Experimental study of evacuated tube collector/storage system containing paraffin as a PCM

This article presents a newly developed concept for evacuated tube collector/storage (ETC/S) system containing a phase-change material (PCM). To serve as the PCM, commercial-grade paraffin was placed inside evacuated tubes equipped with heat pipes. Experiments were performed to assess the impact of paraffin application on the thermal performance of the ETC/S system. The use of paraffin extended the operating time of the solar thermal system by enabling the recovery of stored heat during the discharge cycle. In addition, the lower mean temperature of the heating medium compared with that in a conventional evacuated tube collector (ETC) resulted in less heat loss from both the test stand piping and the ETC/S unit itself. Notably, it was possible to bring the temperature of the heating medium to a useful level (approx. 45 °C). The results also showed that in comparison with an ETC, the total amount of useful heat obtained from the paraffin-integrated ETC/S system was increased by 45-79%, depending on the mass flow rate of the heating medium during the discharge cycle.