scholarly journals Simple Evaluation Method for Effective Thermal Conductivity of a Wick Structure Filled with a Working Fluid

2016 ◽  
Vol 7 ◽  
Author(s):  
Yasushi Koito ◽  
Ryo Yamaguchi ◽  
Toshio Tomimura
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Evaluation Method ◽  
Working Fluid ◽  
Wick Structure ◽  
Simple Evaluation

Experimental Investigation of Thermal Conduction Performance on Silicon-Based Micro Flat Heat Pipe

2015 ◽  
Vol 645-646 ◽  
pp. 1032-1037
Author(s):  
Cong Ming Li ◽  
Yi Luo ◽  
Chuan Peng Zhou ◽  
Liang Liang Zou ◽  
Xiao Dong Wang ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Heat Pipe ◽  
Effective Thermal Conductivity ◽  
Thermal Performance ◽  
Axial Direction ◽  
Filling Ratio ◽  
Parallel Structure ◽  
Working Fluid ◽  
Vacuum Degree ◽  
Structure Dimension

There are several factors that affect heat transfer of heat pipe, for example, structure dimension, filling ratio and vacuum degree of charging. This paper studied the thermal conductivity of micro flat heat pipes (MFHPs) with different structure dimension and with different filling ratio, when the charging vacuum degree of MFHP was decided. When electric power was 2W or 4W, MFHPs with parallel grooves and nonparallel grooves, charged by working fluid with different filling ratio, were carried out. And the filling ratio is 30%, 40% and 50%, respectively. The better thermal performance of MFHP can be evaluated by lower thermal resistance and higher effective thermal conductivity. The experiment results show that MFHP has the highest effective thermal conductivity when the filling ratio is 40%; and the thermal performance of MFHP with nonparallel structure in axial direction is better than that of MFHP with parallel structure.

Experimental Investigation of Graphene Oxide Nanofluids on Thermal Performance of Heat Pipe

2019 ◽  
Author(s):  
Weilin Zhao ◽  
Jun Xu ◽  
Jinkai Li
Keyword(s):  
Thermal Conductivity ◽  
Graphene Oxide ◽  
Heat Pipe ◽  
Effective Thermal Conductivity ◽  
Heat Pipes ◽  
Air Cooling ◽  
Coating Film ◽  
Water Cooling ◽  
Condenser Section ◽  
Wick Structure

Abstract The graphene oxide-deionized water (GO-DW) and graphene oxide-ethylence glycol (GO-EG) nanofluids were synthesized. The better suspension of nanofluids was achieved. The thermal conductivity of both nanofluids was analyzed. It indicates that GO nanoparticles can strengthen the thermal conductivity of DW base fluids by 22.6%–61.7% and EG base fluids by 15.3%–32.8%. Four copper heat pipes charged with GO-DW and GO-EG nanofluids as well as DW and EG base fluids were experimentally researched, it is discovered that the addition of GO nonoparticles in heat pipe can elevate the condenser wall temperature and reduce the temperature difference. Future analysis finds that, with respect to DW and EG fluids heat pipe, the thermal resistances of GO-DW and GO-EG nanofluids heat pipe are respectively decreased 42.6–52.4% and 31.9%–38.4% for air cooling, and 15.5–16.7% and 11.5%–18.9% for water cooling at condenser section. Besides, the wick structure of GO-DW nanofluids heat pipe was examined by Scanning Electron Microscope, and the effective thermal conductivity of fluid-wick combination was evaluated. The outcomes demonstrate that the evaporator wick surface contains about 0375–1.24μm coating film of GO nanoparticles. Assumed the coating film is 0.75μm, the effective thermal conductivity of fluid-wick combination is respectively enhanced by 66.92 % for GO-DW nonofluids heat pipe and 37.32% for GO-EG nonofluids heat pipe at 70 °C.

