Influences of variable porosity on CaO/Ca(OH)2 thermochemical energy storage characteristics in direct/indirect heated reactor

In the present work, the influences of variable porosity of CaO/Ca(OH)(2), which is normally regarded as constant, on the thermochemical energy storage characteristics in direct/indirect heated reactor (DHR/IHR), are comprehensively investigated by establishing a transient multi-physics coupled model. It is found that, unlike the traditional constant porosity assumption, the variable porosity shows significantly two-fold competitive impacts. On the one hand, increasing/decreasing porosity increases/decreases the permeability of reaction bed, which leads to the drop/rise in pressure field and further the local reaction equilibrium temperature drop/rise. Thus, the local reaction rate increases/decreases correspondingly. On the other hand, increasing/decreasing porosity also decreases/increases the heat conductivity of the reaction bed, which leads to the drop/rise in transient temperature field. Thus, the transient reaction rate decreases/increases instantaneously. The results indicate that the constant porosity assumption may over/underestimate the performance of DHR/IHR during the charging (dehydration) process by around 9%, while underestimate the performances of both DHR and IHR during discharging (hydration) process by up to around 19%. It is also found that the variable porosity demonstrates greater influence on the discharging (hydration) process in DHR and on the charging (dehydration) process in IHR.

Automated summary

This study comprehensively investigates the influences of variable porosity on the thermochemical energy storage characteristics in DHR/IHR. It is found that the variable porosity has dual competitive impacts on the reaction rate and temperature field, and the constant porosity assumption may lead to overestimation or underestimation of the performance.