Thermodynamic cycle, correlations and nomograph for NH3NaSCN absorption refrigeration systems

Abstract

The detailed thermodynamic cycle of the NH₃NaSCN absorption refrigeration unit is presented, based on the thermodynamic properties of the working media. Correlations are developed, which express the coefficient of performance and the cooling capacity in terms of the required evaporation temperature, T_ev, and the available ambient temperature, T_amb. A nomograph is also presented, which shows in a compact form the behaviour of the NH₃NaSCN system and allows direct estimation of its main characteristics. It is concluded that if (T_amb − T_ev) varies from 0 to 40°C, the theoretical coefficient of performance decreases linearly from 95 to 77%. For the same range of (T_amb − T_ev) the theoretical cooling capacity varies from 1150 to 1300 kJ/kg NH₃ if T_ev varies from 0 to −15°C. Under the conditions examined, for T_amb − T_ev > 23°C, the coefficient of performance of the NH₃NaSCN system becomes higher than that of the NH₃LiNO₃ system. The observed increase reached 4% at T_amb − T_ev = 40°C.