Determination of the Effective Probabilities of Catalytic Reactions on the Surfaces of Heat Shield Materials in Dissociated Carbon Dioxide Flows

The effect of heterogeneous catalysis on the heat transfer to cold and heated surfaces in subsonic dissociated carbon dioxide jet flows is studied experimentally, using a 100 kW inductive plasma generator, and simulated numerically. The effective probabilities of the heterogeneous reactions CO + O → CO₂ and O + O → O₂ on molybdenum (T_w=300 K) and quartz (T_w=470–620 K) surfaces, the Buran heat shield tile coating (T_w = 1470—1670 K), and two oxidation-resistant carbon-carbon coating materials (T_w=1420—1840 K) are determined by comparing the experimental and calculated data on the heat fluxes at the stagnation point of models at a pressure of 0.1 atm.     

Reduction of Peak Heat Fluxes by Supplying Heat to the Free Stream

A supersonic flow past a blunt body in the presence of an incident oblique shock wave is considered. It is shown that by supplying heat to the free stream it is possible substantially to reduce local heat flux peaks on the body surface. The integral heat flux on the body surface increases by only a small fraction of the heat released into the flow.     

Investigation of Self-Similar Interface Evolution in Carbon Dioxide Sequestration in Saline Aquifers

In this work, we investigate numerically the injection of supercritical carbon dioxide into a deep saline reservoir from a single well. We analyze systematically the sharp-interface evolution in different flow regimes. The flow regimes can be parameterized by two dimensionless numbers, the gravity number, \(\Gamma \) and the mobility ratio, \(\lambda \) . Numerical simulations are performed using the volume of fluid method, and the results are compared with the solutions of the self-similarity equation established in previous works, which describes the evolution of the sharp interface. We show that these theoretical solutions are in very good agreement with the results from the numerical simulations presented over the different flow regimes, thereby showing that the theoretical and simulation models predict consistently the spreading and migration of the created \(\hbox {CO}_{2}\) plume under complex flow behavior in porous media. Furthermore, we compare the numerical results with known analytic approximations in order to assess their applicability and accuracy over the investigated parametric space. The present study indicates that the self-similar solutions parameterized by the dimensionless numbers \(\lambda , \Gamma \) are significant for examining effectively injection scenarios, as these numbers control the shape of the interface and migration of the \(\hbox {CO}_{2}\) plume. This finding is essential in assessing the storage capacity of saline aquifers.     

Heat Transfer of a Cylindrical Body with Catalytic Surface in Subsonic Nonequilibrium Air Plasma Flow

Fluid Dynamics - Steady-state subsonic flows of nonequilibrium air plasma past a cylindrical body with plane face and heat transfer are investigated under the conditions characteristic of testing...     

铸铁滑动摩擦副表面温度对其磨损机制的影响

在铸铁摩擦融油润滑和线接触的滑动条件下，测定了试样摩擦磨损表面层的温度及其温度分布梯度，考察了表面层的相变特点、组织结构和表貌特征，并且分析了温度对磨损机制转化的影响。可以将摩擦磨损表面的热效应分为３个区：弱热效应区（对应于塑性流动磨损区）、热效应区（对应于氧化磨损区）和强热效应区（对应于严重磨损区）。在临界载荷前，表面层的γ相含量增加，但一临界载荷时，由于表面层的剥落，γ相的含量明显减少。摩擦磨     

磨损表面轮廓对点接触热弹流润滑的影响

研究了由磨损引起的接触表面几何轮廓的改变对点接触润滑效应的影响。引入磨平系数ｒｗ来表征接触区的磨平区域大小。在０≤ｒｗ≤的范围内,通过不同工况参数下热弹流的安全数值求解,发现最小膜厚随ｒｗ的增大而减小,中心膜厚随ｒｗ的增大而增大;而ｒｗ的增大而增大;而ｒｗ对油膜最大压力、最高温升及摩擦系数的影响较小。     

热对流条件下考虑球形夹杂分布的材料热弹接触摩擦热影响分析

机械传动关键活动零部件接触副往往受到力载荷和摩擦热载荷的耦合作用,使得接触界面间的接触力学行为的分析变得极其复杂. 利用基于等效夹杂方法建立的考虑热对流非均质材料热弹接触力学分析模型研究不同摩擦系数、夹杂位置和材料属性等参数对材料表面及内部温升及热应力分布影响规律. 此外,进一步分析了接触副材料中含分布球形夹杂时摩擦热造成的影响. 结果表明:接触副表面温升梯度受热对流系数的影响较大;下表面温升和热应力随摩擦系数增大而增大;分布夹杂则将接触副材料下表面温升及热应力分布变得更为复杂.      

