vaporization of

S. Levy; J. M. Healzer; D. Abdollahian

1980-01-01

58

This paper presents a numerical solution of a buoyancy-induced flow and phase-change heat transfer in a vertical porous channel heated symmetrically along its vertical walls. A multiphase mixture model that accounts for complex, interacting physical phenomena such as phase change, capillary action, buoyancy-induced flow convection in the subcooled liquid and multi-dimensional effects was used. It is found that for both

T. S. Zhao; P. Cheng; C. Y. Wang

2000-01-01

59

In this paper a Computer Code COSINAC (Computer Simulation of Natural Convection from Assembly of vertical Cylinders) has been developed to simulate the natural convection heat transfer from an assembly of vertical cylinders of Pakistan Research Reactor-2 (PARR-2), under the steady state reactor operation. The momentum and energy equations in cylindrical co-ordinates, representing the thermal hydraulic behavior of a typical

M. Abdul Basit; Muhammad Rafique; Imran R. Chughtai; Mansoor H. Inayat

2007-01-01

60

Study of Natural Convection Cooling of Multiple Discrete Heat Sources in a Vertical Channel.

National Technical Information Service (NTIS)

Natural convection liquid cooling of simulated electronic components in a vertical channel was investigated. The test surface contained a single column of eight rectangular, protruding heated elements, each simulating a 20 pin dual-in-line package. Temper...

T. D. Willson

1988-01-01

61

Three-dimensional steady and oscillatory flows are simulated in a vertical cylinder partially heated from the side. The vertical wall is heated in a zone at midheight and is insulated above and below this middle zone, while both ends of the cylinder are cooled. The cylinder aspect ratio (A=height?radius) ranges from 2 to 8, whereas a fixed Prandtl number, Pr=0.021, is

D. J. Ma; D. Henry; H. Ben Hadid

2005-01-01

62

Three-dimensional steady and oscillatory flows are simulated in a vertical cylinder partially heated from the side. The vertical wall is heated in a zone at midheight and is insulated above and below this middle zone, while both ends of the cylinder are cooled. The cylinder aspect ratio (A=height\\/radius) ranges from 2 to 8, whereas a fixed Prandtl number, Pr=0.021, is

D. J. Ma; D. Henry; H. Ben Hadid

2005-01-01

63

Heat transfer during condensation in vertical closed thermosiphons

NASA Astrophysics Data System (ADS)

The results are presented of an experimental investigation of the hydrodynamic characteristics of a two-phase layer and of the heat-transfer behavior under characteristic operating conditions of the condensing section of a thermosiphon.

Bezrodnyi, M. K.; Moklyak, V. F.

1986-07-01

64

NASA Astrophysics Data System (ADS)

In the present paper it is proposed to consider the computer cooling capacity using the thermosyphon loop. A closed thermosyphon loop consists of combined two heaters and a cooler connected to each other by tubes. The first heater may be a CPU processor located on the motherboard of the personal computer. The second heater may be a chip of a graphic card placed perpendicular to the motherboard of personal computer. The cooler can be placed above the heaters on the computer chassis. The thermosyphon cooling system on the use of computer can be modeled using the rectangular thermosyphon loop with minichannels heated at the bottom horizontal side and the bottom vertical side and cooled at the upper vertical side. The riser and a downcomer connect these parts. A one-dimensional model of two-phase flow and heat transfer in a closed thermosyphon loop is based on mass, momentum, and energy balances in the evaporators, rising tube, condenser and the falling tube. The separate two-phase flow model is used in calculations. A numerical investigation for the analysis of the mass flux rate and heat transfer coefficient in the steady state has been accomplished.

Bieli?ski, Henryk; Mikielewicz, Jaros?aw

2010-10-01

65

Prediction of critical heat flux for annular flow in vertical pipes. Final report

A previously developed semi-empirical model for adiabatic two-phase annular flow (EPRI-NP-1521) is extended to predict critical heat flux in a vertical pipe for conditions of interest to boiling water reactors. The model exhibits a sharply declining curve of critical heat flux versus steam quality at low steam qualities where it is relatively independent of heat flux distribution. In this region,

S. Levy; J. M. Healzer; D. Abdollahian

1980-01-01

66

Forced convection boiling heat transfer of Freon11 in a vertical annular passage

Forced convection boiling heat transfer coefficient of Freon-11 flowing upward through a vertical annular passage was measured. Heating element was a single inconel heating rod placed in the center of a stainless steel pipe. The range of temperature difference between the rod surface and the saturation temperature of the Freon was 2.2 to 14.5Â°C, and the range of the experimental

D. H. Kihara; H. C. Chai; A. Jr. Ching

1979-01-01

67

An experimental program was conducted to study natural convection heat ; transfer in an array of uniformly heated vertical cylinders in mercury. The ; cylinders were arranged in an equilateral triangular pattern, and three bundle ; spacings, P\\/D = 1.5, 1.3, and 1.1, were studied. The heat transfer results are ; presented as local Nusselt number--modified Grashof number correlations. The

J. C. Dutton; J. R. Welty

1975-01-01

68

Instabilities and pattern evolution in a vertically heated annulus

NASA Astrophysics Data System (ADS)

The convection in an annular container with heated bottom, cooled top and insulated side walls are studied by both linear instability analysis and direct numerical simulation. The onset of convection is investigated by linear stability analysis and corresponding pattern selection mechanisms are discussed. The nonlinear evolution of different flow patterns and the convective heat transfer are simulated. The transition to oscillatory flow is also given by stability analysis where the base flow is a steady three dimensional flow. The stability predictions are in good agreement with the numerical simulations, including both the growth rate and the dimensionless frequency.

Wang, BoFu; Guo, ZhiWei; Ma, DongJun; Sun, DeJun

2013-02-01

69

Optimum fin spacing of rectangular fins on a vertical base in free convection heat transfer

The steady-state natural convection heat transfer from aluminum vertical rectangular fins extending perpendicularly from vertical\\u000a rectangular base was investigated experimentally. Thirty different fin configurations were tested. Experiments were performed\\u000a for fin lengths of 250 and 340 mm. Fin thickness was kept fixed at 3 mm. Fin height and fin spacing were varied from 5 to\\u000a 25 mm and 5.75 to 85.5 mm, respectively. Five

B. Yazicioglu; H. Yüncü

2007-01-01

70

Flow regimes and heat transfer in vertical narrow annuli

In shell side boiling heat exchangers narrow crevices that are formed between the tubes and the tube support structure provide areas for local thermal-hydraulic conditions which differ significantly from bulk fluid conditions. Understanding of the processes of boiling and dryout in flow restricted crevices can help in designing of tube support geometries to minimize the likelihood of tube support plate

A. Ulke; I. Goldberg

1993-01-01

71

Heat transfer during melting around an isothermal vertical cylinder

Research on alternative energy resources has intensified during the past few decades as a consequence of the alarming increase in energy cost. Effective thermal energy storage systems have become a true necessity, especially in solar energy applications. Using the phase change of some materials in thermal energy storage systems is advantageous in various ways. For example, the heat capacity of

P. R. Souza Mendes; A. C. Jr. Pinho Brasil

1987-01-01

72

An analytical study of critical heat flux in a vertical channel with countercurrent flow limitation

A quantitative analysis of critical heat flux (CHF) under countercurrent flow limitation (CCFL) or flooding was successfully carried out using the existing experimental results for vertical circular, rectangular, and annual channels, applying the criteria, proposed by the author, that the CCFL condition could be determined by maximizing the water mass flux falling down in the vertical channels with respect to the water film thickness and a model of dryout of water filmflow at the CHF point. It was clarified that the analytical results give good predictions of the existing experimental results of vertical channels, identifying the factors determining the CHF under CCFL conditions.

Sudo, Yukio

1995-10-01

73

Residential water heating is an important consideration in California?s building energy efficiency standard. Explicit treatment of ground-coupled hot water piping is one of several planned improvements to the standard. The properties of water, piping, insulation, backfill materials, concrete slabs, and soil, their interactions, and their variations with temperature and over time are important considerations in the required supporting analysis. Heat transfer algorithms and models devised for generalized, hot water distribution system, ground-source heat pump and ground heat exchanger, nuclear waste repository, buried oil pipeline, and underground electricity transmission cable applications can be adapted to the simulation of under-slab water piping. A numerical model that permits detailed examination of and broad variations in many inputs while employing a technique to conserve computer run time is recommended.

