The application of solar water heating systems (SWHs) has attracted many attentions in recent years. The main component of a SWH system is the solar collector, and among various types of solar collectors, heat pipe evacuated tube solar collectors (HPETCs) are widely used. However, due to the intermittency in solar intensity, the HPETCs may not work at their maximum functionality. In this study, performance optimization of an HPETC integrated with phase change materials (PCMs), is investigated under normal and on-demand (stagnation) operations via computational fluid dynamics (CFD) modeling. In phase-I, the effect of heat pipe position on the overall performance of the collector is investigated. The results from phase-I show that the phase change process of PCM was expedited by 48 minutes under on-demand operation, for the collector with heat pipe in center, compared with conventional system (heat pipe at top), where in normal operation, the thermal energy storage enhancement is achieved, for the collector with heat pipe in center, by 24% increase in PCM’s melting fraction . In phase-II, the effect of various types of PCMs are investigated, where tritriacontane paraffin, xylitol, and erythritol are selected. In normal mode, the maximum exhibited total energy storage of 295.39 kJ/kg was acheived for paraffin tube, however, the fin temperature of xylitol tube was around 10 °C higher compared with the other tubes throughout the day. In on-demand operation, the maximum energy storage of 413.15 kJ/kg was achived for erythritol tube, however, the paraffin tube shows fin temperature difference of 14 °C compared with other tubes. Consequently, utilization of dual PCM of paraffin/xylitol in normal and paraffin/erythritol in on-demand operations is recommended to enhance system’s thermal performance. The results from this study can be a benchmark for further optimization of HPETCs in thermal energy storage systems.
Dr. Sarvenaz Sobhansarbandi is an assistant professor of mechanical engineering and director of Advanced Renewable/Thermal Energy (ART-E) laboratory at University of Missouri-Kansas city in United Staes. Her research interests include renewable energy, solar energy and computational fluid dynamics focusing on energy analysis of solar thermal collectors. She is also interested in Hydrogen energy and fuel cell technology with application in stationary and portable power generation systems. She has gained several years of research experience in the broad area of Thermo-Fluids, particularly solar energy technology and thermal energy storage materials. She had exposure to design/modeling of technical issues both by simulation and in real field-testing. She is the recipient of Funding for Excellence (FFE) award, ASME 2017 best paper award and ASHRAE 2015-2016 award from North Texas section.