Investigation of equilibrium and dynamic performance of SrCl2-expanded graphite composite in chemisorption refrigeration system

Highlights: • Measured the bi-variant characteristic of (SrCl₂ + expanded graphite)/NH₃ chemisorption. • Developed the SrCl₂-NH₃ equilibrium correlation to describe pseudo-equilibrium zone. • Determined parameters of the modified kinetic equation for SrCl₂-NH₃ reaction. • The COP was 0.3 after one-hour adsorption using the SrCl₂ + expanded graphite (2:1) composite. • The maximum SCP value of 656 W/kg at 2.5 min adsorption using the studied composite. -- Abstract: This work experimentally investigated adsorption equilibrium and reaction kinetics of ammonia adsorption/desorption on the composite of strontium chloride (SrCl₂) impregnated into expanded graphite, and also discussed the potential influence of the addition of expanded graphite on the SrCl₂-NH₃ reaction characteristics. The measured and analysed results can be very useful information to design the system and operating conditions using the similar chemisorption composites. Equilibrium concentration characteristics of ammonia within the studied composite were measured using the heat sources at 90 °C, 100 °C and 110 °C for the decomposition process, where the degree of conversion achieved 50%, 78% and 96% respectively. Therefore, the equilibrium equation reflecting the relationship between temperature, pressure and concentration was developed, and a pseudo-equilibrium zone was found, which should be useful information to setup the system operating condition for the desired global transformation. It was suspected that the addition of expanded graphite altered the reaction equilibrium due to the pore effect and the salt-confinement. The concept of two-stage kinetic model was proposed and kinetic parameters were determined by fitting experimental data. The developed kinetic equations can predict dynamic cyclic performance of a reactive bed in similar geometric structure with reasonable accuracy. Such a chemisorption cycle using the SrCl₂-expnaded graphite (mass ratio 2:1) composite can be used for cooling application, and the maximum SCP value can be achieved as high as 656 W/kg at t = 2.5 min, and the COP can be 0.3 after one hour of synthesis process under the condition of T_ev = 0 °C, T_con = 20 °C, T_heat = 110 °C.