Experimental and CFD investigation of a helical coil heat exchanger coupled with a parabolic trough solar collector for heating a batch reactor: An exergy approach

An experimental and numerical study was conducted to evaluate the performances of an innovative thermal system composed of a batch reactor surrounded by a helical coil heat exchanger (HX), coupled with a parabolic trough solar collector. It was equipped with K-type thermocouples connected to a laptop to instantaneously record the heat transfer fluid temperatures at the inlet and outlet of the HX. Temperature and pressure of water were also measured inside the reactor. It was found that all temperature profiles follow similar trends as the Direct Normal Irradiation (DNI) variation, and the thermal efficiency does not exceed 20% because of significant thermal losses. The exergy analysis was applied to the mathematically modeled HX and simulated using COMSOL Multiphysics software. Temperatures from the CFD simulation and those measured during experiment tests are in good agreement. The Bejan number varies rapidly from 0.6 to 1 because of the strong dominance of heat irreversibilities. The total entropy generation increases with temperature and DNI until reaching its maximum value, then decreases in the cooling phase. A new heat exchanger design was proposed and simulated to reduce thermal losses. Consequently, the destroyed exergy was considerably reduced, and the efficiency was enhanced by almost 16%.