<p>Energy from the sun is the most abundant and absolutely freely available energy on earth. Solar collectors absorb the solar radiation and convert it into heat, that heat can be used to heat up the water for domestic hot water applications. Among various types of solar collectors, evacuated tube solar collector (ETC) has attracted many attentions especially for the application in solar water heating systems (SWHs). In this study, the performance of an HPETC is optimized in two phases, where phase-I is focused on the effect of heat pipe location in stagnation (on-demand) operation, and in phase-II, the effects of various energy storage materials in both normal and on-demand operation are investigated. In conventional HPETCs, the heat pipe is located at the top of the glass tube, in this study, the design optimization of the heat pipe location is performed by reconfiguring the location of the heat pipe to the center, as well as defining a new fin geometry. The performance of the HPETC with modified heat pipe location was compared with the conventional collectors to show the enhancement, where both conventional and modified HPETC are integrated with phase change materials (PCMs) to increase the thermal energy storage of the system. The simulation results show that the solid-to-liquid phase change process was expedited by 48 minutes when the heat pipe shifted from the top to the center of the glass tube. The optimized configuration of the heat pipe is selected for further investigation of various types of PCMs with different melting points and latent heat capacities. The selected types of PCMs are commonly available sugar alcohols (SA), tritriacontane paraffin, xylitol, and erythritol with a melting point of 72˚C, 90˚C, and 118˚C, respectively. During the simulation, the fin temperature and liquid fraction of PCM are investigated. In normal mode, the HPETC system integrated with tritriacontane paraffin exhibited total energy storage of 295 kJ/kg per tube at a mass flow rate of 45 LPH, however, the fin temperature of the tube integrated with Xylitol at each time step was around 10˚C higher compared with the other tubes during the daytime due to its high specific heat capacity. In the stagnation mode, Erythritol shows maximum thermal energy storage of 399.12 kJ/kg per tube, however, the tube integrated with Xylitol shows higher fin temperature at each time step. Consequently, the utilization of tritriacontane paraffin/xylitol in normal operation and erythritol/xylitol in on-demand operation is recommended to enhance the system’s performance.</p><p>Keywords: Heat pipe, Evacuated tube solar collector, Phase change materials, Computational fluid dynamics modeling, Optimization analysis.</p>

Performance Optimization of Thermal Energy Storage Based Solar Collector

Paper Proceedings: https://asmedigitalcollection.asme.org/POWER/POWER2021/volume/85109

ASME 2021 Power Conference (POWER2021)

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