Experimental Research On Gas-liquid Two-phase Flow Of Self-priming Pump During Self-priming Process

Self-priming process is complicated,which is full of physical changes between gas and liquid including separation and mixture.The self-priming performance and self-priming mechanism have something to do with the distribution and moving rules of bubbles in the pump during self-priming process.Researchers are focusing on the variation of gas-liquid two-phase flow and effects of hydraulic performance parameters on self-priming performance,and some other superficial macroscopic phenomena.They have not been engaged in self-riming mechanism.This research focused on self-priming process of external mixing self-priming pump with different hydraulic performance parameters based on hydraulic performance experiments,self-priming performance experiments,transient high-speed photograph experiments to build the bridge between microscopic number,size,motion trajectory of bubbles and macroscopic self-priming performance.As a result,it provides a theoretical basis for the design of self-priming structure.The main investigations and results are as follows:1.An external mixing pump was designed with organic glass material based on self-priming pump design theory,and then the movable tongue structure was designed based on materials properties and characteristics of self-priming pump.Self-priming pump external characteristics test bench was built up to obtain the performance curve of self-priming pump.Experiments were also conducted to make out of the relationship between circumferential velocity at outlet of impeller,tongue gap and self-priming performance.2.A self-priming process transient high-speed photograph experiment system was built to measure rational speed of impeller,pressure and flow rate at inlet or outlet of the pump with different rational rate of motor to find out the differences.At the same time,high-speed photograph experiments were made,and two-phase changes in impeller,volute,and gas-liquid separation chamber were shot as a basis of image processing later.Result showed that self-priming process consists of three periods: beginning process,stable process and great change process.The stable self-priming process takes up the maximum proportion of the whole self-priming time and has the largest effect on the self-priming performance.3.Images of bubbles in the flow during self-priming process were processed in some methods,including filtering denoising,image binarization and filling.Filtering denoising was divided into two steps: removing background noise and smooth denoising.Image difference method was applied to remove background noise in this investigation,then compare three smooth denoising methods: median filter,Gauss filter and Wiener filter.Three result images were separately turned into binarization images with maximum class square error or iteration method.Bubbles in the result images were filled by imfill function in MATLAB to regain lost information due to the binarization process.Result shows that Gauss filter and maximum class square method are better in processing bubble images in this research.4.Information about quantity,size,movement track and velocity of bubbles was received using functions in MATLAB toolbox.Result shows that during self-priming process,bubbles in the left area of volute diffuser which are closer to inlet of gas-liquid separation chamber,are smaller and denser than those in the right.These bubbles are easier to be discharged out of the pump.On the contrary,bubbles in the right area vibrate and rotate which goes against self-priming and wastes energy.As a result,self-priming performance can be improving by decreasing the size of bubbles in the flow to turn the stagnant bubbles into moving bubbles,that's why self-priming time decreases with tongue gap.