不同形状方向性型孔液体润滑端面密封性能对比

表面微孔的方向性可以改变密封间隙中流体的流向,在孔区末端汇聚产生明显的流体动压效应,使摩擦副端面打开,形成全膜润滑。以不同开孔形状(圆形、菱形、椭圆形、长方形)型孔端面密封为研究对象,考虑润滑液膜中的空化现象,基于质量守恒JFO空化算法建立数值模拟模型,采用有限差分法求解Reynolds控制方程,获得端面膜压分布。对比分析了在不同操作参数和几何结构参数下不同开孔端面密封性能。结果表明:相比于圆孔,在低速或高压下,方向性型孔都具有较好的动压效应,且长方形孔的动压开启力最好,菱形孔泄漏率较小。当膜厚h0=1.5~2.5μm,孔深hp=2~3μm,长短轴比γ=3~4,反向开孔比β=0.5,倾斜角α1=30°~50°、α2=120°~140°时,不同形状方向性型孔可获得最佳的动压密封性能。     

微椭圆孔轴面织构油封密封性能仿真模拟及机理探究

提出轴面微椭圆孔织构油封运行时的理论分析模型,通过仿真模拟得到微孔结构参数对其性能的影响规律。结果表明：微椭圆孔轴面织构的润滑减摩性主要体现在相对运动的过程中微织构会使液膜产生显著的动压润滑效应,致使界面间形成非接触式密封和润滑状态;在研究的工况条件下,密封可靠性在微椭圆孔的方向性方面有所体现,合适的方向性能使流体在孔区流程变长,且其受边界阻挠在孔区一侧动压增强另一侧形成空化区,低压的空化区会快速抽吸即将泄漏出的流体从而提高密封可靠性,故而通过改变织构结构尺寸可控制油封的性能。为提高油封的寿命并降低泄漏率,在研究范围内,选用半轴比γ≥0.8（在面积比固定不变的情况下）、孔深h₁=1.5~4μm和旋转角α₁=0°~45°或175°~215°的轴面微椭圆孔织构较为合适。     

大菱形孔端面密封力变形及密封性能分析

针对等深大菱形孔端面液体润滑机械密封,采用有限差分法求解等温及层流不可压缩二维Reynolds方程,获得液膜压力场。利用商用有限元软件计算密封环三维固体变形,对不同操作工况条件下和不同结构的密封环的力变形、摩擦扭矩、液膜刚度及泄漏率等性能参数进行了计算。结果表明：大菱形孔流体动压型机械密封端面产生周向波度和径向锥度变形;改变工况条件可使密封面形成收敛和发散两种不同的变形,密封性能参数因此产生显著变化;当面积比B=0.65～0.75时,大菱形孔端面密封可获得较好的密封性能;辅助密封圈O形圈位置l对径向锥度变形具有很大影响,l优选值范围为2.4～4.0 mm。     

微椭圆孔轴面织构油封密封性能仿真模拟及机理探究

提出轴面微椭圆孔织构油封运行时的理论分析模型,通过仿真模拟得到微孔结构参数对其性能的影响规律。结果表明:微椭圆孔轴面织构的润滑减摩性主要体现在相对运动的过程中微织构会使液膜产生显著的动压润滑效应,致使界面间形成非接触式密封和润滑状态;在研究的工况条件下,密封可靠性在微椭圆孔的方向性方面有所体现,合适的方向性能使流体在孔区流程变长,且其受边界阻挠在孔区一侧动压增强另一侧形成空化区,低压的空化区会快速抽吸即将泄漏出的流体从而提高密封可靠性,故而通过改变织构结构尺寸可控制油封的性能。为提高油封的寿命并降低泄漏率,在研究范围内,选用半轴比γ≥0.8 (在面积比固定不变的情况下)、孔深h_1=1.5～4μm和旋转角α_1=0°～45°或175°～215°的轴面微椭圆孔织构较为合适。     

