Study On Mass Transfer Characteristics Of Underwater Self-excited Aerator

Artificial aeration is an economical and feasible technology for treating black and odorous water bodies without secondary pollution.As the main energy consumption equipment in the black and odorous water treatment system,the efficiency of the aerator affects the operation cost of the whole system.The jet aerator uses bubble diffusion and hydraulic shear to achieve the purpose of aeration and mixing.It was widely used in sewage treatment because of its high oxygen utilization rate and oxygenation capacity,simple installation and operation,small equipment footprint,low operating cost,and no special requirements for water depth.In order to further reduce energy consumption in practical applications,the mass transfer characteristics of self-excited aerator under different operating pressures and operating modes were studied in this thesis.The main task of this project is to design an experimental set-up for aerator clear water oxygenation performance using an underwater self-excited suction aerator developed by the supervisor’s team.The water vapor jet characteristics of the aerator at various operating pressure of 1.0 MPa,1.2 MPa,1.4 MPa,1.6 MPa and operating modes of horizontal placement,30°tilt placement and 45°tilt placement were studied in the experiment,which included the average diameter of the bubbles,the average concentration of the gas,the axial average flow velocity of the water-air jet,the penetration length of the water-air jet and the affected area.Moreover the dissolved oxygen concentration at different moments was obtained through experiments.and indicators which was under different operating pressures and modes for evaluating mass transfer characteristics such as the standard oxygen transfer coefficient(K_las),oxygen transfer rate（OR）,oxygenation capacity（E_L）,oxygen utilization rate（E_A）and power efficiency（E_P）were calculated.The results showed that the bubble size increased with the increase of the distance between it and the nozzle under the aerator,and the average diameter of the bubbles produced when the aerator is placed horizontally should be less than 30°and 45°at an angle.The average suction volume of the aerator all increased with the increase of operating pressure,while differences in average gas concentration were not significant.The average penetration length of water-air jet and the average area of the impact zone increased with the increase of operating pressure.The axial average flow rate increased as the distance between it and the lower nozzle decreased and the operating pressure increased.The dissolved oxygen concentration changed in a similar pattern for different operating modes and pressures,but the time to near saturation varied in speed.The increase in operating pressure favored the transfer of oxygen at different operating modes,which was also influenced by the mode of operation.The maximum oxygen utilization rate E_A was 18.896%,which was obtained when the aerator was placed at an angle of 45°and the operating pressure was 1.6 MPa and the maximum power efficiency E_P was 15.688 kg/（k W-h）,which was obtained when the aerator was placed at an angle of 45°and the operating pressure was 1.0 MPa.The influence of various factors on the mass transfer characteristics of the aerator should be considered comprehensively in actual operation,and the results could provide a reference for the practical application of self-excited suction jet aerators.