Effects of partly-filled encapsulated phase change material on the performance enhancement of solar thermochemical reactor

Solar thermochemical reaction is an efficient way for hydrogen production. Due to cloud transients, solar thermochemical reactor endures low chemical conversion efficiency and deactivation of catalyst. To mitigate adverse effect of solar radiation fluctuation, in present paper, a solar thermochemical reactor design partly filled with encapsulated phase change material (EPCM) is proposed. Firstly, a two-dimensional dynamic model of solar parabolic trough receiver reactors (SPTRR) partly filled with EPCM is established and validated against experimental data. Then, the steady-state performance of SPTRR under steady solar insolation is explored numerically, and the findings motivated us to create a novel multi-part filling pattern of EPCM designed to avoid high-temperature deactivation of catalyst. Furthermore, SPTRR's thermal and chemical behaviors under unsteady condition of solar radiation are analyzed. Finally, an optimal cascaded EPCM (regarding thermal properties) design is selected for the best overall dynamic performance of SPTRR. The results show that under the steady solar radiation, filled with EPCM in multi-part filling pattern, SPTRR can keep high methanol conversion efficiency (0.926) with large filling proportion (0.52) of EPCM, less usage of catalyst (reduced by 48% compared to all-catalyst case) and safe operation. And under the unsteady solar radiation, compared to SPTRR fully packed with catalyst, the delay response time and vibration amplitude of SPTRR with EPCM in 4-part filling pattern can be extended by 63.2% and damped by 48.7%, respectively. The comprehensive unsteady performance indicator of SPTRR with the optimal cascaded EPCM is 23.2% higher than that with non-cascaded EPCM.