Study on the Flow Characteristics of Immiscible Mixtures on Vertical Wall

The condensation heat transfer phenomenon of immiscible mixed vapors often occurs in industrial environments, such as the waste heat recovery process of raw coal gas, biomass gasification gas and other high-temperature gas. The immiscible mixed vapors can be condensed outside the heat exchange wall and generate an immiscible condensate film attached to the wall, so the flow characteristics of immiscible mixtures condensate have significant effect on the heat transfer performance of the heat exchanger. However, there is currently a lack of research on the flow mechanism of immiscible mixtures outside the wall, and there is no effective ways to control the flow pattern on the wall. Therefore, it is necessary to study the flow characteristics of immiscible mixtures outside the wall. In this work, silicone oil and water were used as immiscible mixtures, and the flow characteristics of immiscible mixtures on the vertical wall under different inlet flow velocities were studied by numerical simulations. The results showed that when the immiscible mixtures flowed to a stable state within all the range of study conditions, the silicone oil phase adhered to the wall in the form of a liquid film, while the water phase existed on the oil film. However, the difference of inlet velocity of immiscible mixtures could affect flow patterns. The immiscible mixtures presented a Film-drop flow pattern on the wall at a low inlet flow velocity, that is the water phase existed on the oil film in the form of droplets. As the inlet flow velocity of the mixtures increased, the immiscible mixtures presented a Film-drop and Channel flow pattern, and water existed on the oil film in the form of droplets and channels. During the flow process of the oil-water immiscible mixtures on the wall, the flow velocity of the oil film was always lower than that of the water phase under the different flow patterns. The oil phase dominated the overall flow velocity of the mixtures, and the overall fluidity of the mixtures liquid film could be increased by improving the flow velocity of oil phase. In addition, the flow of the water phase on the oil film could improve the flow velocity of the oil film, increased the shear stress of the oil-phase interface and disturbed the thickness of the oil film. The results can provide reference for the flow characteristics of immiscible condensate film on the wall surface.