5×5棒束通道内流动转捩特性研究

棒束通道的特殊结构导致其内部流动转捩情况较为复杂，探究其内部流动转捩规律具有重要意义。本文针对棒束通道内的流动转捩特性开展实验与CFD模拟研究，通过实验获得了棒束通道内沿程阻力系数的变化规律；采用不同湍流模型进行了数值模拟。结果表明，SST k-ω模型能较好地反映实验结果。进一步对比了不同雷诺数工况下通道内不同位置的沿程阻力系数与湍流强度，发现对于不同子通道，中心子通道湍流强度与沿程阻力系数高于边角子通道；对于同一子通道，子通道中心处湍流强度与壁面切应力高于子通道边缘处。这一结果说明，受壁面影响，棒束内湍流强度、壁面切应力、阻力特性具有不均匀性，这些空间上的不均匀性相互作用会引起总体上棒束转捩点不明显。     

结核分枝杆菌耐药机制研究进展和PE/PPE蛋白在介导细菌耐药中的作用

结核病是一种由结核分枝杆菌感染引起的，以空气传播为主的传染病，目前仍是全球公共卫生安全的重大威胁。随着抗结核抗生素的广泛使用，结核病的耐药问题也愈演愈烈，出现了多耐药结核、广泛耐药结核甚至完全耐药结核。对临床用抗结核药物作用机制和结核分枝杆菌对应耐药机制的研究，有利于我们开发新的抗结核药物，改造现有抗结核药物和研发新的耐药诊断技术。本文综述了近年来有关抗结核新药的作用机制及细菌耐药机制的研究进展，并特别讨论了最新发现的结核分枝杆菌外膜通道蛋白PE/PPE蛋白可能在结核分枝杆菌耐药中的重要作用，以期为后续的相关研究提供一定的参考。     

Trapping region of impinging jets in a cross-shaped channel

This study follows our previous report (Zhang et al., Phys. Fluids, vol. 31, 2019, 034105) by describing the formation and evolution of the engulfment flow in the cross-shaped channel. First, the flow regimes were studied by planar laser induced fluorescence (PLIF). Results show the formation of a spiral vortex in the center of the chamber and the appearance of a well-mixed zone inside the spiral vortex. Second, we proposed a novel experimental method to analyze the residence time of the fluid in the chamber, and discover an unexpected trapping region inside the well-mixed zone. There is almost no fluid transport into or out of this region. Furthermore, three-dimensional numerical simulation is used to reveal the origination of this trapping region. Simulation results reveal that the fluid recirculates in the trapping region and the flow feature is caused by the bubble-type vortex breakdown.     

Numerical investigation of water dynamics in a novel wettability gradient anode flow channel for proton exchange membrane fuel cells

The effective removal and transport of water in flow channels play an important role in the water management of proton exchange membrane fuel cells (PEMFCs). In this paper, a novel design of anode serpentine flow channel with the wettability gradient wall is discussed and numerically investigated by utilizing the volume-of-fluid (VOF) method. The effects of the contact angle and the wettability gradient of channel walls, as well as hydrogen flow velocity and water droplet size, on the droplet dynamic behavior are studied. The results indicate that compared with the conventional flow channel, the water droplet can be more effectively removed from the turning part in the wettability gradient flow channel. And the water removal ability in the turning part is improved with the increase of the wettability gradient. Moreover, the wettability gradient flow channel can also improve the water removal performance for the cases with different hydrogen flow velocities and water droplet sizes. This study provides ideas for guiding the design of flow channel to effectively enhance anode water management.     

Large-scale laboratory study on the evolution law of temperature fields in the context of underground coal gasification

This article presents the evolution law of temperature fields in a large-scale laboratory Underground Coal Gasification reactions using Ulanqab lignite under actual conditions. The results show that in the cultivation stage of oxidation zone, the main direction of the temperature field expansion is consistent with the crack direction of the coal seam. In the gasification stabilization stage, the main direction of the temperature field expansion is along the channel. The temperature of the coal seam and the overlying rock mass at its interface with the furnace directly above the gasification channel is equivalent to that of the coal seam temperature, and this temperature is much greater than the temperatures observed near both side walls of the gasification channel at the interface. However, temperatures perpendicular to the axis of the gasification channel are similar at a vertical distance of 40 cm away from the interface. The temperature distributions indicate that the transmission of heat through the overlying rock mass is more rapid in the vertical direction than in the horizontal direction. Moreover, some degree of thermal dispersion is observed in the vertical direction near the outlet. The thermal dispersion coefficient is 0.72 and dispersion angle γ is 78.7°.     

