Thermal Characteristics of Graphite Foam Thermosyphon for Electronics Cooling

2003 ◽  
Author(s):  
Hongkoo Roh ◽  
Jungho Kim ◽  
Paul J. Boudreaux
Keyword(s):  
Thermal Conductivity ◽  
Thermal Management ◽  
Thermal Characteristics ◽  
Electronics Cooling ◽  
Liquid Level ◽  
Working Fluid ◽  
Low Density ◽  
Thermal Management Of Electronics ◽  
Graphite Foam ◽  
Density Results

Graphite foams consist of a network of interconnected graphite ligaments and are beginning to be applied to thermal management of electronics. The thermal conductivity of the bulk graphite foam is similar to aluminum, but graphite foam has one-fifth the density of aluminum. This combination of high thermal conductivity and low density results in a specific thermal conductivity about five times higher than that of aluminum, allowing heat to rapidly propagate into the foam. This heat is spread out over the very large surface area within the foam, enabling large amounts of energy to be transferred with relatively low temperature difference. For the purpose of graphite foam thermosyphon design in electronics cooling, various effects such as graphite foam geometry, sub-cooling, working fluid effect, and liquid level were investigated in this study. The best thermal performance was achieved with the large graphite foam, working fluid with the lowest boiling point, a liquid level with the exact height of the graphite foam, and at the lowest sub-cooling temperature.

Graphite Foam Thermosyphon Evaporator Performance: Parametric Investigation of the Effects of Working Fluid, Liquid Level, and Chamber Pressure

2002 ◽  
Author(s):  
Johnathan S. Coursey ◽  
Hongkoo Roh ◽  
Jungho Kim ◽  
Paul J. Boudreaux
Keyword(s):  
Thermal Conductivity ◽  
Thermal Diffusivity ◽  
Thermal Management ◽  
Liquid Level ◽  
Chamber Pressure ◽  
Working Fluid ◽  
Low Density ◽  
Thermal Management Of Electronics ◽  
Graphite Foam ◽  
Density Results

Graphite foams have recently been developed at ORNL and are beginning to be applied to thermal management of electronics. These foams consist of a network of interconnected graphite ligaments whose thermal conductivities are up to five times higher than copper. The thermal conductivity of the bulk graphite foam is similar to aluminum, but graphite foam has one-fifth the density of aluminum. This combination of high thermal conductivity and low density results in a thermal diffusivity about four times higher than that of aluminum, allowing heat to rapidly propagate into the foam. This heat is spread out over the very large surface area within the foam, enabling large amounts of energy to be transferred with relatively low temperature difference. The use of graphite foam as the evaporator of a thermosyphon is investigated due to its potential to transfer large amounts of energy without the need for external pumping. A preliminary optimization of the parameters governing evaporator performance is performed using 2-level factorial design. Performance of the system with both PF-5060 and PF-5050 were examined as well as the effects of liquid level and chamber pressure.

Experimental investigation on the thermal performance of Si micro-heat pipe with different cross-sections

2017 ◽  
Vol 31 (30) ◽  
pp. 1750279 ◽  
Author(s):  
Mohammad Hamidnia ◽  
Yi Luo ◽  
Xiaodong Wang ◽  
Congming Li
Keyword(s):  
Thermal Management ◽  
Thermal Performance ◽  
Cross Sections ◽  
Integrated Circuit ◽  
Thermal Characteristics ◽  
Cost Savings ◽  
Working Fluid ◽  
Cross Sectional ◽  
Si Substrates ◽  
Silicon Based

Increasing component densities of the integrated circuit (IC) and packaging levels has led to thermal management problems. Si substrates with embedded micro-heat pipes (MHPs) couple good thermal characteristics and cost savings associated with IC batch processing. The thermal performance of MHP is intimately related to the cross-sectional geometry. Different cross-sections are designed in order to enhance the backflow of working fluid. In this experimental study, three different Si MHPs with same hydraulic diameter and various cross-sections are fabricated by micro-fabrication methods and tested under different conditions of fluid charge ratios. The results show that the trapezoidal MHP associated with rectangular artery which is charged with 40% of vapor chamber’s volume has the best thermal performance. This silicon-based MHP is a passive approach for thermal management, which could widen applications in the commercial electronics industry and LED lightings.

scholarly journals Investigation of Counterflow Microchannel Heat Exchanger with Hybrid Nanoparticles and PCM Suspension as a Coolant

