Abstract
In Part II, fin effectiveness is identified as a better measure of heat transfer enhancement over large roughness elements as opposed to the minimum roughness element surface temperature. The Extended Surface–Discrete Element Method (ES-DEM) is extended to calculate fin effectiveness versus the ratio of the protuberance height to the boundary layer thickness (k/δ) for protuberance heights of 1.7 mm and 2.8 mm in laminar flow. The use of the thermal boundary layer thickness (δT) as a better length scale is discussed. For the same protuberance heights, fin effectiveness versus k/δ in the range of 1.25 >1) in laminar and turbulent flow. The same analysis is repeated for protuberances that are comparable or smaller than the thermal boundary layer thickness and a correlation is developed. The correlation indicates the important parameters for predicting the fin effectiveness for protuberances, and includes a new parameter: the thermal boundary layer correction factor, K. A methodology based on the correlations is presented to calculate the fin efficiency for a hemispherical protuberance in laminar boundary layer with constant heat flux. A correlation is also proposed to predict the heat enhancement for ordered distributions of roughness elements of the same shape in laminar flow. Predictions from the ES-DEM are compared to experimental data from Poinsatte. The results are the first step toward the development and validation of ES-DEM correlations that can be used in heat transfer models of ice accretion codes.
Published Version
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