Abstract
In many industrial cooling and fire safety applications, multimode heat transfer involving radiation, convection, and conduction cools hot objects deposited on substrates. In some cases, the convective cooling is due to impinging jets on a flat surface or a small pedestal on an otherwise flat surface. The literature on jet impingement cooling is extensive, but variation in results using different correlations for nominally similar conditions is significant. For heat transfer from a small pedestal, there are relatively few studies. To characterize the cooling of a hot body that is supported on a substrate by an impinging jet, the convective heat transfer coefficient was measured using the naphthalene sublimation analogy. Two different substrate configurations were tested: bedded, where the object rests on top of the substrate, and embedded, where the top surface of the object is flush with the top of the substrate. After modeling the radiative and convective cooling components, a conductive resistance was inferred. The cooling of the hot object was modeled with good agreement to the experimental data. The error was less than 2% for the bedded case and less than 5% for the embedded. The relative contributions from the different modes of heat transfer were determined. For the embedded configuration, most of the cooling was initially due to conduction. For the bedded configuration on a relatively low thermal effusivity substrate like calcium silicate, most of the losses are due to convection and radiation. Materials with higher thermal effusivities had larger relative contributions to cooling from conduction comparatively.
