Numerical research of the influence of the main parameters of the flow part of feed pumps on their energy characteristics

Background: Impellers and diffusers of multistage feed pumps are the most important components of the unit. The most important parameters of the flow part are: d_hub/D₂, D₀/D₂, D₃/D₂, b₃/b₂, and determining their optimal values is a relevant task, since they contribute to the most efficient operation of the pumps. Conducting a physical experiment to study a large number of parameters is problematic due to significant financial and time costs, but by using three-dimensional mathematical modeling methods, these difficulties can be minimized. The objects of study are multi-stage feed pumps for nuclear power plants with stage specific speed n_s = 71, 103 and 137.

Aim: Using three-dimensional mathematical modeling methods, search for optimal values of the flow path parameters of the feed pump (d_hub/D₂, D₀/D₂, D₃/D₂, b₃/b₂) and determination of their impact on the efficiency of the unit using three-dimensional mathematical modeling methods.

Methods: The search for optimal parameter values was performed using three-dimensional hydrodynamic calculations of viscous fluid flow. The calculation models are full-size, consisting of an inlet, an impeller, and a diffuser of the last stage. The mesh is unstructured. Numerical calculations were performed using the CFD method with varying geometry of the impeller and diffuser.

Results: The numerical research performed showed that d_hub/D₂ should be selected as minimal. The optimal calculated value of D₀/D₂ for n_s = 71, 103, 137 is 0.50; 0.57; 0.60, respectively. The optimal calculated range of b₃/b₂ for n_s = 71, 103, 137 is (1.0…1.3); (1.1…1.4); (1.2…1.5), respectively. The optimal numerical value of D₃/D₂ for the stage with n_s = 71 corresponds to the minimum from the studied range (1.02); for the stage with n_s = 103, there is a tendency to decrease in hydraulic losses with an increase in D₃/D₂ over the entire considered interval (up to 1.08); for the stage with n_s = 137, an increase in the D₃/D₂ parameter does not have a significant effect on the growth of hydraulic losses.

Conclusion: The numerical research and analysis of the obtained results showed that the values of the optimal parameters D₀/D₂ and b₃/b₂ increase with the growth of the stage specific speed. Reducing the hub ratio helps to reduce the flow velocity at the impeller inlet and, consequently, reduces hydraulic losses, so it is necessary to select the minimum value of this parameter taking into account the requirements for strength and reliability. Within the studied range, the optimum D₃/D₂ for n_s = 71 and n_s = 103 is equal to the minimum and maximum values, respectively; for n_s = 137, no clear optimum was identified.