Experimental Study On Concentrate Brine Falling Film Evaporation On Horizontal Tube At Low Temperature

High heat transfer coefficient and low temperature difference can be achieved by fallingfilm evaporation on horizontal tube which has been widely applied in the low temperaturemulti-effect-distillation of seawater, refrigeration, refinement of petroleum, and so on.Research of evaporation of high concentration brine is significant for producing fresh waterand salt, and extracting Potassium and Magnesium. The reuse of the concentrated seawater orbrine can remarkably decrease the energy consumption and the product cost, and enhance theextraction efficiency.A horizontal tube evaporation system for lab experimental study is designed andassembled. And then, the heat transfer performance, pertaining to falling film evaporation ofbrine with different concentration, is investigated systematically.Optimum falling film liquid distributor is selected by experiments regarding the differentnozzle diameters and distances to the tube surface. The minimum irrigation rate is obtainedreferring to visual study of flow behavior of falling film and analysis of photos. Furthermoredifferent spraying rates are determined from the occurrence of droplet, column, and sheet flowrespectively.Evaporation heat transfer coefficients are studied experimentally with smooth tube ofCu-Al alloy having length of 500mm and diameter of 25mm subject to electrical heating. Theinfluences of the liquid irrigation rates, heat flux and evaporation temperature on theevaporation heat transfer coefficients are tested for fresh water, sea water and brine withdifferent concentrations.Evaporation heat transfer coefficients are in the scope of 2500～11000 W/m~2·K with theexperimental pressure of 10kPa, evaporation temperature of 43～68℃, irrigation rate of0.8～0.25kg/m.s, heat flux of 12～42kW/m~2 and salinity 7～25%. The results show that theincrease of salinity has great influence on heat transfer coefficient. However, the increase ofheat flux and evaporation temperature can enhance heat transfer performance to some degreewhile the irrigation rate having negligible impact on heat transfer.