In this paper, the effect of membrane features on flow characteristics in the microfluidic passive valve (MPV) and the membrane behavior against fluid flow are studied using the fluid-structure interaction (FSI) analysis. Firstly, the microvalve model with different numbers of microholes and pitches of microholes are designed to investigate the flow rate of the MPV. The result shows that the number of microholes on the membrane has a significant impact on the flow rate of the MPV, while the pitch of microholes has little effect on it. The constant flow rate maintained by the microvalve (the number of microholes n = 4) is 5.75 mL/min, and the threshold pressure to achieve the flow rate is 4 kPa. Secondly, the behavior of the membrane against the fluid flow is analyzed. The result shows that as the inlet pressure increases, the flow resistance of the MPV increases rapidly, and the deformation of the membrane gradually becomes stable. Finally, the effect of the membrane material on the flow rate and the deformation of the membrane are studied. The result shows that changes in the material properties of the membrane cause a decrease in the amount of deformation in all stages the all positions of the membrane. This work may provide valuable guidance for the optimization of microfluidic passive valve in microfluidic system.

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A microfluidic passive valve (MPV) is important for precise flow control, and it determines the reliability of the microfluidic system. In this paper, a novel MPV capable of delivering a constant flow rate independently of inlet pressure changes is proposed. The flow rate of the MPV is adjusted by the difference between the fluid force on the upper surface of the valve core and the spring force. The constant flow rate of the MPV is maintained by automatically changing the size of the gap channel formed by the groove on the valve core and the baffle on the valve body. The nearly constant flow rate of the MPV is 6.26 mL/min, with a variation of 6.5% under the inlet pressure varied from 1.25 kPa to 3.5 kPa. In addition, the flow characteristics of the MPV are analyzed by numerical simulation. With the increase in the inlet pressure, the maximum velocity gradually increases, while the increment of the maximum velocity decreases. In the movement process of the valve core, the region of pressure drop becomes larger. This work has a certain reference value for the design and research of the MPVs with high throughput liquid delivery.

Hydraulic valve is used as an important hydraulic component, playing a vital role in fluid power transmission and control systems. When the phenomenon of sticking of valve core occurs, it may seriously decrease the accuracy and sensitivity of the hydraulic valve. Micro-deformation is one of the most common faults causing the valve core sticking, which is due to the thermal load. Therefore, studying the mechanism of valve core sticking caused by thermal fluid is of great significance. In this paper, the fluid dynamics in hydraulic valves and the temperature characteristics of valve core are analyzed based on the thermal-fluid-solid coupling method. Results show that the jet angle (θ) will decrease with the increase of opening degree (k), and the maximum velocity and temperature increase with the increase of the opening degree. By loading the temperature field into the thermal analysis as a boundary condition, it shows that the temperature of the U-throttle groove increases with the increase of the opening degree. In addition, with the increase of opening degree, the maximum thermal deformation increases and the contact pressure between valve core and valve body also increases. This work has a certain reference value for researching and improving the phenomenon of valve core stuck in hydraulic valve.

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