INTEGRATION OF THERMAL ENERGY STORAGE MATERIALS IN HEAT PIPE EVACUATED TUBE SOLAR COLLECTOR SYSTEMS FOR ENHANCED SOLAR THERMAL PERFORMANCE

This study investigates integrating thermal energy storage materials (TESM) with a heat pipe evacuated tube solar collector (HP-ETSC) in a water tank. Three TESMs (paraffin wax, RT27, and RT35) were examined numerically using COMSOL software, and experiments were conducted. Different design parameters were discussed, including water tank thickness, TESM tank thickness, TESM types, flow rate, and environmental conditions. The integration of TESM into the HP-ETSC allows the evaluation of various thermal performances, including average water tank temperature, hot water outlet temperature, and duration of hot water availability after sunset. The findings indicate a maximum temperature difference of approximately 37 degrees C at 13:00 on March 19 without TESM. However, with RT35, the temperature difference is around 34.27 degrees C, and with RT27, it is approximately 33.4 degrees C. Additionally, the temperature difference is approximately 2 degrees C higher when TESM is not utilized during the three months at sunset. These results demonstrate improved thermal performance compared to a similar system without TESM. Thermal energy transmission from TESM to water is relatively low, resulting in slightly higher outlet water temperature at night. During cloudy periods, RT27 and RT35 TESM types maintain their melting temperature from 11:00 to 20:00. A water storage tank thickness of 35 mm yields the highest temperature difference with RT27 and RT35 TESM. Increasing TESM thickness allows for more mass and latent heat storage, leading to up to 3.5 hours of heat release. On a mostly sunny day, such as January 9, the HP-ETSC stops heat release around 16:30 without TESM, while the TESM plates prolong the discharge duration by three hours.