High-speed centrifugal pumps with low specific speed have the characteristics of a small flowrate, a high head, and being compact and light weight, making them promising candidates for applications in the thermal management of aerospace and electronic devices. The energy loss in the low specific speed pump is critical and complex due to the large impeller diameter, the narrow and long flow channel, and the small outlet width. In this paper, an analysis method based on an energy loss model and computational fluid dynamics simulations (ELM/CFD) is proposed to analyze the performance of the low specific speed pump with a fully sealed structure. Experiments were carried out under variable water flowrates. The results show that the empirical correlation method failed to accurately predict the performance of high-speed centrifugal pumps, because the bearing clearance leakage and motor channel leakage are ignored. Moreover, the volume loss and hydraulic loss are calculated based on the empirical parameters of commonly used pumps that are different from the high-speed pump with the low specific speed in the complex flow channel structure. The ELM/CFD method calculates various loss power based on the simulation results and can predict the head and efficiency with deviations less than 2% and 5%, respectively. ELM/CFD can accurately analyze the optimization direction of the pump. The hydraulic loss and the volume loss of the impeller are the dominant factors that restrict the pump efficiency under the lower flowrates, while the hydraulic loss of subsequent flow channels becomes important under the larger flowrates.

A high-speed centrifugal pump with a fully sealed structure has the advantages of a small size, no external leakage, and being pollution-free. The inner leakage passage of a pump with a fully sealed structure includes the tip clearance and the hub clearance. The hub clearance, the lubrication passage of the bearing, and the clearance between the stator and the rotor of the built-in motor constitute the internal flow channel. As a consequence of hub leakage, the complexity of the flow field increases and performance of the pump is affected. However, hub leakage also lubricates the bearing and cools the motor by flowing through the internal flow channel. To obtain the actual flow field distribution and external characteristics of the pump, a coupling calculation based on a conventional CFX simulation and MATLAB was carried out. The results show that hub leakage promotes an increase in tip leakage and changes the distribution of the main flow field. Moreover, hub leakage also significantly affects the efficiency of the pump. Compared with hub leakage, the internal flow has a greater impact on the performance of the pump. The numerical simulation results of the internal flow model are similar to the experimental results, with the maximum absolute error of the head at 0.3 m and the maximum absolute error of the efficiency at 1.7%, indicating that the internal flow model is effective at predicting the performance of the high-speed centrifugal pump with a fully sealed structure.

With the rapid development of information technology, researchers have paid attention to the pump-driven two-phase cooling loop technology for data centers, which imposes requirements on the efficiency and size of the pump. A fluid self-lubricating centrifugal pump with R134a refrigerant was developed to reach a higher rotation speed and oil-free system, resulting in a more diminutive size. Due to the high rotation speed and refrigerant pressure approaching saturated vapor pressure, the internal flow characteristics and cavitating characteristics are critical and complex. This paper focuses on the prototype’s head and cavitation performance based on experimental and numerical data. The experiments indicated that the head coefficient of the pump under design conditions is 0.9881, and the pump’s critical cavitation number and breakdown number are 0.551 and 0.412, respectively. The numerical results can predict the head and cavitation with deviations less than 2.6%. To study changing patterns in flow characteristics under the different operating conditions in the refrigerant centrifugal pump, the numerical model based on a modified Sauer-Schnerr cavitation model was built to analyze the distributions of pressure, temperature, relative velocity, and bubble volume across every hydraulic component and different degrees of cavitation, and proposed the influence of the thermal effect on refrigerant cavitating. The cavitating flow characteristics were obtained with the aim of providing guidance for the hydraulic design of a refrigerant centrifugal pump.