Performance investigation of the direct absorption solar collector based on phase change slurry

The conventional solar collectors are usually indirect absorption solar collectors which convert solar energy into thermal energy through a coating surface with high optical absorbency. The direct absorption solar collector, which absorbs the incident radiation directly by the working fluid with high extinction coefficient, shows a better performance than that of the indirect absorption solar collector. The phase change slurry as a novel composite phase change material can work as both heat transfer fluid and energy storage medium due to the large heat capacity and fluidity. In the present study, the phase change slurry is applied in the direct absorption solar collector to further improve the solar collector efficiency, and a numerical model is built to investigate the performance of a parallel plate direct absorption solar collector. The optical properties of the particle of phase change material and the phase change slurry are analyzed based on the theories of the Mie scattering and modified independent scattering. The extinction coefficient of the phase change slurry increases with the increase of solid volume fraction and the absorption index of the particle. The effects of different parameters on the efficiency of the direct absorption solar collector are discussed. The collector efficiency increases first and then decreases with the increase of absorption index of the particle. The solid volume fraction shows different influences depending on the absorption index of particle. The melting of solid particle also plays an important role in the collector efficiency and the temperature distribution. The performances of different types of solar collectors are compared, and the phase change slurry based direct absorption solar collector shows the highest photothermal conversion efficiency. The results are helpful in extending the applications of phase change slurry and direct absorption solar collector as well as in improving the solar collector efficiency.