Correlation and Prediction of Dense Fluid Transport Coefficients. IX. Ionic Liquids

The aim of this paper is to examine the application of a hard-sphere scheme to the correlation and prediction of the viscosity and thermal conductivity of ionic liquids. Ionic liquids present an excellent case, because of their high viscosity. It was found that, regardless of the fact that the scheme had to be extended by orders of magnitude, it was still an excellent scheme for the correlation and prediction of the properties of these liquids; this fact is attributed to its theoretical basis. A database of 461 viscosity and 170 thermal-conductivity measurements for 19 ionic liquids was considered. The average absolute deviation was 2.31 % for the viscosity and 3.15 % for the thermal conductivity, while the expanded uncertainty at the 95 % confidence level was 4.6 % and 6.3 %, respectively. Moreover, if the thermal-conductivity roughness factor is allowed to be temperature dependent, then the average absolute deviation was reduced to 0.91 % for the thermal conductivity, and the expanded uncertainty at the 95 % confidence level to 1.82 %. As the scheme requires knowledge of the density, 1070 measurements of density were employed to derive a Tait-type equation for every ionic liquid considered.     

Correlation and Prediction of Dense Fluid Transport Coefficients. VIII. Mixtures of Alkyl Benzenes with Other Hydrocarbons

The aim of this article is to examine the application of the hard-sphere scheme to the prediction of the viscosity and thermal conductivity of hydrocarbon mixtures, other than n-alkane mixtures. According to this scheme, mixture properties are calculated from the pure components properties. Hence these are obtained first. Furthermore, in addition to the temperature, the density is the important parameter rather then the pressure. A Tait-type equation is employed to successfully correlate the density of the pure liquids. Furthermore, in the first part of this article, a modified form of the equation proposed by Sun and Teja is employed in the scheme, to correlate the viscosity and thermal conductivity of pure alkyl benzenes, some alkanes, some cycloalkanes, and one naphthalene. Following this, the article focuses on the successful prediction of the viscosity and thermal conductivity of mixtures of these compounds.     

Ab Initio Transport Coefficients of Gaseous Hydrogen

The spherical version of the hydrogen intermolecular potential ${\phi_{\rm P}}$ recently determined in ab initio calculations by Patkowski et al. was used to calculate the viscosity and thermal conductivity of hydrogen using a full quantum-mechanical formalism. Viscosities in the temperature range 203 K to 394 K were compared with recent high-accuracy (uncertainty of 0.084 %) measurements of May et al. The measured viscosities all fall in a range between 0.02 % and 0.06 % below the calculated viscosities. This close agreement supports the accuracy of ${\phi_{\rm P}}$ . Classical calculations of the viscosity with ${\phi_{\rm P}}$ fall in a range between 0.4 % and 1.3 % below the experimental values. In the lower temperature range 20 K to 300 K, other measurements typically lie above the theoretical values by a few percent. Above 400 K, measurements fall below the theoretical values by a fraction that increases with temperature, reaching ?4% at 2000 K. For normal hydrogen, the average fractional difference between the calculated thermal conductivity in the temperature range 21 K to 384 K and measurements reported in six publications is (0.1 ± 1.1) %. For para-hydrogen in the temperature range 20 K to 275 K, the average fractional difference between calculations and measurements reported in three publications is (?0.7 ± 1.2) %. At higher temperatures (600 K to 2000 K), measurements range between 4 % and 10 % below the calculated values.     

Transport Coefficients of Eucalyptol through Various Polymeric Films

This study presents the determination of the transport properties of eucalyptol, which is a key aroma compound in fresh tropical herbs through different polymeric packaging materials. Packaging films used in this study were polyethylene, polypropylene, Nylon, polyethylene terephthalate and polylactide (PLA1 and PLA2). Test films were immersed in the 1000 ppm of aroma compound and stored in amber vials. The concentrations of aroma compounds extracted from films were determined using gas chromatography. Diffusion, solubility, permeability and partition coefficients were calculated from sorption kinetics. Results show that the diffusion and solubility coefficients of eucalyptol were lowest in PLA1 and highest in polyethylene. Solubility coefficients were associated with partition coefficients as well as solubility parameters and contact angle values. Primary factor determining solubility was affinity between the aroma compounds and the polymeric films. Transport coefficients of eucalyptol in the vapor phase followed the same trends as in the liquid phase with about 3‐fold greater. Understanding interaction phenomenon between the key aroma compound and major packaging films may contribute to improvements in film selection and the design of food packaging applications. Finding from this research contributes toward future development of the high‐aroma barrier materials. Copyright © 2011 John Wiley & Sons, Ltd.     

