INFLUENCE OF VAPOR BUBBLES ON THE THERMAL PERFORMANCE OF A TWO-PHASE CLOSED THERMOSYPHON LOOP WITH A LIQUID HEAT TRANSFER AGENT

2016 ◽  
Vol 47 (12) ◽  
pp. 1109-1120
Author(s):  
Lingjiao Wei ◽  
Dazhong Yuan ◽  
Chaohong Guo ◽  
Dawei Tang
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Heat Transfer Agent ◽  
Vapor Bubbles ◽  
Two Phase ◽  
Liquid Heat

scholarly journals Flooded Two-Phase Flow Dynamics and Heat Transfer With Engineered Wettability on Microstructured Surfaces

2015 ◽  
Vol 137 (9) ◽  
Author(s):  
Bo Chen ◽  
Zhou Zhou ◽  
Junxiang Shi ◽  
Steven R. Schafer ◽  
Chung-Lung (C. L.) Chen
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Heat Dissipation ◽  
Upward Movement ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Vof Model ◽  
Pulling Forces ◽  
3D Volume ◽  
Hydrophobic Material

Due to excessive droplet feeding, a period of flooding occurs as part of a typical droplet based thermal management cycle. The conventional superhydrophilic surface, which is designed for thin film evaporation because of its highly wettable character, has a limited improvement on the thermal performance during the flooded condition. This paper investigates microstructures which combine micropillars and four engineered wettability patterns to improve the heat dissipation rate during flooding. Using the transient, 3D volume-of-fluid (VOF) model, the bubble behaviors of growth, coalescence, and departure are analyzed within different microstructures and the effects of pillar height and wettability patterns on the thermal performance are discussed. The wettability gradient patched on the pillar's side is demonstrated to promote the bubble's upward movement due to the contact angle difference between the upper and lower interfaces. However, insufficient pulling force results in large bubbles being pinned at the pillar tops, which forms a vapor blanket, and consequently decreases the heat transfer coefficient. When only a patch of hydrophobic material is present on the pillar top, effective pulling forces can be developed to help bubbles in the lower level depart from the pillar forest, since bubble merging between them generates most of the power required to pull the bubbles to the surface. The simulation results, including heat source temperatures and heat transfer coefficients, indicate that a patch of hydrophobic material on the pillar top works best out of all of the cases studied.

Determining the oxygen permeability of a film of liquid heat-transfer agent

1972 ◽  
Vol 14 (6) ◽  
pp. 529-530
Author(s):  
E. I. Frumin ◽  
N. K. Bizik ◽  
A. P. Zhudra
Keyword(s):  
Heat Transfer ◽  
Oxygen Permeability ◽  
Heat Transfer Agent ◽  
Liquid Heat

Heat Transfer From Vertical/Inclined Boundaries of Heat-Generating Boiling Pools

1982 ◽  
Vol 104 (3) ◽  
pp. 465-473 ◽  
Author(s):  
T. C. Chawla ◽  
S. H. Chan
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Thermal Expansion ◽  
Scaling Laws ◽  
Vapor Bubbles ◽  
Two Phase ◽  
Bulk Fluid ◽  
Upward Direction ◽  
Definition Of ◽  
Asymptotic Matching

A model for heat transfer from the sides of a volume heated boiling pool is proposed. Because of the density difference caused by volume boiling and by thermal expansion due to the temperature difference between the bulk fluid and the fluid near the wall, the lighter liquid and vapor bubbles cause movement of the bulk fluid in the upward direction. The rising liquid between the bubbles finds a return path along the walls or sides of the pool and forms a boundary layer which may be laminar in its initial length followed by transition to turbulent depending, of course, on the conditions prevailing at the entry to the sides and in the bulk of the pool. The analysis for the laminar case provides the definition of equivalent Grashof number for the combined two-phase and thermal expansion driven natural convection along the sides of pool. The turbulent boundary layer is analyzed by assuming a two-layer model in which the inner layer is characterized by viscous and conduction terms and the outer by mean convection terms. The similarity analysis of the governing equations yields universal profiles for temperature and velocity and the scaling laws for the inner and outer layers. An asymptotic matching of the temperature profile in the overlap region leads to a heat transfer law which correlates the available experimental data on volume heated boiling pools exceedingly well.

