Heat Transfer from Protuberances

An experiment by Henry et al. (Henry, R. C., Hansman, R. J, Breuer, K. S., 'Heat Transfer Variation on Protuberances and Surface Roughness Elements,'Journal of Thermophysics and Heat Transfer, Vol. 91, Mar. 1995, pp. 175-180.) explored the heat transfer of flows over protuberances in laminar and turbulent flow, simulating conditions during the beginning stages of glaze icing. This paper represents an effort to explain the heat transfer enhancement of roughness elements and protuberances that was observed by Henry et al. In the experiments of Henry et al., a single roughness element was placed on a heated flat plate. The temperature along the flat plate and along the roughness element was measured using an infrared camera to determine the enhancement of heat transfer of the protuberance as opposed to the smooth surface. A one-dimensional extended-surface (fin) analysis was performed to examine the results of Henry et al. Although significant assumptions were made using the extended-surface analysis, the important trends of the Henry et aL data were captured. The extended-surface analysis captured the trends of the apparent enhancement as reported by Henry et al. vs the Reynolds number based on the location from the leading edge of the surface and vs the ratio of the protuberance height to the boundary-layer thickness. Although the absolute magnitudes of the apparent enhancement are overestimated by the extended-surface analysis, the matched trends indicate the importance of the thermal conductivity of the protuberance, the importance of the interaction of the protuberance with the thermal boundary layer, and the importance of radiation into the protuberance.