Addressing the Influence of a Heterogeneous Matrix on Well Performance in Fractured Rocks

We address the influences of heterogeneity and complex geology of the matrix of fractured rocks on transient flow. Fractional constitutive flux laws reflect the stochastic framework that we consider. We model transient diffusion in both the matrix and fracture systems in terms of a continuous time random walk. Our procedure is particularly suited to address a complex geology that may exist on a number of scales and which may include dead ends and discontinuities. The performance of a horizontal well produced through arbitrarily located, multiple hydraulic fractures with distinct properties (length, width, permeability) forms the basis for our thesis. The pressure distribution in a rectangular drainage region where the well may be placed arbitrarily is expressed in terms of the Laplace transformation. The required solutions are obtained numerically. The focus of our work is on long-term behaviors for production at a constant pressure. In addition to numerical solutions, asymptotic results that provide information on the structure of the solutions are presented. Agreement between the asymptotic and numerical solutions is excellent. We show that long-term responses are governed by two distinct, two-parameter Mittag–Leffler functions and are an outcome of the complexities we desire to model in both the matrix and fracture systems. As a consequence, power-law behaviors that reflect the heterogeneity inherent in the system define long-time expectations. We show that the new solutions we derive do reduce to those of classical diffusion; that is, results corresponding to classical diffusion are a subset of the new results obtained here. Our results are particularly suited to model transient flow in shale reservoirs.     

波纹竖板层流降膜蒸发传热的分析

对高粘度液体在等温正弦形波纹壁面上的自由降落与蒸发建立了摄动分析模型。得到了流动的分析解和蒸发传热的数值解。考察了壁面波纹的波幅和波数、液膜表面张力及贝克利数对流动与传热的影响,结果表明,加大波纹的波幅、适当选择波数、减小贝克利数可增强传热,而表面张力对蒸发传热的影响较小。     

Calculation of the Flow Pattern and the Heat Fluxes in the Interaction of a Shock Wave with a Cylinder in a Supersonic Flow

The problem of determining the mechanical and thermal action on a cylinder in a supersonic flow with account for the interference between an incident shock and the detached bow shock has been studied extensively, both experimentally and theoretically, in the last few decades [1–12]. A fairly complete survey can be found in monograph [12]. The interest in the problem is mainly due to the fact that in this case the so-called fourth type of shock interaction can occur, leading to a sharp local increase in the mechanical and thermal loads. As for the problem of the interference flow past a cylinder itself, it can serve as a model problem for testing techniques of calculating the separation flow past the controls of hypersonic flight vehicles.In this paper, we attempt to demonstrate the possibility of using a fairly simple approach to the calculation of the above-mentioned flows, including those with a separation zone. The approach is based on a combination of numerical simulation within the framework of the inviscid gas model and subsequent calculation of the heat transfer parameters and does not require an excessive amount of computing power.     

Transient Free Convection from a Horizontal Surface in a Porous Medium Subjected to a Sudden Change in Surface Heat Flux

This paper presents an analytical and numerical study of transient free convection from a horizontal surface that is embedded in a fluid-saturated porous medium. It is assumed that for time steady state velocity and temperature fields are obtained in the boundary-layer which occurs due to a uniform flux dissipation rate q ₁ on the surface. Then, at the heat flux on the surface is suddenly changed to q ₂ and maintained at this value for . Firstly, solutions which are valid for small and large are obtained. The full boundary-layer equations are then integrated step-by-step for the transient regime from the initial unsteady state ( ) until such times at which this forward marching approach is no longer well posed. Beyond this time no valid solutions could be obtained which matched the final solution from the forward integration to the steady state profiles at large times .     

