An innovative asymmetrical CPC with integrated PCM as an in-line water heater

In the present work, an innovative asymmetrical evacuated tube compound parabolic collector (CPC) with integrated Phase Change Material (PCM) is proposed as an in-line water heater. This solar collector was examined numerically as regards its thermal and optical operation. The optical efficiency was firstly optimized by modifying two independent design variables of the reflector. Then the optical performance was calculated for the finally selected geometry, considering 15 different transversal incident angles. As regards the thermal operation of the collector, the charging and discharging of PCM were investigated in detail. Four different internal fin arrangements were compared to the no-fin case and each other and the optimum one was revealed. The simulations were conducted for the city of Athens in Greece considering the typical clear day in July. It was considered that there is a charging period of five hours from 09:00 to 14:00 (solar time) and then a discharging one with a duration of one hour. For the thermal optimization, a volumetric flow rate of 4 L/min was selected during the discharging phase. The water temperature from the grid was considered to have a temperature of around 20 degree celsius. The main parameters which were evaluated during charging and discharging were the useful power output, the outlet water temperature and the mean PCM temperature. For validation purposes, experimental results from a previous study were used. In the previous study, a PCM heat exchanger with water as the working fluid was examined experimentally. The same heat exchanger was designed in the present study for comparing the results. It was found that the present numerical results are very close to the experimental of the previous study with a mean deviation of 1.60 % and a maximum of 4.24 %. The design and the numerical simulations were conducted with SolidWorks Flow Simulation software. The final results show that the best design leads to 96 % higher daily useful heat production compared to the baseline case without fins.