Numerical Investigation of the Steady State Operation of a Cylindrical Capillary Pumped Loop Evaporator

2000 ◽  
Author(s):  
Y. H. Yan ◽  
J. M. Ochterbeck
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Steady State ◽  
Effective Thermal Conductivity ◽  
Liquid Core ◽  
Phase Region ◽  
Capillary Pumped Loop ◽  
Two Phase ◽  
Cylindrical Capillary ◽  
Wick Structure

Abstract A two-dimensional numerical model was established to study the behavior of a cylindrical capillary pumped loop evaporator under steady-state operations. The influence of heat load, liquid subcooling and effective thermal conductivity of the wick structure on the evaporator performance were studied. It was found that increasing the applied heat flux and degree of liquid subcooling resulted in a decrease the temperature in the liquid core. This helped to prevent the vapor from generating in the liquid core and decreased the length of the two phase region in the wick structure. Decreasing the effective thermal conductivity also decreases the temperature in the liquid core as related to the back wick condition. It was observed that for a given liquid subcooling, a minimum heat flux exists below which vapor will generate in the liquid core and render the evaporator non-operational. It was also observed that for a given heat flux, a minimum required liquid subcooling exists. Vapor may form in the liquid core when the liquid subcooling is less than the minimum value.

Evaluation of Effective Thermal Conductivity of Multilayer Printed Circuit Board

2011 ◽  
Author(s):  
Toshio Tomimura ◽  
Yoshihiro Shiotsu ◽  
Yasushi Koito ◽  
Masaru Ishizuka ◽  
Tomoyuki Hatakeyama
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Printed Circuit Board ◽  
Evaluation Method ◽  
Circuit Board ◽  
Printed Circuit ◽  
Plane Direction ◽  
Simple Evaluation

To perform a rational thermal design of a printed circuit board (PCB) with highly anisotropic heat transfer nature in its initial stage, effective thermal conductivities in thickness direction and in in-plane direction must be given depending on the electric circuit of the board. However, a simple evaluation method for the effective thermal conductivities of such PCB has not been developed yet. In this study, as the first step to propose a simple evaluation method, the heat transfer coefficient by natural convection around a horizontal disk, which is indispensable for measuring the effective thermal conductivity, has been evaluated. Furthermore, the thermal conductivity of the glass epoxy resin in in-plane direction has been evaluated by applying the evaluated heat transfer coefficient, and then, the validity of the proposed thermal conductivity measurements of the anisotropic PCB has been confirmed.

Numerical Investigation of the Steady-State Operation of a Cylindrical Capillary Pumped Loop Evaporator

2003 ◽  
Vol 125 (2) ◽  
pp. 251-260 ◽  
Author(s):  
Y. H. Yan ◽  
J. M. Ochterbeck
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Steady State ◽  
Effective Thermal Conductivity ◽  
Liquid Core ◽  
Phase Region ◽  
Model Parameters ◽  
Capillary Pumped Loop ◽  
Cylindrical Capillary ◽  
Wick Structure

A cylindrical capillary pumped loop evaporator operating under steady-state conditions was studied using a two-dimensional numerical model. Parameters affecting the phase conditions in the wick structure and thermal-fluid behavior in the evaporator liquid core were studied. The influences of heat load, liquid subcooling, and effective thermal conductivity of the wick structure were specifically selected to evaluate evaporator performance. Either increasing the applied heat flux and/or degree of inlet liquid subcooling resulted in decreased liquid core temperature, which is favorable for proper evaporator operation. This helps prevent conditions that may allow vapor formation in the liquid core as well as result in decreased length of the two-phase region in the wick structure. Decreasing the effective thermal conductivity of the wick also decreases the temperature in the liquid core. For a given liquid subcooling, a minimum heat flux exists below which vapor will generate in the liquid core and render the evaporator nonoperational. Additionally, for a given heat flux, a minimum required liquid subcooling exists as conditions are such that vapor potentially may form in the liquid core when the liquid subcooling is less than a minimum value.

