Heat Transfer and Flow Characteristics of Porous Matrices With Radiation as a Heat Source

A theoretical and experimental study of the heat transfer and flow friction characteristics of matrices of high porosity, with incident radiation from one side resulting in an exponential heat source, and with air as a coolant, is reported. In the theory, a transient solution of simultaneous convection and radiation heat transfer equations has been worked out. Used with experimental data taken in the unsteady state, it resulted in the calculation of volumetric heat transfer coefficients by convection in the matrices. Correlations with Reynolds numbers, based on a characteristic length obtained by equating pressure drops to the sum of viscous and inertia resistance terms, were obtained. Using the more familiar hydraulic radius did not result in reducing the relationships to a unified form. The matrices used in the experiments were formed from slit-and-expanded aluminum foils, blackened to high radiant absorptivity. The results of the investigation are believed useful in many solar, nuclear, and space applications.