Moloshnyi O. Influence of the inlet device construction of the sealless close coupled pump with a hollow shaft on its working process and characteristics

The work is focused on the pump construction, which ensures high performance correlated with the safety aspects. It leads to the application of the pump, where the likelihood of the failure of the unit is minimal. The double entry pumps are commonly used due to the reduction of the hydraulic forces and also hermetic units, with closed, seal-less construction. The thesis presents a new solution to the scientific problem, which focuses on the improvement of the design of a sealless double entry close coupled centrifugal pump with a hollow shaft. In this conception, the inside of the hollow shaft is an axial inlet device, which consists of a straight part and diffuser. The design of a sealless close coupled centrifugal pump has been developed. Conducted analyses are based on the results of the investigation of the influence of axial inlet device geometrical features on pump working process in order to achieve minimal energy losses in the flowing part of the pump. The mutual influence of the construction of plain bearings and forces acting on the motion elements of the pump was elaborated. The rotating parts are loaded with the hydrodynamic, magnetic and gravity forces, which are the preliminary design data of bearing. On the other hand, the construction of bearing is severely acting on the mentioned above forces, which leads to the crucial design problem. Conducted numerical simulations made it possible to estimate the flow structure in the flowing part of the pump. In detail, the influence of the axial inlet device with rotating walls and the diffuser before the impeller inlet on the performance of the pump was recognized. The range of optimum values of axial inlet device diameters is also determined in terms of minimum hydraulic losses in the axial inlet device and electric losses in the rotor magnetic circuits of the motor under the condition of a hollow pump shaft with specific speed (ns) in the range from 60 to 70. Moreover, the flow structure at the impeller inlet, the parameters of the distribution of the absolute velocity components and the cavitation processes in the axial inlet device and the impeller were investigated. It is established that the first appearance of the cavitation was observed in the impeller. The reduction of the axial inlet device diameter leads to the change in the locations of the cavitation zones and the direction of their distribution. The methodical recommendations for the design of sealless close-coupled pump with a hollow shaft and the influence of the geometric parameters of the axial inlet device on the structural features of the leading edge of the blades of the impeller were developed. The results obtained by the numerical simulation were experimentally confirmed.