Research On The Heat Transfer Performance Of Horizontal Tube Falling Film Evaporator

Low-temperature multi-effect distillation is one of the main methods inindustrial desalination, it has been widely used due to its special characteristicssuch as high rate of energy utilization, simple pretreatment, usage of low gradewaster heat and cheap materials, et al. Horizontal tube falling film evaporationhas the advantages that the in-tube condensation and out-side evaporationbilateral phase changes happen simultaneously with high heat transfercoefficient. At present, the entired employment of horizontal tube falling filmevaporation in the low-temperature multi-effect sea water desalting plantsmakes the cost of equipment manufacture decreased significantly.In this paper, horizontal tube falling film equipment was designed andprocessed according to horizontal tube falling film evaporation technology. Theflexible connection sealing effect of the heat transfer tube and tube sheet wasinvestigated, and the cold model test of sprinkler pipe was also conducted. Thetest results show that flexible connection has good sealing performance and canprevent the leakage of seawater to the water side of the product. Tap water wastaken as the object to study, the effects of spray density, evaporationtemperature, heat transfer temperature difference and non-condensable gascontent on the evaporation heat transfer coefficient of the out-side tude, thecondensation heat transfer coefficient of the inner-side tude and the total heattransfer coefficient were examined. Increasing spray density, evaporationtemperature and reducing the temperature difference contribute to theimprovement of the total heat transfer coefficient. With the increase ofnon-condensable gas content, the heat transfer effect of the system deteriorates,and the total heat transfer coefficient decreases.Four-effect parallel feed horizontal tube falling film evaporation processwas studied, sea water was taken as the raw material, the performance offour-effect parallel feed horizontal tube falling film evaporation seawaterdesalination device was tested. The effect of operating conditions on theperformance of desalination plant was analyzed. Tests show that increasing thefeed temperature, the first-effect evaporation temperature, spray density and total temperature difference all contribute to the increase of water production ofpilot plant. When the overall system temperature difference is15℃, the waterproduction of pilot plant will be100t/d, the gained output ration (GOR) isaround3.4.