Warner, J.L.; Lutz, J.D.

2006-01-01

74

Pool boiling heat transfer from vertical heater array in liquid nitrogen

The heat transfer from an array of discrete sources is expected to differ from the behavior of a single heat source due to the interaction between the flow induced by individual heat sources. This study details the results from experiments conducted to study the pool boiling heat transfer characteristics from a vertical heater array with flush-mounted heat sources. The lower heaters were found to enhance the heat transfer from upper heaters. The bubble pumped convection due to the lower heaters enhanced the preboiling heat transfer coefficient at the upper heater by as much as 700%. The critical heat flux from the upper heaters was also enhanced up to 15%. Correlations are presented for both these effects. 21 refs.

Chui, C.J.; Sehmbey, M.S.; Chow, L.C.; Hahn, O.J. [Paul Laurence Dunbar High School, Lexington, KY (United States)

1995-04-01

75

This paper investigates convection heat and mass transfer flow in an electrically conducting power law fluid past a vertical porous plate in presence of a transverse magnetic field, thermal radiation, and thermal diffusion. The non–linear partial differential equations governing the flow are transformed into ordinary differential equations using the usual similarity method and the resulting similarity equations are solved numerically

B. I. Olajuwon

2010-01-01

76

NASA Astrophysics Data System (ADS)

A numerical code for solving the boundary-layer equations is used to evaluate the performance of various turbulence models for the natural convection boundary layer along a heated vertical plate. The Cebeci-Smith (1974) model yields wall-heat transfer and turbulent viscosity values that are lower than the experimental values, while the standard k-epsilon model with wall functions for k and epsilon yields high wall-heat transfer values and resonable velocity and temperature profiles. Low-Reynolds-number k-epsilon models provide accurate wall-heat transfer results.

Henkes, R. A. W. M.; Hoogendoorn, C. J.

1989-01-01

77

Natural, mixed, and forced convection in a vertical thermosiphon heated with constant flux

The development of a mixed-laminar-convective-flow region in a vertical channel is investigated analytically in the case in which the parallel plane walls of the channel are heated with constant but not necessarily equal heat-flux densities. Expressions describing the thermal and dynamical development are derived for forced convection favoring the natural convective flow, and for forced convection opposed to natural convection

F. Penot; A.-M. Dalbert

1983-01-01

78

Effect of vertical heat transfer on thermocapillary convection in an open shallow rectangular cavity

In order to understand the effect of the vertical heat transfer on thermocapillary convection characteristics in a differentially\\u000a heated open shallow rectangular cavity, a series of two- and three-dimensional numerical simulations were carried out by means\\u000a of the finite volume method. The cavity was filled with the 1cSt silicone oil (Prandtl number Pr = 13.9) and the aspect ratio ranged from 12

You-Rong Li; Hong-Ru Zhang; Chun-Mei Wu; Jin-Liang Xu

79

Vertical heat transports in the ocean and their effect on time-dependent climate change

In response to increasing atmospheric concentrations of greenhouse gases, the rate of time-dependent climate change is determined\\u000a jointly by the strength of climate feedbacks and the efficiency of processes which remove heat from the surface into the deep\\u000a ocean. This work examines the vertical heat transport processes in the ocean of the HADCM2 atmosphere–ocean general circulation\\u000a model (AOGCM) in experiments

J. M. Gregory

2000-01-01

80

Free convection in a heat-generating porous medium in a finite vertical cylinder

Fluid currents formed in a fluid-saturated porous medium during convective heat transfer have many important applications, such as oil and gas production, cereal grain storage, geothermal energy, and porous insulation. This investigation considers the numerical solution of the steady-state streamlines and isotherms formed by the convective and conduction heat transfer in an air-solid porous medium in an enclosed, short, vertical

W. E. Jr. Stewart; C. L. G. Dona

1988-01-01

81

Gas hydrate fast nucleation from melting ice and quiescent growth along vertical heat transfer tube

During the observation of HCFC141b gas hydrate growth processes outside a vertical heat transfer tube, two exciting phenomena\\u000a were found: fast nucleation of gas hydrate from melting ice, and the spontaneous permeation of water into the guest phases\\u000a along the surface of heat transfer tube to form gas hydrate continuously. These two phenomena were explained with Zhou & Sloan’s\\u000a hypothesis

Yingming Xie; Kaihua Guo; Deqing Liang; Shuanshi Fan; Jianming Gu; Jinggui Chen

2005-01-01

82

Experimental study of natural convective heat transfer in a vertical hexagonal sub channel

NASA Astrophysics Data System (ADS)

The development of new practices in nuclear reactor safety aspects and optimization of recent nuclear reactors, including the APWR and the PHWR reactors, needs a knowledge on natural convective heat transfer within sub-channels formed among several nuclear fuel rods or heat exchanger tubes. Unfortunately, the currently available empirical correlation equations for such heat transfer modes are limited and researches on convective heat transfer within a bundle of vertical cylinders (especially within the natural convection modes) are scarcely done. Although boundary layers around the heat exchanger cylinders or fuel rods may be dominated by their entry regions, most of available convection correlation equations are for fully developed boundary layers. Recently, an experimental study on natural convective heat transfer in a subchannel formed by several heated parallel cylinders that arranged in a hexagonal configuration has been being done. The study seeks for a new convection correlation for the natural convective heat transfer in the sub-channel formed among the hexagonal vertical cylinders. A new convective heat transfer correlation equation has been obtained from the study and compared to several similar equations in literatures.

Tandian, Nathanael P.; Umar, Efrizon; Hardianto, Toto; Febriyanto, Catur

2012-06-01

83

Experimental study of natural convective heat transfer in a vertical hexagonal sub channel

The development of new practices in nuclear reactor safety aspects and optimization of recent nuclear reactors, including the APWR and the PHWR reactors, needs a knowledge on natural convective heat transfer within sub-channels formed among several nuclear fuel rods or heat exchanger tubes. Unfortunately, the currently available empirical correlation equations for such heat transfer modes are limited and researches on convective heat transfer within a bundle of vertical cylinders (especially within the natural convection modes) are scarcely done. Although boundary layers around the heat exchanger cylinders or fuel rods may be dominated by their entry regions, most of available convection correlation equations are for fully developed boundary layers. Recently, an experimental study on natural convective heat transfer in a subchannel formed by several heated parallel cylinders that arranged in a hexagonal configuration has been being done. The study seeks for a new convection correlation for the natural convective heat transfer in the sub-channel formed among the hexagonal vertical cylinders. A new convective heat transfer correlation equation has been obtained from the study and compared to several similar equations in literatures.

Tandian, Nathanael P.; Umar, Efrizon; Hardianto, Toto; Febriyanto, Catur [Faculty of Mechanical and Aerospace Engineering, Institut Teknologi Bandung, Jl. Ganesa 10, Bandung 40132 (Indonesia); Nuclear Technology Center for Materials and Radiometry, National Nuclear Energy Agency, Bandung (Indonesia); Faculty of Mechanical and Aerospace Engineering, Institut Teknologi Bandung, Jl. Ganesa 10, Bandung 40132 (Indonesia); Nuclear Energy Regulation Agency, Jakarta (Indonesia)

2012-06-06

84

Mixed convection heat transfer in a vertical tube with opposing flow (downflow heating) was studied experimentally for Reynolds numbers ranging from about 1,000 to 30,000 at constant Grashof numbers ranging about 1{1/2} orders of magnitude under constant wall temperature (CWT) conditions. Three correlations developed for opposing mixed convection flows in vertical conduits predicted the data reasonably well, except near and into the asymptote region for which these equations were not designed. A critical Reynolds number is developed here, above which these equations can be used for design purposes regardless of the boundary condition. Below Re{sub crit}, the correlations, the asymptote equation should be used for the CWT boundary condition, which is more prevalent in process situations than the uniform heat flux (UHF) boundary condition.

