The film thickness distribution and average thickness outside a horizontal test tube were measured with a film-thickness meter. The effects of liquid load, evaporation boiling point, temperature difference and tube diameter on the film thickness, the waving intensity and, as a result, the heat-transfer film coefficients outside the horizontal tube were studied. Experiments of the heat-transfer coefficient of horizontal-tube evaporation were conducted with various operation parameters. Equations for the evaporation heat-transfer coefficient were set up by regression of experimental data. The conclusion was made that when 200

Keywords:heat transfer;film-thickness measurement;horizontal tube;falling film evaporator;desalination of seawater