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Mushtaq I. Hasan ◽  
Mohammad J. Khafeef ◽  
Omid Mohammadi ◽  
Suvanjan Bhattacharyya ◽  
Alibek Issakhov
Keyword(s):  
Thermal Conductivity ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Pure Water ◽  
Thermal Characteristics ◽  
Hybrid Nanoparticles ◽  
Working Fluid ◽  
Microchannel Heat Exchanger ◽  
Noticeable Increase ◽  
Nanoparticles Concentration

The effect of the hybrid suspension on the intrinsic characteristics of microencapsulated phase change material (MEPCM) slurry used as a coolant in counterflow microchannel heat exchanger (CFMCHE) with different velocities is investigated numerically. The working fluid used in this paper is a hybrid suspension consisting of nanoparticles and MEPCM particles, in which the particles are suspended in pure water as a base fluid. Two types of hybrid suspension are used (Al2O3 + MEPCM and Cu + MEPCM), and the hydrodynamic and thermal characteristics of these suspensions flowing in a CFMCHE are numerically investigated. The results indicated that using hybrid suspension with high flow velocities improves the performance of the microchannel heat exchanger while resulting in a noticeable increase in pressure drop. Thereupon, it causes a decrease in the performance index. Moreover, it was found that the increment of the nanoparticles’ concentration can rise the low thermal conductivity of the MEPCM slurry, but it also leads to a noticeable increase in pressure drop. Furthermore, it was found that as the thermal conductivity of Cu is higher than that for Al2O3, the enhancement in heat transfer is higher in case of adding Cu particles compared with Al2O3 particles. Therefore, the effectiveness of these materials depends strongly on the application at which CFMCHE is employed.

Experimental Analysis of the Impact of Nanoinclusions and Surfactants on the Viscosity of Paraffin-Based Energy Storage Materials

2018 ◽  
Vol 140 (11) ◽  
Author(s):  
Rebecca Weigand ◽  
Kieran Hess ◽  
Amy S. Fleischer
Keyword(s):  
Thermal Conductivity ◽  
Energy Storage ◽  
Thermal Management ◽  
Phase Change Materials ◽  
Positive Impact ◽  
Energy Storage Materials ◽  
Multiwalled Carbon ◽  
Thermal Management Of Electronics ◽  
Transient Thermal ◽  
The Impact

Phase change materials (PCMs) are commonly used in many applications, including the transient thermal management of electronics. For many systems, paraffin-based PCMs are used with suspended nanoinclusions to increase their effective thermal conductivity. The addition of these materials can have a positive impact on thermal conductivity, but can also increase the viscosity in the liquid phase. In this paper, the impact of different nanoinclusions and surfactants on the dynamic viscosity of a common paraffin wax PCM is quantified in order to determine their suitability for thermal energy storage applications. The effect of the nanoparticles on the viscosity is found to be a function of the nanoparticle type with multiwalled carbon nanotubes (MWCNT) yielding the greatest increase in viscosity. The addition of both nanoparticle and surfactant to the base PCM is found to affect the viscosity even when the loading levels of the nanoparticles or surfactant alone are not enough to affect the viscosity, thus the combination must be carefully considered in any heat transfer application.

Graphite Foam Thermal Management of a High Packing Density Array of Power Amplifiers

2005 ◽  
Vol 128 (4) ◽  
pp. 456-465 ◽  
Author(s):  
Z. A. Williams ◽  
J. A. Roux
Keyword(s):  
Thermal Management ◽  
Base Plate ◽  
Cooling Channel ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Chip Technology ◽  
Thermal Management Of Electronics ◽  
Computational Fluid Dynamics Cfd ◽  
Plate Channel ◽  
Graphite Foam

Much focus has been placed on the thermal management of electronics in recent years. An overall reduction in size of electronic components as well as advances in chip technology, leading to ever higher power dissipation, have increased the necessity for innovative cooling designs. While computational fluid dynamics (CFD) software packages have been instrumental in the design of cooling systems, it remains important to validate these CFD predictions through experimentation. The present work focuses on the experimental evaluation of several variations of an air cooled base plate channel design for an array of generic power amplifier modules. In the current study two materials, graphite foam and a microfibrous material, are investigated as mini-heat exchangers to be implemented in the cooling channel of the base plate. Computational simulations have been conducted on some of the proposed designs in order to evaluate certain parameters. Experiments were conducted measuring chip temperatures and the pressure drop across the cooling channel. Effective heat transfer coefficients were also reverse engineered.

