Modeling of an ejector refrigerating system operating in dimensioning and off-dimensioning conditions with the working fluids R142b and R600a

This paper describes a whole simulation program which is useful to evaluate the performance and the characteristics of the operating cycle of an ejector refrigerating system with the working fluids R142b and R600a. The cycle is determined using the temperatures of the three thermal sources and local heat transfer coefficients for the boiler, the condenser and the evaporator. In addition, the simulation program includes a correlation of the ejector entrainment ratio established in different operating conditions at critical point from the conservation equations of the 1-D model available in the literature. Previously, all the components of the system were dimensioned for a refrigerating power of 10 kW, the hot source temperature is equal to 120 and 130 °C, whereas those of the intermediate and the cold sources are fixed at 35 and 10 °C, respectively (dimensioning conditions). Then, the system performance is investigated in dimensioning conditions and in off-dimensioning conditions using the simulation program. Particularly, the analysis of the results shows that at fixed cold source temperature, the intermediate temperature corresponding to the critical mode with image, the system COP decreases when the hot source temperature is higher than that of its dimensioning. Consequently, it is recommended to dimension the system components at the highest possible temperature in order to guarantee better performance in the case of an operating at lower temperature of the hot source. Also, it is noted that R142b leads to better performance of the system in all cases. This can be due to the fact that R142b is a heavier fluid than R600a.