Zeotropic refrigerant mixtures are pivotal for decarbonizing heat pump technologies, particularly in emerging district heating applications, due to their compositional versatility and temperature glide characteristics. However, their complex interfacial behavior, transport properties, and flow dynamics lead to scarce data on evaporator performance and heat transfer coefficients, hindering optimal system design. This work investigates the thermodynamic performance of zeotropic mixture refrigerants (CO 2 /R290, R600/R290, R32/R1234yf, and R1234yf/R1234ze(Z)) in a vertical plate evaporator using computational fluid dynamics (CFD) simulations and experimental validation. Innovatively employing the Volume of Fluid (VOF) method coupled with the Lee phase change model, the CFD framework successfully captured the intricate multiphase flow and evaporation phenomena of diverse mixtures within microscale channels. Results demonstrate that a pinch point temperature difference (PPTD) of ∼4 K achieves optimal heat transfer efficiency. Crucially, CO 2 /R290 exhibited superior performance, achieving a total heat transfer coefficient of ∼9.61 kW/m 2 K, which is significantly higher (up to ∼64%) than mixtures like R1234yf/R1234ze(Z) (∼5.85 kW/m 2 K). Active modulation of water mass flow rates (1.62–3.24 kg/h) effectively compensated for refrigerant-specific limitations, achieving consistent cooling capacities ranging from 29.77 W to 55.83 W across all tested mixtures under the target PPTD. The findings, particularly the outstanding heat transfer characteristics and uniform temperature distribution of CO 2 /R290, emphasize its strong potential as a high-performance candidate for next-generation sustainable heat pump systems. This work underscores the critical role of thermophysical properties and operational parameter optimization in enhancing heat pump efficiency.
Xue et al. (Sun,) studied this question.