The Effects Of Uniaxial Length For Submerged Pump On The Shaft Statics Characteristics And Rotor Natural Frequency In Liquid State

The most significant dynamic source in the production of concentrated sulfuric acid is submerged pump,the stable operation of which is directly related to the reliability and safety of production.The depth of submerged pump often needs to change to meet the requirements of different production conditions.This article took the rotor system of the XDBG700-27 Without sleeve uniaxial submerged pump as the research object,and mainly studied the influence of rotor spindle length change on rotor stability in the absence of change within support methods of submerged pump rotor system,material properties,external loads and other factors.Meantime,it was studied involving calculation of bearing stiffness and oil film stiffness in rotor systems,static analysis of each rotor with rotor spindle length changing,modal analysis and calculation of critical speed.Firstly,impeller radial and axial forces of submerged pump were studied with computational fluid dynamics theory.Fluid force is an significant external load in a rotor system,size and direction of which have a great influence on the rotor system.It,through computation,has been found that the radial and axial forces of the impeller section of the submerged pump are not changed much in steady and unsteady conditions.In the constant calculation,the radial force decreases firstly and then increases with the increase of the flow rate,and the radial force is 179 N in the design condition at least;.In the steady calculation,the axial force decreases as the flow rate increase,and the axial force at design point is 6949.22 N.Secondly,the static analysis of the rotor system with different axial lengths is carried out,the variation of the length of the rotor main shaft including that each 0.1m increment is a length based on the length of the original rotor main shaft.A total of six kinds of rotor systems including the original long rotor are named as original long rotor,rotor one,rotor two,rotor three,rotor five and rotor six,respectively.The original long rotor system has a total shaft length of 3094 mm,and the rotor has a total shaft length of 3594 mm.according to the actual situation,the support and constraint conditions of the rotor system were designed.The external load was also the fluid force,and the stress and strain changes of different rotor system were analyzed.The results showed that the maximum equivalent stress of the rotor concentrates on the top of rotor and varies little the length of main shaft of the rotor,and basically 20MPa;tensile yield strength of rotor material is 215 MPa and a compressive yield strength of 207 MPa,thus the six rotors in the design scheme could meet the material strength requirements of the rotor system operation.Finally,natural frequency and critical frequency of various rotor systems were studied in dry and wet states.Natural frequency of same order decreased with the increase of the axial length of the rotor of various rotors in dry state,which showed that the increase in the support span of the rotor system would lead to a decrease in the natural frequency,and the same for the six rotor systems.There are similarities in the step shape,and the maximum deformation displacement does not exceed 4.5mm.The longest spindle length in the model was rotor five,the first-order natural frequency of the rotor was5.62 Hz,and the first-order critical frequency was 337.302 rpm,which was much higher than the design speed of the rotor system.The critical frequency of same order is decreased obviously in the wet critical speed of the rotor compared with the dry critical speed,and the vibration mode was also different.The first-order natural frequency of rotor 2 dropped to 44.06 Hz,and the first-order natural frequencies of rotor three,rotor four and rotor five were below 30 Hz.The frequency corresponding to the design speed was 0.8 times the frequency of 30 Hz.and rotor systems do not meet the requirements when they are started from rest,the rotor speed would pass its own firstorder critical speed,which may cause resonance phenomenon.The rotor system would become a flexible rotor with they are running at design speed,which is not desirable in engineering operations.It is basically determined that the elongation of the main shaft of the rotor system could not exceed 0.4mm on the basis of the original long rotor through the above research,and the length of safety control is 0.35 m.