Numerical Study of the Near-Wall Gas-Droplet Jet in a Tube with a Heat Flux on the Surface

A model for calculating the flow of a turbulent mixture of air and suspended liquid particles injected into the near-wall region is developed within a unified approach of mechanics of heterogeneous media in the two-velocity and two-temperature approximation of the Eulerian approach. The influence of droplet evaporation in the near-wall jet on heat transfer between the two-phase gas-droplet flow and the wall is studied in the case of heat addition to the latter. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 1, pp. 5–17, January–February, 2006.     

表面处理对AlGaN欧姆接触的影响及机理

研究了溶液表面处理对AlGaN欧姆接触的影响及机理。用氟硝酸（HNO3＋HF）、稀盐酸（HCl）和硫代乙酰胺（CS3CSNH2）溶液处理AlGaN表面后,Ti/Al/Ti/Au电极的比接触电阻率有显著的降低。样品表面Ga3d与O1s的X射线光电子能谱（XPS）测试结果显示：氧元素含量明显降低,表明这三种溶液可以有效地去除AlGaN表面氧化层,其中CS3CSNH2效果最佳;Ga3d峰位在表面处理后发生蓝移现象,相当于AlGaN表面处的费米能级向导带一侧移动,使电子在隧穿过程中的有效势垒高度降低。以上两个因素均对优化AlGaN/GaN欧姆接触有十分重要的意义。     

Heat Transfer on the Surface on a Spherically Blunted Cone Exposed to a Supersonic Spatial Flow with Injection of a Coolant Gas

The heattransfer processes in a supersonic spatial flow around a spherically blunted cone with allowance for heat overflow along the longitudinal and circumferential coordinates and injection of a coolant gas are studied numerically. The prospects of using highly heatconducting materials and injection of a coolant gas for reduction of the maximum temperatures at the body surface are demonstrated. The solutions of the direct and inverse problems in one, two, and threedimensional formulations for different shell materials are compared. The error of the thinwall method in determining the heat flux on the heatloaded boundary of the body is estimated.     

Investigation of Heat and Mass Transfer and Irreversibility Phenomena Within a Three-Dimensional Tilted Enclosure for Different Shapes

Three-dimensional thermosolutal natural convection and entropy generation within an inclined enclosure is investigated in the current study. A numerical method based on the finite volume method and a full multigrid technique is implemented to solve the governing equations. Effects of various parameters, namely, the aspect ratio, buoyancy ratio, and tilt angle on the flow patterns and entropy generation are predicted and discussed.     

Influence of Vertical Vibrations on the Stability of a Binary Mixture in a Horizontal Porous Layer Subjected to a Vertical Heat Flux

Macroscale three-dimensional modeling of fluid flow in a thin porous layer under unsaturated conditions is a challenging task. One major issue is that such layers do not satisfy the representative elementary volume length-scale requirement. Recently, a new approach, called reduced continua model (RCM), has been developed to describe multiphase fluid flow in a stack of thin porous layers. In that approach, flow equations are formulated in terms of thickness-averaged variables and properties. In this work, we have performed a set of experiments, where a wet \(260\hbox {-}\upmu \hbox {m}\)-thin porous layer was placed on top of a dry layer of the same material. We measured the change of average saturation with time using a single-sided low-field nuclear magnetic resonance device known as NMR-MOUSE. We have employed both RCM and the traditional Richards equation-based models to simulate our experimental results. We found that the traditional unsaturated flow model cannot simulate experimental results satisfactorily. Very close agreement was obtained by including the dynamic capillary term as postulated by Hassanizadeh and Gray in the traditional equations. The reduced continua model was found to be in good agreement with the experimental result without adding dynamic capillarity term. Moreover, the computational effort needed for RCM simulations was one order of magnitude less than that of traditional models.     