Joye, D.D. [Villanova Univ., PA (United States). Dept. of Chemical Engineering

1996-07-01

85

Investigation of Heat Transfer in Vapor Condensation in Vertical Packed Tubes.

National Technical Information Service (NTIS)

An investigation of the heat transfer process in the condensation of vapor in vertical packed tubes was performed. The first series of experiments were performed for the empty tube in order to check the accuracy of the experimental method. The second seri...

B. G. Bergo T. A. Bystrova K. P. Berezhnaya

1968-01-01

86

MHD free convection flow along a vertical wavy surface with heat generation or absorption effect

We formulate the problem of free convection from a vertical wavy surface embedded in a uniform porous medium in the presence of an external magnetic field and internal heat generation or absorption effects. Using the appropriate transformations, the boundary layer equations are reduced to non-linear partial differential equations. The transformed boundary layer equations are solved numerically using Runge–Kutta integration scheme

F. M. Hady; R. A. Mohamed; A. Mahdy

2006-01-01

87

A linearized theory is used to study the heat-transfer response of a laminar free convection boundary layer flow of a viscous incompressible and electrically conducting fluid along a vertical plate to surface temperature oscillations, when the mean surface temperature varies as a power n of distance from the leading edge in the presence of a variable transverse magnetic field. Three

M. A. Hossain; S. K. Das; I. Pop

1998-01-01

88

Laminar mixed convection from a vertical heated surface in a crossflow

The present study is concerned with mixed convection from a vertical heated surface in a horizontal crossflow. The governing boundary layer equations were solved numerically using an extension of the technique developed by Cebeci and Keller. The combining law of Churchill and Usagi was utilized to develop a correlation for the average Nusselt number. (AIP)

Evans, G.H.; Plumb, O.A.

1982-08-01

89

Internal radiative heat transport in oxide crystals during their growth via the vertical Bridgman technique is known to promote severely deflected melt\\/crystal interface shapes. These highly curved interfaces are likely to encourage unwanted phenomena such as inhomogeneous distribution of impurities in the solidified crystalline material. Past computational analyses of oxide growth systems have mostly been confined to cylindrical geometries. In

Alexander Virozub; Simon Brandon

1998-01-01

90

Mixed convection along vertical cylinders and needles with uniform surface heat flux

Mixed convection along vertical cylinders and needles with uniform surface heat flux is investigated for the entire mixed convection regime. A single modified buoyancy parameter Ï and a single curvature parameter Î are employed in the analysis such that a smooth transition from pure forced convection (Ï = 1) to pure free convection (Ï = 0) can be accomplished. For

S. L. Lee; T. S. Chen; B. F. Armaly

1987-01-01

91

Natural convection along slender vertical cylinders with variable surface heat flux

Heat transfer by natural convection along a vertical cylinder has been analyzed rather extensively by many investigators using different solution methods. The major restriction to most of these studies is that the solutions are valid only for cylinders with small surface curvature, that is, for cylinders whose diameters are not small. To data no analysis seems to have been presented

J. J. Heckel; T. S. Chen; B. F. Armaly

1989-01-01

92

Multiple buoyancy driven flows in a vertical cylinder heated from below

The structure of axisymmetric buoyancy-driven convection in a vertical cylinder heated from below is probed by finite element solution of the Boussinesq equations coupled with computed-implemented perturbation techniques for detecting and tracking multiple flows and for determining flow stability. Results are reported for fluids with Prandtl number of one and for cylinders with aspect ratio (Lambda) (defined as the height

Y. Yamaguchi; C. J. Chang; R. A. Brown

1983-01-01

93

Steady state heat transfer by natural convection was investigated experimentally from an enclosed assembly of thin vertical cylinders at high Rayleigh numbers. The published literature lacks any information regarding such a study in the turbulent boundary layer regime. All the available literature is for the laminar region for an enclosed assembly. The enclosed assembly consisted of a 3 × 3 array of

Muhammad Arshad; Mansoor Hameed Inayat; Imran Rafiq Chughtai

2011-01-01

94

Numerical Simulation of Heat Conduction to Liquids from a Thin Vertical Cylinder

The paper presents numerical simulations of heat conduction around a circular vertical cylinder immersed in liquids. A finite volume formulation is used, and the numerical analysis is performed in unsteady state with an explicit scheme. The numerical predictions are compared with experiments performed on liquids to find the temperature inside the cylinder, where a thermocouple is located, and at the

F. Gori; M. G. Serranò

2003-01-01

95

This paper reports the results of an experimental study that used a 1/4-scale, water-filled test cell to examine the effect of the natural convection flows created by horizontal and vertical heated surfaces upon thermal stratification in a single-zone enclosure. The study covered the range from pure floor heating to pure wall heating, including various levels of combined floor and wall heating. The presence of a cold window or thermal storage surface was simulated by cooling the wall directly opposite the heated vertical wall. Flow visualization studies were carried out to determine the structure of the flow in the test cell. Correlations are reported for heat transfer, temperature distributions, and thermal stratification as a function of the relative amount of heating that was provided to the floor and wall of the test cell. The results of the study can be used to predict the flow patterns, energy transfer, and levels of thermal stratification that occur in direct gain solar systems that are dominated by natural convection.

Anderson, R.S.; Fisher, E.M.; Bohn, M.S.

1985-09-01

96

Thermal performances of different types of underground heat exchangers

An experiment system with different types of U-vertical ground coupled heat exchanger (UGCHE) in situ was set up, for example, single or double U-pipes with sandstone backfills, and single U-pipe with cement backfills. Experiments on the thermal performance of UGCHE were carried out in different conditions, such as different inlet temperature, flow rate, soil types, backfill materials, number of U-pipes

Xinguo Li; Yan Chen; Zhihao Chen; Jun Zhao

2006-01-01

97

An analytical evaluation of the vertical heat fluxes associated with the mesoscale flow generated by thermal inhomogeneities in the PBL in the absence of a synoptic wind is presented. Results show that the mesoscale fluxes are of the same order as the diabatic beat fluxes. In the sea-breeze case, results show that in the lower layer of the atmosphere the heat flux is positive over the land and negative over the sea with an overall positive horizontal average. In the free atmosphere above the PBL, the mesoscale vertical heat flux is negative over the land and over the sea. The mesoscale flow contributes to the weakening of the atmospheric stability within a region that extends a Rossby radius distance from the coastline and up to an altitude larger than twice the depth of the convective PBL. The average momentum flux equals zero. Sinusoidally periodic thermal inhomogeneities induce periodic atmospheric cells of the same horizontal scale. The intensity of mesoscale cells increases for increasing values of the wavenumber, maximizes when the wavelength of the forcing is of the order of the local Rossby radius, and then decreases as the wavelength of the forcing decreases. The intensity of the vertical velocity and vertical fluxes is only a weak function of the wavenumber, at large wavenumber. The intensity of the mesoscale heat flux does not decrease substantially at high wavenumbers; however, the transport of cool air over small heated patches of land may cut off the temperature gradient in the atmosphere between the land and water early in the day, thereby reducing the duration of the mesoscale activity. Horizontal diffusion of heat in the convective boundary layer can significantly weaken horizontal temperature gradients for large wavenumbers. Periodic square-wave thermal inhomogeneities are more effective than sinusoidal waves in generating mesoscale cells. When dealing with low resolution models the mesoscale heat fluxes have to be introduced in a parametric form.

Dalu, G.A. (Colorado State Univ., Fort Collins (United States) IFA-CNR, Rome (Italy)); Pielke, R.A. (Colorado State Univ., Fort Collins (United States))

1993-03-15

98

Study of heat and mass transfer in a vertical-tube evaporative cooler

NASA Astrophysics Data System (ADS)

Evaporative coolers are three-fluid heat exchangers employed for heat rejection to the environment. A mixture of air and recirculating water is used as the cooling medium. These coolers are considered viable routes for improving thermal efficiencies of power-generating and refrigeration cycles. The heat- and mass-transfer processes taking place in a vertical-tube evaporative cooler are studied. A steady-state, one dimensional model of cooler performance is formulated. This model is validated by experimental measurements, taken in a single-tube exchanger, of the controlling heat- and mass-transfer coefficients. These coefficients occur at the air-water interface. Heat fluxes and enhancement ratios for conditions of interest are measured and calculated, and the results are compared and discussed. The model is found to adequately predict heat-exchanger performance.

