• Energy Research

Abstract To obtain maximum exergy and energy efficiencies of photovoltaic-thermal (PV-T) systems, innovative configurations of coolant tubes are proposed and simulated numerically. The tubes’ configuration is modified using non-uniform wavy tube concept, which forms different styles, including ascending and descending amplitude of coolant tubes. Besides, the influences of geometrical parameters, extending PV panel length, sensitivity analysis on the operating conditions and a comprehensive investigation of different types of heat transfer fluids are analysed for the innovative systems. The results demonstrate that the PV-T performance develops in terms of electrical, thermal, and exergy efficiencies using ascending wavy tubes compared with straight, uniform wavy and descending wavy tubes. The electrical and thermal efficiencies are promoted from 10.94% to 61.04% for the straight tubes to 11.32% and 65.21%, respectively, for the system in which ascending wavy tubes are utilised. A comprehensive study of different coolant fluids proves that when SiC and MPCM-28 are simultaneously employed, the best cooling fluid is achieved, leading to a 0.4% higher electrical efficiency than the case in which water is used.

Abstract This paper concerns the optimum design of double elliptical latent heat storage units during the charging process using three-dimensional numerical simulation. Water and RT35 are employed as the heat transfer fluid and phase change material, respectively. The orientations of both inner and outer elliptical tubes, the number of inner tubes, and the comparison between the straight and wavy configurations for the inner tubes are examined to find the maximum melting rate. Moreover, the sensitivity analysis on the operating conditions, including the Reynolds number and inlet water temperature, is performed. The results show that the best performance is found when the inner and outer tubes are oriented vertically and horizontally, respectively. The performance of the unit enhances as the distance between the inner tube and the bottom wall of the outer tube reduces. Besides, the optimum place for positioning the inner tube is where the minimum distance of the ellipses is 2 mm. It is found that the implementation of double wavy inner pipes increases the heat transfer surface area, which accelerates the melting time by 2.17. The delivered energy rate to the PCM using double wavy inner tubes is 218.75 W/kg, while it is 180.4 W/kg using double straight inner tubes. Eventually, the sensitivity analysis confirms the system is more sensitive to the variations of inlet temperature compared to the Reynolds number regarding the tested operating conditions.

This study aims to assess the effect of adding twisted fins in a triple-tube heat exchanger used for latent heat storage compared with using straight fins and no fins. In the proposed heat exchanger, phase change material (PCM) is placed between the middle annulus while hot water is passed in the inner tube and outer annulus in a counter-current direction, as a superior method to melt the PCM and store the thermal energy. The behavior of the system was assessed regarding the liquid fraction and temperature distributions as well as charging time and energy storage rate. The results indicate the advantages of adding twisted fins compared with those of using straight fins. The effect of several twisted fins was also studied to discover its effectiveness on the melting rate. The results demonstrate that deployment of four twisted fins reduced the melting time by 18% compared with using the same number of straight fins, and 25% compared with the no-fins case considering a similar PCM mass. Moreover, the melting time for the case of using four straight fins was 8.3% lower than that compared with the no-fins case. By raising the fins’ number from two to four and six, the heat storage rate rose 14.2% and 25.4%, respectively. This study presents the effects of novel configurations of fins in PCM-based thermal energy storage to deliver innovative products toward commercialization, which can be manufactured with additive manufacturing.