Experimental investigation of an evacuated tube solar collector incorporating nano-enhanced PCM as a thermal booster

This study investigates the possibility of improving the functionality of a typical evacuated tube collector (ETC) with a new concept of an evacuated tube solar collector (ETSC) incorporating nano-enhanced phase change materials (Ne-PCM) as a latent heat thermal energy storage (LHTES) system. This new system immerses the ETSC's U-pipe inside the Ne-PCM and combines it into a single unit (ETSC/Ne-PCM) to provide heat when the solar intensity is unavailable or insufficient. The new system is used as a thermal booster in which the heat is stored in a PCM to extend the production period of hot water and to reduce fluctuations in the temperature of the water via heat accumulation and thermal insulation of the evacuated tubes. The effect of incorporating Ne-PCM on the performance of the ETSC/Ne-PCM system was studied. The addition of 0.33 wt% of copper/PCM composite to the ETSC was found to increase its efficiency by 32%. In addition, the ETSC/Ne-PCM system can provide hot water up to 50 degrees C for about 2 h longer than typical ETC systems with a specific mass flow of 0.08 L/min. Furthermore, impacts on the ETSC/Ne-PCM system performance of weather conditions and operational parameters such as HTF flow, the number of ETSC tubes and the concentration of nanoparticle are discussed.