Assessment of thermal heat loss from solar cavity receiver with Lattice Boltzmann method

Abstract

Efficiency of concentrating solar power system (CSP) can be significantly reduced by heat losses from the receiver. So, the assessment of heat losses is the key to improve its thermal performance. This paper attempts to present a numerical simulation to assess the heat losses from a cavity receiver by using Lattice Boltzmann Method (LBM) coupled with net radiation method. Combined natural convection and surface radiation heat losses in open rectangular solar cavity receiver is presented. The wall facing the opening is subjected to parabolic temperature profile. The other walls are insulated. Cavity walls are assumed to be diffuse, gray and opaque while the open boundary is assumed to be a fictitious black surface at ambient temperature. Double distribution functions (D2Q9-D2Q4) with different relaxation times are used to predict dynamic and thermal fields. Influence of surface radiation, operating temperature, inclination angle and aspect ratio on heat losses from the hot wall inside the cavity is analyzed and discussed.It was found that convective heat loss is largely increasing by increasing the inclination angle. Concerning surface emissivity effect, an amplification by coefficient of 4 between ε = 0.2 and ε = 1.0 is accomplished for thermal radiation heat loss whereas convective heat loss is marginally reduced. It was also found that total heat loss from the cavity absorber is influenced by operating temperature and aspect ratio. In fact, increasing of operating temperature enhances heat loss while the increasing of aspect ratio reduces it.