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.

Thermal Conductivity and Operating Temperature Effect on the Interline Region in a Micro/Miniature Heat Pipe

2008 ◽  
Author(s):  
Hani H. Sait ◽  
Steve M. Demsky ◽  
HongBin Ma
Keyword(s):  
Thin Film ◽  
Thermal Conductivity ◽  
Heat Flux ◽  
Operating Temperature ◽  
High Heat ◽  
Working Fluid ◽  
High Heat Flux ◽  
Thin Film Evaporation ◽  
Film Evaporation ◽  
Frictional Shear Stress

An analytical model describing thin film evaporation is developed that includes the effects of surface tension, frictional shear stress, wetting characteristics and disjoining pressure. The effects of thermal conductivity of working fluids and operating temperature on the evaporating thin film region are also studied. The results indicate that when the thermal conductivity of the working fluid increases, a high heat flux can be removed from the evaporating thin film region. The operating temperature affects the thin film evaporation. The higher the operating temperature, the more heat flux can be removed from the region. The information of thin film evaporation presented in the paper results in a better understanding of heat transfer mechanism occurring in micro heat pipes.

Application of Al2O3 Nanofluid on Sintered Copper-Powder Vapor Chamber for Electronic Cooling

2013 ◽  
Vol 789 ◽  
pp. 423-428 ◽  
Author(s):  
Nandy Putra ◽  
Wayan Nata Septiadi ◽  
Ranggi Sahmura ◽  
Cahya Tri Anggara
Keyword(s):  
Heat Flux ◽  
Thermal Performance ◽  
Base Fluid ◽  
Cooling System ◽  
High Heat ◽  
Electronic Cooling ◽  
Working Fluid ◽  
High Heat Flux ◽  
Processing Unit ◽  
Vapor Chamber

The development of electronic devices pushes manufacturers to create smaller microchips with higher performance than ever before. Microchip with higher working load produces more heat. This leads to the need of cooling system that able to dissipate high heat flux. Vapor chamber is one of highly effective heat spreading device. Its ability to dissipate high heat flux density in limited space made it potential for electronic cooling application, like Central Processing Unit (CPU) cooling system. The purpose of this paper is to study the application of Al2O3Nanofluid as working fluid for vapor chamber. Vapor chamber performance was measured in real CPU working condition. Al2O3Nanofluid with concentration of 0.1%, 0.3%, 0.5%, 1%, 2% and 3% as working fluid of the vapor chamber were tested and compared with its base fluid, water. Al2O3nanofluid shows better thermal performance than its base fluid due to the interaction of particle enhancing the thermal conductivity. The result showed that the effect of working fluid is significant to the performance of vapor chamber at high heat load, and the application of Al2O3nanofluid as working fluid would enhance thermal performance of vapor chamber, compared to other conventional working fluid being used before.

Development of a High Performance Vapor Chamber for High Heat Flux Applications

2008 ◽  
Author(s):  
Yuan Zhao ◽  
Chung-Lung Chen
Keyword(s):  
Heat Flux ◽  
High Performance ◽  
Experimental Tests ◽  
High Heat ◽  
Heat Fluxes ◽  
High Heat Flux ◽  
Vapor Chamber ◽  
Porous Network ◽  
Heat Spreader ◽  
Wick Structure

This paper introduces a high performance vapor chamber heat spreader with a novel bi-dispersed wick structure. The main wick structure is a sintered porous network in a latticed pattern, which contains not only small pores to transport liquid by capillary forces, but also many slots to provide large passages to vent vapor from heated surfaces. The copper particles have a diameter of approximately 50 μm; they produce an effective pore radius of approximately 13 μm after sintering. The slots have a typical width of approximately 500 μm. Unlike traditional bi-dispersed wick structures, the latticed wick structures provide undisrupted liquid delivery passages and vapor escape channels and thus greatly improve the heat transfer performance. Preliminary experimental tests were conducted and the results were analyzed. It was shown by the experiments that vapor chamber heat spreaders with the latticed wicks present three times improvement on heat spreading performance, comparing with a solid copper heat spreader, and much improved capacity to handle hot spots with local heat fluxes exceeding 300 W/cm2, which will have great impacts on extending heat pipe technology from traditional low to medium heat fluxes to high heat flux applications.

