Numerical study of double diffusive natural convective heat and mass transfer in an inclined rectangular cavity filled with porous medium

Two-dimensional double-diffusive natural convective heat and mass transfer in an inclined rectangular porous medium has been investigated numerically. Two opposing walls of the cavity are maintained at fixed but different temperatures and concentrations; while the other two walls are adiabatic. The generalized model with the Boussinesq approximation is used to solve the governing equations. The flow is driven by a combined buoyancy effect due to both temperature and concentration variations. A finite volume approach has been used to solve the non-dimensional governing equations and the pressure velocity coupling is treated via the SIMPLER algorithm. The results are presented in streamline, isothermal, iso-concentration, Nusselt and Sherwood contours for different values of the non-dimensional governing parameters. A wide range of non-dimensional parameters have been used including, aspect ratio (2 ≤ A ≤ 5), angle of inclination of the cavity (0 ≤ ? ≤ 85), Lewis number (0.1 ≤ Le ≤ 10), and the buoyancy ratio (− 5 ≤ N ≤ 5).     

Numerical study of mixed convection in an inclined two sided lid driven cavity filled with nanofluid using two-phase mixture model

Mixed convection of a nanofluid consisting of water and SiO2 in an inclined enclosure cavity has been studied numerically. The left and right walls are maintained at different constant temperatures while upper and bottom insulated walls are moving lids. Two-phase mixture model has been used to investigate the thermal behaviors of the nanofluid for various inclination angles of enclosure ranging from θ = − 60° to θ = 60°, volume fraction from 0% to 8%, Richardson numbers varying from 0.01 to 100 and constant Grashof number 10⁴. The governing equations are solved numerically using the finite-volume approach. Results are presented in the form of streamlines, isotherms, distribution of nanoparticles and average Nusselt number. In addition, effects of solid volume fraction of nanofluids on the hydrodynamic and thermal characteristics have been investigated. The results reveal that addition of nanoparticles enhances heat transfer in the cavity remarkably and causes significant changes in the flow pattern. Besides, effect of inclination angle is more pronounced at higher Richardson numbers.     

MG250/590采煤机在大倾角工作面的改进

MG250/590W采煤机是多电机横向布置,可以实现电牵引与液压牵引互换。和纵向布置采煤机相比,具有很多优点。为适应兴安矿综采工作面的大倾角,改变了采煤机原设计的技术参数,通过在该矿大倾角工作面的使用,平均日产原煤1 930 t,最高日产2 800 t,效果显著。目前,国内外对大倾角综采工作面(倾角大于35°)的采煤机还处在探索阶段,根据兴安矿大倾角工作面的自然条件及使用采煤机的经验:对MG250/590W采煤进行技术改进,使其牵引力增加了10 t,能较好地适应该矿大倾角综采工作面,为大倾角采煤机的设计选型,提供了参考。困绕该矿多年的综采大倾角工作面采煤机牵引力不足的问题得到了解决。     

倾斜圆管内泡状流空泡份额特性实验研究

采用光纤探针测量方法对倾斜圆管(内径为50 mm)内空气-水两相泡状流空泡份额分布特性进行实验研究。结果表明,截面平均空泡份额随倾斜角度的增加而减小,倾斜角度大于5°时减小速率明显减慢;竖直条件下空泡份额径向分布呈"马鞍形",即空泡份额除在近壁区出现峰值然后迅速降低到最小值外,在其他区域几乎不随位置发生变化;倾斜条件下气泡明显向上壁面聚集,中心线上方近壁区空泡份额峰值增加,中心线下方近壁区空泡份额峰值被削弱,倾斜角度较大时甚至消失。     

ZH2400/14/20B滑移支架在倾斜长壁仰斜工作面中的应用

东保卫煤矿78层煤的顶板为复合顶板,采用单体支柱配合板帽的支护形式难以控制顶板。选用ZH2400/14/20B滑移顶梁液压支架很好地解决了顶板的支护问题,与单体液压支柱支护顶板相比,滑移支架支护工艺的"支回合一",减轻了工人的劳动强度,提高了劳动效率。为滑移支架在倾斜长壁仰斜开采工艺中的应用提供了经验。     