机械端面密封反向螺旋槽空化效应与泄漏控制机理

针对机械端面密封的反向螺旋槽结构,基于遵循质量守恒的JFO空化边界条件,采用SUPG有限元方法求解Reynolds方程,研究了反向螺旋槽的空化效应,基于此,提出了一种新型的正反向螺旋槽组合端面密封结构,分析了不同工况条件下的密封性能。结果表明：反向螺旋槽区域易发生液膜空化,周期性分布的空化区会显著影响端面流场,空化区的低压力可将内径侧流体抽吸到密封端面,实现上游泵送。新型正反向螺旋槽端面密封结构结合了反向螺旋槽产生的泄漏控制作用和正向螺旋槽产生的流体动压效应,同时具备良好的上游泵送能力和动压承载能力。     

机械端面密封反向螺旋槽空化效应与泄漏控制机理

针对机械端面密封的反向螺旋槽结构,基于遵循质量守恒的JFO空化边界条件,采用SUPG有限元方法求解Reynolds方程,研究了反向螺旋槽的空化效应,基于此,提出了一种新型的正反向螺旋槽组合端面密封结构,分析了不同工况条件下的密封性能。结果表明:反向螺旋槽区域易发生液膜空化,周期性分布的空化区会显著影响端面流场,空化区的低压力可将内径侧流体抽吸到密封端面,实现上游泵送。新型正反向螺旋槽端面密封结构结合了反向螺旋槽产生的泄漏控制作用和正向螺旋槽产生的流体动压效应,同时具备良好的上游泵送能力和动压承载能力。     

中低压干气密封螺旋槽结构参数优化

基于完全析因设计方法,开展中低压干气密封端面螺旋槽几何结构参数优化.基于气体润滑理论,对中低压条件下螺旋槽干气密封的动压开启力增长率、气膜刚度和刚漏比等密封特性参数进行分析,获得了中压和低压条件下螺旋槽几何结构参数的优选值范围,提出"螺旋槽干气密封特性参数优化带".结果表明:特性参数优化带能较好地反映螺旋槽干气密封在不同压缩数下的最优性能水平;在中低压高速条件下,当螺旋角b=10°～25°,槽深h_g=5～10 mm时能获得较优的密封性能;当槽坝比a_g=1.5～4.0,槽长宽比l=2～8时能获得较好的动压效应和轴向气膜稳定性;当槽坝比a_g=0.7～1.5,槽长宽比l=2～5时能获得较好的综合密封性能.     

端面锥形参数对锥-孔组合型机械密封性能的影响

给出新型锥-孔组合型端面密封,考虑液膜压场的变化规律与环受力变形的相互作用关系,构建机械密封3D流、固耦合数学模型,并给出相关的数值计算方法,获得了膜压分布规律及端面变形情况,分析锥面结构参数在各工况下对密封性能的影响规律。结果表明：由菱形孔所引起的动压效应可使端面产生周向和径向波状变形,而静压效应随锥度Ф和锥宽比γ的变化,在端面区域范围内所起作用也发生相应变化;对压强较低和低、中转速设备,应选取Ф=5~6或Ф=2~4的收敛锥面密封,且γ=0.8~1.0。对高压和高速设备,应选用Ф=2~3的收敛锥面密封,且γ=1.0或γ=0.2;通过改变锥面结构可有效改变机械密封的特性参数,实现密封运行中的自动调节,特别适合变工况条件。另外,由于锥面结构的变化所引起平衡系数B和膜厚h的变化,低速时可弥补动压效应较小的缺陷,获得较大开启力,也可在大h下工作,故可降低密封端面对平整度和光洁度的要求。     

大菱形孔端面密封力变形及密封性能分析

针对等深大菱形孔端面液体润滑机械密封,采用有限差分法求解等温及层流不可压缩二维Reynolds方程,获得液膜压力场。利用商用有限元软件计算密封环三维固体变形,对不同操作工况条件下和不同结构的密封环的力变形、摩擦扭矩、液膜刚度及泄漏率等性能参数进行了计算。结果表明:大菱形孔流体动压型机械密封端面产生周向波度和径向锥度变形;改变工况条件可使密封面形成收敛和发散两种不同的变形,密封性能参数因此产生显著变化;当面积比B=0.65~0.75时,大菱形孔端面密封可获得较好的密封性能;辅助密封圈O形圈位置l对径向锥度变形具有很大影响,l优选值范围为2.4~4.0 mm。     

