Aiming at the problems of complex structure and unreasonable parameter setting leading to high flow pulsation rate of traditional hydraulic reciprocating pump in high pressure systems, a new reciprocating pump model with a simple structure was proposed based on the principle of variable orifice of mechanical iris mechanisms.First, based on the model of the new reciprocating pump, the analysis equation for flow pulsation is derived. Secondly, Fluent software is used to perform fluid simulation on the new reciprocating pump, verifying the correctness of the pulsation equation and analyzing the pressure distribution contour map and velocity distribution contour map of the internal flow field of the new reciprocating pump during the cycle. Finally, according to the analysis equation, the variation curve of flow pulsation rate with the number of new reciprocating pumps and the crank-connecting rod ratio is obtained, and optimization suggestions for the parameter setting of the crank-connecting rod in the new reciprocating pump are proposed. The results show that: The derived analytical formula for flow pulsation of the new reciprocating pump is correct. The flow pulsation rate increases with the increase of the crank-connecting rod ratio, and when the number of new reciprocating pumps is 5, the influence of the crank-connecting rod ratio on the flow pulsation rate reaches 87%. The degree of oscillation of the inertial force experienced by the slider decreases as the crank rod ratio decreases. To increase the maximum and minimum values of the instantaneous flow rate and reduce the oscillation degree of the inertial force experienced by the slider, the crank rod ratio should be controlled within the range of 0.2 to 0.3. This new reciprocating pump enriches the structure of the pump and provides certain references for reducing flow pulsation in reciprocating pumps as well as decreasing the oscillation degree of the inertial force experienced by the slider.

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In recent years, electronic devices have become smaller and denser. For example, fans mounted in steam exhaust units are required to be thinner from the standpoint of installation space, while maintaining performance. In this study, an optimization design method for thin multi-blade fans was developed by combining design of experiments, three-dimensional steady and unsteady CFD analysis, response surface methods, and optimization methods. The performance of the optimized fan obtained by this design method was verified through performance tests, and the aerodynamic loss was quantitatively evaluated by developing a loss analysis method for centrifugal fans. As a result, the total pressure coefficient of the optimized fan increased and the power coefficient decreased compared to the original fan, and the total pressure efficiency improved by about 12.7% at the best efficiency point flow rate in the experimental value. This is because the theoretical total pressure coefficient decreased due to the smaller blade outlet angle of the optimized fan compared to the original fan, while the total aerodynamic loss decreased significantly due to the decrease in casing loss, impeller loss, and impeller friction loss in the impeller.

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Based on Computed Tomography (CT) tomography images of the human heart, a 3D reconstruction and wall optimization of the heart was performed by using Mimics to model the motion of the left ventricular overflow wall. The non-Newtonian blood flow in the left ventricle was numerically simulated using the dynamic mesh technique based on User Defined Functions (UDF) programming of the left ventricular wall motion. When the left ventricle is diastolic, the internal pressure gradually increases, the blood flow structure approximates the physiological blood flow pattern, the rate at the mitral orifice first increases and then decreases, and a local high stress zone appears. When the left ventricle is systolic, the pressure gradient is significant, the internal pressure decreases and the rate at the aortic valve orifice shows a pattern of increasing and then decreasing. The dynamic simulation of left ventricular blood flow provides a feasible technical solution for the fluid dynamics analysis of cardiac physiological and pathological processes.

