Prediction of thermal diffusion in binary mixtures of nonelectrolyte liquids by the use of nonequilibrium thermodynamics

A derivation based on nonequilibrium thermodynamic leads to this expression for the thermal diffusion factor, _T=M ₂(h ₂ ^xs -h ₁ ^xs )/RT ₂, where M ₂ is the molecular weight of the lighter of the two components, h ₁ ^xs is the partial excess enthalpy of component i, J/g, R is 8.314 J · K ^–1 · mol ^–1, T is temperature in K, and ₂ is the thermodynamic correction factor (1 + d ln ₂/d ln X ₂), where ₂ is an activity coefficient and X ₂ is the mole fraction. The correctness of this theoretical prediction is verified for the liquid system ethanol-water at 298 K.Paper submitted to the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

Composition dependence of the thermal conductivity of low-density polyatomic gas mixtures

We present a predictive scheme for the composition dependence of the thermal conductivity of mixtures containing polyatomic gases at zero density. This supplements earlier work which developed a method to interpolate for the composition dependence of dense gas mixtures, as well as an earlier procedure to calculate the thermal conductivity of mixtures of monatomic gases. In all cases, the algorithm makes use of accurately measured values of the thermal conductivity of pure gases and is validated with the aid of almost equal accurately measured values of selected binary mixtures. Such accurate data have been obtained mostly in transient hot-wire instruments. The formulae proposed for the calculations use the Monchick-Pereira-Mason kinetic-theory analysis as a starting point but contain a number of detailed improvements. The present algorithm is tested by comparison with measurements on 22 mixtures, which show absolute average deviations from the predictions ranging from 0.7 to 2.7%, with one unexplained case, that of CF₄-He mixtures, which show deviations reaching as much as 7%. We estimate that the algorithm predicts the zerodensity thermal conductivity of binary mixtures, containing at least one polyatomic component, with a probable error in the order of 2%.     

Numerical investigation of diesel particulate matter dispersion in an underground development face during key mining activities

Diesel particulate matter (DPM) is carcinogenic to humans. Underground miners have a high risk of over-exposure to high concentrations of DPM. To control DPM effectively, it is essential to understand the DPM dispersion characteristics. In this study, the DPM distributions of three key and representative mining activities, shotcreting, charging and loading activity, in an underground development face were studied. A computational model for the mining activities was developed using 3D imagery, onsite data and OpenFOAM. Tracer gas experiments were first conducted in the underground mine for the validation of CFD simulation. The simulations were carried out at a steady-state using the standard k-ε turbulence model, and the transport and dispersion of DPM were modelled using a segregated species transport model. DPM distribution characteristics for each mining activity were analysed, and the regions with high concentration (>0.1 mg/m³) were identified, and the reasons for the high concentrations were also discussed. At last, the efficiency of the current auxiliary ventilation system on DPM dilution was evaluated based on the simulation results. The results show that a broader region with high DPM concentration was identified in the downstream of the loader during the loading activity, and this issue could be solved by simply increasing the ventilation rate. The findings in this paper could be used for optimizing the auxiliary ventilation design for future mining activities in this development face.     

Gas-phase transport phenomena at low temperatures: Thermal diffusion in an Ar-Kr system

A metal two-bulb apparatus for the measurement of the thermal diffusion factor, _T , especially at temperatures below room temperature, has been designed and constructed. The results for the argon-krypton system are reported, and these cover five mixture compositions (25, 40, 50, 60, and 75% of krypton). The top bulb is maintained at 293.2 K, while the temperature of the lower bulb is varied in the range 102–250 K. The measured _T values are estimated to be accurate within ±4%. The positive minimum in the present _T values is less pronounced than that reported by some other workers, and this is attributed to the operating conditions and to the apparatus geometry.     

Nonequilibrium Molecular Dynamics Simulations of Coupled Heat and Mass Transport in Binary Fluid Mixtures in Pores

Molecular dynamics simulations were carried out for a binary fluid mixture in a slit pore. The fluid was an argon-like Lennard–Jones/spline model. The pore wall was represented by the Steele model for a layered graphite structure. The pore had a heat source in one end and a heat sink in the other, resulting in a lateral temperature gradient, a Soret effect, and a thermal creep flow along the pore wall. Potential models with various depths were used to examine the effect of wetting and adsorption on the thermal creep flow. The main results were as follows, (a) A relatively strong creep flow was generated parallel to the wall by the temperature gradient. For strongly attracting fluid–wall potentials, the flow occurred from the cold to the hot end of the pore near the wall (except for the very narrow pore) and oppositely in the center of the pore. For a purely repulsive potential, the flow was weak and mostly in the opposite direction, (b) The thermal diffusion coefficient was comparable to that in bulk fluid at the same overall density, except when the creep flow was strong, in which case the thermal diffusion was blurred by the convective mixing.     