Perez-Blanco, H.; Bird, W. A.

1982-11-01

99

Mixed Convection Heat Transfer in Micropolar Nanofluid over a Vertical Slender Cylinder

NASA Astrophysics Data System (ADS)

Analysis is carried for the problem of boundary layer steady flow and heat transfer of a micropolar fluid containing nanoparticles over a vertical cylinder. The governing partial differential equations of linear momentum, angular momentum, heat transfer and nano concentration are reduced to nonlinear coupled ordinary differential equations by applying the boundary layer approximations and a suitable similarity transformation. These nonlinear coupled ordinary differential equations, subject to the appropriate boundary conditions, are then solved by using the homotopy analysis method. The effects of the physical parameters on the flow, heat transfer and nanoparticle concentration characteristics of the model are presented through graphs and the salient features are discussed.

Abdul, Rehman; Nadeem, S.

2012-12-01

100

Buoyancy effects on the laminar boundary layer heat transfer along vertically moving cylinders

NASA Astrophysics Data System (ADS)

The local similarity method (Lloyd, Sparrow, 1970) is used to study the effects of buoyancy force on the laminar boundary layer heat transfer along vertically moving cylinders. Cases of prescribed surface temperature and wall heat flux in power of streamwise distance are analyzed. Local similarity solutions are obtained to show the effects of the transverse curvature of the cylinder surface and buoyancy parameters on the surface friction and heat transfer rate. It is known, however, that the local non-similarity method (Sparrow, Quack, Boerner, 1970) and the finite difference method (Mucoglu, Chen, 1979) would give more accurate results.

Lin, H.-T.; Shih, Y.-P.

1981-01-01

101

The effect of oscillations on the heat transfer in a vertical tube has been studied experimentally. A vertical tube was mounted\\u000a on a plate and the whole plate was subjected to oscillations in the vertical plane using a mechanical oscillator to provide\\u000a low frequency oscillations. A section of the tube in the middle is subjected to a constant heat flux.

Rajashekhar Pendyala; Sreenivas Jayanti; A. R. Balakrishnan

2008-01-01

102

This paper presents a numerical and experimental study concerning cooling characteristics of a pulsating heated vertical\\u000a plate sandwiched between a substrate of phase change material (PCM) and an enclosure of water, forming a composite vertical\\u000a rectangular enclosure. The vertical plate is assumed to have a uniform pulsating (on\\/off) volumetric heat source. The PCM\\u000a considered in the present study is n-Octadecane.

C. J. Ho; Y. T. Cheng

1999-01-01

103

This work presents the experimental research on the steady laminar natural convection heat transfer of air in three vertical thin rectangular channels with different gap clearance. The much higher ratio of width to gap clearance (60-24) and the ratio of length to gap clearance (800-320) make the rectangular channels similar with the coolant flow passage in plate type fuel reactors. The vertical rectangular channels were composed of two stainless steal plates and were heated by electrical heating rods. The wall temperatures were detected with the K-type thermocouples which were inserted into the blind holes drilled in the steal plates. Also the air temperatures at the inlet and outlet of the channel were detected. The wall heat fluxes added to the air flow were calculated by the Fourier heat conduction law. The heat transfer characteristics were analyzed, and the average Nusselt numbers in all the three channels could be well correlated with the Rayleigh number or the modified Rayleigh number in a uniform correlation. Furthermore, the maximum wall temperatures were investigated, which is a key parameter for the fuel's integrity during some accidents. It was found that even the wall heat flux was up to 1500 W/m{sup 2}, the maximum wall temperature was lower than 350 C. All this work is valuable for the plate type reactor's design and safety analysis. (author)

Lu, Qing; Qiu, Suizheng; Su, Guanghui [State Key Laboratory of Multi Phase Flow in Power Engineering, Xi'an JIaotong University, Xi'an, Shaanxi 710049 (China); School of Nuclear Science and Technology, Xi'an Jiaotong University, Xi'an, Shaanxi 710049 (China); Tian, Wenxi; Ye, Zhonghao [School of Nuclear Science and Technology, Xi'an Jiaotong University, Xi'an, Shaanxi 710049 (China)

2010-01-15

104

Experimental study on flow boiling heat transfer of LNG in a vertical smooth tube

NASA Astrophysics Data System (ADS)

An experimental apparatus is set up in this work to study the upward flow boiling heat transfer characteristics of LNG (liquefied natural gas) in vertical smooth tubes with inner diameters of 8 mm and 14 mm. The experiments were performed at various inlet pressures from 0.3 to 0.7 MPa. The results were obtained over the mass flux range from 16 to 200 kg m-2 s-1 and heat fluxes ranging from 8.0 to 32 kW m-2. The influences of quality, heat flux and mass flux, tube diameter on the heat transfer characteristic are examined and discussed. The comparisons of the experimental heat transfer coefficients with the predicted values from the existing correlations are analyzed. The correlation by Zou et al. [16] shows the best accuracy with the RMS deviation of 31.7% in comparison with the experimental data.

Chen, Dongsheng; Shi, Yumei

2013-10-01

105

NASA Astrophysics Data System (ADS)

Steady state free convection heat transfer from horizontal isothermal cylinders in vertical arrays of two to eight, at low Rayleigh numbers, is studied, experimentally. Effects of Rayleigh number and cylinder to cylinder separation distance on the heat transfer behavior of the cylinders are investigated. Heat transfer from the bottom cylinder remains the same as that of a single cylinder. However, for other cylinders we may have either reduction or improvement of heat transfer which depends on their location in the array and the geometry of the array. Results show that there is an optimum separation distance for the best overall convection heat transfer of each array. A correlation is presented to calculate the array Nusselt number in terms of Rayleigh number, cylinder spacing to diameter ratio and number of cylinders in the array.

Sadeghipour, M. Sadegh; Asheghi, M.

1994-01-01

106

The problem of unsteady, two-dimensional, laminar, boundary-layer flow of a viscous, incompressible, electrically conducting and heat-absorbing fluid along a semi-infinite vertical permeable moving plate in the presence of a uniform transverse magnetic field and thermal and concentration buoyancy effects is considered. The plate is assumed to move with a constant velocity in the direction of fluid flow while the free

Ali J. Chamkha

2004-01-01

107

Natural convection in a vertical rectangular enclosure with localized heating and cooling zones

NASA Astrophysics Data System (ADS)

Experimental and numerical studies of natural convection in a single phase, closed thermosyphon were carried out using a vertical, rectangular enclosure model. Only one vertical plate plays the role of heat transfer surface having 100mm height and 100mm width, and others act as the adiabatic wall made of transparent plexi-glass. The heat transfer surface is separated into three horizontal zones with an equal height; top 1/3 and bottom 1/3 of the surface are cooling and heating zones, respectively and intermediate section is an adiabatic zone. Water is used as the working fluid. Variable parameters are distance D between the heat transfer surface and an adiabatic plate opposite to the heat transfer plate, and temperature difference ?T between heating and cooling zones. By changing both D and ?T, three regimes of the natural convection flow; quasi-two-dimensional steady, three-dimensional steady and unsteady flows are observed by means of thermo-sensitive liquid crystal powder and numerically simulated very well by solving a set of governing equations.

Ishihara, I.; Matsumoto, R.; Senoo, A.

108

Heat transfer to water from a vertical tube bundle under natural-circulation conditions. [PWR; BWR

The natural circulation heat transfer data for longitudinal flow of water outside a vertical rod bundle are needed for developing correlations which can be used in best estimate computer codes to model thermal-hydraulic behavior of nuclear reactor cores under accident or shutdown conditions. The heat transfer coefficient between the fuel rod surface and the coolant is the key parameter required to predict the fuel temperature. Because of the absence of the required heat transfer coefficient data base under natural circulation conditions, experiments have been performed in a natural circulation loop. A seven-tube bundle having a pitch-to-diameter ratio of 1.25 was used as a test heat exchanger. A circulating flow was established in the loop, because of buoyancy differences between its two vertical legs. Steady-state and transient heat transfer measurements have been made over as wide a range of thermal conditions as possible with the system. Steady state heat transfer data were correlated in terms of relevant dimensionless parameters. Empirical correlations for the average Nusselt number, in terms of Reynolds number, Rayleigh number and the ratio of Grashof to Reynolds number are given.