GaN基异质外延生长的ZnO单晶电输运特性研究

报道了一种新方法生长的ZnO单晶的电输运特性,利用该方法在GaN外延膜表面生长了尺寸为25 mm×25 mm,平均厚度7 mm的ZnO单晶块。通过研究ZnO单晶不同深度处的电输运特性,判断了ZnO单晶内部不同位置的结晶质量。以GaN表面为起始面,沿[0002]方向,随着距GaN表面距离的增加,常温下的ZnO单晶载流子浓度从1.28×10¹⁹降到4.00×10¹⁷ cm^-3,载流子迁移率从64.9升至144 cm²/(V·s),电阻率从7.53×10^-3升至1.09×10^-1Ω·cm。位错密度计算结果表明,随着远离GaN衬底,晶体内位错密度逐渐减少,二次离子质谱测试结果中,Ga⁺等杂质含量随着远离GaN衬底逐渐减少,在距离GaN表面约4 mm以后,主要杂质含量明显降低。由此表明,采用价格相对较低的GaN衬底可以获得较大尺寸,品质较好的ZnO单晶。     

New Initiatives on Comparison of Whole-field Experimental and Numerical Results

Abstract: A simple approach to plot photoelastic fringes in grey scale and also in colour from finite element (FE) results is presented for better recognition and comparison with experiments. This requires proper identification of the plotting variable from FE results. For comparison with transmission photoelasticity, post-processing of principal stress difference is needed and for reflection photoelasticity the principal strain difference is to be used. The importance of the use of appropriate correction factors for comparison with reflection photoelastic results is emphasised. A newer approach to evaluate R _f for complicated geometries is indicated. Plotting of experimental fringes from finite elements is useful not only for validating the numerical model based on experiments but also for validating the experiments. To illustrate this, the problem of an interfacial crack in a bi-material Brazilian disc is discussed.     

Theoretical Calculation of the Low-Density Transport Properties of Monatomic Silver Vapor

Calculations of low-density transport property collision integrals are used to obtain the high-temperature transport properties of silver atoms as a function of temperature. The collision integrals depend on the two-body interaction potentials between silver atoms in various electronic states. Contributions are included from the ground and excited molecular electronic states of the silver dimer that dissociate to two ground-state silver atoms and from the excited molecular state that dissociates to a ground state and an excited state silver atom. Spectroscopic constants are available for these three electronic states, and these spectroscopic constants have been used to determine the Hulburt–Hirschfelder (HH) potentials for these three states. The HH potential is perhaps the best general-purpose potential for representing atom–atom interactions. This potential depends only on the spectroscopic constants, and can be used to calculate the viscosity and diffusion collision integrals for the three molecular electronic states. The collision integrals are then degeneracy averaged over the three states. The heat capacity of silver atoms is also calculated at high temperatures. These results provide the information required to obtain the thermal conductivity, viscosity, and self-diffusion coefficients of silver atoms over a wide temperature range from the boiling point of silver to temperatures at which ionization becomes important.     

Prediction of the Vapor Pressure of Environmentally Acceptable Halocarbons1

The vapor pressure and its dependence on temperature of halocarbons for 0.002< p _R<1 have been analyzed in terms of universal behavior. Results for CFC-114, HCFC-123, HCFC-141b, HCFC-142b, HCFC-143a, HFC-23, HFC-32, HFC-134, HFC-125, HFC-134a, and HFC-152a for reduced temperatures between 0.55 and 1.0 show that the reduced vapor pressure can be expressed as a function of 1–T _R by a Padé approximant. Deviations of the correlated data from the universal function do not amount to more than ±0.06 MPa, with an average deviation of 0.025 MPa. Predictions of the saturation vapor pressures of HCFC-124, HCFC-225ca, and HCFC-225cb, which are the systems used to test the capability of this scheme, agree within 0.025 MPa, that is, within the accuracy of the corresponding states correlation. However, for HFC-236ea, the deviations are as large as –0.07 MPa. The present scheme can be used to calculate the Pitzer acentric factor, and an average value of =0.269±0.015 is obtained for all the fluids.     

混合制冷剂饱和气体密度的推算

在对比态原则下,作者发现混合工质饱和气体密度与其纯组分饱和气体密度的无量纲对比关系有同一化规律;同时,还寻找到利用纯组分的临界点密度与临界压力拟合混合工质临界点密度与临界压力的关系式,确立了混合工质的这两个特征参数。进而给出了计算混合制冷剂饱和气体密度的通用方程,该方程是隐式的。比较了文献中5种二元和三元混合工质的推算值与文献值,误差基本在±2%内。     

Simultaneously Estimating the Time-Dependent Damping and Stiffness Coefficients with the Aid of Vibrational Data

For the inverse vibration problem a mathematical method is required to determine unknown parameters from the measurement of vibration data. When both damping and stiffness functions are identified, it is a rather difficult problem. In this paper we will propose a feasible method to simultaneously estimate both the time-dependent damping and stiffness coefficients through three mathematical transformations. First, the second-order equation of motion is transformed into a self-adjoint first-order system by using the concept of integrating factor. Then, we transform these two ODEs into two hyperbolic type PDEs. Finally, we apply a one-step group preserving scheme for the semi-discretizations of PDEs to obtain two uncoupled algebraic equations, of which the first one is used to estimate the damping coefficient while the second one is used to estimate the stiffness coefficient. The estimated results are acceptable for that used in vibrational engineering. We also discuss the use of velocity and acceleration data as inputs in the estimation. However, it leads to a bad result, and is not suggested for the use in estimation.     