A Numerical Model of a Reciprocating-Mechanism Driven Heat Loop for Two-Phase High Heat Flux Cooling

2016 ◽  
Vol 8 (4) ◽  
Author(s):  
Olubunmi Popoola ◽  
Ayobami Bamgbade ◽  
Yiding Cao
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Numerical Model ◽  
Performance Optimization ◽  
Numerical Study ◽  
High Heat ◽  
Working Fluid ◽  
High Heat Flux ◽  
Two Phase ◽  
Transfer Device

An effective design option for a cooling system is to use a two-phase pumped cooling loop to simultaneously satisfy the temperature uniformity and high heat flux requirements. A reciprocating-mechanism driven heat loop (RMDHL) is a novel heat transfer device that could attain a high heat transfer rate through a reciprocating flow of the two-phase working fluid inside the heat transfer device. Although the device has been tested and validated experimentally, analytical or numerical study has not been undertaken to understand its working mechanism and provide guidance for the device design. The objective of this paper is to develop a numerical model for the RMDHL to predict its operational performance under different working conditions. The developed numerical model has been successfully validated by the existing experimental data and will provide a powerful tool for the design and performance optimization of future RMDHLs. The study also reveals that the maximum velocity in the flow occurs near the wall rather than at the center of the pipe, as in the case of unidirectional steady flow. This higher velocity near the wall may help to explain the enhanced heat transfer of an RMDHL.

Flow Boiling Enhancement in Microchannels With Diffusion Bonded Wire Mesh

2007 ◽  
Author(s):  
Hailei Wang ◽  
Richard Peterson
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
High Heat ◽  
Wire Mesh ◽  
Working Fluid ◽  
High Heat Flux ◽  
Vapor Quality ◽  
Heating Wall

Flow boiling and heat transfer enhancement in four parallel microchannels using a dielectric working fluid, HFE 7000, was investigated. Each channel was 1000 μm wide and 510 μm high. A unique channel surface enhancement technique via diffusion bonding a layer of conductive fine wire mesh onto the heating wall was developed. According to the obtained flow boiling curves for both the bare and mesh channels, the amount of wall superheat was significantly reduced for the mesh channel at all stream-wise locations. This indicated that the nucleate boiling in the mesh channel was enhanced due to the increase of nucleation sites the mesh introduced. Both the nucleate boiling dominated and convective evaporation dominated regimes were identified. In addition, the overall trend for the flow boiling heat transfer coefficient, with respect to vapor quality, was increasing until the vapor quality reached approximately 0.4. The critical heat flux (CHF) for the mesh channel was also significantly higher than that of the bare channel in the low vapor quality region. Due to the fact of how the mesh was incorporated into the channels, no pressure drop penalty was identified for the mesh channels. Potential applications for this kind of mesh channel include high heat-flux electronic cooling systems and various energy conversion systems.

Nucleate Boiling of Dielectric Liquids on Hydrophobic Patterned Surfaces

2014 ◽  
Author(s):  
Nihal E. Joshua ◽  
Denesh K. Ajakumar ◽  
Huseyin Bostanci
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Nucleate Boiling ◽  
High Heat ◽  
Copper Surface ◽  
Dielectric Liquid ◽  
Working Fluid ◽  
Patterned Surfaces ◽  
High Heat Flux ◽  
Dielectric Liquids

This study experimentally investigated the effect of hydrophobic patterned surfaces in nucleate boiling heat transfer. A dielectric liquid, HFE-7100, was used as the working fluid in the saturated boiling tests. Dielectric liquids are known to have highly-wetting characteristics. They tend to fill surface cavities that would normally trap vapor/gas, and serve as active nucleation sites during boiling. With the lack of these vapor filled cavities, boiling of a dielectric liquid leads to high incipience superheats and accompanying temperature overshoots. Heater samples in this study were prepared by applying a thin Teflon (AF400, Dupont) coating on 1-cm2 smooth copper surfaces following common photolithography techniques. Matching size thick film resistors, attached onto the copper samples, generated heat and simulated high heat flux electronic devices. Tests investigated the heater samples featuring circular pattern sizes between 40–100 μm, and corresponding pitch sizes between 80–200 μm. Additionally, a plain, smooth copper surface was tested to obtain reference data. Based on data, hydrophobic patterned surfaces effectively eliminated the temperature overshoot at boiling incipience, and considerably improved nucleate boiling performance in terms of heat transfer coefficient and critical heat flux over the reference surface. Hydrophobic patterned surfaces therefore demonstrated a practical surface modification method for heat transfer enhancement in immersion cooling applications.

Sign in / Sign up

Export Citation Format

Share Document