Performance analysis and system parameters optimization of a packed bed solar thermal energy storage having spherical packing elements with pores

Abstract

World energy demand is rising sharply from last few decades. Solar energy is capable to achieve this increasing energy demand as it is plenty in nature and pollution free by behavior. However, solar energy is associated with unsteady energy supply due to its intermittent nature. Therefore, solar energy systems require a storage unit for continuous supply of energy. The packed bed storage system (PBSS) is a feasible heat storage technique for solar thermal energy systems. Moreover, it is found most suitable technology for the applications of low temperature. The shape of the packing elements influences the performance of the PBSS and packed bed of spheres is found to have highest thermo-hydraulic efficiency among other shapes of packing elements investigated so far. Therefore, the influence of pores over the spherical surface on the performance of PBSS is analyzed and attempted to optimize the packing element parameters under this study. Pore depth to sphere diameter ratio, perforation index and pore to sphere diameter ratio are design parameters, whereas, temperature rise parameter and Reynolds number are considered as operating parameters under this study. The analysis is carried out in terms of thermo-hydraulic efficiency and the optimized value of investigated parameters under different operating conditions are presented. The present study may be useful for the designing of PBSS integrated with low temperature solar thermal applications.