A Titanium Based Flat Heat Pipe

2008 ◽  
Author(s):  
Changsong Ding ◽  
Gaurav Soni ◽  
Payam Bozorgi ◽  
Brian Piorek ◽  
Carl D. Meinhart ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Aspect Ratio ◽  
Heat Pipe ◽  
Carrying Capacity ◽  
High Aspect Ratio ◽  
Capillary Flow ◽  
Titanium Substrate ◽  
Heat Pipes ◽  
Working Fluid ◽  
Wick Structure

We are developing innovative heat pipes based on Nano-Structured Titania (NST) with a potential for high heat carrying capacity and high thermal conductivity. These heat pipes have a flat geometry as opposed to a cylindrical geometry found in conventional heat pipes. The flatness will enable a good contact with microprocessor chips and thus reduce the thermal contact resistance. We refer to it as a Thermal Ground Plane (TGP) because of its flat and thin geometry. It will provide the ability to cool the future generations of power intensive microprocessor chips and circuit boards in an efficient way. It also brings the potential to function in high temperature (>150°C) fields because of its high yield strength and compatibility [1]. The TGP is fabricated with Titanium. It adopts the recently developed high aspect ratio Ti processing techniques [2] and laser packaging techniques. The three main components of the TGP are 1) a fine wick structure based on arrays of high aspect ratio Ti pillars and hair like structures of Nano-Structured Titania (NST), 2) A shallow Ti cavity welded onto the wick structure and 3) the working fluid, water, sealed between the cavity and the wick. The heat carrying capacity and the thermal conductivity of a heat pipe are generally determined by the speed of capillary flow of the working fluid through its wick. The TGP wick has the potential to generate high flow rates and to meet the growing challenges faced by electronics cooling community. The TGP wick structure, developed by etching high aspect ratio pillars in a titanium substrate and growing nano scale hairs on the surface of the pillars, is super hydrophilic and capable of wicking water at velocities ∼ 10−2 m/s over distances of several centimeters. The thermal conductivity of the current TGP device was measured to be k = 350 W/m·K. The completed TGP device has the potential of attaining a higher conductivity by improving the wicking material and of carrying higher power density. Washburn equation [3] for dynamics of capillary flow has been employed to explain the results of our experiments. The experiment shows a good agreement with Washburn equation.

A Vapor Chamber Using Graphite Foams as Wicks for Cooling High Heat Flux Electronics

2005 ◽  
Author(s):  
Minhua Lu ◽  
Larry Mok ◽  
R. J. Bezama
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
High Heat ◽  
High Thermal Conductivity ◽  
Working Fluid ◽  
High Heat Flux ◽  
Vapor Chamber ◽  
Capillary Limit ◽  
Wick Structure ◽  
Graphite Foam

A vapor chamber using high thermal conductivity and permeability graphite foam as a wick has been designed, built and tested. With ethanol as the working fluid, the vapor chamber has been demonstrated at a heat flux of 80 W/cm2. The effects of the capillary limit, the boiling limit, and the thermal resistance in restricting the overall performance of a vapor chamber have been analyzed. Because of the high thermal conductivity of the graphite foams, the modeling results show that the performance of a vapor chamber using a graphite foam is about twice that of one using a copper wick structure. Furthermore, if water is used as the working fluid instead of ethanol, the performance of the vapor chamber will be increased further. Graphite foam vapor chambers with water as the working fluid can be made by treating the graphite foam with an oxygen plasma to improve the wetting of the graphite by the water.

A Graphite Foams Based Vapor Chamber for Chip Heat Spreading

2005 ◽  
Vol 128 (4) ◽  
pp. 427-431 ◽  
Author(s):  
Minhua Lu ◽  
Larry Mok ◽  
R. J. Bezama
Keyword(s):  
Thermal Conductivity ◽  
Oxygen Plasma ◽  
High Thermal Conductivity ◽  
Working Fluid ◽  
Vapor Chamber ◽  
Capillary Limit ◽  
Wick Structure ◽  
Overall Performance ◽  
Heat Spreading ◽  
Graphite Foam

A vapor chamber using high thermal conductivity and permeability graphite foam as a wick has been designed, built, and tested. With ethanol as the working fluid, the vapor chamber has been demonstrated at a heat flux of 80W∕cm2. The effects of the capillary limit, the boiling limit, and the thermal resistance in restricting the overall performance of a vapor chamber have been analyzed. Because of the high thermal conductivity of the graphite foams, the modeling results show that the performance of a vapor chamber using a graphite foam is about twice that of one using a copper wick structure. Furthermore, if water is used as the working fluid instead of ethanol, the performance of the vapor chamber will be increased further. Graphite foam vapor chambers with water as the working fluid can be made by treating the graphite foam with an oxygen plasma to improve the wetting of the graphite by the water.

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