Heat-transfer film coefficients of falling film horizontal tube evaporators

Abstract

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< Re<2500, the growth of liquid load Γ helped to increase total heat-transfer coefficient K; K could also be increased by means of reducing piping diameter, increasing the evaporation boiling point t 2 and reducing the total temperature difference Δt. The steam flow velocity ν s must remain at a certain value, but the increment of v, would be useless for multi-effect distillation. These results provide a basis for further developing a high efficiency heat-transfer process and novel evaporators.