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The roto-jet pump mainly features the synchronous rotation of the impeller and the rotary shell as the structure, which is beneficial to reduce the friction loss of the disc and improve the pump efficiency. The synchronous rotation state of the impeller and the rotary shell, however, does not represent the optimal operating condition of the roto-jet pump. In order to examine the mechanism and the effect of the rotary shell speed on the performance of the roto-jet pump, an experimental research was carried out under two states, namely, rotating and fixed rotary shell, using the open test bench of the roto-jet pump as the research object. A simulation test was performed at rotating shell speed ratio i = 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6. The results show a relatively high entropy production and dissipation at the inlet of the collecting pipe and the outlet of the impeller at each operating point, and a large energy loss. In addition, the energy loss in the wall area of the rotary shell is basically proportional to the rotational speed of the rotary shell. The collecting pipe has a significant influence on the vortex structure inside the rotary shell, and the surrounding vortices are mainly generated on the upstream surface and the wake area of the collecting pipe. At constant impeller speed, the radial pressure gradient of the liquid in the rotary shell can be increased by increasing the rotary shell speed. The liquid pressure in the area of relative radius s smaller than 1 corresponds inversely to the rotary shell speed, while the liquid pressure in the area of s larger than 1 corresponds proportionally to the rotary shell rotating speed. The minimum value of the total disc friction loss for this pump occurs at position i = 0.8. At this point, the friction loss of the impeller disc is 83.8% of the total loss. The friction loss of the rotary shell disc is 16.2%, and the pump efficiency has the highest value, 1.3% higher than that of the rotary shell synchronous rotation operating point. The optimum rotating speed ratio between the rotating shell and the impeller is 0.8, and the research results can be a reference for the differential operation of the impeller and rotary shell of the roto-jet pump.

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Upstream pumping spiral grooves provides an effective way to realize design of mechanical seals with long service life as well as low leakage rate, which largely lies on precise design of spiral grooves under gas-liquid lubricating boundary conditions. The originality of this paper is to consider the gas phase pressure boundary in order to be suitable for more complex gas-liquid seal analysis. An numerical analysis of performance of upstream pumping spiral groove mechanical face seals is carried outunder gas-liquid boundary conditions. Opening force and leakage rate are calculated taking account of gas-liquid fluid medium boundary conditions as well as cavitation effect. The results show that the opening force and leakage rate decrease obviously under gas-liquid boundary conditions, compared with the full liquid boundary conditions, exceeding 50% in degree. Besides, the groove parameters such as spiral angle, slotting ratio and groove number present obvious and complex influence on the opening force and leakage rate. This research may provide the reasonable basis for the design of upstream pumping spiral groove mechanical face seals.

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This paper adopts the theory of jet energy transfer analysis and computational fluid dynamics (CFD) technology to improve annular jet pump (AJP). The nozzle of AJP is improved so that the annular nozzle is wrapped by the suction nozzles on both sides, which creates a double-suction annular jet pump (DAJP). The primary flow injected into suction chamber is surrounded by the secondary flow. The energy loss caused by direct contact of the primary flow with the wall is reduced. CFD was used to analyze the flow mechanism and performance in order to optimize its structure. Simulation results show that: the performance of the jet pump with a nozzle distance of 8mm from the wall is better than that of the other three DAJPs and the prototype pump. Its maximum efficiency can reach 51.77%. When the flow rate ratio is less than 0.4, the turbulent kinetic energy (TKE) is larger. It causes instability and irregular fluid motion, which ultimately leads to fluid energy loss and flow resistance increase. The smaller the flow ratio, the larger the backflow area in the suction chamber. The backflow area disappears when the flow ratio is greater than 0.4. The prototype pump only appears the backflow area near the axis of the suction chamber, while the DAJP also has a backflow area near the wall where the nozzle connects with the suction chamber.

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With the development of screw pumps towards high speed, high pressure, and large flow rate, cavitation in screw pumps has become a phenomenon that cannot be ignored. Based on ANSYS CFX, use SST turbulence model and combine with Rayleigh-Plesset equation to effectively simulate the internal flow of mixed transport twin screw pump, analyze the changes in cavitation morphology and the evolution of cavitation within the entire cycle of the pump, and explore the degree of cavitation on the surface of the screw rotor and the changes in pressure and velocity at the monitoring point with rotation period under different inlet pressures and speeds, and then analyze the changes in cavitation of the twin screw pump under different temperature. The calculation results indicate that cavitation first occurs at the inlet and then gradually penetrates into the interior of the chamber, mainly concentrated in the inlet section and the first chamber. The inlet pressure has a significant impact on cavitation phenomenon. As the inlet pressure decreases, the cavitation intensity continues to strengthen, and the cavitation area also continues to expand. Rotating speed can also affect cavitation, but the effect of speed changes on cavitation is not as significant as that of inlet pressure changes. In addition, increasing the water temperature will also increase the cavitation area. This study reveals the characteristics of cavitation flow in mixed transport twin screw pump, which is of great significance in avoiding cavitation and improving pump performance.

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