Controlling Corrosion Resistance of a Biodegradable Mg–Y–Zn Alloy with LPSO Phases via Multi-pass ECAP Process

Mg-RE(rear earth) alloys with long period stacking(LPSO) structures have great potential in biomedical applications. The present work focused on the microstructure and corrosion behaviors of Mg 98.5 Y_1 Zn_(0.5) alloys with 18 R LPSO structure after equal channel angular pressing(ECAP). The results showed that the ECAP process changed the grain size and the distribution of LPSO particles thus controlled the total corrosion rates of Mg 98.5 Y_1 Zn_(0.5) alloys. During the ECAP process from 0 p to 12 p, the grain size reduced from 160–180 μm(as-cast) to 6–8 μm(12 p). The LPSO structures became kinked(4 p), then started to be broken into smaller pieces(8 p), and at last comminuted to fine particles and redistributed uniformly inside the matrix(12 p). The improvement in the corrosion resistance for ECAP samples was obtained from 0 p to 8 p, with the corrosion rate reduced from 3.24 mm/year(0 p) to 2.35 mm/year(8 p) in simulated body fluid, and the 12 p ECAP alloy exhibited the highest corrosion rate of 4.54 mm/year.     

等通道转角挤压制备超细晶材料的最新研究进展

等通道转角挤压(Equal channel angular pressing,ECAP)方法是制备性能优异超细晶材料最常见的大塑性变形方法之一。模角、挤压路径、挤压道次、挤压温度和挤压速度等因素都会影响等通道转角挤压制备超细晶材料的性能;等通道转角挤压的模具也在不断地优化,如背压-等通道转角挤压(Back pressure ECAP,BP-ECAP)模具、可加热的模具以及在等通道转角挤压基础上形成的板材连续剪切技术等,这些新的模具可以改变ECAP变形过程中的组织均匀性。本文综述了等通道转角挤压制备超细晶材料的最新研究进展,并指出了几个需要深入研究的问题及方向。     

Microstructure and mechanical properties of fine grained uranium prepared by ECAP and subsequent intermediate heat treatment

The microstructure and mechanical properties of fine grained uranium prepared by equal channel angular pressing (ECAP) and subsequent intermediate heat treatment were investigated systematically by the confocal laser scanning microscope (CLSM), electron backscatter diffraction (EBSD) and split Hopkinson pressure bar (SHPB). The results show that the initial coarse grained uranium was refined from about 1000 to 6.5 μm prepared by ECAP at 3 passes and subsequent heat treatment, and the corresponding dynamic yield strength increased from 135 to 390 MPa. For the ECAPed uranium samples, the relationship between grain size and yield strength could be described by classical Hall–Petch relationship, and the fitting Hall–Petch relationship for the fine grained uranium samples prepared by ECAP was drawn.     

预掘双回撤通道末采应力分布特征与围岩控制研究

针对万利一矿31煤工作面末采期间矿压显现剧烈、回撤通道变形大而影响回撤效率的问题,通过现场监测、数值模拟、理论分析等方法,研究了回撤通道顶板结构及裂隙发育情况,并通过建立的FLAC3D数值模型,分析了工作面前方的应力矢量分布规律和末采期间回撤通道的塑性区演化规律,基于此,结合工程类比提出针对性的回撤通道补强支护方案,现场应用后有效控制了围岩失稳,效果良好。     

Numerical investigation of pressure drop characteristics of gas channels and U and Z type manifolds of a PEM fuel cell stack

Fluid flow manifold plays a significant role in the performance of a fuel cell stack because it affects the pressure drop, reactants distribution uniformity and flow losses, significantly. In this study, the flow distribution and the pressure drop in the gas channels including the inlet and outlet manifolds, with U- and Z-type arrangements, of a 10-cell PEM fuel cell stack are analyzed at anode and cathode sides and the effects of inlet reactant stoichiometry and manifold hydraulic diameter on the pressure drop are investigated. Furthermore, the effect of relative humidity of oxidants on the pressure drop of cathode are investigated. The results indicate that increase of the manifold hydraulic diameter leads to decrease of the pressure drop and a more uniform flow distribution at the cathode side when air is used as oxidant while utilization of humidified oxidant results in increase of pressure drop. It is demonstrated that for the inlet stoichiometry of 2 and U type manifold arrangement when the relative humidity increases from 25% to 75%, the pressure drop increases by 60.12% and 116.14% for oxygen and air, respectively. It is concluded that there is not a significant difference in pressure drop of U- and Z-type arrangements when oxygen is used as oxidant. When air is used as oxidant, the effect of manifold type arrangement is more significant than other cases, and increase of the stoichiometry ratio from 1.25 to 2.5 leads to increase of pressure drop by 527.3%.