Numerical Investigation of Laminar Forced Convection and Entropy Generation in a Helical Coil with Constant Wall Heat Flux

In this article, laminar forced convection and entropy generation in a helical coil with constant wall heat flux are investigated numerically. Both the entrance and fully developed regions are included. Water (Prandtl number 5.98) has been selected as working fluid in the present study. The cases studied cover a Reynolds number range from 1,000 to 7,500, and wall heat fluxes of 160, 320, and 640 W/m2. The development of flow fields, including secondary flow motion, distributions of temperature, Nusselt number, and friction factor, are given and discussed. In particular, the distributions of entropy generation rate in the helical coil are highlighted. According to the minimum entropy generation principle and thermodynamic second law, the analysis of optimal Reynolds number for the helical coil flow with constant wall heat flux is carried out, through which the optimal Reynolds numbers are found to be related to the wall heat flux. The optimal Reynolds number is suggested to be chosen as the flow operating condition so that the thermal system can have the least irreversibility and best exergy utilization.