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.     

高温冲击拉伸试验中的快速接触加温技术

本文阐述了高温冲击拉伸试验技术中基于大热容量热惯性温升极大值原理的快速接触加温技术;研制了稳定性好、加热效率高、总体热惯性大、断电温升至极大值的稳定时间长的一对新的加温炉。测试结果表明,可以在试件上获得了最高可达1073K的近似稳定和均匀的温度场。通过实验研究建立了试件温度、稳定炉温和加温炉加热自动断电设定温度之间的标定关系。利用此标定关系,可以根据试验所需要的试件温度方便地确定加温炉自动断电设定温度,并通过监控稳定炉温来实施的所需试件温度下的冲击拉伸试验。本文还对高温冲击拉伸试验中的相关问题进行了分析讨论。     

Numerical Simulation of Turbulent Flow and Heat Transfer in a Three-Dimensional Channel Coupled with Flow Through Porous Structures

This study investigates numerically the turbulent flow and heat transfer characteristics of a T-junction mixing, where a porous media flow is vertically discharged in a 3D fully developed channel flow. The fluid equations for the porous medium are solved in a pore structure level using an Speziale, Sarkar and Gatski turbulence model and validated with open literature data. Overall, two types of porous structures, consisted of square pores, are investigated over a wide range of Reynolds numbers: an in-line and a staggered pore structure arrangement. The flow patterns, including the reattachment length in the channel, the velocity field inside the porous medium as well as the fluctuation velocity at the interface, are found to be strongly affected by the velocity ratio between the transversely interacting flow streams. In addition, the heat transfer examination of the flow domain reveals that the temperature distribution in the porous structure is more uniform for the staggered array. The local heat transfer distributions inside the porous structure are also studied, and the general heat transfer rates are correlated in terms of area-averaged Nusselt number accounting for the effects of Reynolds number, velocity ratio as well as the geometrical arrangement of the porous structures.     

金属板材高温压缩试验

本文介绍了直接接触式加热器及金属板材800℃压缩试验技术。用自动描绘的力变形曲线测得弹性模量E和屈服强度σ_(0.2)。该试验技术所用设备简单,耗电少,操作方便,并提高了工作效率和试验精确度。     

Multiscale Creep Compliance of Epoxy Networks at Elevated Temperatures

Epoxy networks are thermoset polymers for which an important structural length scale, molecular weight between crosslinks (M _c), influences physical and mechanical properties. In the present work, creep compliance was measured for three aliphatic epoxy networks of differing M _c using both macroscale torsion and microscale depth-sensing indentation at temperatures of 25 and 55°C. Analytical relations were used to compute creep compliance (J(t)) for each approach; similar results were observed for the two techniques at 25°C, but not at 55°C. Although creep compliance measurement differed at elevated temperatures, there were clear correlations between M _c, glass transition temperature, T _g, and the observed time-dependent mechanical behavior via both techniques at 55°C, but these correlations could not be seen at 25°C. This work demonstrates the capacity of depth-sensing indentation to differentiate among epoxy networks of differing structural configurations via J(t) for small material volumes at elevated temperatures.     

不同温度下砷化镓表面摩擦诱导选择性刻蚀特性研究

利用摩擦诱导选择性刻蚀的方法,可在砷化镓表面加工一系列的纳米结构;该纳米加工方法无需掩膜,且加工效率高、成本低,具有应用前景.为了进一步研究砷化镓表面摩擦诱导选择性刻蚀的特性,优化加工参数,本文作者在不同温度下利用H_2SO_4-H_2O_2溶液对砷化镓表面进行选择性刻蚀,考察了刻蚀后所形成的凸起高度及砷化镓表面粗糙度随刻蚀时间和刻蚀温度的变化规律,阐释了温度对砷化镓表面刻蚀的影响机制;最后从加工高度和表面粗糙度着眼,探讨了砷化镓表面摩擦诱导选择性刻蚀的最佳条件.本研究为砷化镓表面选择性刻蚀加工的条件优化提供了重要依据.     

Analysis of Heat and Mass Transfer in a Vertical Annular Porous Cylinder Using FEM

The present study is intended to study heat and mass transfer in a vertical annular cylinder embedded with saturated porous medium. The inner surface of cylinder is maintained at uniform wall temperature and uniform wall concentration. The governing partial differential equations are non-dimensionalised and solved by using finite element method (FEM). The porous medium is discritised using triangular elements with uneven element size. Large number of smaller-sized elements are placed near the walls of the annulus to capture the smallest variation in solution parameters. The results are reported for both aiding and opposing flows. The effects of various non-dimensional numbers such as buoyancy ratio, Lewis number, Rayleigh number, aspect ratio, etc on heat and mass transfer are discussed. The temperature and concentration profiles are presented.     

流体静压型机械密封的三维传热数学模型及端面温度分析

建立了静环倾斜时流体静压型机械密封的三维稳态传热模型,考虑流体黏度随压力、温度的变化,建立了压力、温度的控制方程,采用有限差分法,分析研究了倾斜量、结构参数及操作参数对机械密封温度分布的影响规律.结果表明,端面的最大液膜压力和最高温度随静环倾斜量的增加而增大,倾斜量越大,压黏效应越显著;端面温升受密封的结构参数、操作参数影响明显.静环端面锥角越大,温升越小;流体注入温度越低,温升越大;动环转速越高,温升越大.     

