Hydraulic And Reoxygenation Of Characteristic Research On Aeration Flow In Venturi Tube With Perforates

The dissolved oxygen concentration (DOC) in water is an important index to water quality. If the DOC keeps too low, it will cause the lower growth rate, reproduction capacity, and death of aquatic organisms. It has vital significance to ensure the appropriate water DOC. Reaeration is one source of dissolved oxygen in water. This thesis aims at the investigation of Venturi tube with perforates aeration with numerical simulation method, after the validation with related experimental data. The influence law of the gas volume fraction and the dissolved oxygen recovery coefficient caused by the hydraulic parameters and geometric parameters is also analyzed.First of all, a three-dimensional mathematical model of mixed water and air flow in the Venturi tube with perforates was established in this paper. The transport and diffusion of dissolved oxygen was programmed by using UDF method of FLUENT software. The gas volume fraction and dissolved oxygen recovery coefficient has been verified respectively with the physical model and other related literature date. The results show that the calculated values agree with measured values approximately.Then, DOC, dissolved oxygen recovery coefficient and the gas volume fraction at the exit have been computed under different inlet DOC, flow velocity, hole diameter, tube length downstream of the perforates and contraction ratio conditions respectively using the validated mathematical model.Based on the analysis of the streamline, the velocity field, the turbulence kinetic energy of, the turbulence dissipation rate of and the gas volume fraction distribution, it is found that the gas volume fraction on the upper part of the tube is larger due to the gravity effect which is not good at dissolved oxygen recovery. Secondary flow area near the throat and diffusion section is one of the important area of energy loss. Furthermore, the strong secondary flow is conducive to the bubbles breakup and the retention time increase of air bubbles.Hydraulic and geometric parameters have an important influence on the gas volume fraction and dissolved oxygen recovery coefficient. The gas volume fraction increases and then decreases with the decreasing area contraction ratio. The gas volume fraction increases with the decreasing inlet water velocity. The gas volume fraction increases with increasing hole diameter, but the increasing amplitude decreases gradually. The dissolved oxygen recovery coefficient decreases with increasing water velocity, decreasing tube length downstream of the perforates, respectively. The dissolved oxygen recovery coefficient increases and then decreases with decreasing area contraction ratio, With increasing hole diameter within a certain range, the dissolved oxygen recovery coefficient increases. The temperature plays a negative effect on the saturation dissolved oxygen. The saturation dissolved oxygen concentration reduced with the increase of temperature, while the dissolved oxygen recovery coefficient increased. Based on dimensional analysis and least squares method, the empirical formula of dissolved oxygen recovery coefficient was generalized and validated considering hole diameter, tube diameter, throat diameter, tube length downstream of the perforates, inlet section average water velocity, kinematic viscosity coefficient and the inlet DOC. It can be used to compute the dissolved oxygen recovery coefficient.The thesis can provide some references for the design and application of Venturi tube flow with perforates and reoxygenation.