The adsorption refrigeration characteristics of alkaline-earth metal chlorides and its composite adsorbents

A study was conducted on the adsorption characteristics of the adsorption refrigeration working pairs using alkaline-earth metal chlorides as adsorbents and ammonia as refrigerant. The adsorption isotherms between alkaline-earth metal chlorides and nitrogen were studied. The study shows that the adsorbents of CaCl2, SrCl2 provide better adsorption capability associated with ammonia when compared to that of MgCl2, BaCl2. CaSO4 was added into the CaCl2, SrCl2 with a mass ratio 20%, respectively, in order to solve the swelling and smashing problems encountered with CaCl2, SrCl2 adsorbent particles. The adsorption refrigeration experiments of composite adsorbents were investigated. The results show that the refrigeration capacity of the unit adsorbent of CaCl2/CaSO4 is 1.26 times higher than that of CaCl2, and SrCl2/CaSO4 is 1.6 times higher than that of SrCl2 at 100 °C. The mechanism of NH3 adsorption and the gelatification of CaSO4 were also discussed. BET (Brunauer–Emmett–Teller) specific surface area and pore structure of adsorbents were examined. Results show that the BET specific surface area and pore structure of composite adsorbents are retained well. This study indicates that the refrigeration capacity could be enhanced by compositing the adsorbents which indicates that composite adsorbents can perform better in adsorption refrigeration, and can be employed in adsorption refrigeration system using low-grade heat source.