Modelling of isobaric stages of adsorption cooling cycle: An optimal shape of adsorption isobar

This paper addresses the effect of the adsorption isobar shape on dynamics of the isobaric stages of adsorption chillers which are considered as real alternative to common compression and absorption machines. We used a mathematical model of coupled heat and mass transfer in a spherical adsorbent grain that is in thermal contact with a metal plate subjected to a fast temperature jump/drop from 60 °C to 70 °C. Several model isobars of water adsorption (stepwise, linear and exponential) are tested to elucidate the effect of the isobar shape. Temporal evolution of radial profiles of the temperature, pressure and adsorbed water concentration inside the grain is calculated and analysed. In most cases, the calculated dependencies of the average water uptake/release can be satisfactorily described by an exponential function up to the dimensionless conversions of 0.7–0.8. The characteristic ad-/desorption time τ is found to be strongly dependent on the isobar shape. Both adsorption and desorption processes are fastest for the step-like isobar, with the step positioned at temperature as much different from the final temperature of the metal plate as possible, because in this case the driving force for ad-/desorption process is maximal. Appropriate recommendation on enhancing the adsorption chiller dynamics is made.

► A Fickian diffusion model is used to study dynamics of adsorption chillers (AC).
► Effect of the adsorption isobar shape on AC dynamics has been numerically studied.
► Characteristic (exponential) adsorption time strongly depends on the isobar shape.
► Special type of step-like adsorption isobar provides the best chiller dynamics.