Effect of phase change materials on the performance of direct vapor generation solar organic Rankine cycle system

Phase change materials used for the storage of thermal energy can play a critical role in the efficient use and conservation of solar energy. The effect of the different types of phase change materials on the thermodynamic performance of a direct vapor generation solar organic Rankine cycle system is evaluated in this study. The system consists of an array of evacuated flat plate collectors, phase change material based thermal storage, expander, condenser, and organic fluid pump. The thermodynamic cycle model of the ORC system is integrated with phase change material heat storage tank that is modeled using the finite difference method in MATLAB. The thermodynamic performance of the system is analyzed by using 12 different phase change materials. Effect of phase change materials on the thermodynamic performance of organic Rankine cycle including the net power output, rise and fall in the working fluid temperature, and on the amount of energy stored and released are evaluated and compared for charging and discharging mode. The results indicate that MgCl₂·6H₂O has shown the highest overall system's efficiency. However, KNO₂–NaNO₃ and Acetamide have resulted in maximum ORC and collector efficiency, respectively. Moreover, Acetamide, KNO₂–NaNO₃ and Mg(NO₃)₂·6H₂O have shown maximum rise and fall in organic fluid temperature, maximum net power and maximum amount of energy stored and released during charging and discharging mode. Salt hydrates have shown overall better performance among the selected PCMs in terms of overall system efficiencies and the amount of energy stored and released.