The Thickness Measurement And Heat Transfer Experiment Of Falling Film Outside The Horizontal Tube

The evaporation of falling film outside the horizontal tube is an efficient technologyfor water saving. The research of thickness distribution and heat transfer efficiency outsidethe horizontal tube will be of great importance in the development and promotion of thistechnology. In this paper, the experimental table of falling film outside the horizontal tubewas built with falling film evaporation as the background. The experimental table can beused to measure the film thickness and make the heat transfer experiment on falling film.A technology of camera measurement and I digital image processing was used in theexperiment. The mean film thickness within5seconds were obtained on8differentdiameters of tube over the annular angle range of30°-150°with5different spray densitiesat room temperature and in atmosphere. Through a regressive analysis of the test data anexperimental correlation formula was got for the relationship of annular angle, tubediameter, spray density and liquid film thickness. The fitting correlation coefficient is0.98.In the experimental conditions, the phenomenon of water film demonstrates in such waythat the larger the tube diameter, the thicker the water film; the larger the spray density, thethicker the water film; with the increasing of annular angle, water film vary from thick tothin, and then from thin to thick, and the minimum value of film thickness appears at theannular angle between90°to120°. The position of thinnest film shifts downstream withthe increase of tube diameter, and moves upstream with the spray density increased.Furthermore, at the condition of5different hot water inlet temperatures, thecoefficients of heat transfer were obtained on7different diameters of tube with5differentspray densities. The results show that the coefficient of heat transfer decreased with theincrease of tube diameter; with the spray density increasing, the heat transfer coefficientincreased first, and then decreased.In this experiment, the diameter scope of commonly used for heat transfer in theindustry was covered, and also the spray density scope commonly used in falling film evaporation was included. The variation law and correlation obtained from analysis andcalculation provide references for the applying of falling film evaporation outside thehorizontal tube.