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How to change the heat transfer coefficient of the thin film evaporator?

Date:2018/9/4Read:1513

    The thin film evaporator starts from the modified tube bundle to reduce the thickness of the liquid film to increase the evaporation intensity. For example, a research institute in China conducted condensation experiments on a variety of different types of tubes, and selected a better tube with a longitudinal groove on the outside of the tube, that is, 48 longitudinal grooves, isobutane vapor, were opened outside the φ22×2 mm aluminum tube. Condensation outside the tube, cold water in the tube, the total heat transfer coefficient is larger than under the same conditions.
    In foreign countries, in the copper tube with internal and external longitudinal grooves of 50.8mm in inner diameter and 2.44m in length, the evaporation experiment of clear water under normal pressure is carried out, and the total heat transfer coefficient obtained is higher than that of the smooth tube under the same conditions. ~ 4 times. The steam condenses on the outer tank peak of the tube to produce condensate, which flows into the groove due to the surface tension, and then passes down along the groove by gravity, so as to keep a thin layer of liquid near the peak and its vicinity. The membrane, and the upper and lower ends of the tube are substantially the same, so that the thermal resistance of the tube is small, which solves the disadvantage that the condensation heat transfer coefficient decreases on the condensate film on the vertical smooth tube. When the longitudinal groove is opened on the boiling liquid side, for example, in the rising film evaporator, the solution passes from the bottom to the bottom of the groove and then to the peak, so that the heat transfer surface keeps the film evaporated, and the steam is pulled at a high speed. Ascending, the boiling heat transfer coefficient on the solution side becomes high.
    In addition, the addition of a surfactant to the solution can reduce the surface tension of the solution, increase the wettability of the heat transfer surface, so as to avoid the occurrence of dry spots, so that the entire wall can conduct heat transfer, and the surfactant acts between the vapor and liquid phases. Lubrication, reduce flow resistance; because the surface of the pipe is covered with surfactant, it can not form a scale layer on the side wall of the solution, reducing heat transfer resistance. The surfactant can be recycled. The recovery method is to drum the air in the completion liquid, and the active agent is foamed on the surface of the solution, and 95% to 97% of the active agent can be recovered.

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