Experimental Characterization of a Carbon Fiber Composite Material Heat Sink in Boiling Heat Transfer Using FC-72

2006 ◽  
Author(s):  
Venugopal Gandikota ◽  
Harish Chengalvala ◽  
Amy S. Fleischer ◽  
G. F. Jones
Keyword(s):  
Heat Transfer ◽  
Composite Material ◽  
Carbon Fiber ◽  
Thermal Management ◽  
Thermal Performance ◽  
Heat Sink ◽  
Heat Fluxes ◽  
Two Phase ◽  
Operating Temperatures ◽  
Power Densities

The on-going trend towards increasing device performance while shrinking device size often results in escalating power densities and high operating temperatures. High operating temperatures may lead to reduced reliability and induced thermal stresses. Therefore, it is necessary to employ new and innovative thermal management techniques to maintain a suitable junction temperature at high power densities. For this reason, there is interest in a variety of liquid cooling techniques. This study analyzes a composite material heat sink. The heat sink consists of a very large number of small cross-section fins fabricated from carbon pitch fibers and epoxy. These carbon pitch fibers have a high thermal conductivity along the length of the fin. It is expected that the longer length will result in more heat transfer surface area and a more effective heat sink. This experimental study characterizes the thermal performance of the carbon-fiber heat sink in a two-phase closed loop thermosyphon using FC-72 as the operating fluid. The influence of heat load, thermosyphon fill volume, and condenser operating temperature on the overall thermal performance is examined. The results of this experiment provide significant insight into the possible implementation and benefits of carbon fiber heat sink technology in two-phase flow leading to significant improvements in thermal management strategies for advanced electronics. The carbon fiber heat sink yielded heat transfer coefficients in the range of 1300-1500 W/m2 K for heat fluxes in the range up to 3.2 W/cm2. Resistances in the range of 0.20 K/W – 0.23 K/W were achieved for the same heat fluxes. Condenser temperature and fill ratio did not show a significant effect on any of the results.

Spray Cooling of High Aspect Ratio Open Microchannels

2007 ◽  
Vol 129 (8) ◽  
pp. 1052-1059 ◽  
Author(s):  
Johnathan S. Coursey ◽  
Jungho Kim ◽  
Kenneth T. Kiger
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Thermal Performance ◽  
High Aspect Ratio ◽  
Flat Surface ◽  
Spray Cooling ◽  
Heat Sinks ◽  
Projected Area ◽  
Two Phase ◽  
Flux Flow

Direct spraying of dielectric liquids has been shown to be an effective method of cooling high-power electronics. Recent studies have illustrated that even higher heat transfer can be obtained by adding extended structures, particularly straight fins, to the heated surface. In the current work, spray cooling of high-aspect-ratio open microchannels was explored, which substantially increases the total surface area and allows more residence time for the incoming liquid to be heated by the wall. Five such heat sinks were constructed, and their thermal performance was investigated. These heat sinks featured a projected area of 1.41×1.41cm2, channel width of 360μm, a fin width of 500μm, and fin lengths of 0.25mm, 0.50mm, 1.0mm, 3.0mm, and 5.0mm. The five enhanced surfaces and a flat surface with the same projected area were sprayed with a full cone nozzle using PF-5060 at 30°C and nozzle pressure differences from 1.36–4.08atm(69–121ml∕min). In all cases, the enhanced surfaces improved thermal performance compared to the flat surface. Longer fins were found to outperform shorter ones in the single-phase regime. Adding fins also resulted in the onset of two-phase effects (and higher-heat transfer) at lower wall temperatures than the flat surface. The two-phase regime was characterized by a balance between added area, changing flow flux, flow channeling, and added conduction resistance. Spray efficiency calculations indicated that a much larger percentage of the liquid sprayed onto the enhanced surface evaporated than with the flat surface. Fin lengths between 1mm and 3mm appeared to be optimum for heat fluxes as high as 124W∕cm2 (based on projected area) and the range of conditions studied.

Thermal performance of self-rewetting gold nanofluids: Application to two-phase heat transfer devices

2021 ◽  
Vol 174 ◽  
pp. 121322
Author(s):  
Ibrahim Zaaroura ◽  
Souad Harmand ◽  
Julien Carlier ◽  
Malika Toubal ◽  
Aurélie Fasquelle ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Two Phase ◽  
Two Phase Heat Transfer
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