Investigation of heat transfer enhancement in dimpled pipe flows

It is well established that dimpling of tubes can help enhance the heat convection coefficient. The effects of the dimples shape, depth and distribution on heat transfer and pressure drop for laminar and turbulent flows are of interest to this study. The aim of this paper is to quantify the effects of dimpling on the performance of 11mm ID tubes used in a submarine shell and tube heat exchanger. Both experiments and calculations were conducted, using water as the working fluid, over a wide range of Reynolds numbers ranging from 1500 to 24000, based on bulk velocity and tube diameter. Four tubes with different dimpling arrangements were tested. The CFD results show that a tube with 2mm deep single dimples arrangement, operating in the laminar flow regime, gives the maximum improvements in heat transfer of 10.23% over the smooth tube. The largest pressure drop increase recorded was 102.8% under identical flow conditions for the same dimpled tube. Temperature contour plots were used to demonstrate the mixing effect of the dimples under laminar flow conditions inside the tube.