THE MAXWELL-STEFAN FORMULATION OF IRREVERSIBLE THERMODYNAMICS FOR SIMULTANEOUS HEAT AND MASS TRANSFER

We consider constitutive relations for diffusion and simultaneous heat conduction in an n-coraponent non-ideal fluid mixture. Using the ideal gas treatment of Hirschfelder, Curtiss and Bird as a basis, we develop the generalization of the Maxwell-Stefan diffusion equations. The application of the second law of thermodynamics is shown to impose non-negativity constraints on the defined diffusion coefficients, D _ik The practicalusefulness of the Generalized Maxwell-Stefan formulation is demonstrated by a few examples.     

THE MAXWELL-STEFAN FORMULATION OF IRREVERSIBLE THERMODYNAMICS FOR SIMULTANEOUS HEAT AND MASS TRANSFER

We consider constitutive relations for diffusion and simultaneous heat conduction in an n-coraponent non-ideal fluid mixture. Using the ideal gas treatment of Hirschfelder, Curtiss and Bird as a basis, we develop the generalization of the Maxwell-Stefan diffusion equations. The application of the second law of thermodynamics is shown to impose non-negativity constraints on the defined diffusion coefficients, D_ik The practicalusefulness of the Generalized Maxwell-Stefan formulation is demonstrated by a few examples.     

THERMODYNAMICS OF SOLVENT EXTRACTION

ABSTRACT

The fundamental thermodynamic characteristics of aqueous electrolyte solutions and organic solutions which affect solvent extraction are summarized and the influence of metal complexation and hydration on the distribution ratios is discussed. The thermodynamics of extraction systems, including synergistic systems, is reviewed. The influence of structural aspects of the complexing extractant agents on these thermodynamic parameters is also reviewed.     

THERMODYNAMICS OF THE WATER-FOODSTUFF EQUILIBRIUM

The thermodynamic analysis of the water-foodstuff equilibrium is reviewed, showing how partial molar and integral enthalpies and entropies can be obtained and indicating how to manipulate the experimental data for this purpose. The need for accurate and precise data is stressed and one experimental approach is recommended. Experimental results of desorption of water from Granny Smith apples provide information which is consistent from the thermodynamical standpoint. It is noted that the value of monolayer thickness corresponding to a minimum in integral entropy is substantially different from the value predicted by the BET equation.     

THERMODYNAMICS OF CONCENTRATED ELECTROLYTE SOLUTIONS

A new equation is derived for the activity coefficient of an electrolyte in a liquid solvent (such as water) as a function of electrolyte concentration. This equation contains contributions from long-range electrostatic forces and from short-range attractive forces; it holds from high dilution to the solubility limit. The new equation is based upon extended Debye-Huckel theory for long-range effects and upon the local-composition concept for short-range effects. For a single-electrolyte solution, the new equation contains only one adjustable energy parameter and three other parameters that are ion-specific, not electrolyte-specific. Therefore, extension to multicomponent electrolyte solutions follows without additional assumptions. Ion-specific parameters are reported for H⁺, K⁺, Li^-, Br^- and Cl^- ions. Calculated and experimental activity coefficients are in excellent agreement for aqueous solutions of HBr, HC1, KBr, KCl, LiBr and LiCl.     

THERMODYNAMICS OF THE WATER-FOODSTUFF EQUILIBRIUM

The thermodynamic analysis of the water-foodstuff equilibrium is reviewed, showing how partial molar and integral enthalpies and entropies can be obtained and indicating how to manipulate the experimental data for this purpose. The need for accurate and precise data is stressed and one experimental approach is recommended. Experimental results of desorption of water from Granny Smith apples provide information which is consistent from the thermodynamical standpoint. It is noted that the value of monolayer thickness corresponding to a minimum in integral entropy is substantially different from the value predicted by the BET equation.     

THE IRREVERSIBLE ADSORPTION OF PLUTONIUM HEXAFLUORIDE†

The room temperature adsorption of PuF_6(g) on a solid substrate was compared to the adsorption of UF6(g) on the same surface. Significantly more PuF_6(g) was adsorbed at pressures in the range of 1.2 to 0.2torr, accompanied by the evolution of molecular fluorine. The adsorbed UF₆ was easily desorbed by reducing the pressure. Most of the adsorbed PuF₆ remained on the surface when subjected to the same treatment.     

THERMODYNAMICS OF ALKANOLAMINE+WATER SYSTEM

Design of gas treating processes requires knowledge of the vapor-liquid equilibrium behavior of the (acid gas + aqueous alkanolamine) system. The present study is focused on thermodynamics and associated nonideal behavior of binary MEA + H₂O, DEA + H₂O, and MDEA + H₂O systems, which is required to predict the vapor-liquid equilibrium of acid gases such as CO₂ and H₂S over aqueous alkanolamine solutions. Determination of binary interaction parameters and analytical prediction of infinite dilution activity coefficient, heats of solution at infinite dilution, the excess Gibbs free energy, and excess enthalpy for nonideal alkanolamine-water systems are the objectives of this study.     

