The Effect of Fill Volume on Heat Transfer From Air-Cooled Thermosyphons

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Christina A. Pappas ◽  
Paul M. De Cecchis ◽  
Donald A. Jordan ◽  
Pamela M. Norris
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Air Flow ◽  
Condenser Section ◽  
Evaporator Temperature ◽  
Evaporator Section ◽  
Fill Volume ◽  
Inner Diameter ◽  
Cooling Air Flow

The effect of fill volume on the heat transfer performance of a cylindrical thermosyphon with an aspect ratio (ratio of the length of the evaporator section to the inner diameter) of 2.33 immersed in a cooling air flow is investigated. The fill volume was systematically varied from 0% to 70.3% of the volume of the evaporator section in a copper-water thermosyphon having an inner diameter of 19 mm. The condenser section was immersed in a uniform air flow in the test section of an open return wind tunnel. The heat transfer rate was measured as a function of evaporator temperature and fill volume, and these results were characterized by three distinct regions. From 0% to roughly 16% fill volume (Region I), the low rate of heat transfer, which is insensitive to fill volume, suggests that dry out may be occurring. In Region II (extending to approximately 58% fill volume), the heat transfer rate increases approximately linearly with fill volume, and increasing evaporator temperature results in decreased rate of heat transfer. Finally, in Region III (from roughly 58–70.3%), the rate of heat transfer increases more rapidly, though still linearly, with fill volume, and increasing evaporator temperature results in increased rate of heat transfer. The thermosyphon rate of heat transfer is greatest at 70.3% fill volume for every evaporator temperature.

Experimental Investigation of the Heat Transfer Performance of a Hybrid Cooling Fin Thermosyphon

2014 ◽  
Vol 136 (10) ◽  
Author(s):  
Christina A. Pappas ◽  
Donald A. Jordan ◽  
Pamela M. Norris
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Heat Transfer Performance ◽  
Working Fluid ◽  
Transfer Performance ◽  
Maximum Heat ◽  
Hybrid Cooling ◽  
Evaporator Section ◽  
Fill Volume

The effect of fill volume on the heat transfer performance of a hybrid cooling fin thermosyphon, characterized by an airfoil cross-sectional shape and a slot-shaped cavity, is investigated. The performance was examined at three fill volumes, expressed as a percentage of the evaporator section: 0%, 60%, and 240%. These were chosen to represent three distinct regimes: unfilled, filled, and overfilled evaporator sections, respectively. The cross section of this copper–water thermosyphon has a NACA0010 shape with a chord length of 63.5 mm and an aspect ratio (ratio of the length of the evaporator section to the cavity width) of 1.109. The evaporator length comprises 8.3% of the total thermosyphon length. The air-cooled condenser section was placed in a uniform air flow in the test section of an open return wind tunnel. The rate of heat transfer, or performance, was measured as a function of fill volume and evaporator temperature. The heat transfer performance increased by 100–170% by adding 0.86 ml of working fluid (de-ionized water), i.e., when the fill volume increased from 0% to 60%, which illustrates the improvement of a cooling fin's heat transfer rate by converting it to a hybrid cooling fin thermosyphon. Of the fill volumes investigated, the thermosyphon achieves a maximum heat transfer rate and highest average surface temperature at the 60% fill volume. Overfilling the evaporator section at 240% fill results in a slight decrease in performance from the 60% fill volume. The results of this study demonstrate the feasibility of hybridizing a cooling fin to act both as a cooling fin and a thermosyphon.

Heat-transfer rate in the condenser section of a heat pipe

1973 ◽  
Vol 25 (3) ◽  
pp. 1115-1117
Author(s):  
V. Ya. Sasin ◽  
A. Ya. Shelginskii
Keyword(s):  
Heat Transfer ◽  
Heat Pipe ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Condenser Section

The Sonic Limit in Sodium Heat Pipes

1973 ◽  
Vol 95 (2) ◽  
pp. 218-223 ◽  
Author(s):  
E. K. Levy ◽  
S. F. Chou
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Heat Pipes ◽  
Vapor Condensation ◽  
Condensation Process ◽  
Recombination Reaction ◽  
Condenser Section ◽  
Sonic Point ◽  
Limit Heat Transfer

The results of an analytical study of the vapor dissociation–recombination and homogeneous vapor condensation phenomena in sodium heat pipes are described. It is shown that neither the dissociation–recombination reaction nor the vapor condensation process has a large influence on the sonic-limit heat transfer rate. The single most important factor is shown to be the wall shear stress in the heat-pipe vapor passage. The friction effects control the location of the sonic point, determine if the flow in the condenser section will be subsonic or supersonic, and decrease the sonic-limit heat transfer rate to values which can be substantially lower than those which are predicted from inviscid analyses.

