Heat transfer enhancement of heat exchanger using rectangular channel with cavities

Abstract Heat transfer enhancement is required for numerous situations, i.e., gas turbines, nuclear power plants, micro and macro scale heat transfer, airfoil cooling, electronic cooling, semiconductors, biomedical and combustion chamber lines, etc. One of the prominent ways of increasing the heat transfer coefficient from the surface of a heat exchanger is by moving the position of the thermal boundary layer to make it either thinner or break the same partially. It requires making use of an increased surface area/fins. Accordingly, the research progressed in heat transfer enhancement by using concavities/dimples of the heat exchanger surfaces to improve the heat transfer coefficient and heat transfer rate. These impregnations are made on the internal flow tubes/surfaces of the heat exchanger surfaces. The present research work aims at the experimental investigation of a heat exchanger to determine the airflow pattern and computation of heat transfer rate on the dimpled surfaces. This research work will be beneficial and applicable to heat transfer enhancement applications like micro heat transfer, where space constraint is considered. The geometries considered for the experiment include flat plates and dimpled surfaces. The parameters like Reynolds number (varied from 20,000 to 50,000), dimple depth to imprint diameter ratio (varied from 0.2 to 0.4), and heater input to the test plates (varied from 75 to 120 W) are considered for the comparisons. The results with dimpled surfaces are compared with the flat plate surfaces having no dimples. The Reynolds and Nusselt numbers rise in direct proportion to the heater input. For pin fin and dimpled plate, the ratio of Nusselt number to area average Nusselt number drops for 75 W and 100 W input. The dimpled plate with a ratio of 0.3 between imprint diameter to dimple depth had the highest ratio of Nusselt number to Nusselt number value for the entire group.