Large-eddy simulation of fluid mixing in tee with sintered porous medium

Mixing processes of hot and cold fluids in a tee with and without sin- tered copper spheres are simulated by FLUENT using the large-eddy simulation （LES） turbulent flow model and the sub-grid scale （SGS） Smagorinsky-Lilly （SL） model with buoyancy. Comparisons of numerical results of the two cases with and without sintered copper spheres show that the porous medium significantly reduces velocity and temper- ature fluctuations because the porous medium can effectively restrict the fluid flow and enhance heat transfer. The porous medium obviously increases the pressure drop in the main duct. The porous medium reduces the power spectrum density （PSD） of tempera- ture fluctuations in the frequency range from 1 Hz to 10 Hz.

MHD Effects on Mixed Convective Nanofluid Flow with Viscous Dissipation in Surrounding Porous Medium

In existence of concerning magnetic field, heat together with mass transfer features on mixed convective copper-water nanofluid flow through inclined plate is investigated in surrounding porous medium together with viscous dissipation. A proper set of useful similarity transforms is considered as to transform the desired governing equations into a system as ordinary differential equations which are nonlinear. The transformed equations for nanofluid flow include interrelated boundary conditions which are resolved numerically applying Runge-Kutta integration process of sixth-order together with Nachtsheim and Swigert technique. The numerical consequences are compared together with literature which was published previously and acceptable comparisons are found. The influence of significant parameters like as magnetic parameter, angle for inclination, Eckert number, fluid suction parameter, nanoparticles volume fraction, Schmidt number and permeability parameter on concerning velocity, temperature along with concentration boundary layers remains examined and calculated. Numerical consequences are presented graphically. Moreover, the impact regarding these physical parameters for engineering significance in expressions of local skin friction coefficient in addition to local Nusselt together with Sherwood numbers is correspondingly examined.

A Mixed Convection Boundary Layer Flow over a Vertical Wall in a Porous Medium, with Exponentially Varying Fluid Viscosity

This study investigates a mixed convection boundary layer flow over a vertical wall embedded in a highly porous medium. The fluid viscosity is assumed to decrease exponentially with temperature. The boundary layer equations are transformed into a non-similar form using an appropriate non-similar variable ξ and a pseudo-similar variable η. The non-similar equations are solved using an efficient local non-similarity method. The effect of viscosity variation parameter on the heat transfer, skin friction and the velocity and temperature distribution within the boundary layer is investigated. The viscosity variation parameter, the viscous dissipation parameter and non-simi-larity variable are shown to have a significant effect on velocity and thermal boundary layer and also on the skin friction coefficient and heat transfer at the wall.

Unsteady Mixed Convection Slip Flow around a Stretching Sheet in Porous Medium

The heat and mass transfer of unsteady MHD two-dimensional mixed convection boundary layer flow over an exponentially porous stretching sheet is presented in this paper. Multiple slip conditions, radiation, suction or blowing, heat generation or absorption along with magnetism and porous medium are incorporated. We reduce the leading equations which are partial differential equations into a family of ordinary differential equations that are non-linear using a set of similarity transformations. The resulting equations with coupled boundary conditions are solved numerically with the aid of bvp4c solver with MATLAB package. The impacts of several non-dimensional governing parameters on the flow fields such as velocity, temperature and concentration profiles along with friction coefficient, temperature gradient and concentration gradient are portrayed graphically and discussed in detail. The result indicates that the magnetic parameter decreases the skin friction coefficient. Thermal boundary layer thickness reduces with increasing radiation parameters and enhances with increasing Prandtl number. It is also observed that the thermal slip parameter depreciates the heat transfer rate and the mass slip parameter diminishes the mass transfer rate. A comparison has been made between the current results and the numerical results of previous studies and observed a very close good agreement.

Efect of double dispersion on non-Darcy mixed convective flow over vertical surface embedded in porous medium

A numerical study of a non-Darcy mixed convective heat and mass transfer flow over a vertical surface embedded in a dispersion, melting, and thermal radiation is porous medium under the effects of double investigated. The set of governing boundary layer equations and the boundary conditions is transformed into a set of coupled nonlinear ordinary differential equations with the relevant boundary conditions. The transformed equations are solved numerically by using the Chebyshev pseudospectral method. Comparisons of the present results with the existing results in the literature are made, and good agreement is found. Numerical results for the velocity, temperature, concentration profiles, and local Nusselt and Sherwood numbers are discussed for various values of physical parameters.

