Experimental Study Of Falling Film Evaporation On Horizontal Tubes

Falling film evaporation on horizontal tubes is advantageous as an effective heat transfer mechanism because it has high heat transfer rates, small temperature differences, and high transfer performance at low temperature etc, and also can make use of the low quality heat energy. So it now has been widely used in desalination devices, refrigeration systems, and petrochemical plants etc.This experiment is about falling film evaporation on horizontal tubes which is based on the large-scale desalination experiment for attaining the main data affecting the desalination system.Experiment was conducted using 14 mm outer diameter HAL77-2A type Al-brass tubes heated by internal electrical heaters so that a uniform heat flux was generated on the outside tube surface. Results were attained about the heat transfer coefficients variety with the effect of liquid load, evaporation temperature, temperature difference between wall and water, no-condensing gas, heat flux rate, and salt concentration of the sea-water. Experiment was carried out under low pressure condition and it was found that salt concentration is not the mail reason to affect the heat transfer coefficient.In the experiment, the least liquid load and three flow patterns: the droplet mode-liquid, the jet mode-liquid, the sheet mode-liquid were attained after analyzing the pictures of the flow pattern.The conclusion was made that when 0.01kg /(m · s) <Γ <0.07kg/(m·s), the evaporative heat transfer coefficient increase with the growth of liquid feeding, increasing of the evaporation temperature and increasing heat flux. But with the increasing of the concentrate of sea-water, the evaporative heat transfer coefficients decrease but very little. The average evaporative heat transfer coefficients in the experimental data areabout 700W /(m~2 ·K)≤(h|~) ≤ 3000W /(m~2 · K). When there is little no-condensing gas or steam in the experimental system, heat transfer coefficients will be decreased badly.