Experimental investigation on adiabatic two-phase frictional pressure drop of R290, R600a, and their mixtures in a horizontal minichannel.

To support the application of eco-friendly refrigerants, this study reports the adiabatic two-phase frictional pressure drop of R290, R600a, and their mixtures (mass fractions 70/30, 50/50, 30/70) in a 1.54 mm horizontal minichannel. Experiments were conducted under specific operating conditions: mass fluxes of 200-400 kg/ (m2 ⋅s), saturation temperatures of 22-26◦C, and vapor quality ranging from 0 to 1.0. Key influencing factors were systematically analyzed, and results were compared with fluorinated refrigerants (R32, R1234ze(E), their mixtures) and existing predictive correlations. The results indicate that the frictional pressure drop is significantly influenced by mass flux, vapor quality, and R600a mass fraction. An increase in these parameters leads to a substantial rise in pressure drop, attributed to intensified gas-liquid interfacial shear stress and the thermophysical properties of R600a (low liquid-vapor density and high liquid viscosity). Within the narrow investigated temperature span (22-26◦C), saturation temperature has a negligible impact, as the variation in reduced pressure is insufficient to cause significant shifts in thermophysical properties. While R290/R600a mixtures exhibit higher pressure drop than fluorinated refrigerants, they offer superior environmental performance (zero ozone depletion potential, ultra-low global warming potential). The Tran et al. correlation shows the highest predictive accuracy, with a mean absolute relative deviation of 10.75%, mean relative deviation of 6.15%, and 92.06% of data within ±30% deviation. This work enriches the pressure drop database for hydrocarbon mixtures in minichannels. It provides a reliable design tool and lays a foundation for optimizing compact heat exchangers using eco-friendly mixed refrigerants, especially in environmentally sensitive scenarios.