AUGMENTATION OF CONVECTIVE HEAT TRANSFER FROM HIGH-POROSITY PERFORATED SURFACES
Empirical equations are derived predicting the laminar heat transfer and friction loss performance of perforated heat transfer surfaces, valid for the surface porosity of up to forty percent. It is disclosed that perforations induce a second laminar-flow regime in which significant increase in heat transfer and friction factors is achieved. Also derived are the empirical expressions predicting the critical Reynolds numbers for the onset of the second laminar flow regime. When the Reynolds number exceeds a critical value, self-sustained flow oscillations due to free shear layer instability occur in the perforations, resulting in the generation of periodic vortex shedding from the downstream edge of the hole. Perforations exert no influence on transport phenomena at a flow lower than the critical value, namely in the first laminar flow regime. The transport performances in higher flow ranges are also determined. A critical porosity is found to be about twenty-one percent beyond which augmentation in heat transfer and friction loss becomes very prominent.