Experimental analysis on the flow patterns and conversion mechanisms of condensing flow with non-azeotropic mixtures in spiral tube

The flow patterns have a significant impact on the flow and heat transfer characteristics of the working fluid, making it fundamental for the study of complex two-phase flows. To investigate the condensation flow pattern and flow pattern transformation mechanism with mixed hydrocarbon in a spiral tube, a two-phase flow pattern experimental system was designed. The effects of mass flux (196–540 kg/m⁻²·s⁻¹), vapor quality (0–1), and operating pressure (2–4 MPa) on flow patterns of methane/ethane/propane/isobutane mixed fluid in spiral tubes were analyzed. The results showed that with the increase in vapor quality, flow patterns such as bubbly flow, intermittent flow, wavy-stratified flow, and annular flow were observed in sequence. Additionally, through a comparative analysis of the experimental observations with existing flow pattern maps, a new flow pattern map tailored for the condensation two-phase flow of mixed hydrocarbon working fluids has been established. Based on the influence of inertial force, surface tension, gravity, shear force and other forces, Martinelli number, Soliman We and Soliman Fr are selected for the development of flow pattern conversion criteria. The new flow pattern map accurately predicts the majority of flow patterns.