Experimental based numerical approach for determination of volumetric heat transfer coefficients of modified graphite foams

Graphite-based porous materials are emerging as attractive alternatives to metals for use as heat dissipation elements in thermal management applications. While having several desirable features such as high thermal conductivity and low density, graphite foam heat sinks also tend to have low permeability that can limit transport of working fluid within the component and result in inefficient heat transfer. In order to improve their heat dissipation performance, graphite foams can be modified by channels drilled in various arrangements. However, the heat transfer characteristics of such modified graphite foams are not well characterized. In order to address this problem, we report novel empirical correlations for graphite foams modified in a specific configuration where circular channels with 2 mm diameter are drilled in graphite foam along the flow direction in a staggered arrangement. Then, volumetric heat transfer coefficients between the modified graphite foam and a stream of air are obtained by using transient single-blow technique (TSBT). The transient one-dimensional local thermal nonequilibrium (LTNE) model is employed for determination of the volumetric heat transfer coefficient from experimentally obtained data. Nine different modified graphite foam samples of various L/H ratios are studied in experiments and an empirical correlation of the form Nu(v) = CRea for each sample is derived. Empirical correlations for three different sample lengths (L = 27 mm, 52 mm, 76 mm) at a fixed height are also developed in the form of Nu(v) = CRea(L/H)(b). The novel empirical correlations in question are valid for the Reynolds (Re) number varying from approximately 1000 to 10000. Results show that Nuv generally increases with the increasing value of Re and L at a fixed value of H and the uncertainties associated with Re and Nu(v) are evaluated to be less than 1.3% and 3.6%, respectively. Consequently, we anticipate that the proposed correlations will be useful in reliable design of a new generation of electronic devices.