Modeling of isobaric stages of adsorption cooling cycle: Transient and quasi-stationary regimes

Abstract

Isobaric water ad-/desorption on/from a spherical adsorbent grain of 1.5 mm in diameter, which is in thermal contact with a metal plate, is studied by numerical simulation based on a Fickian diffusion model. The plate is subjected to a fast temperature drop/jump (60 °C ↔ 70 °C) that initiates changing the adsorbed water uptake/release. Several model adsorption isobars (linear, exponential and stepwise) are used to describe the adsorbent–water equilibrium.We have investigated the formation of quasi-stationary ad-/desorption regimes which are established after a short transient period right after the temperature drop/jump. The instant rate of water ad-/desorption is found to be a linear function of the difference of the metal plate temperature and the current temperature of the grain. As a result, the water ad-/desorption is faster when this average temperature difference is larger. Under studied conditions, the vapor pore diffusivity affects the overall ad-/desorption dynamics, although the dynamics is more sensitive to variation of heat transfer parameters. For a monolayer configuration, the heat transfer from the plate to the grain is the main rate limiting process at most realistic situations. Intraparticle water diffusion is the main rate limiting factor at unfeasible values of the pore diffusivity (lower than 10−10–10−11 m2/s).