The Research On Calculation And Design Method Of The Thrust Of The New-type Axial Thrust Balancing Device Of Centrifugal Pump

The method of balancing the axial force has been one of the important pr ojects in the field of pump research. According to consult the related literature data of the axial force balancing method, the range of use and ability to balan ce axial force of axial thrust balancing devices applied at present have certain limitations. In this paper, a new-type axial thrust balancing device of centrifug al pump was put forward in view of the disadvantages and shortages of variou s balancing devices. A pair of dynamic and static rings are installed in the bal ance cavity of single stage centrifugal pump or the last stage impeller of multi stage centrifugal pump. By changing the outer radius of the dynamic and staticring and the axial clearance, this paper have carried on the thorough research to the change rule of pressure distribution, leakage and axial force on the dy namic ring of the liquid in the axial clearance of the balancing device by ado pting the method of theoretical analysis and numerical calculation. The main re search contents of this paper are as follows:1. Theoretical analysis of the liquid flow in the radial clearance and axial clearance of the balancing device were carried out. The calculation formula of the fluid leakage in axial clearance and the liquid pressure and axial force on the dynamic ring are obtained by using the N-S equation for incompressible viscous fluid motion and the continuity equation. This paper takes the centrifugal pump that IS80-50-315 as research subject. Theoretical calculation of fluid leakage in axial clearance and axial force on the dynamic ring under the design condition were carried out under the condition of outer radius of the dynamic and static ring is 45 mm, 52.5mm, 57.5mm,62.5mm. The result shows that the fluid leakage in axial clearance increases with axial clearance, but the axial force on the dynamic ring decreases with axial clearance.From the point of controlling the axial force on the dynamic ring and reducing the fluid leakage in axial clearance, the appropriate axial clearance was from 0.4 to0.8mm.2. Model pumps with different outer radius of the dynamic and static ring and axial clearance were calculated with the method of numerical calculation under the condition of the full flow. The effect of axial clearance on pump performance was obtained. The results shows that the pump head decreases with axial clearance, and the different models pump head decrease obviously when in smaller flow(5~20m3/h).The trend of decreasing is not obvious when in large flow(25~40 m3/h). The variation of axial clearance has little effect on the efficiency and the shaft power.3. The liquid pressure distribution of axial clearance was studied under the design condition. The results shows that the liquid pressure in axial clearance increases gradually along the radius, while the change of its value is negligible along axial direction. And the pressure-radius relation curves are oblique straight line. But both the ratio of the outer radius to the inner radius of the dynamic and static ring and the size of axial clearance have an obvious effect on the slope.4. In order to analyze and calculate the dynamic performance of the similar balancing device, the dimensionless parameters, such as the rotational Reynolds number, the leakage coefficient, the axial force coefficient and the gap-diameter ratio were introduced. The curves of simulated leakage coefficient and calculation of leakage coefficient with the gap-diameter ratio and the curves of simulated axial force coefficient and calculation of axial force coefficient with the gap-diameter ratio were drawn under the design condition. The result shows that the leakage coefficient is rapidly increased and then tends to be flat while the axial force coefficient has a sharp decrease and then tends to be flat with the increase of the gap-diameter ratio. Simulation results and calculation results of fluid leakage in axial clearance and axial force on the dynamic ring have litter difference. The reliability of numerical calculation is illustrated.5. Theoretical calculation of balance cavity area of liquid acting on the impeller hub of axial force was carried out when the balance cavity is not installed balancing device. And it was compared with the axial force of the liquid acting on the dynamic ring when the balancing device installed in the balance cavity. The result shows that the balancing device is installed in the balance cavity has an obvious effect on reducing the axial force.