Abstract:

Continuing efforts to improve the energy efficiency and reduce the environmental impact of air-conditioning systems based on vapor-compression cycles have motivated the expanding use of zeotropic refrigerant mixtures. These mixtures exhibit temperature glide and phase-dependent composition variation, which must be accounted for in system-level modeling and dynamic simulation during equipment design and performance analysis processes. This work analyzes interpolation-based thermophysical property models for cycles with these zeotropic refrigerant mixtures that are designed to balance accuracy and computational cost. We examine the standard formulation of governing equations in pressure/specific enthalpy coordinates and identify associated limitations for mixture behavior, and then propose a framework using pressure/vapor quality as an alternative set of coordinates. We describe the accompanying changes to the conservation equations used to describe the system behavior to improve numerical efficiency and robustness in dynamic simulations of vapor-compression cycles using zeotropic refrigerants, and demonstrate the efficacy of these approaches in the simulation of both the standalone refrigerant properties and the overall cycle dynamics.