中温温拌再生沥青性能研究

本文对中温再生沥青制备工艺以及性能进行研究,通过试验研究了制备温度、剪切时间、中温再生剂掺量对中温再生沥青性能的影响。研究结果表明,(1)制备中温再生沥青的工艺条件为:70#基质沥青加热温度为120℃,中温再生剂加热温度为80℃,中温再生剂在沥青中的剪切时间为90min;(2)中温再生剂提高了沥青的低温延展性,降低了沥青的黏度,提高了施工和易性;(3)老化沥青的针入度随着中温再生剂掺量的增加而增加,软化点随着中温再生剂掺量的增加而降低,对于70#基质沥青而言,中温再生剂的最佳掺量为沥青质量的4%。

磁场强化非均相分离技术的工业应用进展

概述了磁场分离技术在分离多相混合介质中的研究和应用进展,对磁场分离技术的应用原理和分离优势进行了分析。根据混合相内的介质类别,分别针对固、液、气不同应用领域,介绍了磁场分离工艺在矿物精选、污水处理、气体除杂中的典型应用,并分析了相应运行工况下的磁场排布规律和介质分离特性。从组合工艺的研究视角出发,总结了磁场分离技术与气浮分离技术、膜分离技术、旋流分离技术的耦合应用现状,并分析了上述组合工艺的技术特点、运行成效。为拓宽磁场分离技术的适用范围,讨论了磁种在磁场分离工艺中的辅助应用,以强化该技术对无磁性介质的分离。

等离子射流在模拟液体发射药中扩展特性的数值模拟

为了深入认识液体工质电热化学炮中等离子射流的点火过程,开展了等离子射流在液体发射药LP1846模拟工质中扩展特性的研究,建立了等离子射流在液体中扩展的二维轴对称非稳态数学模型,并基于液体工质为水的文献实验进行模型验证。在此基础上对等离子射流在LP1846液体发射药模拟工质中的扩展过程进行数值模拟,分析等离子射流在扩展过程中形态的变化以及射流场压力、速度和温度的分布特性。结果表明,扩展过程中由于Taylor-Helmholtz不稳定性,等离子射流和液体发射药模拟工质两相间存在湍流掺混现象,并随着扩展逐渐加剧,表现为射流头部凸出并逐渐轴向拉长形成尖头,同时射流卷吸液体发射药模拟工质在Taylor空腔中产生液滴,且数量逐渐增多。此外,等离子射流扩展过程中近喷孔处由于液体发射药模拟工质回流而出现颈缩现象。射流场由于膨胀波-压缩波交替作用而存在波动现象,且在近喷孔处尤为剧烈,表现为压力场呈现高低压相间分布,速度场也呈类似分布。

大掺量中温再生沥青混合料性能研究

采用中温再生剂制备了中温再生沥青,研究了中温再生沥青混合料的拌和成型温度以及其路用性能。通过绘制中温沥青的黏温曲线并联合中温再生沥青混合料的马歇尔试验结果,确定了中温再生沥青混合料的制备成型温度。通过马歇尔指标参数确定了中温再生沥青混合料的最佳配合比,并将中温再生沥青混合料和热拌再生沥青混合料的路用性能进行对比。研究结果显示:(1)中温再生沥青混合料的最佳拌和温度为135℃,最佳压实温度为125℃,比热拌再生沥青混合料低40℃;(2)中温再生沥青混合料的高温性能、水稳定性和低温性能均优于热拌再生沥青混合料;(3)随着RAP掺量的增加,中温再生沥青混合料的高温稳定性逐渐升高,但RAP掺量的增加会降低水稳定性和低温性能。

BCJ-4I型混装炸药车在石碌铁矿中深孔爆破的应用

针对石碌铁矿上向中深孔人工装药过程中,存在安全隐患大、工人劳动强度大、返粉率高、作业环境恶劣、作业效率低等缺点,引进先进的混装炸药车,应用专用乳胶基质及敏化剂溶液、闭环比例控制、无线遥控寻孔和自动送、退管等关键技术,实现装药作业机械化、自动化、智能化,降低了炸药成本,改善了爆破效果,同时减小了工人劳动强度,提高了作业安全性。

