Experimental Studies Of The Mass And Heat Transfer Optimization Of Membrane Distillation System

The membrane distillation is one of membrane separation technologies, which uses hydrophobic microcellular membrane and takes steam pressure difference of the both sides as a driving influence. The most significant merit of the membrane distillation is that it can use the energy which is inexpensive and low-grade, like solar energy, geothermal, and so on. And on the minus side, membrane flux is low. Therefore, the urgent issue to realize the industrial application is to find the solution to the problem of raising the membrane flux.Desalinating the bitter salty water with membrane distillation is taken as the research background for the thesis and Air Gap Membrane Distillation is chosen as the research subject. In order to cause the temperature boundary layer and the density boundary layer being destroyed effectively to get ideal effect of the mass and heat transfer and obtain high membrane flux, the membrane module uses the three directions circle tangential influx as the supply way of working substance. The method of the orthogonal experiment has been adopted to research the variable structural parameters of muzzle using circle tangential influx, which areα,δandβ. According to machining accuracy of muzzle and actual operating condition, the value of relevant factor and level has been determined. Designed program has been used to carry on the orthogonal experiments about different population of parameter of tangential influx structure and during the course water and salt water have been used as working substance. The analysis, which is based on the intuitive analysis of the comparison of average value of membrane flux size on each level of parameter, using membrane flux as the analysis factor, shows that the best population of parameter is"α=70°,δ=2mm,β=45°", which uses water and salt water as working substance under the same other operating mode of experiment and different temperature differences. Furthermore, the result has been proved to be true through additional experiments. The values of ranges under temperature differences having been analyzed, the strongest impact parameter of the membrane flux that is"β"has been determined. Besides, the result has been proved to be true as well by the other two orthogonal experiments, which are the experiment of regulating flow under the same temperature and the experiment using the temperature of the hot side of the membrane surface as the analysis factor. Optimized membrane distillation system has been used to carry on the applied research about brackish water desalting. Brackish water from the Tuoketuo, Hohhot, has been collected and analyzed as water sample. The water is pretreated by designed permutite precipitator and then the water is desalinated by the optimized membrane distillation system. The experimental result shows that the membrane flux rises to 35kg/m2·h while the inlet temperature of the hot side is 60℃. The result of monitoring the quality of output water shows that the quality of output water meets the China Sanitary Standard for Drinking Water, with the mineralization rate 8mg/L, fluoride content 0.05mg/L and arsenic content 0.001mg/L.