Experimental study of heat transfer performance of horizontal-tube falling film evaporator

In this study, an experiment was conducted to analyze the heat transfer performance of a horizontal-tube falling film evaporator. The evaporator performance was tested with water and sodium chloride brine. The heat transfer performance of the crest and column sections for liquid film flow outside the tubes in a columnar flow pattern was investigated. The effects of the flow rate, tube spacing, outer tube diameter, feed temperature, and salinity on the local heat transfer coefficient outside the titanium-made heat exchange tube were studied. According to the findings of this study, (i) the local heat transfer coefficient of the crest section increases with flow rate and feed temperature, decreases with tube spacing and salinity, (ii) the local heat transfer coefficient of the column section increases with an increase in the flow rate, tube spacing, feed temperature, but decreases with salinity, and (iii) the influence of outer tube diameter on the local heat transfer coefficient of the crest and column sections varies with the circumferential angle. However, when D-2 = 19 mm, the variation in the local heat transfer coefficient is not consistent with that of other horizontal tubes because of D-2 < D-1. In a columnar flow pattern, the crest and column formed by the flow outside the liquid film tube are two important fluctuation areas of the liquid film. In this paper, the local heat transfer coefficient of the crest and column is obtained through the experiment, which provides the foundation for improving the heat transfer performance of the horizontal-tube falling film evaporator.