A pressure drop study for packed bed adsorption thermal energy storage

Adsorption thermal energy storage has received considerable attention as it can overcome the mismatch between supply and demand of renewables, providing high energy storage per volume. In the packed bed adsorption thermal energy storage, pressure drop is of key concern since higher pressure drop leads into lower energy storage efficiency. In this paper, an experimental and modeling investigation on the pressure drop inside the adsorption packed beds is performed. An accurate semi-analytical closed-form relationship is proposed to calculate the pressure drop inside a column of adsorbent materials, taking into account the Laplacian friction, as well as the inertial effects. The model covers a wide range of porosity, between low-permeability medium, a dense packed bed of spherical particles, and high-permeability media, a pure viscous fluid. A modified permeability is defined to consider the inertial effect for a moderate range of the particle Reynolds number (0 < Rep < 300). An experimental apparatus is designed for measuring the pressure drop for different bed sizes and inlet air velocities. The proposed model shows good agreement with the experimental data with the relative difference of 7.6% at 0.73 m/s for silica gel and 15.3% at 0.84 m/s for zeolite 4A packed beds. The experiment reveals that the effect of water uptake on the pressure drop of packed bed with wet adsorbent is negligible in the tested particle Reynolds number range, with a relative difference of less than 1.0% compared to dry adsorbent for 18-30 cm long columns. The proposed formula for pressure drop, consequently, can be applicable for wet adsorbents regardless of the water uptake amount, with a good level of accuracy. Moreover, the analytical model shows up to ±2% change in pressure drop due to heat of adsorption of the tested adsorber columns.