Effects of Multi-objective Optimization of the First-stage Impeller on the Energy Loss Characteristics of a Multistage Molten Salt Pump

To mitigate the prohibitive cost of simultaneously modifying all stages in multistage molten salt pumps used in concentrating solar power plants, address the substantial degradation of hydraulic performance under off-design operating conditions, and resolve the difficulty of tracing cross-stage flow-loss coupling mechanisms, this paper presents a cost-effective retrofit strategy that limits geometric modifications to the first-stage impeller and harnesses the interstage flow-matching effect to improve system-wide performance. The methodology proceeds in four sequential phases. First, a comprehensive sample database is constructed using Latin hypercube sampling combined with high-fidelity computational fluid dynamics simulations. Second, the Adam optimization algorithm is used to train a backpropagation neural network, establishing a computationally efficient surrogate model to replace time-intensive numerical simulations. Third, the surrogate model is coupled with the NSGA-II multi-objective evolutionary algorithm to perform Pareto-front optimization, simultaneously maximizing hydraulic head and efficiency at the design operating point. Finally, based on entropy production theory, the evolution of energy loss before and after optimization is systematically characterized at four hierarchical levels: total entropy production, component-level entropy production, wall entropy production, and vortex structure evolution, through the joint analysis of local entropy production rate distributions and vortex identification using the Q-criterion. The optimization yields notable improvements: the hydraulic efficiency of the first-stage impeller increases from ۷۸.۴۲% to ۸۱.۸۳%; total entropy production under design conditions decreases by ۸.۶۳%; and entropy production within the first-stage guide vanes decreases by ۴۵.۲۳% at ۱.۲ times the design flow rate. Crucially, the second-stage impeller geometry remains unchanged, confirming that first-stage optimization propagates performance gains to all downstream stages through the interstage flow-matching mechanism. By limiting the scope of hydraulic modification from the full pump assembly to a single stage, the proposed framework establishes a practical pathway for low-cost hydraulic optimization of multistage molten salt pumps.

کلیدواژه ها:

Molten salt pump ، NSGA-II ، Entropy generation analysis ، Numerical calculation ، Performance optimization