Modeling of an absorption refrigeration machine and test of alkane working fluid mixtures

The present study considers a refrigeration absorption cycle based system with the aim to test well chosen hydrocarbon mixtures as working fluids, subtitutes to the banned CFC's and HCFC's. Two different types of cooling were considered, with water at 25°C and with air at 35°C. Six hydrocarbon binary sytems were used among which three can be regarded as being tested for the first time. Two thermodynamic models, namely UNIFAC and NRTL along with the viriel and Peng-Robinson equations of state, depending on the pressure, were used in the modeling of the machine operation, predicting the behavior of these hydrocarbon systems in liquid and vapor phases, as well as determining the vapor-liquid equilibria taking place in certain machine compartments. Numerical simulation were carried out and indicated that quite good machine performances could be achieved, reaching COP's of 0.632 and 0.6 for C3Hs/nC10H24 and nCaHιo/nCιοH24, respectively. Also the obtained results showed the limitations of the UNIFAC model in the adopted machine conditions as well as indicating that water cooling could lead to better performances.