中锰低温钢富氩混合气体保护焊工艺研究

较高的锰含量给中锰低温钢焊接带来了挑战,这在一定程度上限制了中锰低温钢在工业生产中的应用。采用富氩混合气体保护焊对中锰低温钢进行焊接试验,研究不同焊接热输入条件下,焊接接头显微组织和力学性能的变化规律。结果表明:除焊缝及母材外,焊接接头各区域均为局部硬化区,且硬化程度随热输入的增加而增大;当热输入由12 kJ/cm增加到22 kJ/cm时,焊接接头的屈服强度由820 MPa降至775 MPa,抗拉强度由983 MPa降至925 MPa;当热输入为12 kJ/cm和16.8 kJ/cm时,其焊接接头在-40℃条件下均有着良好的冲击韧性,且后者焊接接头各区域冲击吸收功较为均匀,在45 J左右;焊缝区细小的夹杂物及针状铁素体提供了高密度的大角度晶界,减缓了裂纹扩展速率。热影响区稳定性较低的残余奥氏体在受到冲击载荷作用时发生相变诱导塑性(TRIP)效应,提高了焊接接头的低温冲击韧性。

废旧锂离子电池放电方案的试验分析

以废旧手机锂离子电池为研究对象,分析不同放电方案下废旧锂离子电池的放电效果,并对最佳放电溶液中Li、Co等金属离子的含量以及滤渣成分进行表征。研究表明,当NaCl质量浓度为10%时,放电1 h放电率约54%;石墨掩埋和铜粉掩埋2.7 h最高放电率分别为35.96%和12.34%,且存在电压反弹现象,石墨粉和NaCl溶液混合可增强放电效果。最佳放电方案为,在120 r·min^(-1)搅拌的条件下,将废旧锂离子电池浸泡在10%NaCl溶液与40 g·L^(-1)80目石墨粉的混合溶液中,放电80 min,放电率为81.87%。过滤放电溶液并用ICP-OES分析滤液,结果表明,滤液含Li、Co离子,且Li、Co离子质量浓度随放电时间的延长而增加,放电80 min后,Li、Co的离子质量浓度分别为0.128、0.01 g·L^(-1),之后变化缓慢;用FT-IR表征烘干后的滤渣,其主要成分为石墨,未检测到有机物杂质;Li、Co离子质量浓度以及石墨粉成分的变化为放电溶液的重复利用并从中回收有价金属提供参考。

A MIXED ELECTRIC BOUNDARY VALUE PROBLEM FOR AN ANTI-PLANE PIEZOELECTRIC CRACK

The analytical continuation method is adopted to solve a mixed electric boundary value problem for a piezoelectric medium under anti-plane deformation.The crack face is partly conductive and partly impermeable.The results show that the stress intensity factor is identical with the mode Ⅲ stress intensity factor independent of the conducting length.But the electric field and the electric displacement are dependent on the electric boundary conditions on the crack faces and are singular not only at the crack tips but also at the junctures between the impermeable part and conducting portions.

On an Application of the Improved Maximum Product Criterion to Inverse Acoustic Scattering in a Layered Medium

In this paper, we consider the numerical treatment of an inverse acoustic scattering problem that involves an impenetrable obstacle embedded in a layered medium. We begin by employing a modified version of the well known factorization method, in which a computationally effective numerical scheme for the reconstruction of the shape of the scatterer is presented. This is possible, due to a mixed reciprocity principle, which renders the computation of the Green function at the background medium unnecessary. Moreover, to further refine our inversion algorithm, an efficient Tikhonov parameter choice technique, called Improved Maximum Product Criterion (IMPC) is exploited. Our regularization parameter is computed via a fast iterative algorithm which requires no a priori knowledge of the noise level in the far-field data. Finally, the effectiveness of IMPC is illustrated with various numerical examples.

MHD Effect on an Oscillatory Mixed Convective Flow Past an Infinite Vertical Porous Plate with Radiation

A parametric study to investigate the effects of magnetic field and radiation on a mixed convective flow past an infinite vertical porous plate with constant suction velocity when the free stream varies periodically with time about a steady mean is presented. A uniform magnetic field is applied normal to the plate. The Rosseland approximation is used to describe the radiative heat flux in the energy equation and the resultant set of non-dimensional equations are solved analytically by adopting regular perturbation technique. The profiles of velocity, temperature, skin-friction and nusselt number are demonstrated graphically for various values of the parameters involved in the problem and the results are physically interpreted.

Mixed graphite cast iron for automotive exhaust component applications

Both spheroidal graphite iron and compacted graphite iron are used in the automotive industry. A recently proposed mixed graphite iron exhibits a microstructure between the conventional spheroidal graphite iron and compacted graphite iron. Evaluation results clearly indicate the suitability and benefits of mixed graphite iron for exhaust component applications with respect to casting, machining, mechanical, thermophysical, oxidation, and thermal fatigue properties. A new ASTM standard specification(A1095) has been created for compacted, mixed, and spheroidal graphite silicon-molybdenum iron castings. This paper attempts to outline the latest progress in mixed graphite iron published.

