Pool Boiling Heat Transfer With Binary Mixture on Open Microchannel Surface

2013 ◽  
Author(s):  
Ankit Kalani ◽  
Satish G. Kandlikar
Keyword(s):  
Binary Mixture ◽  
Heat Dissipation ◽  
Surface Effect ◽  
Pure Water ◽  
Pool Boiling ◽  
Electronics Cooling ◽  
Working Fluid ◽  
Two Phase ◽  
Maximum Heat ◽  
Fluid Medium

Two-phase cooling is considered an attractive option for electronics cooling due to its ability to dissipate large quantities of heat. In recent years, pool boiling has shown tremendous ability in high heat dissipation applications. Researchers have used various fluid medium for pool boiling including water, alcohol, refrigerants, nanofluids and binary mixture. In the current work, binary mixture of water with ethanol was chosen as the working fluid. Plain copper chip was used as the boiling surface. Effect of various concentrations of binary mixture was investigated. A maximum heat flux of 1720 kW/m2 at a wall superheat of 28°C was recorded for 15% ethanol in water. It showed a 1.5 fold increase in CHF over pure water.

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.

Enhanced Pool Boiling With HFE7000 Over Selectively Sintered Microchannels

2017 ◽  
Author(s):  
Travis S. Emery ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Heat Dissipation ◽  
Pool Boiling ◽  
Electronics Cooling ◽  
Fold Increase ◽  
High Heat ◽  
Heat Fluxes ◽  
Dielectric Fluid ◽  
Maximum Heat ◽  
Maximum Heat Transfer

As the need for efficient thermal management grows, pool boiling’s ability to dissipate high heat fluxes has gained significant interest. The objective of this work was to study the performance of pool boiling at atmospheric pressure using a dielectric fluid, HFE7000. Both plain and enhanced copper surfaces were tested, and these results were then compared to similar testing performed with water and FC-87. The enhanced surfaces utilized microchannels with porous coatings selectively located on different regions of the heat transfer surface. A maximum critical heat flux (CHF) of 41.7 W/cm2 was achieved here, which translated to a 29% CHF increase in comparison to a plain chip. A maximum heat transfer coefficient (HTC) of 104.0 kW/m2°C was also achieved, which translated to a 6-fold increase in HTC when compared to a plain copper chip. More notably, this HTC was achieved at a wall temperature of 38.4 °C. This HTC enhancement was greater than that of water and FC-87 when using the same enhanced surface. The effect of sintering location was found to have a similar effect on CHF with HFE7000 in comparison with water. The effect of microchannel size was shown to have similar effects on CHF when compared with FC-87 and water. From the results found here, it is concluded that the employment of selectively sintered open microchannels with HFE7000 has significant potential for enhanced heat dissipation in electronics cooling applications.

Pool Boiling of FC-87 Over Microchannel Surfaces at Atmospheric Pressure

2012 ◽  
Author(s):  
Ankit Kalani ◽  
Satish G. Kandlikar
Keyword(s):  
Atmospheric Pressure ◽  
Pool Boiling ◽  
Electronics Cooling ◽  
Dielectric Fluid ◽  
Two Phase ◽  
Maximum Heat ◽  
Wall Superheat ◽  
Maximum Heat Flux ◽  
Two Phase Cooling ◽  
Surface Area Increase

Advances in technology and trends towards higher processing speeds have generated a greater need for thermal management. Two-phase cooling (boiling) has the ability to dissipate large amounts of heat and is attractive because of lower mass flow requirement and uniform substrate temperature. Further improvements can be obtained through passive surface enhancements. The objective of this work is to investigate the effect of microchannel surfaces on pool boiling performance at atmospheric pressure with FC-87. Being a dielectric fluid with a low normal boiling point, FC-87 has desirable characteristics for an electronics cooling fluid. A maximum heat flux of 550 kW/m2 at a wall superheat of 37°C was obtained with the microchannel surface. Surface area increase is noted as the primary reason for the enhanced performance for FC-87 on microchannel surfaces.

Effects of Varying Geometrical Parameters on Boiling From Microfabricated Enhanced Structures

2003 ◽  
Vol 125 (1) ◽  
pp. 103-109 ◽  
Author(s):  
C. Ramaswamy ◽  
Y. Joshi ◽  
W. Nakayama ◽  
W. B. Johnson
Keyword(s):  
Heat Dissipation ◽  
Layer Structure ◽  
Single Layer ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Geometrical Parameters ◽  
Small Range ◽  
Two Phase ◽  
Wall Superheat

The current study involves two-phase cooling from enhanced structures whose dimensions have been changed systematically using microfabrication techniques. The aim is to optimize the dimensions to maximize the heat transfer. The enhanced structure used in this study consists of a stacked network of interconnecting channels making it highly porous. The effect of varying the pore size, pitch and height on the boiling performance was studied, with fluorocarbon FC-72 as the working fluid. While most of the previous studies on the mechanism of enhanced nucleate boiling have focused on a small range of wall superheats (0–4 K), the present study covers a wider range (as high as 30 K). A larger pore and smaller pitch resulted in higher heat dissipation at all heat fluxes. The effect of stacking multiple layers showed a proportional increase in heat dissipation (with additional layers) in a certain range of wall superheat values only. In the wall superheat range 8–13 K, no appreciable difference was observed between a single layer structure and a three layer structure. A fin effect combined with change in the boiling phenomenon within the sub-surface layers is proposed to explain this effect.

