Impact of inclination angle on flow boiling heat transfer of refrigerants in elliptical mini-channel with micro fins

Flow boiling in mini-channels, known for its high heat transfer efficiency, holds significant application value in modern energy and refrigeration systems. This study focuses on elliptical mini-channels with micro fins, systematically investigating the effects of inclination angle on the flow boiling heat transfer performance of refrigerants R134a, R410A, and R454B. A nonlinear adaptive boiling prediction model suitable for elliptical mini-channels was proposed and validated by constructing a three-dimensional physical model and combining numerical simulations with experimental validation. The study conducted an in-depth analysis of temperature distribution, inlet and outlet pressure drops, and heat and mass transfer characteristics within the channels. It also revealed the flow pattern characteristics of vapor–liquid two-phase flow under different inlet vapor qualities and inclination angles. The results indicate that the inclination angle significantly influences vapor–liquid distribution, flow dynamics, and heat transfer performance. Different refrigerants exhibit distinct heat and mass transfer mechanisms at the microscale, with R454B showing a heat transfer coefficient 1.4 times higher than that of R134a under the same conditions, while its pressure drop is only 62.5 % of R134a, highlighting its advantages as an environmentally friendly alternative refrigerant. Furthermore, the effects of inclination angle and wall position on the heat transfer coefficient exceed 14.5 %. This study comprehensively considers the coupled effects of inclination angle, geometric characteristics, turbulent flow, and wall roughness, providing a theoretical foundation and design reference for optimizing mini-channel boiling heat transfer technologies.