高温下混凝土化学塑性-损伤耦合本构模拟及破坏分析

提出了一个用于模拟高温下混凝土中化学-热-湿-力学耦合行为的化学塑性-损伤耦合本构模型.发展了用于积分率形式的耦合本构方程的三步算子分裂算法.导出了化学-热-湿-力学(CTHM)耦合本构模型的一致性切线模量矩阵,以保证对于全局耦合控制方程Newton迭代过程的二阶收敛率.算例数值结果显示了本文发展的化学塑性-损伤耦合本构模型在重现火灾和热辐射条件下的混凝土中化学-热-湿-力学耦合行为的有效性.     

Stress-Dependent Elastic Behaviour of a Titanium Alloy at Elevated Temperatures

In this study the influence of stress and temperature on the elastic modulus during fully-reversed low cycle fatigue of the titanium alloy Ti6242 is examined. The change of the elastic properties with stress manifests itself in a crescent-like shaped hysteresis loop of stress vs. plastic strain at very low amplitudes, i.e. below the technical yield stress. A quadratic extension of Hooke??s law with a second constant ??k?? is applied. The parameters are determined all along the unloading curve in tension and compression. The approach results in the alignment of the hysteresis loop so that they become vertical, i.e. the elastic strain is accurately described. The value and sign of ??k?? depend on whether the deformation occurs in tension or compression. Like the Young??s modulus E ₀, ??k?? also depends on temperature. At temperatures up to 550°C the values of ??k?? in tension and compression do not change during fatigue life. However, at 650°C thermally activated slip processes lead to changes of both, E ₀ and ??k??.     

Wettability Alteration to Intermediate Gas-Wetting in Porous Media at Elevated Temperatures

Wettability alteration to intermediate gas-wetting in porous media by treatment with FC-759, a fluorochemical polymer has been studied experimentally. Berea sandstone was used as the main rock sample in our work, and its wettability before and after chemical treatment was studied at various temperatures from 25 to 93°C. We also studied recovery performance for both gas/oil and oil/water systems for Berea sandstone before and after wettability alteration by chemical treatment. Our experiment shows that chemical treatment with FC-759 can result in: (1) wettability alteration from strong liquid-wetting to stable intermediate gas-wetting at room temperature and at elevated temperatures; (2) neutral wetting for gas, oil, and water phases in two-phase flow; (3) significant increase in oil mobility for gas/oil system; and (4) improved recovery behavior for both gas/oil and oil/water systems. This work reveals a potential for field application for improved gas-well deliverability and well injectivity by altering the rock wettability around wellbore in gas condensate reservoirs from strong liquid-wetting to intermediate gas-wetting.     

Modeling of Heat and Mass Transfer in a Fractured Porous Medium

While fractured formations are possibly the most important contributors to the production of oil worldwide, modeling fractured formations with rigorous treatments has eluded reservoir engineers in the past. To date, one of the most commonly used fractured reservoir models remains the one that was suggested by Warren and Root nearly four decades ago. In this paper, a new model for fractures embedded in a porous medium is proposed. The model considers the Navier-Stokes equation in the fracture (channel flow) while using the Brinkman equation for the porous medium. Unlike the previous approach, the proposed model does not require the assumption of orthogonality of the fractures (sugar cube assumption) nor does it impose incorrect boundary conditions for the interface between the fracture and the porous medium. Also, the transfer coefficient between the fracture and matrix interface does not need to be specified, unlike the cases for which Darcy's law is used. In order to demonstrate the usefulness of the approach, a two-dimensional model of a fractured formation is developed and numerical simulation runs conducted.

The proposed model is derived through a series of finite element modeling runs for various cases using the Navier-Stokes equation in the channel while maintaining the Brinkman equation in the porous medium. Various cases studied include different fracture orientations, fracture frequencies, and thermal and solutal constraints. The usefulness of the proposed model in modeling complex formations is discussed. Finally, a series of numerical runs also provided validity of the proposed model for the cases in which thermal and solutal effects are important. Such a study of double diffusive phenomena, coupled with forced convection, in the context of fractured formations has not been reported before.     

等离子堆焊Stellite合金高温摩擦磨损特性研究

采用等离子堆焊技术在气门用钢基体上制备了Stellite 1和Stellite F合金堆焊层,对堆焊层的金相组织、物相组成和硬度等进行了研究,在MMU-10G高温端面摩擦磨损试验机上考察了不同温度条件对2种堆焊层摩擦磨损性能的影响,并分析了堆焊层的磨损机理.结果表明:高温条件下,随着温度的上升,2种合金堆焊层的摩擦系数增大,磨损体积减小;温度为400℃时,Stellite 1和Stellite F合金堆焊层分别产生了大量的疲劳裂纹和宽大的犁沟,磨损较为剧烈;温度为500和600℃时,2种合金堆焊层磨损机制相似,主要磨损机制分别为疲劳剥落和磨粒磨损;氧化膜的快速形成以及上试样硬度的下降减小了磨损,磨痕中心区域变窄,磨痕边缘的磨屑不断堆积并被碾压产生了严重的黏着磨损,导致摩擦系数增加.     