Gruszczynski, M.J.; Viskanta, R.

1983-01-01

109

A model for transient natural convection in a vertical cylinder with sidewall heating

A model is needed to predict the fluid velocities and temperature stratification in the crude oil in the more than 50 oil-filled Strategic Petroleum Reserve (SPR) caverns during long-term storage in order to understand processes such as fluid mixing and temperature stratification. A simple two-region model has been developed to predict the transient velocity and temperature distribution in a vertical cylinder with sidewall heating. The two regions are a boundary layer region along the vertical walls and a central core region in the middle. The boundary layer behavior is analyzed by the local similarity method which has been modified to conserve energy and to include turbulence and mixed convection effects. The central core region is broken up into a number of vertical control volumes. 16 refs., 5 figs.

Webb, S.W.

1989-01-01

110

Two-Gradient Convection in a Vertical Slot with Maxwell-Cattaneo Heat Conduction

We study the effect of the Maxwell-Cattaneo law of heat conduction (MCHC) on the 1D flow in a vertical slot subject to both vertical and horizontal temperature gradients. The gravitational acceleration is allowed to oscillate, which provides an opportunity to investigate the quantitative contribution of thermal inertia as epitomized by MCHC. The addition of the time derivative in MCHC increases the order of the system. We use a spectral expansion with Rayleigh's beam functions as the basis set, which is especially suited to fourth order boundary value problems (BVP). We show that the time derivative (relaxation of the thermal flux) has a dissipative nature and leads to the appearance of purely real negative eigenvalues. Yet it also increases the absolute value of the imaginary part and decreases the absolute value of the real part of the complex eigenvalues. Thus, the system has a somewhat more oscillatory behavior than the one based on Fourier's heat conduction law (FHC)

Papanicolaou, N. C. [Department of Computer Science, University of Nicosia, P.O. Box 24005, 1700 Nicosia (Cyprus); Christov, C. I. [Department of Mathematics, University of Louisiana at Lafayette, LA 70504-1010 (United States); Jordan, P. M. [Entropy Reversal Consultants (L.L.C), P. O. Box 691, Abita Springs, LA 70420 (United States); Code 7181, Naval Research Lab., Stennis Space Ctr., MS 39529 (United States)

2009-10-29

111

Critical heat flux in a vertical tube at low and medium pressures

This paper presents experimental CHF data obtained for vertical up flow in an 8 mm I.D. test section, for a wide range of exit qualities (5–75%) and exit pressures ranging from 5 to 40 bar. The experiments were carried out for heated lengths of 0.75, 1, 1.4, 1.8, 2.5 and 3.5 m. A number of different coordinate systems are used

A. Olekhnovitch; A. Teyssedou; A. Tapucu; P. Champagne; D. C. Groeneveld

1999-01-01

112

Wall heat flux partitioning during subcooled forced flow film boiling of water on a vertical surface

Subcooled flow film boiling experiments were conducted on a vertical flat plate, 30.5cm in height, and 3.175cm wide with forced convective upflow of subcooled water at atmospheric pressure. Data have been obtained for mass fluxes ranging from 0 to 700kg\\/m2s, inlet subcoolings ranging from 0 to 25°C and wall superheats ranging from 200 to 400°C. Correlations for wall heat transfer

Phani K. Meduri; Gopinath R. Warrier; Vijay K. Dhir

2009-01-01

113

The problem of steady, laminar, free convection flow over a vertical porous surface in the presence of a magnetic field and heat generation or absorption is considered. The governing three-dimensional partial differential equations for this investigation are transformed into ordinary differential equations using three-dimensional similarity variables. The resulting equations are solved numerically by an accurate, implicit, iterative finite-difference methodology and

Ali J. Chamkha

1999-01-01

114

Steady gas hydrate growth along vertical heat transfer tube without stirring

The hydration characteristics of a quiescent reactor with inner-placed vertical heat transfer tube were researched, the reaction materials were 300ppm sodium dodecyl sulfate water solution and R141b. The growth morphology were described through the photos taken during the growth\\/decomposition processes. The temperatures of two points inside the reactor were also recorded and analyzed. The mass transfer mechanism was explained by

Yingming Xie; Kaihua Guo; Deqing Liang; Shuanshi Fan; Jianming Gu

2005-01-01

115

Multiple Byoyancy-Driven Flows in a Vertical Cylinder Heated from below

The structure of axisymmetric buoyancy-driven convection in a vertical cylinder heated from below is probed by finite-element solution of the Boussinesq equations coupled with computer-implemented perturbation techniques for detecting and tracking multiple flows and for determining flow stability. Results are reported for fluids with a Prandtl number of one and for cylinders with aspect ratio Lambda (defined as the ratio

Y. Yamaguchi; C. J. Chang; R. A. Brown

1984-01-01

116

On natural convection from a vertical plate with a prescribed surface heat flux in porous media

This paper presents a theoretical and numerical investigation of the natural convection boundary-layer along a vertical surface, which is embedded in a porous medium, when the surface heat flux varies as (1 +x2)µ), where µ is a constant andx is the distance along the surface. It is shown that for µ > -1\\/2 the solution develops from a similarity solution

S. D. Wright; D. B. Ingham; I. Pop

1996-01-01

117

The rate of heat flow through a flat vertical wall due to conjugate heat transfer

Free convection along both sides of a vertical flat plate is studied within the framework of the laminar boundary-layer theory and for the case where only the temperature of the fluid far away from the wall is prescribed. Corrections to the Pohlhausen solution for the temperature at the plate surface are calculated. It is found that for good thermal conductors,

T. Kranjc; J. Peternelj; J. Kozak

2010-01-01

118

NASA Astrophysics Data System (ADS)

An unsteady mixed convective flow and heat transfer in a vertical corrugated channel containing porous and fluid layers are considered. The equations of momentum and energy are solved under appropriate boundary and interface conditions with the assumption that the solution consists of a mean part and a perturbed one. The exact solutions are obtained in the long-wave approximation. Separate solutions are matched at the interface with the use of suitable matching conditions. The effects of pertinent parameters, such as the Grashof number, viscosity ratio, width ratio, conductivity ratio, frequency, and the wave parameter on the flow field and heat transfer characteristics are studied.

Umavathi, J. C.; Shekar, M.

2013-07-01

119

Augmentation of heat transfer in a bubble agitated vertical rectangular channel

NASA Astrophysics Data System (ADS)

This paper presents the results of an experimental study of convective heat transfer between three parallel vertical plates symmetrically spaced with and without bubble agitation to ascertain the degree of augmentation of the heat transfer coefficients due to agitation. The centre plate was electrically heated, while the other side plates were water-cooled forming two successive parallel vertical rectangular channels of dimensions 20 cm × 3.5 cm × 35 cm (length W, gap L, height H) each. At the bottom of the hot and cold plates air spargers were fitted. Water/ethylene glycol (100%) was used to fill the channels. The superficial gas velocity ranged from 0.0016 to 0.01 m/s. Top, bottom and sides of the channels were open to the water/ethylene glycol in the chamber which is the novel aspect of this study. Experimental data have been correlated as under: Natural convective heat transfer: Nu = 0.60 Gr 0.29, r = 0.96, ? = 0.186, 1.17 E6 < Gr < 1.48 E7; Bubble agitated heat transfer: St = 0.11( ReFrPr 2)-0.23, r = 0.82, ? = 0.002, 1.20 E-2 < ( ReFrPr 2) < 1.36 E2.