Comparison of Interval Analysis and Standard Statistical Methods for Estimating Experimental Data with Uncertainty

Measurement Techniques - Interval analysis procedures are used to estimate the parameters of an experimental chemical process under conditions of noise and uncertainty in the probabilistic...     

蒸发冷却式热管与蒸气压缩复合数据中心空调系统性能实验研究

为解决传统数据中心空调系统能耗高和冷却效率低等问题,本文提出了带有蒸发式冷凝器的制冷剂泵驱动热管与蒸气压缩复合数据中心空调系统,实验分析了不同室外温度与冷凝器风速下系统的运行性能.结果表明:在热管模式下,当室外温度低于0℃时,降低冷凝器风速能够提升系统COP;当室外温度高于0℃时,增大室外机风速能够提高系统节能性.降低...     

Ideal Gas Thermodynamic Properties of Propyl tert-Butyl Ethers from Density Functional Theory Results Combined with Experimental Data

Ideal gas thermodynamic properties, S°(T), C _p°(, T), H°(T)–H°(0), _f H°(T), and _f G°(T), are obtained on the basis of density functional B3LYP/6-31G(d,p) and B3LYP/6-311 + G(3df,2p) calculations for two propyl tert-butyl ethers. All torsional motions about C–C and C–O bonds were treated as hindered internal rotations using the independent-rotor model. An empirical approximation was assumed to account for the effect of the coupling of rotor potentials. The correction for rotor–rotor coupling was found by fitting to entropy values determined from calorimetric measurements. Enthalpies of formation were calculated using isodesmic reactions.     

化学气相运输法制备正交黑磷

黑磷(Black phosphorus, BP)以其优异而独特的物理化学性质在能源储存与转换、微纳器件、光/电催化和生物医药等领域展现出良好的应用前景。高质量正交BP前体制备是实现二维BP和零维BP量子点应用的关键。本工作采用无温度梯度的化学气相运输(CVT)法研究了矿化剂组分和比例对BP生长的影响。结果表明, 只有锡(或铅)和碘共存且比例合适时才能制备得到正交BP; 生长BP所需的锡碘质量比w(Sn/I₂)范围较宽, 当w(Sn/I₂)=0.47时制得的BP尺寸为1.2 cm, 且产率高、晶体质量较优。结合BP的成核生长机理可知, 锡和碘都对BP的成核生长具有重要作用; 碘的矿化效果较锡明显, 而足量的锡有利于无温度梯度条件下大尺寸块体BP晶体的合成。w(Sn/I₂)=0.47为本工作中制备BP的最佳砂化剂配比。     

The Transport Properties of Sodium Atoms and the Heat Capacity of Sodium Dimers at High Temperatures

Including the contribution of excited state atoms can improve calculations of dilute gaseous transport properties at high temperatures. For sodium, experimental and/or theoretical information is available about the potential energy curves associated with each of ten low-lying states of the sodium dimer. These include the ${{\rm X}^{1}\Sigma_{\rm g}{}^{+}}$ and ${^{3}\Sigma_{\rm u}{}{}^{+}}$ states that dissociate to two ground state ²S sodium atoms and the four ${^{3}\Sigma_{\rm g,u}{}^{+},\,^{1}\Sigma _{\rm g,u}{}^{+},\,^{1}\Pi _{\rm g,u},\,^{3}\Pi _{\rm g,u}}$ gerade/ungerade pairs of states that dissociate to a ground state ²S atom and an excited state ²P atom. Nine of these are bound states and have been fitted with the Hulburt–Hirschfelder potential, a very good general purpose atom–atom potential. The ³Π_g state is not bound and has been fitted with the exponential repulsive potential. We have used these potentials to calculate viscosity collision integrals as a function of temperature, and employed degeneracy-weighted averaging to determine the viscosity and translational contribution to the thermal conductivity of the sodium atoms. These same potentials have been used to calculate the heat capacity, ${C_{p}^{\rm o}}$ , of the sodium dimer using an approach that depends on the second virial coefficient and its first two temperature derivatives. Again, the inclusion of molecular states that dissociate to an excited state atom allows ${C_{p}^{\rm o}}$ to be determined with improved accuracy at higher temperatures. Thus, thermophysical property calculations for sodium have been extended to 25,000 K. These results are compared with previous results, including heat capacities given in the NIST-JANAF Thermochemical Tables.     

Determination of Thin-film Absorption Coefficients from Photoacoustic Data

Abstract

A photoacoustic measurement technique is described to obtain absorption coefficients of PbF₂ layers. Different deposition conditions have been investigated and the evaporation parameters producing the least absorption are given.