纳米尺度下体系自由能对扩散模型的影响

讨论了纳米尺度下体系自由能的改变对扩散模型的影响.随着体系尺度的逐渐减小,扩散模型由Fick扩散定律转变为Cahn-Hilliard扩散方程和非均匀体系非线性动力学扩散模型,原子的扩散系数也随体系自由能的变化呈现出与局部原子浓度紧密相关的趋势.纳米尺度下体系自由能的变化是导致扩散模型改变的根本原因,体系非均匀性对自由能的贡献越大导致需采用非均匀体系非线性动力学扩散模型描述扩散.     

湿度变化对TEOM1400a系列环境颗粒物监测仪PM10质量浓度观测的影响

为评价环境湿度变化对TEOM(R)1400a·系列环境颗粒物监测仪进行PM10观测的影响,在2004年1月到2005年1月的观测过程中,获得了30 min平均的大气PM10质量浓度,并观测了地面气象条件及降水过程中仪器的响应.结果表明,湿度变化较大时仪器记录的PM10浓度明显受到滤膜上吸附的水汽含量变化的影响.仪器提供的PM10质量浓度反映出明显的日变化规律,分别在800～930和1800～2300出现峰值而在1200～1530出现谷值;此变化规律反映了大气污染物的日变化特征,但也受到空气湿度变化的影响.应用该仪器时对空气湿度的影响应当予以考虑.     

范德瓦尔斯氮气的低温热力学性质研究

采用热力学方法,根据实验测得的氮气的维里系数,导出了氮气的范德瓦尔斯系数a、b.结果表明,实验方法得到的范德瓦尔斯系数与临界参数(Vc,Tc,Pc)确定的范德瓦尔斯系数有明显差异,在低温(90 K-250 K)区,范德瓦尔斯系数随温度改变有显著变化,这些变化对低温氮气的状态方程和热容量等重要热力学性质的影响是显著的.如果不考虑这些变化,可能导致不合理的错误结果.     

Transport in simple dense fluids

A transport theory for Lennard-Jones (LJ) fluids is described. The underlying mean-field kinetic theory models the LJ potential by adding a hard-sphere core to the attractive tail of the LJ potential. The transport coefficients discussed here — shear viscosity, thermal conductivity, and self-diffusion coefficient — exhibit Enskog-like forms, but now the radial distribution function (rdf) bears explicit dependence on the LJ tail as well as on the hard-sphere core. The hardsphere diameter is determined according to the well-known WCA method used in equilibrium statistical mechanics to mimic the LJ fluid. Hence the transport theory employs no adjustable parameters. Numerical results are compared to simulation and experimental results for many states, including saturated liquid, triple point, and dense gas. In general, a quantitatively accurate transport theory is obtained for the states considered. This represents improvement, both numerically and conceptually, over an earlier theory.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

顶空-气相色谱法测定卷烟主流烟气粒相物中吡啶

为研究气相色谱测定卷烟主流烟气粒相物中吡啶含量,采用碳酸钠水溶液作基质校正剂,通过顶空进样、DB-WAXETR色谱柱分离、火焰离子化检测器检测。结果表明:吡啶在0.20~16.20μg/mL质量浓度范围内线性拟合度为0.9998,加标回收率在98.4%~104.7%之间,定量限为0.08μg/支,RSD小于5%,该方法可以快速、准确地测定卷烟主流烟气粒相物中吡啶。     

某火箭试验台低温甲烷排放过程数值模拟

以低温甲烷安全排放为目的,采用数值模拟方法对某试验台甲烷高空排放系统进行研究,分别采用AMESim软件及Fluent软件对排放管内的流动和管外的扩散情况进行了分析,安全排放准则为甲烷云团向上飘动或者水平扩散,研究工况包括了长期稳定排放及大流量短期排放。计算结果表明:排放流量越小越安全,长期稳定排放时甲烷的最大排放流量不能超过75g/s;试验台常规排放流量200 g/s最长的排放时间不得超过300 s,最长排放时间随着排放流量的增加而减小。     

Application of the Taylor dispersion method in supercritical fluids

This paper describes some of the experimental and theoretical problems encountered when the Taylor dispersion method is applied to the measurement of diffusion coefficients near gas-liquid critical points. We have used our own measurements of diffusion of benzene and toluene in supercritical carbon dioxide, along with measurements from several other sources, to illustrate some of the experimental challenges. Special attention is given to the peak shape. The intercomparisons are greatly simplified by comparing the experimental data as functions of density, rather than pressure. We find large and unexplained discrepancies between the various experimental sources. We discuss the theoretical predictions for the relationships between the diffusion coefficients and diffusivities obtained from Taylor dispersion and dynamic light scattering in fluids near critical points. We conclude that there is no strong reason to press for Taylor dispersion measurements near the gas-liquid critical point of the carrier gas.Paper dedicated to Professor Joseph Kestin.     

