Second law analysis and multi-criteria optimization of turbulent heat transfer in a tube with inserted single and double twisted tape

Present paper deals with numerical modeling of heat transfer in a tube with two types of twisted tape inserted in a circular tube. Single twisted tape and double twisted (coaxial) tape as two enhancing elements are added to the circular tube. A numerical investigation conducted to explore the effects of these elements on the pressure drop (Delta P), convective heat transfer coefficient (h) and entropy generation (S). The results demonstrate that increasing the Reynolds number has a positive effect on the convective heat transfer coefficient in all cases due to enhance the flow swirling which improves the heat transfer on the tube wall. The results represent that the coaxial tape in the lower twisted ratio (TR) has a better performance than single tape while the opposite is true for a high twisted ratio. The results of pressure drop for two studied cases reveal that pressure drop in the coaxial tape is higher than single tape in all TRs and with increasing TRs the pressure drop experience a decrement. It can be concluded that the lower TR in two types of inserts leads to the lower total entropy generation. Also, the results of exergy destruction rate and second law efficiency demonstrate coaxial tape exhibit better performance than single tape. A genetic algorithm based multi-objective optimization for coaxial tape implemented. The results of optimization displays, the best performance can be achieved in the case TR, Reynolds number and heat flux are 3.46, 9008.93 and 97894.1 W/m(2), respectively.