The effect of absorbed moisture on the properties of six neat epoxy resins (3501-5, 3501-6, 3502, 5208, 934, and NMD 2373) and three epoxy composites (AS/3501-5, B/5505, and hybrid B/5505-AS/3501-5) is explored. Excellent agreement among the diffusion coefficients, activation energy, and activation entropy is observed for all resins with the exception of NMD 2373. Good correlation exists between neat resins and corresponding composites. The effect of a weekly thermal cycle on the diffusivity and equilibrium moisture content of two resins and three composites is presented. Correlations are developed between preconditioning temperature and relative humidity on the magnitude of the anomalous moisture absorption. In addition, the effect of absorbed water on the glass transition temperature of six neat epoxy resins and two composites using thermomechanical analysis is considered. The water generally behaves as a classical plasticizer of the epoxy resin, lowering the glass transition temperature as predicted from theory. Comparison between neat 3501-5 resin and AS/3501-5 reveals generally good correlation in Tg at comparable resin moisture levels, but plasticized hybrid boron-graphite/epoxy laminate exhibits a somewhat lower Tg than predicted from theory.

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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.