Experimental investigation of heat transfer and fluid flow behavior of packed bed solar thermal energy storage system having spheres as packing element with pores

Abstract

Packed bed storage system is one of the viable options of solar thermal energy storage which can be utilized in various applications of wide temperature range. The enhancement in heat transfer coefficient between heat transfer fluid and packing element results in improved thermal performance of it. The heat transfer coefficient is also a function of shape of packing elements. From the literature review, it was found that the solid spheres as packing element comes out with best thermo-hydraulic performance in category of large size packing elements. In this paper, an experimental study has been conducted to investigate the heat transfer and fluid flow characteristics of packed bed solar thermal energy storage system. The outcomes of the experimental investigation are carried out on using large size spherical shaped packing element having pores of various diameters and depths on their surface in packed bed solar thermal energy storage system for low temperature applications. The experimentations are performed for different values of sphere diameter to pore diameter ratio (D/d) from 5 to 15, sphere diameter to pore depth ratio (D/t) from 5 to 20 and Reynolds number from 200 to 800. For the range of parameters investigated, the maximum value of thermo-hydraulic parameter has been obtained as 0.241 correspond to D/d of 5, D/t of 15 and Reynolds number of 800. Based on experimental results it is found that using spheres having pores on the surface as packing elements improve the thermal performance and momentum transport in packed bed solar thermal energy storage system.