This paper explores the recent research developments in high-heat-flux thermal management. Cooling schemes such as pool boiling, detachable heat sinks, channel flow boiling, microchannel and mini-channel heat sinks, jet-impingement, and sprays, are discussed and compared relative to heat dissipation potential, reliability, and packaging concerns. It is demonstrated that, while different cooling options can be tailored to the specific needs of individual applications, system considerations always play a paramount role in determining the most suitable cooling scheme. It is also shown that extensive fundamental electronic cooling knowledge has been amassed over the past two decades. Yet there is now a growing need for hardware innovations rather than perturbations to those fundamental studies. An example of these innovations is the cooling of military avionics, where research findings from the electronic cooling literature have made possible the development of a new generation of cooling hardware which promise order of magnitude increases in heat dissipation compared to today's cutting edge avionics cooling schemes.

Assessment of high-heat-flux thermal management schemes

Boiling water in small channels that are formed along turbine blades has been examined since the 1970s as a means to dissipating large amounts of heat. Later, similar geometries could be found in cooling systems for computers, fusion reactors, rocket nozzles, avionics, hybrid vehicle power electronics, and space systems. This paper addresses (a) the implementation of two-phase microchannel heat sinks in these applications, (b) the fluid physics and limitations of boiling in small passages, and effective tools for predicting the thermal performance of heat sinks, and (c) means to enhance this performance. It is shown that despite many hundreds of publications attempting to predict the performance of two-phase microchannel heat sinks, there are only a handful of predictive tools that can tackle broad ranges of geometrical and operating parameters or different fluids. Development of these tools is complicated by a lack of reliable databases and the drastic differences in boiling behavior of different fluids in small passages. For example, flow boiling of certain fluids in very small diameter channels may be no different than in macrochannels. Conversely, other fluids may exhibit considerable “confinement” even in seemingly large diameter channels. It is shown that cutting-edge heat transfer enhancement techniques, such as the use of nanofluids and carbon nanotube coatings, with proven merits to single-phase macrosystems, may not offer similar advantages to microchannel heat sinks. Better performance may be achieved by careful optimization of the heat sink’s geometrical parameters and by adapting a new class of hybrid cooling schemes that combine the benefits of microchannel flow with those of jet impingement. [DOI: 10.1115/1.4005300]

Two-Phase Microchannel Heat Sinks: Theory, Applications, and Limitations

Thermal management and temperature uniformity enhancement of electronic devices by micro heat sinks: A review

Review of databases and predictive methods for heat transfer in condensing and boiling mini/micro-channel flows

This paper explores the recent research developments in high-heat-flux thermal management. Cooling schemes such as pool boiling, detachable heat sinks, channel flow boiling, micro-channel and mini-channel heat sinks, jet-impingement, and sprays, are discussed and compared relative to heat dissipation potential, reliability, and packaging concerns. It is demonstrated that, while different cooling options can be tailored to the specific needs of individual applications, system considerations always play a paramount role in determining the most suitable cooling scheme. It is also shown that extensive fundamental electronic cooling knowledge has been amassed over the past two decades. Yet there is now a growing need for hardware innovations rather than perturbations to those fundamental studies. An example of these innovations is the cooling of military avionics, where research findings from the electronic cooling literature have made possible the development of a new generation of cooling hardware which promise order of magnitude increases in heat dissipation compared to today's cutting edge avionics cooling schemes.

An 820-Watt clamshell module was fabricated and tested in order to assess the feasibility of cooling future high heat flux avionic hardware via subcooled phase change. One half of the module was constructed from aluminum 7075-T6 and populated with 16 heat sources simulating microelectronic chips. The other half was substituted with a transparent plastic cover to facilitate optical access to the boiling taking place in the module cavity. A dielectric coolant, Fluorinert FC-72, was sup­plied to, and rejected from the module via sleeveless quick connection couplers. Tests were performed with an inlet coolant pressure of 1.52 bar (22 psia) and inlet temperatures ranging from 27 to 47° C. These tests yielded power dissipation ex­ceeding 410 Wper half module for coolant flow rates and pressure drops as small as 0.023 kg/s (0.221 gpm) and 0.149 bar (2.16psia), respectively, and the device and rib guide temperatures were maintained below 80 and 60°C, respectively. The pressure drop remained constant with increasing module power proving, as was confirmed visually, it is possible to condensate all the vapor within the module cavity, allowing only liquid to exit the module. Thus, coolant conditioning external to the module can be greatly simplified by employing a simple single-phase liquid flow loop. 1 Introduction Since the introduction of the silicon integrated circuit, there has been a continuing trend of miniaturization of integrated circuit feature size, which is currently smaller than 0.025 mi­crons for silicon MOSFETS. These technological advances, aided, in part, by an increase in chip size, have made possible an excess of five orders-of-magnitude increase in the number of components integrated in a single chip. The quest for greater functionality per unit area has also driven the industry to squeeze a large number of chips on a single board. This ever increasing rate of integration has led to alarming increases in heat dissipation in many cutting-edge commercial and military electronic technologies. Thermal management is a primary design need in modern electronic packaging for both military and commercial systems. High temperature environments and excessive heat induce high failure rates and unacceptable reliability. Regardless of the thermal environment, electronic device junctions must be maintained at temperature levels consistent with performance and reliability objectives. Passive conduction/convection tech­niques, applicable to low power electronics of the past three decades, are no longer suitable for the higher thermal densities now encountered and coming in future systems.

Immersion-Cooled Standard Electronic Clamshell Module: A Building Block for Future High-Flux Avionic Systems

A new type of immersion cooled module, the BTPFL-C2, was developed for thermal management of future high flux avionics while conforming to the geometrical constraints of existing military modules and avionic enclosures. The BTPFL-C2 houses two circuit boards separated by a flow distribution plate and employs two sleeveless quick connection coolant couplers. The flow distribution plate supplies the coolant inside the module into parallel narrow channels formed between the distribution plate and the surfaces of the chips. Theoretical predictions of the thermal performance of the BTPFL-C2 were substantiated by experimental data using a test module populated with ten chips. Increasing the coolant subcooling at the module inlet was found to decrease pressure drop across the module, decrease the coolant flow rate requirements, and extend the upper cooling limit of the BTPFL-C2. These results reveal the BTPFL-C2 is capable of dissipating an order of magnitude more heat than today’s most advanced avionic module. At an inlet subcooling of 40.3°C, the BTPFL-C2 could dissipate over 3000 W using only about 0.051 kg/s (0.50 gpm) of Fluorinert FC-72 and a pressure drop of only 2.8 kPa (0.41 psi).

Peter E. Jimenez

Papers

Immersion-Cooled Standard Electronic Clamshell Module: A Building Block for Future High-Flux Avionic Systems

A Multi-Kilowatt Immersion-Cooled Standard Electronic Clamshell Module for Future Aircraft Avionics

Immersion-Cooled Standard Electronic Clamshell Module: A Building Block for Future High-