Numerical Simulation And Test Of Self-suction Jet Aerator With Triple Branch Pipes

As the core process of sewage biochemical treatment, aeration is the major energyconsumption item in sewage treatment system. Aerator’s structure and oxygenation directlyaffect the overall performance of the aeration system. Jet aerator has the advantages of simplestructure, low energy consumption, high mass transfer and mixing efficiency which can wellmeet aeration system’s requirements of aerator. However, oxygen-transfer efficiency of bothdomestic and foreign jet aerator is low, limiting its popularization and application.The major contents of the thesis are as follows:1．A kind of self-suction jet aerator with triple branch pipes was proposed in the thesis. Asthe key innovative point of the aerator, triple radically distributed branch pipes were added to theend of traditional jet aerator’s mixing tube to replace the ordinary diffusion tube. The mainbenefit of jet aerator’s structural innovation was that liquid-gas mixed flow was led into tripleisolated branch pipes after being cut by the shunting cone, therefore, bubble coalescence andescape were avoided and utilization efficiency of inhaled air was improved. Radial distributionof the branch pipes could increase aeration service area and fully stir the water, improving theoverall aeration effect.2．A CFD simulation method based on VOF model was adapted to conduct unsteady analysisof the working process of the aerator. Internal phase distribution, velocity and pressuredistribution during the working process were obtained through the research. Numericalsimulation results showed that liquid-gas mixing effect of the aerator mainly occurred in thebranch pipes where turbulence was intense and vortex flows were formed, thus, liquid and gaswere mixed homogeneously. Comparison between numerical simulation and experimental resultsshowed that pressure error between simulation and measured value at the entrance of workingwater was2.2%and velocity error was3.95%, indicating that the numerical simulation resultswere correct and reliable.3．Orthogonal experiment with oxygen-transfer efficiency as index was conducted so as tofind out the relationship between oxygen-transfer efficiency and structural parameters under low-power working condition. Conclusions reached from the orthogonal experiment results were as follows:①Ranking of influence degree of the structural parameters on oxygen-transfer efficiency was as follows:throat-to-nozzle area ratio m, area ratio of suction chamber to nozzle n, aspect ratio of throat k, taper angle of shunting cone β and throat-branch angle α; influence of m and n on oxygen-transfer efficiency were highly significant.②ptimal parameter combination under experimental condition was:m=2.56, n=11.56, k=4, α=40°and β=40°; the oxygen-transfer efficiency obtained under optimal parameter combination was E=2.34kgO2/(kw·h).③A significant interaction existed between m and n, whose influence degree was lower than m, n and higher than k,β, α. An interaction between m and k also existed, whose influence degree was similar to β.