Mitra, Asish; Dutta, Tapas Kumar; Ghosh, Dibyendu Narayan

2012-04-01

120

NASA Astrophysics Data System (ADS)

It is well known that the main direct effect of aerosols is the cooling of the surface and warming of the atmosphere, which impact atmospheric dynamics via the weakening of convection and the inhibition of cloud forming. In order to be able to fully understand and parameterize this throughout the atmosphere, a detailed vertical profile of the aerosol induced surface cooling and atmospheric heating is required. To get a vertical profile like this, detailed vertically resolved data on aerosol optical properties are required. Such data have now become available from CALIOP lidar onboard CALIPSO satellite. Its near-nadir viewing geometry allows for viewing curtains of the atmosphere, thereby defining with sufficient accuracy the vertical position of aerosols and clouds. In this study, CALIOP Level 2-Version 3 Layer and Profile data for the Mediterranean region from January 2007 to December 2011 have been used. The Mediterranean region was chosen, as it is an area with a mixture of aerosol types, both natural and anthropogenic, where aerosol radiative effects take large values. Furthermore, it is in the proximity of Sahara desert dust, making the area one with large aerosol load. The original CALIOP data have been regridded at a 1°x1° latitude-longitude resolution and at 160 vertical layers. The use of both Layer and Profile data has enabled the derivation of useful 'climatological' products, like spatial properties of aerosol layers, as well as optical properties of them. A comparison with the recently distributed (December 2011) CALIOP Level 3 data, as well as with other satellite data, is presented. Initial results, in agreement with previous studies, reveal that CALIOP aerosol optical depth (AOD) is biased low by around 20%, when compared to other satellite products, such as MODIS. The regridded data are subsequently used in a spectral radiative transfer model and the vertical profile of direct radiative effect is computed. From that, a vertical heating rate profile due to aerosols is derived for each model grid. The geographical and seasonal variability of these rates are investigated, in relation with the corresponding variability of aerosol optical properties. According to preliminary results, the determination of the cooling/heating rate above the surface and within the atmosphere is not affected by the aforementioned bias of CALIOP AOD. The findings of this study are expected to be particularly useful to future studies that deal with the modelling of the aerosol direct, indirect and semi-direct effects (e.g.. Monitoring Atmospheric Composition and Climate II) while the aerosol induced modification of atmospheric lapse rates will be the basis for further studies of aerosol effects on atmospheric dynamics.

Pappas, Vasileios; Hatzianastassiou, Nikos; Matsoukas, Christos; Vardavas, Ilias

2013-04-01

121

Influence of strongly-varying properties of supercritical-pressure fluids on turbulent convective heat transfer is investigated using direct numerical simulation. We consider thermally-developing upward flows in a vertical annular channel where the inner wall is heated with a constant heat flux and the outer wall is insulated. CO2 is chosen as the working fluid at a pressure to 8 Mpa, and the inlet Reynolds number based on the channel hydraulic diameter and the bulk velocity is Re0 = 8900. It is shown that turbulent convective heat transfer characteristics of supercritical flow are significantly different from those of constant-property flow mainly due to spatial and temporal variations of fluid density. Non-uniform density distribution causes fluid particles to be accelerated either by expansion or buoyancy force near the heated wall, while temporal density fluctuations change the transport characteristics of turbulent heat and momentum via the buoyancy production terms arising from the correlations such as p1u1x, p1u1r and p1h1. Among various turbulence statistics, the streamwise turbulent heat flux shows a very peculiar transitional behavior due to the buoyancy effect, changing both in sign and magnitude. Consequently, a non-monotonic temperature distribution is developed in the flow direction, causing severe impairment of heat transfer in supercritical flows.

D. M. McEligot; J. H. Bae; J. Y. Yoo; H. Choi; James R. Wolf

2005-10-01

122

Modeling vertical exchange of heat, salt, and other dissolved substances in the Cariaco Basin

NASA Astrophysics Data System (ADS)

A simple 1.5-dimensional model of vertical exchange for heat, salt, and other dissolved substances has been developed for the Cariaco Basin. The model parameters are derived based on the temperature and salinity data collected monthly at a deepwater station in the eastern part of the basin from 1995 through 2007 during the CARIACO time series program. The model describes the processes of turbulent (eddy) diffusion, which includes the integrated effect of diffusive exchange mechanisms acting in the basin, and of vertical advection, which arises following injection of dense water into deep layers following an inflow from the Caribbean Sea. The model takes into account the changes in the horizontal cross-section area of the basin with respect to depth. Temporal variability is an important feature of the hydrography of the Cariaco Basin. To assess profiles of the vertical eddy diffusion coefficient and vertical advection velocity, we examined a time series of CTD profiles (potential temperature and salinity). Two distinct time intervals were identified as the result of this examination. During the first period, the thermohaline structure of the basin was apparently influenced by one or more inflows. The second period, in contrast, showed little or no influence of an inflow. The data from the second period, where no inflows were observed, were incorporated into corresponding transfer equations to assess the profile of the vertical eddy diffusion coefficient, k(z). Then, the result of this assessment was used with the data from the first period to estimate the profile of the vertical advection velocity, W(z), for a time when the effects of an inflow were evident. For that case, the transfer equations include the terms describing the effect of the inflow. Analysis of the vertical profile of the turbulent diffusion coefficient suggests that, in the upper stratified part of the water column, the diffusion mechanism is mostly associated with transient mixing events, which occur due to shear instability in the field of low frequency internal waves. We speculate that below 400 m bottom friction over the sloping bottom and geothermal heat flux play the decisive role in the vertical exchange. Analysis of the W(z) profiles reveals two layers dominated by the entrainment of the ambient fluid into the down flow of dense water from the Caribbean Sea, and two layers where this down flow breaks down through the formation of isopycnal intrusions.

Samodurov, A. S.; Scranton, M. I.; Astor, Y.; Ivanov, L. I.; Chukharev, A. M.; Belokopytov, V. N.; Globina, L. V.

2013-01-01

123

The vertical eddy-heat flux as a stabilizer of cold accretion disks

NASA Astrophysics Data System (ADS)

The time-dependent vertical structure of cold accretion disks and their thermal stability have been studied with turbulent heat transfer being included. A strong turbulent heat transport enforces a nearly adiabatic stratification and the disk evolves quasi-homologously, although homology is broken by the outer boundary condition. The radiative energy loss scales with the disk's optical depth tau like Q(-~) T_c(4/tau ^m) with T_c the midplane temperature. The disk is only stable if the resulting m fulfills the stability criterion 3+mleft({n/2}-qright ) > 0, with n and q taken from the opacity law kappa ~rho (n) T(q) . For rather cool disks with n=1/3 and q=10 the vertical structure proves to be thermally unstable unless the turbulent Prandtl number (the ratio between the eddy viscosity and turbulent heat conductivity) is less than, say, 0.1. For weaker temperature power-laws of the opacity (smaller q) the disks become more and more stable even without the stabilizing support of the eddy-heat flux. Numerical simulations confirm the quasi-analytically derived stability criterion.

Fröhlich, H.-E.; Rüdiger, G.

1999-03-01

124

An energetic and exergetic modeling of a solar-assisted vertical ground-source heat pump (GSHP) greenhouse heating system (SAGSHPGHS) for system analysis and performance assessment is presented in this study. Energy (heating coefficient of performance ‘COP’) and exergy efficiencies at various reference and entering water temperatures are also determined. The actual thermal data collected are utilized for the model calculations at different

Onder Ozgener; Arif Hepbasli

2007-01-01

125

Conduction heat transfer into a vertical free burning slab was measured as a function of time and distance from the leading edge, and its contribution to the known values of effective heat of gasification was analyzed. The present set of experiments was performed using clear and black PMMA (polymethylmethacrylate) samples. The heat conduction into the pyrolyzing surface was deduced from

A. K. KULKARNI; C. I. KIM

1990-01-01

126

In this study the mixed convection heat transfer in a coil-in-shell heat exchanger for various Reynolds numbers, various tube-to-coil diameter ratios and different dimensionless coil pitch was experimentally investigated. The experiments were conducted for both laminar and turbulent flow inside coil. Effects of coil pitch and tube diameters on shell-side heat transfer coefficient of the heat exchanger were studied. Different characteristic lengths were used in various Nusselt number calculations to determine which length best fits the data and several equations were proposed. The particular difference in this study in comparison with the other similar studies was the boundary conditions for the helical coils. The results indicate that the equivalent diameter of shell is the best characteristic length. (author)

Ghorbani, N. [School of Mechanical Engineering, University of Leeds, Leeds, England (United Kingdom); Taherian, H. [Department of Engineering Technology and Industrial Distribution, Texas A and M University, College Station, TX (United States); Gorji, M. [Department of Mechanical Engineering, Babol Noushirvani University of Technology, Babol (Iran); Mirgolbabaei, H. [Department of Mechanical Engineering, Islamic Azad University, Jouybar branch, Jouybar (Iran)

2010-10-15

127

Self Heating Effects of High Power SOI Vertical DMOS Transistor with Lateral Drain Contacts

NASA Astrophysics Data System (ADS)

Self heating effects in silicon-on-insulator (SOI) high power Vertical Diffused MOS (VDMOS) transistors have been investigated by electro-thermal simulations. Unlike other conventional VDMOS devices, here we work on a modified VDMOS transistor with drain contacts at the surface. In this work we study two different aspects of this transistor namely: (1) Effect of self heating on the device performance and (2) effect of the elevated temperature on the device characteristics. Our simulation results indicate that the temperature distribution is concentrated at the drift region under the gate area and spreads down toward the drain area. The self heating effect gives a notable effect on our newly proposed VDMOS in the on-state (when Vg > Vt), and the breakdown point decreases. As we increase the ambient temperature the breakdown point decreases further.