基于JFO空化和幂律模型的螺旋槽液膜密封流体动压特性

密封端面间润滑流体的非牛顿特性对密封的性能有重要影响。基于满足质量守恒的JFO空化边界条件及描述流体非牛顿特性的幂律模型,建立了考虑流体非牛顿特性的螺旋槽液膜密封数学模型。采用有限差分法对控制方程进行离散,通过SOR迭代方法对离散方程进行求解,得到了密封端面液膜压力分布。探讨了润滑流体的非牛顿特性对螺旋槽液膜密封的液膜承载能力、泄漏量、摩擦扭矩等性能参数及液膜中空化发生情况的影响规律。结果表明：随着幂律指数的增大,液膜承载能力先增大后减小,泄漏量和空化率增大,摩擦扭矩减小;幂律指数为0.96时,相对于牛顿流体,液膜承载能力提升约4.6%,密封端面空化率下降约98.6%,泄漏量下降约5.8%,摩擦扭矩增加约0.3%;随着操作参数的改变,不同幂律指数下的流体动压性能参数变化规律具有相似性;润滑流体的合理选择对液膜密封性能改善有重要意义。     

唇形密封轴表面方向性微孔的润滑特性

为研究方向性微孔对唇形密封润滑特性的影响,建立了遵循质量守恒的JFO空化边界条件的唇形密封润滑理论模型,采用有限单元法求解雷诺控制方程,获得了泵汲率、摩擦力等性能参数,对比分析了椭圆形、矩形、菱形、等腰三角形4种不同形状方向性微孔织构唇形密封的润滑特性。结果表明:微孔结构对称于轴切向时泵汲率为零,而与轴线呈45°倾斜时具有最大泵汲率;微孔结构沿轴切向形成的油楔尺寸最小时,具有最小摩擦力;增加微孔深度将使泵汲率下降,但能减小摩擦力;增大形状因子既可以提高泵汲率,又能减小摩擦力;相同条件下,矩形微孔具有最大泵汲率和最小摩擦力。     

High-Pressure Synthesis of Heat-Resistant Diamond Composite Using a Diamond-TiC0.6 Powder Mixture

The sintering behavior of synthetic diamond with a grain size of 2-4 µm was investigated at high pressure and high temperatures (6.5 GPa and 1600°-1900°C, respectively) in the presence of TiC_0.6 or TiC. No well-sintered diamond composite was synthesized from a diamond-TiC powder mixture under the examined conditions; however, a well-sintered diamond composite with a homogeneous microstructure was synthesized under the conditions of 6.5 GPa and temperatures >1800°C using a diamond-TiC_0.6 powder mixture. The diamond composite was hard (Vickers hardness of 45 GPa) and was composed of diamond and TiC, in which TiC was formed via the reaction of TiC_0.6 and carbon atoms of diamond. Neither graphitization nor cracking was observed in or on the composite after successive heat treatment at 900°-1400°C for 30 min each under vacuum. The Vickers hardness of the composite that was treated at 1500°C decreased to 40 GPa, whereas the Vickers hardness values for composites treated at temperatures of <1400°C were not changed. The present diamond composite is believed to be one of the most heat-resistant materials among the superhard composites and can be used as heat-resistant tools for superhard materials.     

Formation process of diamond from supercritical H2O–CO2 fluid under high pressure and high temperature conditions

The formation process of diamond from supercritical H₂O–CO₂ fluid was studied using ¹³C-graphitic carbon and oxalic acid dihydrate, (COOH)₂·2H₂O, as starting materials under a diamond stable high pressure–high temperature (HP–HT) condition of 7.7 GPa and 1600°C. The exchange reaction between ¹³C-graphitic carbon and ¹²CO₂ in the supercritical H₂O–CO₂ fluid, which was first formed by the decomposition of oxalic acid dihydrate, occurred very rapidly and became nearly equilibrated after 6 h. At the same time, graphite was recrystallized and coexistent with the fluid until traces of diamond were first observed after 8 h. All graphite transformed into diamond after 17 h, showing that a considerably long induction time was present for the formation of diamond in this fluid system.     