Enhanced Pool Boiling With Ethanol at Subatmospheric Pressures for Electronics Cooling

2013 ◽  
Vol 135 (11) ◽  
Author(s):  
Ankit Kalani ◽  
Satish G. Kandlikar
Keyword(s):  
Thermal Management ◽  
Heat Dissipation ◽  
Pool Boiling ◽  
Saturation Temperature ◽  
Electronics Cooling ◽  
High Heat ◽  
Working Fluid ◽  
Practical Implementation ◽  
High Heat Flux ◽  
Cooling Systems

The growing trend in miniaturization of electronics has generated a need for efficient thermal management of these devices. Boiling has the ability to dissipate a high heat flux while maintaining a small temperature difference. A vapor chamber with pool boiling offers an effective way to provide cooling and to maintain temperature uniformity. The objective of the current work is to investigate pool boiling performance of ethanol on enhanced microchannel surfaces. Ethanol is an attractive working fluid due to its better heat transfer performance and higher heat of vaporization compared to refrigerants, and lower normal boiling point compared to water. The saturation temperature of ethanol can be further reduced to temperatures suitable for electronics cooling by lowering the pressure. Experiments were performed at four different absolute pressures, 101.3 kPa, 66.7 kPa, 33.3 kPa, and 16.7 kPa using different microchannel surface configurations. Heat dissipation in excess of 900 kW/m2 was obtained while maintaining the wall surface below 85 °C at 33 kPa. Flammability, toxicity, and temperature overshoot issues need to be addressed before practical implementation of ethanol-based cooling systems can occur.

High-Flux Thermal Management With Supercritical Fluids

2016 ◽  
Vol 138 (12) ◽  
Author(s):  
Brian M. Fronk ◽  
Alexander S. Rattner
Keyword(s):  
Heat Flux ◽  
Thermal Management ◽  
Heat Sink ◽  
Electronics Cooling ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Management Approach ◽  
High Heat Flux ◽  
Two Phase ◽  
Pump Design

A novel thermal management approach is explored, which uses supercritical carbon dioxide (sCO2) as a working fluid to manage extreme heat fluxes in electronics cooling applications. In the pseudocritical region, sCO2 has extremely high volumetric thermal capacity, which can enable operation with low pumping requirements, and without the potential for two-phase critical heat flux (CHF) and flow instabilities. A model of a representative microchannel heat sink is evaluated with single-phase liquid water and FC-72, two-phase boiling R-134a, and sCO2. For a fixed pumping power, sCO2 is found to yield lower heat-sink wall temperatures than liquid coolants. Practical engineering challenges for supercritical thermal management systems are discussed, including the limits of predictive heat transfer models, narrow operating temperature ranges, high working pressures, and pump design criteria. Based on these findings, sCO2 is a promising candidate working fluid for cooling high heat flux electronics, but additional thermal transport research and engineering are needed before practical systems can be realized.

Promising Technology for Electronic Cooling: Nanofluidic Micro Pulsating Heat Pipes

2013 ◽  
Vol 135 (2) ◽  
Author(s):  
Kambiz Jahani ◽  
Maziar Mohammadi ◽  
Mohammad Behshad Shafii ◽  
Zahra Shiee
Keyword(s):  
Magnetic Field ◽  
Thermal Resistance ◽  
Thermal Management ◽  
Thermal Performance ◽  
Microelectromechanical Systems ◽  
Heat Pipes ◽  
Electronic Cooling ◽  
Working Fluid ◽  
Pulsating Heat Pipe ◽  
Thermal Management Of Electronics

Currently, the thermal management of microelectromechanical systems (MEMS) has become a challenge. In the present research, a micro pulsating heat pipe (MPHP) with a hydraulic diameter of 508 μm, is experimented. The thermal performance of the MPHP in both the transient and steady conditions, the effects of the working fluid (water, silver nanofluid, and ferrofluid), heating power (4, 8, 12, 16, 20, 24, and 28 W), charging ratio (20, 40, 60, and 80%), inclination angle (0 deg, 25 deg, 45 deg, 75 deg, and 90 deg relative to horizontal axis), and the application of magnetic field, are investigated and thoroughly discussed. The experimental results show that the optimum charging ratio for water is 40%, while this optimum for nanofluids is 60%. In most of situations, the nanofluid charged MPHPs have a lower thermal resistance relative to the water charged ones. For ferrofluid charged MPHP, the application of a magnetic field substantially reduces the thermal resistance. This study proposes an outstanding technique for the thermal management of electronics.

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.

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