Experimental study on working pairs for two-stage chemisorption freezing cycle

• Four working pairs are investigated and compared for two stage adsorption refrigeration.
• COP, cooling capacity and SCP range 0.215–0.285, 2–3.65 kW and 161.4–260.74 W kg−1.
• CaCl2–NaBr–NH3 shows the best SCP and COP, which are 260.74 W kg−1 and 0.285, respectively,
• For CaCl2–BaCl2–NH3, the matrix of ENG-TSA improves SCP by 76.9% than that of ENG.

Recently CaCl2–BaCl2–NH3 chemisorption freezing cycle driven by low temperature heat source has been successfully developed. In order to develop one working pair with more desirable performance than CaCl2–BaCl2–NH3, working pairs of CaCl2–NaBr–NH3, CaCl2–BaCl2–NH3, SrCl2–BaCl2–NH3 and SrCl2–NH4Cl–NH3 were investigated and compared. Most of composite adsorbents were developed with new type matrix of expanded natural graphite treated with sulfuric acid (ENG-TSA), leaving one working pair with expanded natural graphite (ENG) for comparison. For SrCl2–NH4Cl–NH3 and CaCl2–NaBr–NH3, experimental results show that the maximum adsorption quantities are 95.4% and 88.6% of theoretical values, respectively. Simulation results show that for different working pairs coefficient of performance (COP), cooling capacity, and specific cooling power (SCP) range from 0.215 to 0.285, 2 to 3.65 kW and 161.4–260.74 W kg−1, separately. The best results are obtained from CaCl2–NaBr–NH3, and its SCP and COP are as high as 260.74 W kg−1and 0.285, which are improved by 15.1% and 5.6% if compared with the values for CaCl2–BaCl2–NH3. Comparisons also show that the matrix of ENG-TSA improves SCP effectively. Taking CaCl2–BaCl2–NH3 as an example, its SCP is improved by 76.9% if compared with the result obtained from working pair with the matrix of ENG.