Solutions using the Recursive Operator Method for the Dynamic Equations of Heat and Mass Transfer in Hardening Concrete under Heat Treatment in a Heating Chamber

A recursive operator method was used to obtain a general solution of the system of linearized differential equations of heat and mass transfer in hardening concrete in a heating chamber. The solution contains arbitrary analytic functions determined from the boundary and initial conditions.     

Some Considerations on Modeling Heat and Mass Transfer in Porous Media

In this paper some considerations are presented about the equations needed to set up a model of the process of heat and mass transfer in porous media. A clear classification is made of the various types of equations used and of their physical meaning. Special attention is paid to the thermodynamic equilibrium equations and to their derivation since they are too often taken for granted. The importance of the various transport mechanisms (of mass and energy) is analyzed and the consequences that can arise when some term is neglected are indicated.     

Modelling of Two-Component Turbulent Mass and Heat Transfer in Air-Fed Pressurised Suits

In this paper the modelling of an important industrial problem is addressed, which involves the two-component turbulent flow with heat transfer that takes place inside protective clothing. The geometry of the flow boundaries is reconstructed in a CAD system from photogrammetry scan data. The overall model is sufficiently realistic to allow, after validation, design improvements to be tested. Those presented here allow the reduction of hotspots over the worker’s body surface and increase thermal comfort.     

Role of Thermal Diffusion on Heat and Mass Transfer in Porous Media

In this paper, thermal diffusion phenomena in a porous cavity are investigated. The Brinkman model, coupled with the energy and the mass balance equations was solved numerically using a finite element techniques. A two-component system was included in the model. Different models were investigated to demonstrate the importance of the Soret effect with the presence of gravity vector. We do not take into consideration the pressure effect in the thermal diffusion. Even with such simplification to the problem, results reveal that the thermal diffusion is important and drives a strong convection. A series of convection cells are observed and steady-state solutions are obtained. Asymmetric solutions are obtained for various cases of dual-porosity porous media. Variations in the gravity vector indicated that the convection patterns, as well as the role of Soret coefficient, are profoundly impacted. Finally, the importance of including thermal diffusion in petroleum reservoir simulation is discussed.     

Mg-3Al-0.4Si镁合金的高温磨损行为研究

在20~200℃温度下,利用销盘式磨损试验机研究Mg-3Al-0.4Si合金的磨损行为,评价载荷和温度对磨损速率的影响.应用扫描电子显微镜观察磨损表面形貌以确定高温下的磨损机制,通过光学显微镜观察磨损亚表层组织演变,然后采用显微硬度计测量硬度变化.研究结果表明:随着磨损温度提高,Mg-3Al-0.4Si合金的磨损率随载荷增加而上升的趋势更为明显.其磨损行为可分为轻微和严重磨损,增加磨损温度显著降低轻微-严重磨损转变载荷.轻微-严重磨损前后的亚表层组织和硬度变化表明,摩擦热诱发磨损亚表层发生动态再结晶(DRX)组织转变引起的热软化是造成轻微-严重磨损转变的主要原因.     

A Methodology for Obtaining Material Properties of Polymeric Foam at Elevated Temperatures

A new methodology to characterise the elastic properties of polymeric foam core materials at elevated temperatures is proposed. The focus is to determine reliable values of the tensile and compressive moduli and Poisson’s ratio based on strain data obtained using digital image correlation (DIC). In the paper a detailed coverage of the source of uncertainties in the experimental procedure is provided. The uncertainties include those associated with the load introduction, the measurement and the data processing. The design of the specimens and loading jigs are developed and assessed in terms of the introduction of uniform strain. It is shown that due to the mismatch in stiffness between the jig material and the foam the introduction of a uniform strain through the cross section of the specimens is difficult to obtain. A means for correcting for the non-uniform strain across the specimen cross section is developed. To validate the methodology, tests are firstly conducted at room temperature on Divinycell PVC H100 foam. It is shown that the material is highly anisotropic with a stiffness of 50% less in the plane of the foam sheet compared to the through-thickness direction. It is also shown that because of the compliance of the foam, jig misalignment causes large errors in the measurement, and a means for correcting for this is defined. Tests are then conducted in a temperature controlled chamber at elevated temperatures ranging from 20°C to 90°C. A nonlinear reduction in Young’s modulus is obtained with significant degradation occurring after 70°C. The Poisson’s ratio remains fairly stable at different temperatures. A strong theme in the paper is the accuracy and precision of the DIC data and the factors which introduce scatter in the data, along with the uncertainties that this introduces. Particular attention is paid to the affect of the correlation parameters on the derived strain data.     

DNS and Highly-Resolved LES of Heat and Mass Transfer in Two-Phase Counter-Current Condensing Flow

Flow, Turbulence and Combustion - A comprehensive study of direct-contact condensation heat transfer for turbulent, counter-current, liquid/vapour flow in a nearly horizontal channel at high...