中等应变速率轧制制备多尺度混晶镁合金工艺及组织性能

为了研究中等应变速率轧制下AZ31镁合金的组织演变过程和力学性能,获得同时提升强度和塑性的优良轧制工艺,对均匀化铸态AZ31镁合金进行平均应变速率分别为1.9 s^(-1)、4.8 s^(-1)和7.8 s^(-1),变形温度分别为370℃、410℃和460℃,下压量为75%的中等应变速率轧制,并构建嵌入式混晶结构的增塑模型。结果表明:中等应变速率轧制可制备多尺度混晶镁合金板材,410℃时可形成粗晶镶嵌在多层细晶中的嵌入式结构组织,在(410℃、4.8 s^(-1))时可形成细晶、中等晶粒和粗晶占比均匀并夹极少量超细晶和粗大晶粒的嵌入式结构组织;在410℃时轧制板材具有较好的强度和塑性匹配,尤其是在(410℃、4.8 s^(-1))时的轧制板材强度和塑性最为均衡,抗拉强度达279.4 MPa、伸长率达21.2%;相较于高应变速率轧制的细晶镁合金轧板,中等应变速率轧制的多尺度混晶组织镁合金轧板的强度明显提高,最大提高了19.7%,伸长率亦有提高;在410℃时轧制板材以韧性断裂为主,其他以韧-脆性断裂为主;微观组织为粗晶镶嵌在多层细晶中的嵌入式结构相比其他混晶结构具有更好的塑性。

冬小麦覆被农田地表多层非均质混合电磁散射模型研究

冬小麦种植区域分布广泛,为监测与评估其生长信息和生长环境,本文通过引入三相混合介质模型表征植被层,引入高斯随机粗糙面表征农田粗糙地表,构建了一种冬小麦覆被农田地表的多层非均质混合电磁散射模型。首先分别对比本文提出的多层非均质混合模型与水云模型、Oh模型在冬小麦拔节期及孕穗期的后向散射系数预测结果,对本模型的有效性进行分析和验证;随后,通过分析该模型等效介电常数,并求解其电磁散射及辐射传输方程,获取植被生长信息、植被含水率及土壤粗糙度等因素对覆被农田地表等效介电常数和雷达后向散射系数的影响规律。结果表明,本文提出的多层非均质混合模型与水云模型及Oh模型预测结果有较好的一致性,同时与双弥散模型获得的小麦层等效介电常数R2分别为0.9817、0.9922、0.9863、0.9711,同样具有较好的一致性;此外,本文提出的模型对拔节期、孕穗期小麦含水率的预测结果与实际测量值的均方根误差分别为0.88%、4.65%,该模型能够较好地模拟覆被农田地表电磁散射特征,为后续无人机微波反演冬小麦生长及土壤水分信息提供坚实理论基础。

Hydrodynamic Anisotropy Effects on Radiation-Mixed Convection Interaction in a Vertical Porous Channel

The effects of hydrodynamic anisotropy on the mixed-convection in a vertical porous channel heated on its plates with a thermal radiation are investigated analytically for fully developed flow regime. The porous medium is anisotropic in permeability whose principal axes are oriented in a direction that is oblique to the gravity. The generalized Brinkman-extended Darcy model which allows the no-slip boundary-condition on solid wall is used in the formulation of the problem. The flow reversal, the thermal radiation influence for natural, and forced convection are considered in the limiting cases for low and high porosity media. It was found that the anisotropic permeability ratio, the orientation angle of the principal axes of permeability and the radiation parameter affected significantly the flow regime and the heat transfer.

烧结矿冷却废气余热驱动的ORC系统热力性能研究

将烧结环冷机低温段冷却废气余热引入有机朗肯循环(ORC),建立ORC热力循环过程计算模型,研究混合工质组分、工质蒸发温度和过热度对系统热力性能的影响。研究结果表明:随着工质蒸发温度升高,系统发电功率先增大后减小,而系统火用效率逐渐增大;工质冷凝温度越高,系统发电功率和火用效率均越小;在工质蒸发温度和过热度变化范围内,系统火用效率随混合工质中R245fa质量分数增大先减小后增大,纯工质R245fa的系统火用效率最大。当工质在蒸发器出口为饱和蒸汽时,系统可获得较大系统发电功率,并且混合工质中R245fa质量分数为0.8时的系统发电功率最大。