This action provides continued funding for the second five year term of the Industry/University Cooperative Research Center (I/UCRC) for Compact High Performance Cooling Technologies. This I/UCRC addresses research and development needs of industries in the area of high-performance heat removal from compact spaces. All product sectors in the electronics industry (High-Performance, Cost/Performance, Telecommunications, Hand-held, Automotive, and Military/Avionics) face critical electronics cooling challenges, and the Center brings together faculty from the Schools of Mechanical Engineering, Electrical and Computer Engineering and Aeronautics and Astronautics at Purdue University, and contribute complimentary competencies in heart transfer, microfluidics, microfabrication, refrigeration, computational techniques, mechatronics, controls, acoustics, sensing and actuation and diagnostics and measurements.
Cooling Technologies Research Center (CTRC) Purdue University, Suresh Garimella, Director, 765.494.5621, sureshg@purdue.edu Center website: https://engineering.purdue.edu/CTRC/ The Cooling Technologies Research Center (CTRC) addresses the research and development needs of member companies and organizations in the area of high-performance heat removal from compact spaces. In order to address the diverse needs of the electronics industry, the center research strategy targets several high-impact research areas. The major project outcomes of these research areas are described below, and their broader impact explained. Investigation of high-performance liquid cooling techniques is required for cooling of hybrid vehicle electronics, high-power density processors, switching transistors, servers, and military electronics. As such, researchers at CTRC have extensively investigated compact microchannel heat sinks (Image 1) for nearly 10 years. As part of these investigations, the heat transport characteristics have been experimentally measured for a variety of fluids (water/dielectrics) and potential heat sink materials (copper/aluminum/silicon). In addition, comprehensive flow regime maps for flow boiling have been developed, encompassing a wide range of microchannel dimensions, mass fluxes, and heat fluxes. Projects have increased the fundamental understanding of fluid flow in microchannels through development of novel non-invasive measurement techniques to quantitatively measure the liquid flow field, liquid film thicknesses, and vapor void area during boiling. Other examples of liquid cooling technologies investigated in the center include construction of testing facilities capable of evaluating jet impingement and novel liquid micro-pumping techniques to facilitate compact, embedded cooling systems. Detailed multi-physics models and prototypes have been developed for both electrically-actuated droplets (Image 2) and traveling-wave electrohydrodynamic micropumps. A contrasting, but equally prevalent, research area is the development of low-power, low-noise air cooling technologies. There are an increasing number of low-profile products, such as laptops and cell phones, where there is no surplus space to implement conventional thermal management solutions. Example technologies that have been addressed in the center are ionic wind cooling, piezoelectric fans, and synthetic jets. Ionic, or electrically driven, winds have been shown to provide a significant local heat transfer enhancement. Studies have also been completed to test and characterize the thermal, electromechanical, fluid dynamic and acoustic performance of piezoelectric fans (Image 3). More recently, synthetic air jet studies are being performed to optimize their cooling potential while minimizing noise production. All of these technologies are well suited to provide supplemental cooling in hot spots and other stagnant areas in devices where rotary fan action is ineffective. With this research, center members have new products aligned to use this technology in ways that will give them a marketing edge. Other air cooling enhancement research advances have been made by characterizing metal foams (Image 4) in an air stream to enhance heat transfer. In every electronics package there are numerous interfaces between components that hinder heat removal. Therefore, thermal interface materials are ubiquitously used in electronics packaging to reduce the thermal resistance between materials. The objective of research within CTRC is to improve the reliability and performance of thermal interface materials. The immediate need for this type of research is constantly being requested by industry members and the thermal interface materials research that comes out of CTRC is immediately used by the member companies in power electronics, telecommunications, cellular base stations, automotive electronics, portable electronics, electric vehicle batteries, power distribution systems in computers, large-scale servers, military electronics, and avionics. Research outcomes include development of a tool to predict contact resistance across metallically coated joints, development of a novel random network model for particulate filled interface materials, and generation of optimum geometries for hierarchical interface surfaces. Additionally, novel high-performance interface materials, such as two-sided carbon nanotube (Image 5) and graphene-based interfaces, and novel interface resistance characterization techniques have been developed. In addition to the research areas above, the center addresses a myriad of other technologies that are pertinent to the industries served in the center. A series of studies have been completed to evaluate compact vapor compression refrigeration systems for electronics cooling. System level models have identified critical research needs and drive component level research projects such as modeling and design of miniature-scale diaphragm and linear compressors, and determination of the performance of refrigerant flow boiling in microchannel evaporators. Additionally, a comprehensive understanding of the underlying physical mechanisms of evaporation from a liquid meniscus is critical for miniaturization of heat pipes, cold-plates, and other thermal management solutions. Therefore, a series of fundamental research projects have developed experimentally validated models for thin-film evaporation in various geometries (Image 6) which can be used to predict performance of devices. Lastly, an emerging area of research is the development of technologies for sustainable energy utilization. An assessment was performed to estimate the system performance of multiple alternative waste heat recovery cycles. For cycle options with high potential system efficiencies using waste heat from electronics cooling systems, an experimental system was constructed.