Shear-induced phase changes in mixtures

A thermodynamic theory to account for the behavior of liquid mixtures exposed to a shear is developed. One consequence of the theory is that shear-induced phase changes are predicted. The theory is based on a thermodynamics that includes specifically the shear rate in the formalism and is applied to mixtures by a straightforward modification of the corresponding states, conformalsolution approach. The approach is general but is used here for a mixture of Lennard-Jones particles with a Lennard-Jones equation of state as a reference fluid. The results are discussed in the context of the Scott and Van Konynenberg phase classification. It is shown that the influence of a shear does affect substantially the type of the phase behavior. Results from the model mixture are equated loosely with those from real polymeric liquids.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

7050铝合金第二相溶解行为EI北大核心CSCD

研究热轧态7050铝合金在固溶过程中的平衡态η(MgZn2)相、T(Al2Mg3Zn3)相、S(Al2CuMg)相及含铁Al7Cu2Fe难溶相的溶解行为。采用原位扫描的组织检测方法获得上述平衡相的溶解动力学实测数据。在体扩散控制的溶解动力学模型基础上,引入曲率和界面反应对原子迁移速率的作用,建立η,T和S相溶解动力学模型。结果表明:在7050铝合金常规固溶温度(470℃)条件下,η和T相在2 min内即可完全溶解,S相保温较长的时间才能完全溶解,含Fe相不发生溶解;曲率对溶解行为影响较小,界面反应会大幅度降低溶解速率;本工作建立的η,T和S等第二相溶解动力学模型预测结果与实测结果吻合,能够为优化Al-Zn-Mg-Cu合金固溶工艺提供指导作用。     

The Temperature Dependence of the Coefficients of Thermal and Isothermal Slip of a Diatomic Gas with Rotational Degrees of Freedom

A model kinetic equation is suggested for diatomic gases with rotational degrees of freedom of molecules. The free parameters of the model are related to Eucken's partial factors. This model is used to solve the problem on the slip of a diatomic gas along a plane surface. The coefficients of thermal and isothermal slip are obtained in the form of functions dependent on the transport coefficients and the frequency of inelastic collisions of gas molecules and, as a consequence, on the temperature.     

Modelling and simulation of heavy gas dispersion on the basis of modifications in plume path theory

An analytical model for heavy gas dispersion based on the modifications in plume path theory has been developed. The model takes into account the variations in temperature, density, and specific heat during the movement of heavy gas plume.

The model has been tested for three hazardous gases — chlorine, natural gas and liquefied petroleum gas. The results have been compared with the recently generated experimental data as also with the outputs of other models. A good agreement is observed qualitatively as well as quantitatively.

A study has also been carried out to simulate the effect of the wind speed, density of the gas, and venting speed on dispersion. Based on the simulation study a set of empirical equations has been developed. The equations are validated by theoretical as well as experimental studies.     

Thermomechanical analysis of multilayered plates in terms of Reddy-type higher-order theory

A Reddy-type higher-order plate theory considering transverse normal thermal strain (HPTC) has been presented for thermomechanical analysis of multilayered plates. Displacement variables in model HPTC have not increased although transverse normal deformation is considered. Based on the proposed model, analytical solutions of simply-supported plates under thermal and mechanical combined loads are presented. Analyzing thermomechanical behaviors of composite plates, effects of number of layers, transverse normal strain and thermal expansion coefficients on displacements, and stresses of composite plates have been studied. Numerical results showed that transverse normal strain and thermal expansion coefficients have a significant impact on behaviors of composite plates.     

二元系纳米多层薄膜非线性互扩散研究

采用非均匀体系非线性动力学离散模型计算AB二元系纳米多层薄膜的非线性互扩散,研究了A、B原子间作用力之差VBB-VAA和有序能V对纳米多层薄膜浓度分布和界面结构的影响.对于V≤0的纳米多层薄膜,随着VSS-VAA由0减小到-0.05eV,扩散过程中多层薄膜浓度偏离对称分布,界面由宽化向平直转变,有序能V由0减小到-0.025eV,导致多层薄膜的扩散速度加快.当V>0时,扩散过程中多层薄膜出现相分离趋势导致的上坡扩散,初始宽化互混的界面变得平直,且随着VBB-VAA由0减小到-0.05V,多层薄膜扩散过程中形成的浓度起伏长大成为新的亚层.AB二元系纳米多层薄膜扩散过程中的浓度分布和界面结构演变与扩散非对称性系数m'、有序能V和初始时刻的浓度梯度有关.     

Transport properties of Freon-152a and Freon-142b in the temperature range of 280–510 K

The thermal conductivity of 1,1 difluoroethane (Freon-152a) and 1 chloro-1 difluoroethane (Freon-142b) are measured at several pressures in the range 29.7–75.8 kPa and as a function of temperature in the range 280–510 K. The thermal conductivity column instrument is employed, and the experimental values are estimated to be accurate within a maximum uncertainty of ±5.6% at the lowest temperature, which reduces to ±2.4% at the highest temperature. These conductivity values are compared with the predictions of Chapman-Enskog kinetic theory, with the correction factor for the internal energy transport estimated from Hirschfelder's theory, and the Lennard-Jones (12-6) potential. The experimental conductivity data are also utilized to generate the values for the two other transport properties in conjunction with the interrelations obtained between different properties on the basis of kinetic theory. The data on transport properties are employed to give the best possible estimates of Prandtl and Schmidt numbers as a function of temperature.