Theory of Heat Transfer From a Surface Covered With Hair

1990 ◽  
Vol 112 (3) ◽  
pp. 662-667 ◽  
Author(s):  
A. Bejan
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Air Flow ◽  
The Body ◽  
Total Heat ◽  
Uniform Density ◽  
Total Heat Transfer ◽  
Optimum Diameter ◽  
Hair Strand

This paper describes the fundamental mechanisms of heat transfer through a surface covered with perpendicular hair strands of uniform density. An air flow parallel to the skin seeps through the spaces created between the hair strands. It is shown that the total heat transfer rate from the surface is due to two contributions: (i) the heat conducted through the hair strands, which act as fins, and (ii) the heat convected from the bare portions of the skin. When the air flow is slow enough to conform to the Darcy regime, there exists an optimum hair strand diameter for which the total heat transfer rate is minimum. The optimum diameter increases as the square root of the length swept by the air flow, that is the linear size of the body of the animal covered with hair.

Air Flow and Heat Transfer in Louver-Fin Round-Tube Heat Exchangers

2006 ◽  
Vol 129 (2) ◽  
pp. 200-210 ◽  
Author(s):  
H. L. Wu ◽  
Y. Gong ◽  
X. Zhu
Keyword(s):  
Heat Transfer ◽  
Boundary Conditions ◽  
Heat Transfer Rate ◽  
Heat Exchangers ◽  
Transfer Rate ◽  
Air Flow ◽  
Fluid Temperature ◽  
Round Tube ◽  
Flow And Heat Transfer ◽  
Representative Unit Cell

Experimental investigations were conducted to understand the air flow and heat transfer in louver-fin round-tube two-row two-pass cross-counterflow heat exchangers. The Colburn factor j and friction factor f were obtained by using the ε-NTU approach. A three-dimensional computational fluid dynamics model was developed based on a representative unit cell with periodical and symmetric boundary conditions. Analysis of tube-side circuiting effect has been conducted and showed improvement by applying overall nonlinear tube-side fluid temperature boundary conditions. Comparison of heat transfer rate of the first and second rows showed that the first row was much more effective, achieving 68-53% of the total heat transfer rate, when air velocity changes from 1.02m∕sto2.54m∕s. A dimensionless parameter, F, was introduced to describe the louver interaction for different fin designs with various louver angles. Using j′∕f1∕3 as a criterion to evaluate the heat transfer and pressure loss performance, an optimal F was predicted around 0.62.

Numerical Study on Heat Transfer Enhancement in a Circular Dimpled Surface by Using Inline and Staggered Pattern at Laminar Flow Regimes

2015 ◽  
Vol 813-814 ◽  
pp. 754-759
Author(s):  
T.S. Ravikumar ◽  
S. Seralathan ◽  
T. Micha Premkumar ◽  
Kumar Guntamadugu Hemanth
Keyword(s):  
Heat Transfer ◽  
Laminar Flow ◽  
Flow Velocity ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Air Flow ◽  
Heated Plate ◽  
Flow Conditions ◽  
Air Flow Velocity ◽  
Laminar Flow Conditions

This paper presents the numerical studies of an irregular surface – a circular dimpled surface with different patterns of dimple arrangement (i.e., inline and staggered) and to identify the one that gives maximum heat transfer rate under laminar flow conditions. The comparative studies are made with a flat plate. The studies are carried out with inlet velocities 1 m/s and 49 m/s at laminar flow regimes. The investigations revealed that heat transfer rate increases as the air flow velocity increases and it decreases as the air flow velocity is decreased. Also, air flow contact with heated plate plays a vital role in heat transfer rate. Based on the study, it is concluded that the heat transfer rate depends on the surface area, air flow velocity and the air flow contact with the heated plate. At air velocities 1 m/s and 49 m/s, the heat transfer rate is highest for the circular dimple with staggered pattern under the laminar flow conditions.

Ferro-nanofluid squeeze film lubrication with heat transfer

2021 ◽  
pp. 135065012110276
Author(s):  
Manimegalai Kavarthalai ◽  
Vimala Ponnuswamy
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Contact Time ◽  
Transfer Rate ◽  
Fluid Layer ◽  
Darcy Law ◽  
Squeeze Film ◽  
Mean Temperature ◽  
Special Cases ◽  
The Impact

A theoretical study of a squeezing ferro-nanofluid flow including thermal effects is carried out with application to bearings and articular cartilages. A representational geometry of the thin layer of a ferro-nanofluid squeezed between a flat rigid disk and a thin porous bed is considered. The flow behaviours and heat transfer in the fluid and porous regions are investigated. The mathematical problem is formulated based on the Neuringer–Rosensweig model for ferro-nanofluids in the fluid region including an external magnetic field, Darcy law for the porous region and Beavers–Joseph slip condition at the fluid–porous interface. The expressions for velocity, fluid film thickness, contact time, fluid flux, streamlines, pathlines, mean temperature and heat transfer rate in the fluid and porous regions are obtained by using a perturbation method. An asymptotic solution for the fluid layer thickness is also presented. The problem is also solved by a numerical method and the results by asymptotic analysis, perturbation and numerical methods are obtained assuming a constant force squeezing state and are compared. It is shown that the results obtained by all the methods agree well with each other. The effects of various parameters such as Darcy number, Beavers–Joseph constant and magnetization parameter on the flow behaviours, contact time, mean temperature and heat transfer rate are investigated. The novel results showing the impact of using ferro-nanofluids in the two applications under consideration are presented. The results under special cases are further compared with the existing results in the literature and are found to agree well.

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