| As an energy conversion device,the centrifugal pump always has energy loss and vibration.However,the vibration problem of variable frequency centrifugal pump has not been completely solved at present.For a qualified centrifugal pump,it is often caused by hydraulic factors.Therefore,the research on the vibration of centrifugal pump is mostly concentrated in the range of flow field,hoping to describe the flow field more accurately and analyze the cause of vibration of centrifugal pump.However,it is very difficult to describe the complex and variable flow field inside the centrifugal pump.As early as the 1920 s,scholars have devoted themselves to the description of the internal flow field of the centrifugal pump.Until recently,it has not been able to quantitatively describe the vibration intensity change of the centrifugal pump.Quantitative analysis of vibration intensity change of centrifugal pump is the only way to avoid economic loss caused by excessive vibration intensity.This thesis analyzes the vibration of centrifugal pump from the perspective of energy conservation.There must be energy loss in the operation of centrifugal pump.According to the law of energy conservation,these energy losses will not disappear out of thin air,but will be transformed into vibration,noise and internal energy during the operation of centrifugal pump.The correlation between energy loss and centrifugal pump is analyzed theoretically.Therefore,by determining the energy loss value corresponding to the determined vibration level of the centrifugal pump,the purpose of quantitatively analyzing whether the vibration of the centrifugal pump will cause economic loss is achieved.In the process of theoretical analysis,it is decided to use the input energy and operation efficiency of centrifugal pump to predict the energy loss value,while the operation efficiency of variable frequency centrifugal pump is mostly based on similar theory.However,in the further study,it was found that the similarity theory believed that the operating efficiency of similar operating points remained unchanged and there was a large error with the actual situation.Some scholars also found this problem,and believed that only when the frequency changed little can the error be ignored and the similarity theory be used directly.This thesis proposes to modify the equivalent efficiency curve of the similarity theory,so that the operating efficiency of the centrifugal pump at each operating point can be calculated.The energy loss of centrifugal pump is divided into main energy loss and secondary energy loss.Finally,the change of energy loss is expressed by the change of liquid flow angle,and the equivalent efficiency curve formula is obtained.The vibration intensity test at the working point of equal efficiency was carried out.It is verified that the energy loss of centrifugal pump is related to the vibration intensity,and the critical energy loss can be measured in the experiment.If the energy loss does not exceed the critical value,the service life will not be reduced.The compensation formula of the iso-efficiency curve is verified,and the fitting effect is good in the data fitting,which provides a certain scientific basis for the compensation formula.In the experiment,two rules of vibration intensity change of centrifugal pump are found: 1.At the same frequency,the vibration intensity of centrifugal pump increases first and then decreases with the flow rate decreasing;2 With the same vibration intensity,the lower the frequency,the greater the energy loss required. |