离心惯性力效应对超临界二氧化碳干气密封流场与密封特性影响分析

为揭示离心惯性力效应对S-CO₂干气密封流场与密封特性的影响规律,以螺旋槽干气密封为研究对象,引用考虑离心惯性力效应的Reynolds方程,在考虑气膜真实气体效应、黏度随压力与温度双重变化的同时,基于N-S方程与能量守恒定律,建立了绝热状态下考虑离心惯性力效应作用的能量控制方程.然后,采用有限差分法对压力控制方程与能量控制方程进行耦合求解,并对考虑离心惯性力效应与没有考虑离心惯性力效应下的压力分布、温度分布以及密封特性进行了分析讨论.研究表明:离心惯性力效应具有削弱流场内压力与温度的作用;从避免凝结流动角度考虑,离心惯性力效应引起的温降将不利于S-CO₂干气密封;考虑离心惯性力效应作用时,气膜开启力在不同槽深与转速下存在最佳工况点,泄漏率随着转速的增加显著减小,而离心惯性力效应与膜厚之间没有强交互作用;考虑离心惯性力效应作用的气膜开启力、泄漏率、出口温度均比不考虑离心惯性力效应作用的小,且这种差异随着转速的增大而增加,而随着膜厚的变化没有改变.这些结果为进一步研究S-CO₂干气密封奠定了一定的理论基础.     

固体表面润湿性对滑块-盘接触润滑供油的影响

基于荧光技术,研究了固体表面润湿性对滑块-盘面接触供油的影响. 试验中以静止滑块和旋转玻璃盘构成摩擦副,润滑油围绕该面接触区构成一个供油油池. 结果表明:充分供油条件下,滑块表面的润湿性影响油池润滑剂的分布,但仍能保证接触区润滑剂的充分供给. 限量供油条件下,接触区外滑块表面润湿性影响了油池分布以及入口润滑剂的供给,低润湿性加剧接触区乏油程度,直接导致膜厚的降低. 润滑剂的高表面张力及在盘表面的低粘附都会改善润滑剂在润滑轨道上的回流;润滑剂在盘表面的反润湿现象导致了离散分布的微液滴,对润滑轨道上的回流和润滑油膜的形成起到了正面作用.      

碳滑板电滑动温升及其对滑板磨损影响的试验研究

使用高速载流摩擦磨损试验机,研究了碳滑板与接触线电滑动摩擦时接触压力、相对滑动速度、电流和电弧放电能量变化对碳滑板温升的影响,比较了不同温升时碳滑板的磨损形貌.结果表明:滑板的温升随滑动速度、电流、电弧放电能量的增加而增加,随接触压力的增加而减小.碳滑板的磨损形貌观察显示:碳滑板的温升会显著影响滑板的磨损形貌,随着温升的增加,碳滑板的磨损就越严重.碳滑板的不同温升对应着不同的磨损机制:温升50℃左右时,碳滑板表面以片状剥离的机械磨损为主;温升90℃左右时,碳滑板表面以机械磨损为主,并出现少量的烧蚀区域;温升在180~200℃左右时,碳滑板表面出现大量的烧蚀区域,以电弧烧蚀磨损为主;温升在300℃左右时,碳滑板易出现疲劳裂纹,以电弧烧蚀磨损为主.     

Investigation on the Thermoelastic Constant of Carbon Fibre Composites

Orthotropic materials show different thermo-elastic constants depending on their fibre orientation. While most materials undergo a positive elongation with increasing temperature, carbon fibres present a heat-shrink behaviour, which in carbon fibre composites has an important consequence on thermoelastic constants. A decrease in thermoelastic constant with frequency has already been observed in glass fibre composites. Experiments made on uniaxial carbon fibre composites showed that the longitudinal thermoelastic constant increases with the frequency, while the transverse constant decreases. Furthermore, due to the opposite signs of the thermoelastic carbon fibre constant and of the surrounding resin matrix, the absolute values of the longitudinal thermoelastic constant were ten times lower in CFRPs than in GFRPs. An analytical model could successfully reproduce the frequency dependence of the longitudinal thermoelastic constant, thus helping to explain the reason for the observed behaviour. Two calibration samples were used to obtain the thermoelastic constants in the longitudinal and transverse directions. The values of the thermoelastic constants were then applied to a test sample with fibres forming an angle of 10° to the load direction. The expected theoretical results were compared with the results experimentally obtained, showing good agreement. A preliminary calibration of the longitudinal and transverse thermoelastic constants proved to be a useful approach to obtaining the correct value of the thermoelastic constant in a generic direction.