斜排微孔端面机械密封富集效应的理论研究

在周向部分开孔直排微孔端面机械密封富集效应研究的基础上,建立了周向部分开孔斜排微孔端面机械密封的理论分析模型,并采用有限元方法求解雷诺方程,获得了斜排微孔密封的端面液膜压力分布,分析了微孔斜排倾斜角、孔栏数、端面半径比等几何参数在不同转速、不同介质压力等操作条件下对端面液膜刚度、开启力和泄漏率的影响规律,指出了斜排微孔端面密封产生承载力的机理。结果表明,当倾斜角在60°～90°之间取值,且每栏微孔的径向微孔数与周向微孔数相等或相差±1个时,密封综合性能最优。     

Transfer and Reaction Performances of Selective Catalytic Reduction of N2O with CO over Monolith Catalysts

This work tries to identify the relationship between geometric configuration of monolith catalysts, and transfer and reaction performances for selective catalytic reduction of N2O with CO. Monolith cat...     

The effects of nitrogenation on the electrochemical properties of nanocrystalline diamond films

The effect of the nitrogenation on the electrochemical properties of nanocrystalline diamond films produced by microwave plasma CVD in CH₄–Ar–H₂–N₂ gas mixtures was studied systematically, using cyclic voltammetry and electrochemical impedance spectroscopy measurements, for the first time. Differential capacitance, kinetic parameters of reactions in [Fe(CN)₆]^3-/4-redox system and potential window were found to be sensitive to the nitrogen concentration in the process gas. With its increase (from 0 to 25%), a transition of the NCD film behavior from “poor conductor” to metal-like character takes place. The heavily N-doped nanocrystalline diamond films have satisfactory electrochemical properties to be used as electrodes.     

Diamond Synthesis from Graphite in the Presence of MnCO3

In order to investigate the catalytic effect of MnCO₃, a typical transition-metal carbonate, a graphite and MnCO₃ (60:40 by weight) mixture was subjected to temperature and pressure ranges of 6.5–7.7 GPa and 1700°–2100°C, respectively. Diamonds were synthesized from graphite in the presence of MnCO₃, at 2000°C and 7.7 GPa, where MnCO₃ was confirmed to be in a molten state. Although MnO was found to be decomposed from the samples that were subjected to the aforementioned PT conditions, no diamond formation was detected from an MnO and graphite system for identical experimental conditions. Therefore, it was concluded that MnCO₃ solvent catalyzed diamond formation from graphite.     

THE EFFECT OF A MAGNETIC FIELD ON NATURAL CONVECTION IN A SHALLOW CAVITY HEATED FROM BELOW

A numerical study is presented for magnetohydrodynamic free convection of an electrically conducting fluid in a shallow cavity heated from below and cooled from above. The side walls are maintained adiabatic. A uniform magnetic field, inclined with an angle 0 with respect to the horizontal plane, is externally imposed. The investigation covers the range of the Rayleigh number, Ra, from 1.8 × 10₃ to 3 x 10₄the Hartmann number, Ha, from 0 to 35, the Prandtl number, Pr, from 0.005 to 1 and aspect ratio of the cavity, A = 6. The effect of the magnetic field on the flow structure is presented. For supercritical convection it is found that, upon increasing Ha, the number of roll cells in the cavity increases when it is perpendicular to it. The imposition of an inclined magnetic field gives rise to new flow patterns with tilted lateral cell walls. The effect of both strength and orientation of the magnetic field on the overall heat transfer is found to be significant.     

CrO2-Cr2O3 Phase Boundary Under High O2 Pressures

The phase boundary between CrO₂ and Cr₂O₃ was reinvestigated under high O₂ pressures by using a new type of gas compressor. The boundary curve can be represented as log Po₂= 7.16-(3579/ T ). Using the observed data, Δ G °, Δ H °, and Δ S ° for the reaction 2CrO₂⇋Cr₂O₃+½O₂ were calculated to be: Δ G °= -(1.55/100) T +7.60 kcal/mol, Δ H °= -8.19 kcal/mol, and Δ S °= (-15.8/ T )+0.0155 kcal/mol.