Study on MnCl2/CaCl2–NH3 two-stage solid sorption freezing cycle for refrigerated trucks at low engine load in summer

•A two-stage adsorption freezing system is designed and constructed for the refrigerated truck.•Composite adsorbents of MnCl2 and CaCl2 with the matrix of ENG-TSA are developed.•The average refrigerating capacity of 2.2 kW in the adsorption process is obtained.•The chilled air outlet temperature of the evaporator is controlled at about −5 °C.•The COP is 0.13 when the heating and refrigerating temperatures are 230 °C and −5 °C.

A novel MnCl2/CaCl2–NH3 two-stage solid sorption freezing cycle is designed and established for the refrigerated truck with the rated power of 80 kW. The conventional sorption/desorption process and the resorption process are combined in the two-stage cycle. Theoretical analysis shows that such a cycle could adapt to the low heat source temperature and the high cooling temperature of the sorption beds very well, which is quite essential for the truck when the running speed and the load are low in summer. The expanded natural graphite treated with sulfuric acid (ENG-TSA) is chosen as the matrix, and composite adsorbents of MnCl2/ENG-TSA and CaCl2/ENG-TSA are developed. The hot air heated by the electric heater is used to simulate the engine exhaust gas to drive the system. When the hot air, the ambient air and the refrigerating temperature are 230 °C, 30 °C and −5 °C, respectively, the average refrigerating capacity is 2.2 kW in the sorption process. Correspondingly, the COP and SCP are 0.13 and 91.7 W/kg, respectively. The average refrigerating capacity of 1.1 kW in one cycle is gotten, which could meet the required refrigerating capacity of the light refrigerated truck at the low engine load engine in summer.

Graphical abstractA MnCl2/CaCl2–NH3 two-stage solid sorption freezing cycle driven by the engine exhaust gas is proposed for refrigerated trucks.Figure optionsDownload full-size imageDownload as PowerPoint slide