Performance estimation of adsorption cooling cycle with sorption hysteresis

• The thermodynamic adsorption cooling cycle with hysteresis included is identified.
• The impact of sorption hysteresis on adsorption cycle performance is investigated.
• Over-estimation of cycle COP increases as the extent of hysteresis increases.

Sorption hysteresis is the phenomenon where the adsorption and desorption isotherms for an adsorbate-adsorbent pair do not correspond. Despite such hysteresis being present for some common adsorbate-adsorbent pairs used in adsorption-based cooling systems, to date few previous studies take this into consideration when presenting the sorption (cooling) cycles and estimating their performances. This report addresses this deficiency by identifying the cycle on P-T diagram and developing a simulation model. We first provide the sorption characteristics of a silica gel/water pair that demonstrates sorption hysteresis. These sorption characteristics are then used with an newly developed equilibrium model to facilitate a comparison of the ideal cycle coefficient of performance (COP) with and without hysteresis for a range of operating conditions. Results show the cycle COP is over-estimated by around 14% when sorption hysteresis is ignored for the silica gel/water system. It is also shown that this over-estimation increases as the extent of hysteresis increases. The results suggest that, when it exists to any significant extent, sorption hysteresis should be accounted for when seeking to predict the performance of adsorption-based cooling systems.