Dynamic modeling of an R245fa ejector based refrigeration system

Abstract

The dynamic behavior of the ejector refrigeration system (ERS) plays an important role in its performance prediction and control system design. This paper numerically and experimentally investigated ERS dynamic behavior by connecting generator, condenser and evaporator dynamic models into a single ERS dynamic model, as the heat exchangers dominate ERS thermal dynamics. The developed dynamic models of the heat exchangers were based on the moving boundary approach. A 1-D thermodynamic model of the ejector was also developed to evaluate the fluid behavior through the ejector. The pump and expansion valve were modeled using algebraic equations, as they were considered as steady state components in the system. The developed ERS dynamic model was validated experimentally by measuring the transient response to the step change of the pump speed. The validation studies revealed that the model is able to capture the refrigeration system's dynamics in terms of the pressures and outlet specific enthalpies of the heat exchangers, with relative errors of less than 3.78 and 0.5%, respectively.