Optimization of heat transfer using CFD simulation for concentric helical coil heat exchanger for constant temperature outer wall

Abstract

Thermodynamic Optimization in heat transfer of a concentric coiled tube-in-tube heat exchanger under constant wall temperature condition, based on Fluid–Fluid heat transfer is focused in this paper. The parameters which influence the nature of flow in a helical coil are pitch coil diameter, pitch and tube diameter in helical coils. CFD analysis was carried out and their variation on thermal and hydraulic characteristics were analyzed, with varying Reynolds number (hot fluid) and varying tube-to-coil diameter ratios for a given flow velocity of cold fluid. The analysis was carried with Ansys 13.0 Fluent, for turbulent counter-flow with fluid water. The correlations for heat transfer and drop in pressure were analyzed. Thus, Nusselt number and friction factor were also calculated. Graphs were plotted between Nusselt number, friction factor, pressure drop and power loss with Reynolds number. The point where the friction fraction intersects with the Nusselt number is the point where the heat transfer is optimum, corresponding to that Reynolds number. Beyond that Reynolds number, the friction factor decreases rapidly, hence the pressure drop increases and so the power loss also increases. Various velocity and temperature contours were also obtained. Hence, we found the optimum value of Reynolds number for the corresponding tube-to-coil diameter ratios. It thus minimizes the degradation of thermal energy and viscous dissipation of mechanical energy.