Numerical simulation of factors affecting flow characteristics of double-circular-arc gear pump

Objective: Analyzed the influencing factors of the internal flow field pulsation characteristics of the new double circular arc gear pump, and adopt reasonable parameters to improve the output efficiency of the gear pump. Methods: The two-dimensional flow field simulation model of the gear pump was established, and the computational fluid dynamics software Fluent was used for simulation analysis to study the influence of different tip clearance, different gear eccentricity, load and speed on the instantaneous flow, flow pulsation and flow field characteristics of the oil outlet of the gear pump. Results: As the tooth tip clearance increased, the outlet flow rate of the gear pump gradually decreased. When the tooth tip clearance was 0.09 mm, the minimum pulsation coefficient of the outlet flow rate was 0.135, which was the optimal tooth tip clearance for the gear pump under this structural parameter. Due to the influence of load pressure and rotational speed, the central axis of the gear pump deviates. As the eccentricity of the central axis of the gear pump rotor increased, the outlet flow rate of the gear pump gradually increased. When the eccentricity was 0.05 mm, the outlet flow rate of the gear pump increased by 5.09% compared to without central deviation, improving the flow output. Conclusion: The main influencing factors on the flow characteristics of gear pumps are rotor speed and tooth tip clearance, and the influence of center deviation is relatively small

Gab2 Promotes Hematopoietic Stem Cell Maintenance and Self-Renewal Synergistically with STAT5

Grb2-associated binding (Gab) adapter proteins play major roles in coordinating signaling downstream of hematopoietic cytokine receptors. In hematopoietic cells, Gab2 can modulate phosphatidylinositol–3 kinase and mitogen associated protein kinase activities and regulate the long-term multilineage competitive repopulating activity of hematopoietic stem cells (HSCs). Gab2 may also act in a linear pathway upstream or downstream of signal transducer and activator of transcription-5 (STAT5), a major positive regulator of HSC function. Therefore, we aimed to determine whether Gab2 and STAT5 function in hematopoiesis in a redundant or non-redundant manner.), reduced HSC survival, and dramatic loss of self-renewal potential as measured by serial transplantation.These data demonstrate new functions for Gab2 in hematopoiesis in a manner that is non-redundant with STAT5. Furthermore, important synergy between STAT5 and Gab2 was observed in HSC self-renewal, which might be exploited to optimize stem cell-based therapeutics

Tribological Properties of Polyether–Ether–Ketone-Based Coating under Mixed and Boundary Aviation Kerosene-Lubrication Condition

Because of its excellent tribological performance, polyether–ether–ketone (PEEK)-based coatings have been used extensively under mixed and boundary water-lubrication conditions. To verify that the PEEK-based coating is applicable to aviation kerosene, one advanced coating was proposed and two typical metals, namely, alloy steel 38CrMoAlA and tin bronze ZQPb17-4-4, were selected as counterparts. Four sets of experiments that involved a scuffing (step load) and Stribeck curve (step speed), constant load, and strengthened load were carried out, which showed that the counterpart material’s properties, such as its hardness, thermal conductivity, and composition, had an important effect on the tribological performance of the PEEK-based coating. Scuffing experiments showed that the PEEK-based coating against ZQPb17-4-4 exhibited better scuffing performance. Stribeck curve experiments showed that the PEEK-based coating against 38CrMoAlA was under the mixed lubrication condition over a wider range of speeds, and wear experiments (constant load and strengthened load) showed that the PEEK-based coating against 38CrMoAlA exhibited a relatively low coefficient of friction and low wear rate. The formation and appearance of the tribofilm on the surface of the counterparts influenced the wear mechanism of the PEEK-based coating. The PEEK-based coating showed excellent properties, especially when rubbed against 38CrMoAlA.</jats:p

Design of a high water-based fluid, high-pressure, and large-flow safety valve

Aiming at solving the problem of low unloading sensitivity, bad dynamic performance and poor stability of high-pressure and large-flow relief valve in hydraulic support system, a new differential type of high-pressure and large-flow relief valve, functioned by high water-based hydraulic medium, is designed. Through analysing the influence of spool form, elastic element, and working principle on valve performance, a structural scheme of large-flow and high-pressure safety valve is put forward. The three-dimensional fluid–solid coupling model of differential safety valve is established; through ADINA software, three-dimensional fluid–solid coupling simulation of relief valve's orifice from shutdown to full opening is carried out to analyse the distribution of internal pressure in the flow field of the safety valve and the pressure change of the structure field. The physical simulation model of safety valve is established by using AMESim software, and the dynamic performance of safety valve is simulated under the given signal of nominal flow and small flow. According to the design structure, the safety valve with the rated flow of 3000 L/min is manufactured and tested. The simulation and experimental results show that the safety valve has good dynamic performance and high sensitivity