LAMINAR flow and heat transfer of two thermal expansion fluid in protruded and pin-finned channels

Flow characteristics and heat transfer performance of water and ethanol in the channels with flow control structures were investigated in this study. Protrusion and pin-fin were used as two flow control structures and arranged on one side of the channels, the relative depth δ/D of the flow control structures was all 0.2, and heat flux was applied on bottom of the channels. The researches were carried out with various flow rates with the Reynolds number less than 20 in three different kind of channels. Thermal expansions and contractions were considered while the fluid temperature ranging from 293 K to 320 K. In all examined cases, varying levels of heat transfer enhancements were observed, complex flow patterns such as deflection and circumfluence caused by the variation of cross-section area along the stream-wise direction were discussed. The results reveal that the natural convection plays an important role in heat transfer when inlet velocity is low, and also it can suppress the forced convective heat transfer in some extents. Both protruded and pin-finned control structures can enhance heat transfer but also increase the friction. At last, heat transfer performance is worse when ethanol was employed as the working substance although it has much larger thermal expansion coefficient. Water is better to be chosen as heat transfer fluid due to its large specific heat capacity and thermal conductivity.