Pinardi, Kuntjoro; Heinle, Ulrich; Bengtsson, Stefan; Olsson, Jörgen

128

The effect of internal heat generation\\/absorption on a steady two-dimensional natural convection flow of viscous incompressible fluid along a uniformly heated vertical wavy surface has been investigated. The equations are mapped into the domain of flat vertical plate, and then solved numerically employing the implicit finite difference method, known as Keller-box scheme. Effects of the pertinent parameters, such as the

Lun Shin Yao

2004-01-01

129

Buoyant instabilities in downward flow in a symmetrically heated vertical channel

This study of the downward flow of nitrogen in a tall, partially heated vertical channel (upstream isothermal at T{sub in}*, heated region isothermal at T{sub s}* downstream adiabatic) shows the strong effects of buoyancy even for small temperature differences. Time-dependent oscillations including periodic flow reversals occur along the channel walls. Although the flow and heat transfer are asymmetric, the temperature and axial component of velocity show symmetric reflections at two times that are half a period apart and the lateral component of velocity shows antisymmetric reflections at the two times. There is strong interaction between the downward flow in the central region of the channel and the upward flow along the heated channel walls. At the top of the heated region, the upward buoyant flow turns toward the center of the channel and is incorporated into the downward flow. Along the channel centerline there are nonmonotonic variations of the axial component of velocity and temperature and a large lateral component of velocity that reverses direction periodically. Results are presented for Re = 219.7 and Gr/Re{sup 2} = 1.83, 8.0, and 13.7. The heat transfer and the frequency of the oscillations increases and the flow and temperature fields become more complex as Gr/Re{sup 2} increases. The results have applications to fiber drying, food processing, crystal growth, solar energy collection, cooling of electronic circuits, ventilation, etc.

Evans, G. [Sandia National Lab., Livermore, CA (United States); Greif, R. [Univ. of California, Berkeley, CA (United States)

1996-07-01

130

Task T-222 of the International Thermonuclear Experimental Reactor (ITER) program addresses the manufacturing and testing of permanent components for use in the ITER divertor. Thermalhydraulic and critical heat flux performance of the heat sinks proposed for use in the divertor vertical target are part of subtask T-222.4. As part of this effort, two single channel, medium scale, bare copper alloy, hypervapotron mockups were designed, fabricated, and tested using the EB-1200 electron beam system. The objectives of the effort were to develop the design and manufacturing procedures required for construction of robust high heat flux (HHF) components, verify thermalhydraulic, thermomechanical and critical heat flux (CHF) performance under ITER relevant conditions, and perform analyses of HHF data to identify design guidelines and failure criteria and possibly modify any applicable CHF correlations. The design, fabrication, and finite element modeling of two types of hypervapotrons are described; a common version already in use at the Joint European Torus (JET) and a new attached fin design. HHF test data on the attached fin hypervapotron will be used to compare the CHF performance under uniform heating profiles on long heated lengths with that of localized, highly peaked, off nominal profiles.

Youchison, D.L.; Marshall, T.D.; McDonald, J.M.; Lutz, T.J.; Watson, R.D. [Sandia National Labs., Albuquerque, NM (United States); Driemeyer, D.E. Kubik, D.L.; Slattery, K.T.; Hellwig, T.H. [McDonnell Douglas Aerospace, St. Louis, MO (United States)

1997-09-01

131

Free convection boundary layers on a vertical surface in a heat-generating porous medium

NASA Astrophysics Data System (ADS)

The natural convection boundary-layer flow on a solid vertical surface with heat generated within the boundary layer at a rate proportional to (T - T{infty})p (p [?] 1) is considered. The surface is held at the ambient temperature T{infty} except near the leading edge where it is held at a temperature above ambient. The behaviour of the flow as it develops from the leading edge is examined and is seen to become independent of the initial heat input; however, it does depend strongly on the exponent p. For 1 [?] p [?] 2, the local heating eventually dominates at large distances and there is a convective flow driven by this mechanism. For p [?] 4, the local heating does not have a significant effect, the fluid temperature remains relatively small throughout and the heat transfer dies out through a wall jet flow. For 2 < p < 4, the local heating has a significant effect at relatively small distances, with a thermal runaway developing at a finite distance along the surface.

Mealey, L.; Merkin, J. H.

2008-02-01

132

Two-phase distribution in the vertical flow line of a domestic wet central heating system

NASA Astrophysics Data System (ADS)

The theoretical and experimental aspects of bubble distribution in bubbly two-phase flow are reviewed in the context of the micro bubbles present in a domestic gas fired wet central heating system. The latter systems are mostly operated through the circulation of heated standard tap water through a closed loop circuit which often results in water supersaturated with dissolved air. This leads to micro bubble nucleation at the primary heat exchanger wall, followed by detachment along the flow. Consequently, a bubbly two-phase flow characterises the flow line of such systems. The two-phase distribution across the vertical and horizontal pipes was measured through a consideration of the volumetric void fraction, quantified through photographic techniques. The bubble distribution in the vertical pipe in down flow conditions was measured to be quasi homogenous across the pipe section with a negligible reduction in the void fraction at close proximity to the pipe wall. Such a reduction was more evident at lower bulk fluid velocities.

Fsadni, A.-M.; Ge, Y. T.

2013-04-01

133

Modeling Vertical Structure and Heat Transport within the Oceans of Ice-covered Worlds (Invited)

NASA Astrophysics Data System (ADS)

Indirect observational evidence provides a strong case for liquid oceans beneath the icy crust of Europa and several other frozen moons in the outer solar system. However, little is known about the fluid circulation within these exotic oceans. As a first step toward understanding circulations driven by buoyancy (rather than mechanical forcing from tides), one must understand the typical vertical structure of temperature, salinity, and thus density within the ocean. Following a common approach from terrestrial oceanography, I have built a "single column convection model" for icy world oceans, which describes the density structure of the ocean as a function of depth only: horizontal variations are ignored. On Earth, this approach is of limited utility, because of the strong influence of horizontal wind-driven currents and sea-surface temperature gradients set in concert with the overlying atmosphere. Neither of these confounding issues is present in an icy world's ocean. In the model, mixing of fluid properties via overturning convection is modeled as a strong diffusive process which only acts when the ocean is vertically unstable. "Double diffusive" processes (salt fingering and diffusive layering) are included: these are mixing processes resulting from the unequal molecular diffusivities of heat and salt. Other important processes, such as heating on adiabatic compression, and freshwater fluxes from melting overlying ice, are also included. As a simple test case, I considered an ocean of Europa-like depth (~100 km) and gravity, heated from the seafloor. To simplify matters, I specified an equation of state appropriate to terrestrial seawater, and a simple isothermal ocean as an initial condition. As expected, convection gradually penetrates upward, warming the ocean to an adiabatic, unstratified equilibrium density profile on a timescale of 50 kyr if 4.5 TW of heat are emitted by the silicate interior; the same result is achieved in proportionally more/less time for weaker/stronger internal heating. Unlike Earth's oceans, I predict that since icy worlds' oceans are heated from below, they will generally be unstratified, with constant potential density from top to bottom. There will be no pycnocline as on Earth, so global ocean currents supported by large-scale density gradients seem unlikely. However, icy world oceans may be "weird" in ways which are unheard-of in terrestrial oceanography The density of sulfate brine has a very different equation of state than chloride brines: does this affect the vertical structure? If the ocean water is very pure, cold water can be less dense than warm. Can this lead to periodic catastrophic overturning, as proposed by other authors? These and other questions are currently being investigated using the single-column convection model as a primary tool.