倾斜煤层动压巷道围岩应力分布规律的数值分析

针对倾斜煤层巷道围岩应力分布规律问题,建立了不同岩层倾角的数值计算模型,计算分析了倾斜煤层在动压作用下的围岩应力变化过程。通过对计算结果的分析,得知在岩层倾角为30°~40°时,围岩集中应力区域向两帮顶角区域转移;50°~60°时,向下帮底角区域转移;70°~80°时,转移至下帮顶角区域;同时由40°开始,围岩开始显现较强的不对称性,并随岩层倾角的增大快速增大。在动压作用下,围岩不同位置处的应力随动压的增大近似同比例增大;当岩层倾角在10°~50°时,应力提高率处于0.5~2.3;50°~80°时,基本处于0.5左右。针对围岩应力分布的不对称系数分析得知,岩层倾角越大,不对称系数越大;在岩层倾角为30°~80°时,不对称系数在动压作用下基本保持不变,说明在动压作用下围岩应力会持续处于不对称状态。     

倾斜管实验的膏体流变特性规律研究

针对膏体流变特性难以真实测量的现象,自制一套能够有效还原工业现场的倾斜管道实验装置,对膏体流变特性参数进行测量,运用通径分析法探究膏体浓度、灰砂比对流变特性的影响规律。结果表明:膏体浓度、灰砂比对膏体流变参数的影响均为正相关,其中,浓度对屈服应力的影响水平比灰砂比对其影响水平大一个数量级,当灰砂比接近1∶25时,灰砂比的增大与减小并不能引起屈服应力明显的单调递增递减现象;浓度对塑性黏度的影响水平比灰砂比对其影响水平大,但在同一个数量级,膏体浓度较低时,会产生浓度低黏度大的现象。     

倾斜菱形孔端面密封的性能研究

基于流体润滑理论模型,采用数值模拟的方法分析几何参数和操作参数对机械密封泄漏率、液膜刚 度和开启力的影响规律,探讨倾斜菱形孔上、下游泵送效应对密封性能的影响机理。结果表明,双向倾斜菱形孔织 构端面能够使机械密封的动压效应显著增强,泄漏率明显降低及液膜稳定性更可靠;在较低转速时,双向倾斜菱形 孔织构可使密封端面迅速打开,能够有效减少启动时两端面间的摩擦和磨损,同时还能降低倾斜菱形孔织构密封的 泄漏率;在研究的工况条件下,非倾斜菱形孔织构密封的液膜稳定性(即变工况自适应能力)在三者(即双向、单向与 非倾斜菱形孔织构密封)中是最佳的;并得到了倾斜菱形孔端面密封的反向开孔比、孔倾角、面积比和孔深等几何参 数的优化取值范围。     

PLC显示灯壳的牛角销斜滑块抽芯注塑模设计

分析了显示灯塑料壳的使用要求及结构特点,阐述了PLC显示灯外壳注塑模的设计过程。该套模具采用两板式潜伏式点浇口,采用斜导柱侧抽芯和牛角销斜滑块抽芯两种侧抽芯结构,结构合理,运行可靠。     

川东红层缓倾角地层中降雨引起滑带土饱和对滑坡的稳定性影响

以四川省宣汉县天台乡滑坡为例,研究了降雨引起滑带土饱和对滑坡的稳定性影响。首先通过土工试验分别测试了天然和饱和状态下滑带土的剪切强度,结果显示滑带土饱和时的剪切强度比天然状态时下降较大;然后利用Geostudio软件对降雨条件下天台乡滑坡坡体内的渗流场进行了模拟,并分别计算坡体在上述渗流场作用下滑带土天然及饱和状态时滑坡的稳定系数,结果表明,滑带土饱和对川东红层缓倾角滑坡的稳定性影响较大,川东红层缓倾角滑坡的形成是降雨引起坡体内应力变化和滑带土强度降低共同作用的结果。