Investigation of melting and solidification process in different geometry latent heat storage systems

Since 2011 in Spain and since 2013 in Arizona, solar thermal power plants have been established using molten salt thermal energy storage systems. The energy stored in the molten salt is transferred to water through heat exchangers and the steam required by the steam turbines is generated. By using these systems, the power plants can also generate electrical energy at night. During this process called thermal discharge molten salt solidifies and, as with any phase-changing material, only heat conduction comes into play instead of natural convection. Experimental studies on the solidification of phase change materials (PCM) usually focus on materials with a melting point below 80oC, such as paraffin, in a latent heat thermal energy storage with concentric tubes. In this study, the performance of solar salt as a PCM in a latent heat thermal energy storage system (LHTES) with six different three-dimensional geometries was tested using ANSYS FLUENT. In the first example, the performance of the shell one-tube LHTES (double pipe) was tested. In the second example, the performance of the shell and two-tube LHTES was tested. In the third example, the right triangular shell with three-tube LHTES was analyzed to investigate the effect of inclined surfaces. The fourth example is the trapezoidal shell with six tubes status tested in terms of performance. Then the trapezoidal shell with the same number of tubes was inverted and tested. In the sixth example, the performance of a hexagonal shell with seven tubes filled with solar salt was tested. In the seventh example, melting in a two-dimensional triplex with fins LHTES filled with paraffin PCM is investigated. Finally, Hitec salt was used instead of solar salt in the first six examples of three-dimensional LHTES and the performance between these two PCMs was investigated based on water outlet temperature and PCM's liquid-mass fraction.