Thermal Management of Airbourne Early Warning and Electronic Warfare Systems Using Foam Metal Fins

Abstract

This program, addresses the need for thermal management of increasingly powerful and densely packaged electronic devices. Open-celled foams and lattice structures offer the promise of much improved heat transfer between the coolant and the solid structure of the lattice compared to traditional finned heat exchangers. The focus of this program is to evaluate integration of foam and lattice materials as heat exchanger cores and as electronic racks. The potential benefits of this approach include reduction in the volume and weight of the heat exchanger core and/or device junction temperature as well as direct attach cooling of high power electronics. To begin we have selected two major applications, a liquid cooling system heat exchanger, and avionics rack cooling. There is little data on foam metal heat transfer in the regime we anticipate for aircraft applications. Our approach begins with the measurement of heat transfer characteristics of compressed foam metals under conditions suitable for aircraft applications. Basic heat transfer data is being obtained for heat removal from a heated surface by “foam metal fins” with air flowing through the foam. Effective heat transfer coefficient and airflow resistance have been measured. The test method and apparatus are briefly described. Results of heat transfer measurements to date are presented. A theoretical model of “foam metal fins” has been developed and is applied for scaling foam metal fins within our test matrix. Using the model we determine the heat transfer coefficient between the air and foam ligaments. These heat transfer coefficients are compared with cylinders in cross flow. We applied our measured heat transfer characteristics to the design, fabrication and verification test of a highly efficient heat exchanger core. A laboratory scale thermal performance demonstration core was sized based on our test results. Initial tests of a single air / liquid heat exchanger core leg validates our core sizing. Our results can also be applied to cooling of individual electronic components as well as cold plates for electronics.

Permeability and Thermal Transport in Compressed Open-Celled Foams

“…Metal foams were recommended for use in compact heat exchangers since the thermal resistance was shown to be lower, and the efficiency greater, than that of existing heat exchangers. Klein et al [14] constructed a heat exchanger using compressed foams and studied the thermal performance relative to the extent and direction of compression for Reynolds number of 100-1000. The thermal performance was observed to be independent of the direction of compression.…”

Comparative design study of a diesel exhaust gas heat exchanger for truck applications with conventional and state of the art heat transfer enhancements

“…• A metal foam filled plate heat exchanger was sized based on data adapted from Lu et al [21], Klein et al [22] and ERG corporation [23], • The evaporation heat transfer coefficient in tubes of the shell&tube exchangers is calculated according to Shah's method [24], • The Logarithmic Mean Temperature Difference method LMTD is used to calculate heat output [9], • The pumping power required to operate each system of heat exchangers is calculated as the product of pressure drop and volume flow rate.…”

Assessing the influence of four cutting methods on the thermal contact resistance of open-cell aluminum foam

“…It is assumed that this results in a superior thermal contact, often leading to the assumption of a negligible TCR (see e.g. [4,[20][21][22][23] amongst many others). Besides bonding method, the available contact surface area is observed to be a second significantly influencing factor on TCR.…”

“…There is much interest to apply such foams in thermal applications, e.g. compact heat exchangers [2][3][4], heat exchangers comprising a screen of foam coated tubes [5], high heat flux cooling [6], heat sinks for electronics [7], LED cooling in automotive applications [8], to name a few. An important asset of open-cell foams is its quasi-optimal distribution of solid material in the foam domain, which is due to the surface energy minimization principles [9].…”