Low Specific Speed Centrifugal Pump Design Theory

The efficiency of centrifugal pump usually is very low. To solve the problem, designer presented the increasing flow rate theory. These increasing coefficients are regresses from the successful case. These increasing coefficients have no theory base in practice, and usually they are found not to be rational. The thesis put its emphasis on the analysis of relations between the design parameter and increasing coefficients using theory method, and relations between the design parameter and the pump performance. Combine these relations, and we can get the increasing coefficients when the pump efficiency is relatively high and the dimension of the pump is relatively small. So the primary consent two problems are how to predict the performance of pump only according to its figure parameters and how to get the most rational increasing coefficients from the point view of theory. Study and solving of the two problems are very significant in practice and theory to the design theory of low specific speed centrifugal pump, analysis of the hydraulic loss mechanism and the development of the software of pump CAD.The main research work of the thesis is as follows1. The flow in volute is analyzed and the pressure and velocity distribution in volute are obtained.2. The reverse flow model is induced when calculated the hydraulic losses in impeller.3. The simple formulae for the mix loss at the outlet of impeller is presented.4. The relation between the design parameters, the figure parameters of flow passage and increasing coefficients is deduced.5. The area ratio principle in increasing flow rate method is discussed, and the formulae for the area ratio value, the power of pump and the throat area are presented when the width of the impeller outlet is increased.6. The prediction models of leakage, the hydraulic efficiency, and the mechanical efficiency are compared and the preferable model is adopted to calculate the type of 100AY 120 centrifugal oil pump and 701 plastic pump. The calculation results show that the errors are very low comparing with the experimental data.7. Combine the increasing flow rate method with pump performance prediction method, the impeller outlet width of the 100AY120 centrifugal oil pump is increased gradually from the primary value that is obtained from the primary design parameter according to the traditional design theory, and performances of the pump with different impellers outlet width are predicted, and the preferable impeller outlet width is obtained, then the increasing coefficients are obtained in reverse.8. The rational increasing coefficients are obtained on condition that the head at design condition is constant, which are compared with the experience data.