Two-Phase Flow in Microchannels

2001 ◽  
Author(s):  
G. Hetsroni ◽  
A. Mosyak ◽  
Z. Segal
Keyword(s):  
Heat Sink ◽  
High Speed ◽  
Single Phase ◽  
Flow Boiling ◽  
Electronics Cooling ◽  
Working Fluid ◽  
Microchannel Heat Sink ◽  
Two Phase ◽  
Infrared Radiometry ◽  
Phase Water

Abstract Experimental investigation of a heat sink for electronics cooling is performed. The objective is to keep the operating temperature at a relatively low level of about 323–333K, while reducing the undesired temperature variation in both the streamwise and transverse directions. The experimental study is based on systematic temperature, flow and pressure measurements, infrared radiometry and high-speed digital video imaging. The heat sink has parallel triangular microchannels with a base of 250μm. According to the objectives of the present study, Vertrel XF is chosen as the working fluid. Experiments on flow boiling of Vertrel XF in the microchannel heat sink are performed to study the effect of mass velocity and vapor quality on the heat transfer, as well as to compare the two-phase results to a single-phase water flow.

scholarly journals Heat transfer and entropy generation in a microchannel with longitudinal vortex generators using Nanofluids

2020 ◽  
Author(s):  
Amin Ebrahimi ◽  
Farhad Rikhtegar Nezami ◽  
Amin Sabaghan ◽  
Ehsan Roohi
Keyword(s):  
Heat Transfer ◽  
Entropy Generation ◽  
Single Phase ◽  
Pure Water ◽  
Vortex Generators ◽  
Longitudinal Vortex ◽  
Working Fluid ◽  
Two Phase ◽  
Rectangular Microchannel ◽  
Important Conclusion

Conjugated heat transfer and hydraulic performance for nanofluid flow in a rectangular microchannel heat sink with LVGs (longitudinal vortex generators) are numerically investigated using at different ranges of Reynolds numbers. Three-dimensional simulations are performed on a microchannel heated by a constant heat flux with a hydraulic diameter of 160 μm and six pairs of LVGs using a single-phase model. Coolants are selected to be nanofluids containing low volume-fractions (0.5%–3.0%) of Al2O3 or CuO nanoparticles with different particle sizes dispersed in pure water. The employed model is validated and compared by published experimental, and single-phase and two-phase numerical data for various geometries and nanoparticle sizes. The results demonstrate that heat transfer is enhanced by 2.29–30.63% and 9.44%–53.06% for water-Al2O3 and water-CuO nanofluids, respectively, in expense of increasing the pressure drop with respect to pure-water by 3.49%–16.85% and 6.5%–17.70%, respectively. We have also observed that the overall efficiency is improved by 2.55%–29.05% and 9.78%–50.64% for water-Al2O3 and water-CuO nanofluids, respectively. The results are also analyzed in terms of entropy generation, leading to the important conclusion that using nanofluids as the working fluid could reduce the irreversibility level in the rectangular microchannel heat sinks with LVGs. No exterma (minimums) is found for total entropy generation for the ranges of parameters studied.

Dropwise Condensation on Carbon Steel Surface

2016 ◽  
Author(s):  
Fangyu Cao ◽  
Sean Hoenig ◽  
Chien-hua Chen
Keyword(s):  
Heat Transfer ◽  
Carbon Steel ◽  
Power Plants ◽  
Heat Dissipation ◽  
Low Cost ◽  
Condensation Heat Transfer ◽  
Working Fluid ◽  
High Heat Flux ◽  
Dropwise Condensation ◽  
Two Phase

The increasing demand of heat dissipation in power plants has pushed the limits of current two-phase thermal technologies such as heat pipes and vapor chambers. One of the most obvious areas for thermal improvement is centered on the high heat flux condensers including improved evaporators, thermal interfaces, etc, with low cost materials and surface treatment. Dropwise condensation has shown the ability to increase condensation heat transfer coefficient by an order of magnitude over conventional filmwise condensation. Current dropwise condensation research is focused on Cu and other special metals, the cost of which limits its application in the scale of commercial power plants. Presented here is a general use of self-assembled monolayer coatings to promote dropwise condensation on low-cost steel-based surfaces. Together with inhibitors in the working fluid, the surface of condenser is protected by hydrophobic coating, and the condensation heat transfer is promoted on carbon steel surfaces.

