Novel ammonia sorbents “porous matrix modified by active salt” for adsorptive heat transformation: 4. Dynamics of quasi-isobaric ammonia sorption and desorption on BaCl2/vermiculite

A novel composite sorbent of ammonia BaCl2/vermiculite has recently been proposed and tested for adsorption cooling. The aim of this paper was a detailed study of its dynamic operation under conditions of isobaric stages of an adsorption chiller cycle. Experiments were performed by a Large Temperature Jump method at the ammonia pressures 5.8, 6.9, 12.2 and 15.8 bar. The ad- and desorption temperatures were fixed, respectively, at 15, 20, 25, 30, 35 °C and 65, 70, 80, 90 °C. All kinetic curves were described by an exponential function with a single characteristic time τ. The rate constant k = 1/τ was found to be a linear function of the temperature difference which drives the process, hence, heat transfer between the sorbent layer and the plate heat exchanger determines the process dynamics. The appropriate heat transfer coefficient does not depend on the ammonia pressure and process temperatures and equals 90 W/(m2•K). The data obtained were used for analyzing the dynamic performance of adsorption chiller with this composite as a solid sorbent. Appropriate recommendations on optimization of working cycle are made. The analysis showed that the specific cooling power could reach 690–860 W/kg at the cycle duration of 100–300 s.