Flow, heat transfer, and pressure drop in the near-wall region of louvered-fin arrays

Using the naphthalene sublimation technique and complementary flow visualization, the effects of bounding walls on flow and heat transfer in louvered-fin arrays are studied. Results for spatially periodic flow far from the walls are compared to results for the near-wall flow, where the impact of the bounding surface is important. In contrast to flow in the spatially periodic region, the nearwall flow is characterized by large separation zones between the louvers, and unsteadiness is manifest at much lower Reynolds numbers than in the spatially periodic region. At low Reynolds numbers (Re ≈ 600 and below in this study) the large separation zones cause a decrease in heat transfer of up to 50%. However, if the Reynolds number is high enough to promote unsteady flow near the wall, the net effect is to locally increase heat transfer by up to approximately 15% (at Re = 1400). Unfortunately, this increased heat transfer is accompanied by a several hundred percent increase in pressure drop. A formula for characterizing the spatial extent of these wall effects is presented.