Experimental research on condensation flow and heat transfer characteristics of immiscible binary mixed vapors on different wettability wall surfaces

In the process of biomass gasification syngas waste heat recovery, water and organic compounds in the syngas will condense at the same time, resulting in immiscible condensates adhering to the wall, which can reduce the heat exchanger heat transfer efficiency and working life. Changing the wettability of the wall surface can affect the condensate flow state on the wall surface, thus affecting the condensation heat transfer performance. Water and organic cyclohexane were used as immiscible working fluids in this paper, the condensation flow and heat transfer characteristics of the mixed vapors on hydrophilic, super-hydrophilic, and super-hydrophobic wall surfaces were experimentally investigated. The results showed that cyclohexane in immiscible condensates existed as a liquid film on hydrophilic, super-hydrophilic, and super-hydrophobic wall surfaces, while the water existed in droplets on the hydrophilic and super-hydrophobic wall surfaces, and there were two forms of channels and droplets on the super-hydrophilic wall surface. The condensation heat transfer coefficient on the super-hydrophobic wall surface was higher than that on the hydrophilic wall surface and the super-hydrophilic wall surface, with a maximum of 34% higher than hydrophilic and 45% higher than super-hydrophilic, which was related to the smaller droplet departure diameter on the super-hydrophobic surface. In addition, the super-hydrophilic wall surface had better heat transfer performance than the hydrophilic wall surface only when the immiscible condensate was a "film-channel" flow pattern. The results can provide guidance for enhancing the condensation heat transfer of the water and organic compounds binary mixed vapors.