Abstract:

This paper compares two alternative approaches to the transient simulation of vapor-compression air-conditioning cycles that use different descriptions of the thermofluid behavior on the refrigerant side of the heat exchangers. While one of the most common modeling assumptions for two-phase refrigerant flow in transient cycle simulation is that the liquid and gas phases travel at the same velocity, a condition that is referred to as homogeneous flow, the two phases in real heat exchangers in vapor-compression cycles move at different velocities, requiring a heterogeneous flow model. Though both of these modeling approaches can be used to describe the transient cycle behavior, this paper demonstrates the extent to which the choice of the refrigerant flow model can have an impact on some of the aspects of the simulated cycle behavior, such as the heat exchanger mass inventory. These simulations are developed in the next-generation modeling language Modelica, which uses an acausal, equation-oriented approach to describe physical systems. The effect of the software implementation on the model performance is also discussed.