Optimum design of a double elliptical latent heat energy storage system during the melting process

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.