Metallic and graphitic open-cell foams are being used as extended surfaces in some designs of compact heat exchangers. The shape and orientation of the solid material in the foam is hard to describe in classical terms and harder still to model. There appears to be a clear need for a method of characterizing foams that allows flexible, optimized design of a foam-fin heat exchanger. To be most useful, the description should be expressed in terms that are consistent with current heat exchanger design methods. The heat transfer performance of a foam-fin can be calculated if three parameters are known: the product hmAc* (the convective conductance per unit volume) as a function of flow rate, the product ksAk* (the effective conductive conductance as a fin), and Rbond, the effective thermal resistance between the foam fin and the surface to which it is attached. An experimental method is presented by which these three properties can be determined using the results from two tests: a conventional heat exchanger core test (single-blow-transient or cyclic) to measure hmAc* and a new type of "one-heated-wall" test, described here, from which the temperature distribution in the foam can be inferred. Results from these two tests can be combined to evaluate the three necessary parameters: hmAc*, ksAk* and Rbond. In this paper we describe the theory behind this approach and present sample calculations showing the type of data that are expected and demonstrating that the necessary parameters can be measured with these tests. Experimental testing of the method is underway but has not yet been completed, hence no data are available at this time to confirm the validity or practicality of the method.
Developing a New Type of Jointing the Metal Plates of a Heat Exchanger