Reciprocating-Mechanism Driven Heat Loops and Their Applications

2003 ◽  
Author(s):  
Yiding Cao ◽  
Mingcong Gao
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Electronics Cooling ◽  
Working Fluid ◽  
High Heat Flux ◽  
Two Phase ◽  
Condenser Section ◽  
Evaporator Section ◽  
Two Phase Heat Transfer ◽  
Transfer Device

This paper introduces a novel heat transfer mechanism that facilitates two-phase heat transfer while eliminating the so-called cavitation problem commonly encountered by a conventional pump. The heat transfer device is coined as the reciprocating-mechanism driven heat loop (RMDHL), which includes a hollow loop having an interior flow passage, an amount of working fluid filled within the loop, and a reciprocating driver. The hollow loop has an evaporator section, a condenser section, and a liquid reservoir. The reciprocating driver is integrated with the liquid reservoir and facilitates a reciprocating flow of the working fluid within the loop, so that liquid is supplied from the condenser section to the evaporator section under a substantially saturated condition and the so-called cavitation problem associated with a conventional pump is avoided. The reciprocating driver could be a solenoid-operated reciprocating driver for electronics cooling applications and a bellows-type reciprocating driver for high-temperature applications. Experimental study has been undertaken for a solenoid-operated heat loop in connection with high heat flux thermal management applications. Experimental results show that the heat loop worked very effectively and a heat flux as high as 300 W/cm2 in the evaporator section could be handled. The applications of the bellows-type reciprocating heat loop for gas turbine nozzle guide vanes and the leading edges of hypersonic vehicles are also illustrated. The new heat transfer device is expected to advance the current two-phase heat transfer device and open up a new frontier for further research and development.

Compact Gravity Driven and Capillary-Sized Thermosyphon Loop for Power Electronics Cooling

2013 ◽  
Author(s):  
Francesco Agostini ◽  
Thomas Gradinger ◽  
Didier Cottet
Keyword(s):  
Electronics Cooling ◽  
Total Power ◽  
Working Fluid ◽  
Mutual Arrangement ◽  
Vertical Position ◽  
Two Phase ◽  
Air Temperatures ◽  
Power Modules ◽  
Gravity Driven ◽  
Valid Solution

A novel two-phase thermosyphon based on automotive technology is presented as a valid solution for the cooling of power-electronic semiconductor modules. A horizontal evaporator configuration is investigated. This solution is based on a 90°-shaped thermosyphon that allows an optimal geometrical arrangement of the cooler with limited volume occupancy, reduced air pressure drop, and weight as well as optimal thermal performance compared to standard heat-sink technology. The 90°-shape refers to the mutual arrangement of the evaporator body and the condenser; which are in a horizontal and vertical position, respectively. The evaporator cools three power modules with a total power loss between 500 and 1500 W. Experimental results are presented for inlet air temperatures ranging from 20 to 50 °C and for different air volume flow rates between 200 and 400 m3/h. The working fluid is refrigerant R245fa. The maximum thermal resistance (cooler base to air) attained values between 40 and 50 K/kW.

Experimental Investigation of Enhanced Two-Phase Evaporator Using Aluminum Foams

2015 ◽  
Author(s):  
Francesco Agostini ◽  
Waylon Puckett ◽  
Ryan Nelson ◽  
Daniele Torresin ◽  
Bruno Agostini ◽  
...  
Keyword(s):  
Aluminum Foam ◽  
Metal Foam ◽  
Electronics Cooling ◽  
Base Plate ◽  
Heat Fluxes ◽  
Experimental Results ◽  
Working Fluid ◽  
Vapor Flow ◽  
Base Temperature ◽  
Two Phase

A novel two-phase thermosyphon with a metal foam based evaporator is presented as a solution for the cooling of power-electronic semiconductor modules. A horizontal evaporator configuration is investigated: the evaporator consists of an aluminum chamber, with aluminum foam brazed to the base plate in three different configurations. One of the configurations has an open vapor chamber above the foam, another has foam filling the entire evaporator chamber, and the third has bores drilled in the foam parallel to the base plate from inlet to outlet along the direction of the vapor flow. The aluminum foam has a porosity of 95%, and a pore density of 20 PPI (pores per inch). A liquid distribution and a vapor collector chamber are respectively present at the entrance and at the exit of the evaporator. The power modules are attached on the evaporator body that collects the heat generated during the operation of the semiconductor devices. A vapor riser guides the vapor to a finned-tube air-cooled heat exchanger. A liquid downcomer from the condenser constantly feeds the evaporator channels. The system works with gravity-driven circulation only. The described system was designed and tested with an extensive experimental campaign. The evaporators were tested for power losses ranging between 500 and 3000 W, corresponding to applied heat fluxes between 3 and 20 W/cm2. The experimental results will be presented for inlet air at ambient temperature of 20°C with volumetric flow rates between 100 and 680 m3/h. The working fluid was refrigerant R245fa. The fluid filling effect was investigated. For each evaporator the results will be presented in terms of maximum thermal resistance and cooler base temperature. The base temperature distribution between different evaporators will also be presented and discussed being an important design parameter in power electronics cooling. Thermal resistances were measured between 15 and 30 K/kW. The experimental results indicated a promising conclusion favoring the implementation of aluminum foam evaporators for enhancement of heat transfer during pool boiling.

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