Goodman, J. C.

2010-12-01

134

Natural convection from a isothermal vertical surface to a thermally stratified fluid is studied numerically. A wide range of stratification levels is considered. It is shown that at high levels of ambient thermal stratification, a portion at the top of the plate absorbs heat, while a horizontal plume forms around a location where the plate temperature equals the ambient temperature. The plume is shown to be inherently unsteady, and its transient nature is investigated in detail. The effect of the temperature defect in striating the plume is discussed. Average Nusselt number data are Presented for Pr = 6.0 and 0.7. 22 refs., 12 figs., 1 tab.

Angirasa, D. (Univ. of Colorado, Boulder (United States)); Srinivasan, J. (Indian Institute of Science, Bangalore (India))

1992-11-01

135

Radiation Effects on Oscillating Vertical Plate with Uniform Heat and Mass Flux

NASA Astrophysics Data System (ADS)

Thermal radiation effects on flow past an impulsively started infinite vertical oscillating plate with uniform heat and mass flux is studied. The fluid considered here is a gray, absorbing-emitting radiation but a nonscattering medium. The dimensionless governing equations are solved using the Laplace-transform technique. The velocity, temperature and concentration are studied for different physical parameters such as the radiation parameter, phase angle, Schmidt number and time. The variation of the skin-friction for different values of the parameters is also shown in a table

Chandrakala, P.; Bhaskar, P. Narayana

2013-08-01

136

Downflow heat transfer in a heated ribbed vertical annulus with a cosine power profile

Experiments designed to investigate downflow heat transfer in a heated, ribbed annulus test section simulating one of the annular coolant channels of a Savannah River Plant production reactor Mark 22 fuel assembly have been conducted at the Idaho National Engineering Laboratory. The inner surface of the annulus was constructed of aluminum and was electrically heated to provide an axial cosine power profile and a flat azimuthal power shape. Data presented in this report are from the ECS-2c series, which was a follow on series to the ECS-2b series, conducted specifically to provide additional data on the effect of different powers at the same test conditions, for use in evaluation of possible power effects on the aluminum temperature measurements. Electrical powers at 90%, 100%, and 110% of the power required to result in the maximum aluminum temperature at fluid saturation temperature were used at each set of test conditions previously used in the ECS-2b series. The ECS-2b series was conducted in the same test rig as the previous ECS-2b series. Data and experimental description for the ECS-2b series is provided in a previous report. 18 refs., 25 figs., 3 tabs.

Anderson, J.L.; Condie, K.G.; Larson, T.K.

1991-10-01

137

Natural, mixed, and forced convection in a vertical thermosiphon heated with constant flux

NASA Astrophysics Data System (ADS)

The development of a mixed-laminar-convective-flow region in a vertical channel is investigated analytically in the case in which the parallel plane walls of the channel are heated with constant but not necessarily equal heat-flux densities. Expressions describing the thermal and dynamical development are derived for forced convection favoring the natural convective flow, and for forced convection opposed to natural convection with upward and downward flow. A finite-differences method is employed in the numerical solution of the equations for air with Prandtl number 0.71 and Grashof numbers from 0.1 to 1000, and the results are illustrated graphically. The estimated flow rates and wall temperatures are considered in terms of their implications for flow behavior.

Penot, F.; Dalbert, A.-M.

1983-11-01

138

NASA Astrophysics Data System (ADS)

To analyze the laminar natural convection heat transfer and fluid flow distribution in vertical rectangular cavities with or without inner partitions, the personal computer finite difference program entitled CAV is used. The CAV program was tested successfully for slender cavities with aspect ratios as high as R = H/L = 90 and for the Grashof numbers, based on the cavity height, up to GrH = 3x109. To make the CAV program useful for a number of applications, various types of boundary conditions can also be imposed on the program calculations. Presented are program applications dealing with the 2-D numerical analysis of natural convection heat transfer in very slender window cavities with and without small inner partitions and recommendations are made for window design. Professor, Mechanical Engineering.

Novak, Milos H.; Nowak, Edwin S.

1993-12-01

139

A frequent problem in heat exchange equipment is the deposition of particulates entrained in the working fluid onto heat transfer surfaces. These deposits increase the overall heat transfer resistance and can significantly degrade the performance of the heat exchanger. Accurate prediction of the deposition rate is necessary to ensure that the design and specified operating conditions of the heat exchanger adequately address the effects of this deposit layer. Although the deposition process has been studied in considerable detail, much of the work has focused on investigating individual aspects of the deposition process. This paper consolidates this previous research into a mechanistically based analytical prediction model for particulate deposition from a boiling liquid onto vertical heat transfer surfaces. Consistent with the well known Kern-Seaton approach, the model postulates net particulate accumulation to depend on the relative contributions of deposition and reentrainment processes. Mechanisms for deposition include boiling, momentum, and diffusion effects. Reentrainment is presumed to occur via an intermittent erosion process, with the energy for particle removal being supplied by turbulent flow instabilities. The contributions of these individual mechanisms are integrated to obtain a single equation for the deposit thickness versus time. The validity of the resulting model is demonstrated by comparison with data published in the open literature. Model estimates show good agreement with data obtained over a range of thermal-hydraulic conditions in both flow and pool boiling environments. The utility of the model in performing parametric studies (e.g. to determine the effect of flow velocity on net deposition) is also demonstrated. The initial success of the model suggests that it could prove useful in establishing a range of heat exchanger. operating conditions to minimize deposition.

Keefer, R.H.; Rider, J.L.; Waldman, L.A.

1993-10-01

140

We present a numerical study of the drying by natural convection of coffee grains contained between two vertical walls subjected to a uniform heat flux. The coffee grains bed is assumed to be in a porous medium, heat and mass transfers which are described by the classical natural convection equations and the Darcy-Brinkman momentum equation. The discretisation of these equations

J. Bathiebo; M. Daguenet; B. Zeghmati; C. MBow

2003-01-01

141

This paper reports experimental data on the heat transfer between an electrically heated vertical finned tube bundle and cracking catalyst, fluidized with air in the downcomer of a circulating fluidized bed system. The effects of the air fluidizing velocity, bed temperature and external recirculation of solids were investigated. We were particularly interested in low gas velocities in the downcomer. Up

S. Ouyang; X.-G. Li; G. Davies; O. E. Potter

1996-01-01

142

The enhancement of heat transfer in a thermal storage system consisting of a cylindrical vertical tube with internal longitudinal fin arrangement is discussed in this paper. This configuration that forms a V-shaped enclosure for the phase change material (PCM) gives maximum benefit to the fin arrangement. A theoretical model that also accounts for the circumferential heat flow through the tube

R. Velraj; R. V. Seeniraj; B. Hafner; C. Faber; K. Schwarzer

1997-01-01

143

Melting of a solid adjacent to a heated vertical cylinder with or without subcooling of the solid

Experiments were performed to provide quantitative heat transfer data corresponding to the problem of melting about a heated vertical cylinder embedded in a solid phase change material. The phase change material employed was 99 percent pure n-eicosane paraffin having an experimentally determined melting point of 36.4 C. Experiments were conducted with the solid phase either at the melting point or

R. G. Kemink

1981-01-01

144

Natural convection heat transfer coefficients for vertical cylinders with variable surface temperature distribution must be found by complex numerical integration of the corresponding system of governing differential equations. Its evaluation for practical heat transfer calculations is always based on more or less complex correlations fitted to numerical or experimental results. This paper presents alternative approximate formulas for the calculation of

José L. Muñoz-Cobo; José M. Corberán; Sergio Chiva

2003-01-01

145

NASA Astrophysics Data System (ADS)