Experimental study on condensation flow patterns and heat transfer characteristics of non-azeotropic and immiscible binary mixed vapors

Abstract

The condensation phenomenon of non-azeotropic and immiscible mixed vapors always occurs in the waste heat recovery process of biomass gasification gas. During the condensation process, the immiscible condensation products, such as tar and water, have a different flow pattern from the pure working fluid, which can affect the waste heat recovery efficiency and the service life of the heat exchanger. However, the relationship between the flow pattern of immiscible condensates and condensation heat transfer is not clear at present. In this paper, water and cyclohexane were used as non-azeotropic and immiscible working fluids. The effects of different mixed vapors mass ratios, cooling water inlet temperatures, and vapor mass flow rates on the condensation heat transfer characteristics of the binary mixed vapors on the vertical wall were studied. And the condensate flow patterns were combined for analysis and discussion. The experimental results showed that the condensation on the wall surface of the mixed vapors presented a film-drop flow pattern comparing with the filmwise condensation of water vapor or cyclohexane vapor. The film-drop flow pattern was manifested as that the cyclohexane condensate was attached on the condensation wall in the form of liquid film, and the water condensate was attached on the cyclohexane film in the form of droplets. And the flow of water droplets on the cyclohexane liquid film can enhance the condensation heat transfer of the mixed vapors. In addition, different from water vapor and cyclohexane vapor, the heat transfer coefficient of the mixed vapors decreased with the increase of the cooling water inlet temperature, which was related to the film-drop condensation flow pattern.