Theoretical analysis of ammonia-water absorption cycles for refrigeration and space conditioning systems

Abstract

This paper presents an investigation of an ammonia‐water absorption cycle for solar refrigeration, airconditioning and heat pump operations at higher heat supply temperatures. The system consists of a solar driven generator, rectifier, condenser, evaporator, absorber and heat exchangers for preheating and subcooling within the system. A steady state thermodynamic cycle analysis based on mass and heat balances along with the state equations for the thermodynamic properties of the ammonia‐water mixture has been carried out. A numerical computer simulation of the system with input component temperatures, refrigerant concentration/mass flow rate and effectiveness of the heat exchangers has been made to evaluate the relative heat transfer rates (i.e. coefficients of performance) and the mass flow rates for the cooling/heating modes. It is found that unlike the low generator temperature behaviour the coefficients of performance for both cooling and heating modes are reduced at higher generator temperatures. However, an increase of condenser temperature for each mode of operation improves the performance of the systems at higher generator temperatures. A choice for keeping the absorber temperature equal to/lower than that of the condenser is also predicted at lower/higher generator temperatures, respectively. In general the results are more pronounced for the refrigeration mode than for the heat pump mode and are least effective for the airconditioning mode.

Computer Simulation of an Ammonia-Water Absorption Cycle for Refrigeration: Using a Distillation Tower to Replace the Generator

“…Since the results of the above works indicate that the operating conditions of the generator such as temperature, pressure and mass flow rates of water and ammonia play a major role in determining the COPs of the whole cycle (which can be controlled by the governing operating principles of distillation towers), it reminds us that the generator of the cycle may be replaced by a distillation tower. This idea was first innovated by Kaushik and Bhardwaj [11] who added a rectifier on the top of generator. From the results of their theoretical analysis, they found that an increase of condenser temperature can improve the performance of the cycle at higher generator temperatures.…”

Thermal modelling and parametric study of two stage absorption refrigeration and air-conditioning systems

“…The use of absorption cycles for refrigeration and air-conditioning applications is quite well established in the available literature (Ellington et al, 1957;Ward, 1979;Allen et al, 1976;Auh, 1977;Kaushik, undated;Kaushik and Bhardwaj, 1982). Both the water-LiBr and NH,-H20 combinations as refrigerant-absorbent pairs have been widely used by many investigators.…”