Thermodynamic study of multistage absorption cycles using low-temperature heat

Abstract

SUMMARYThe use of low-temperature heat (between 50 and 908C) is studied to drive absorption systems in two different applications: refrigeration and heat pump cycles. Double-and triple-stage absorption systems are modelled and simulated, allowing a comparison between the absorbent-refrigerant solutions H 2 O-NH 3 , LiNO 3 -NH 3 and NaSCN-NH 3 . The results obtained for the double-stage cycle show that in the refrigeration cycle the LiNO 3 -NH 3 solution operates with a COP of 0.32, the H 2 O-NH 3 pair with a COP of 0.29 and the NaSCN-NH 3 solution with a COP of 0.27, when it evaporates at À158C, condenses and absorbs refrigerant at 408C and generates vapour at 908C. The results are presented for double-and triplestage absorption systems with evaporation temperatures ranging between À40 and 08C and condensation temperatures ranging from 158C to 458C.The results obtained for the double-stage heat pump cycle show that the LiNO 3 -NH 3 solution reaches a COP of 1.32, the NaSCN-NH 3 pair a COP of 1.30 and the H 2 O-NH 3 mixture a COP of 1.24, when it condenses and absorbs refrigerant at 508C, evaporates at 08C and generates vapour at 908C. For the double-and triple-stage cycles, the results are presented for evaporation temperatures ranging between 0 and 158C. The minimum temperature required in the generators to operate the refrigeration and heat pump cycles are also presented.

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