Turbulence Generator Inner Flow And Experimental Study On Medium Consistency Pump

This study is financial supported by the China National Key Technology R&D Program-Key Technology and Running Strategy of Typical Process Pumps (No: 2011BAF14B02), and A Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (No:PAPD).Rheological model parameters were established based on the study on flow mechanism and the measurement of rheological properties of medium consistency pulp suspension. The bubble velocity and trajectory equations were put forward through theoretical analyses and experiment, and the fluid velocity and turbulent kinetic energy were analyzed at different speed. The design method of turbulence generator was preliminary proposed based on the investigation of internal flow of turbulence generator. The characteristic of gas-liquid separation in the medium consistency pulp pump (MC pump) was investigated using CFD. The MC pump testing bed was built, and the operation and performance characteristics of MC pump in different conditions were studied using sonar flowmeter and monitoring system.The main contributions and creative achievements of this work are presented as follows.1. The density, shear stress and shear rotational speed of medium consistency pulps was investigated by experiment, and the rheology of medium consistency pulp fluidzation was studied. The experiment data was ready for realizing medium consistency pulp suspension turbulence and pumping.2. The motion characteristic of bubble in turbulence generator was researched by theoretical analysis and experiment. The forces of bubble in turbulence generator were analyzed. The velocity and trajectory equations were established, and the dynamic characteristics of bubble were studied. A set of platform, which allows visualization of the two-phase flow flied, was established. The high speed photography technology was used to photograph the bubble movement in turbulence generator. The image processing was programmed. By tracking characteristic parameters of objective bubble, the transient motion paths of different diameter were obtained at 80,130 and 200r/min. The exponential relationship between radial position and rotational degree is found, and radial position decreases rapidly with diameter and rotational speed increasing. The results reveal that increasing angular velocity could accelerate centripetal motion; the relatively long diameter bubble was more easily to arrive at the axial wall.3. The flow characteristic in turbulence generator of medium consistency pump was studied using PIV (particle image velocimetry) steup. A new PIV test rig was established. Through adjusting the angle and position of mirror,2D-plane flow field was fast and effectively acquired. For investigate the effect of speed on flow field, velocity and turbulent kinetic energy were measured at speed 80,130 and 200r/min. Dimensionless method was adopted to analyze flow field by quantitative approach. The results show that on vertical flow plane axial velocities decreased with radius increasing in the region of turbulence generator blade, and axial velocity direction was changed and increase with radius increasing outside the region of turbulence generator blade. Internal flow direction of turbulence generator is at opposite direction with outside flow. Fluid flows from inlet to outlet of turbulence generator blade and then goes back to inlet, which forms a circle. On horizontal flow plane, circumferential velocity increases with radius increasing firstly, and then the maximum appears at outer diameter of turbulence generator, and last it decreases gradually. Turbulent kinetic energy increases with rotational speed increasing at inner of turbulence generator flow field, and high turbulent kinetic energy mainly concentrates near the blade inlet and external diameter of turbulence generator.4. Based on flow theoretical analysis and experimental research, turbulence generator design method was preliminary established and perfected. The velocity distribution in turbulence generator (shear chamber) was investigated when medium consistency pulp is at turbulent state, and the medium consistency pulp turbulence critical condition was determined. In combine with medium consistency rehology data, the equation of turbulence generator blade diameter was proposed. According to bubble trajectory, the separation time was obtained, so axial length of turbulence generator calculating method was acquired. The inlet of turbulence generator blade design method was determined according to the distribution characteristics of turbulent kinetic energy.5. The characteristic of gas-liquid separation in MC pump was studied using numerical simulation. The Eulerian-Eulerian model was used to simulate unsteady gas-liquid separation. The effects of rotational speed, vacuum degree and flow rate on gas-liquid separation and transient gas-liquid separation process were studied. The results show that high gas volume fraction is concentrated in the back of blade in turbulence generator and gas in impeller decreases with rotational speed increasing. The region area of high gas volume fraction decreases gradually with flow rate increasing, and gas is concentrated in the back blade root of turbulence generator at large flow rate. The further separation is done by back blade of impeller. Lots of gas is concentrated on discharge port of impeller, which is accompanied with strong interaction of gas-liquid two phases. Study on characteristic of gas-liquid separation can provide design reference for structure of gas-liquid separation and degas system.6. Effect of different conditions on MC pump performance was studied by experiment. A MC pump test bed was established using sonar flowmeter and monitoring system. The head, efficiency, gas fraction and max flow rate were studied with pulp concentration 7.52%,9.3%,12.1%, speed 960 r/min,1140 r/min,1500r/min and different degas vacuum degree at vacuum housing. The results show that at constant flow rate, pump head and efficiency decrease with increase of pulp concentration. Vacuum degree has significant effect on pump performance. MC pump can pump concentration 7.52% pulp without vacuum, but pump head and efficiency decrease obviously with flow rate increasing. With vacuum degree increasing pump head increases, and gas fraction decrease at pump outlet. Head increases with rotation speed increasing, but gas fraction of pulp decreases at pump outlet. Vacuum degree decreases with rotation speed increasing, so enhancing pump speed can improve gas-liquid separation. Gas fraction and degas vacuum degree increase with concentration increasing. The max flow rate decreases with increase of concentration and increases with rotation speed increasing.