A comparison of transient heat pump cycle simulations with homogeneous and heterogeneous flow models

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. International Refrigeration and Air Conditioning Conference at Purdue This work may not be copied or reproduced in whole or in part for any commercial purpose. Permission to copy in whole or in part without payment of fee is granted for nonprofit educational and research purposes provided that all such whole or partial copies include the following: a notice that such copying is by permission of Mitsubishi Electric Research Laboratories, Inc.; an acknowledgment of the authors and individual contributions to the work; and all applicable portions of the copyright notice. Copying, reproduction, or republishing for any other purpose shall require a license with payment of fee to Mitsubishi Electric Research Laboratories, Inc. All rights reserved. Copyright c ©Mitsubishi Electric Research Laboratories, Inc., 2014 201 Broadway, Cambridge, Massachusetts 02139