管翅式换热器的不可逆损失分析

以热力学第二定律为基础讨论了波纹翅片管换热器的不可逆损失,重点考察了换热器的几何尺寸对换热过程中不可逆损失的影响.[JP+2]不可逆损失用温差传热和流动摩阻所引起的熵产之和来表征.计算结果表明：换热器单位换热量的熵产随翅片波纹角的增加略有增加,但几乎不受翅片间隔的影响.当管的排数增加时,单位换热量的熵产先减后增,在特定管排数处取得极小值.单位换热量的熵产随空气流速的增加而单调增加.     

THERMODYNAMICS OF MOISTURE SORPTION IN ALFALFA PELLETS

Experimental data on sorption isotherms of alfalfa pellets were used to determine the thermodynamic functions (differential heat of sorption, spreading pressure, net integral enthalpy and entropy) of the pellets. The thermodynamic functions were then utilized in modeling the specific heats of pellets as a function of moisture content. The estimated values of the thermodynamic functions at different moisture contents confirmed the results of an earlier study on the influence of moisture sorption on the physical integrity of the pellets. The changes in the thermodynamic properties and physical integrity were prominent when the moisture of the pellets were between 0.10 and 0.12 (mass fraction basis). Using the differential heat of sorption, it was determined that alfalfa pellets have higher affinity for moisture uptake when compared to wheat and lentils. The specific heat of the solids of alfalfa pellets had a parabolic relationship with moisture whereas the specific heat of water fraction increased linearly with moisture content of the pellets.     

THERMODYNAMICS OF MOISTURE SORPTION IN ALFALFA PELLETS

ABSTRACT

Experimental data on sorption isotherms of alfalfa pellets were used to determine the thermodynamic functions (differential heat of sorption, spreading pressure, net integral enthalpy and entropy) of the pellets. The thermodynamic functions were then utilized in modeling the specific heats of pellets as a function of moisture content. The estimated values of the thermodynamic functions at different moisture contents confirmed the results of an earlier study on the influence of moisture sorption on the physical integrity of the pellets. The changes in the thermodynamic properties and physical integrity were prominent when the moisture of the pellets were between 0.10 and 0.12 (mass fraction basis). Using the differential heat of sorption, it was determined that alfalfa pellets have higher affinity for moisture uptake when compared to wheat and lentils. The specific heat of the solids of alfalfa pellets had a parabolic relationship with moisture whereas the specific heat of water fraction increased linearly with moisture content of the pellets.     

尿素工艺进展

论述了国外尿素生产中几种主要工艺技术的最新进展;介绍了国外公司新技术和新工艺的开发,应用及其意义;并对我国的尿素生产技术和装置改造提出了相应的建议。     

表面活性剂在液固界面吸附的热力学

对已有的表面活性剂液固界面吸附等温线进行了系统的分类,并提出了非均匀表面两阶段吸附模型．用此模型导出的吸附等温方程式能很好地描述各种类型的吸附等温线.     

SUBORDINATION OF STATIONARY PROCESSES

Abstract. Let X ={ X ( t ), t ε T ∁ R} be a ( L ₂ -) stationary process and suppose that N ={ N ( t ), t ≥ 0} is an infinitely divisible process, independent of X. Then ={ ( t ) = X ( N ( t )), t ≥ 0} is again a stationary process. In this paper, we relate the spectral properties of the original process X and the derived or subordinated process .     

温度载荷对复合材料热力学性能的影响

由于复合材料内部纤维与树脂的热膨胀系数差异很大,尤其是树脂性能对温度载荷较为敏感,服役时复合材料环境的高低温变化将使其热力学性能与常温状态产生较大差异。采用Maxwell本构模型,探讨了温度变化对树脂材料本构关系的影响。假设纤维为稳定材料,即其性能不随温度变化,依据复合材料细观力学理论选择六边形代表体积元为分析对象,建立了复合材料在温度载荷下热力学的本构模型。并分别讨论了温度载荷下复合材料内部纤维体分比和纤维排列方式变化对其热力学性能的影响,实现了热-力耦合作用下复合材料的跨尺度分析。     

双酚A-苯酚加合物热力学性质的研究

<正> 引言 双酚A是生产聚碳酸酯、环氧树脂的关键原料.双酚A-苯酚加合物晶体是双酚A生产过程中的重要中间产物,该加合物晶体是由双酚A和苯酚形成的等摩尔比的结晶化合物,其结构式如下:     

铌锌酸铅基陶瓷相变的热力学分析

ＰＺＮ基陶瓷在烧结过程中都要经历由焦绿石相朝钙钛矿相的转变。ＰＺＮ基陶瓷中钙钛矿相含量的多少与添加剂的种类及数量密切相关，本工作根据化学热力学理论，讨论了内应力对化学势的影响，建立了一个热力学模型，并用该模型讨论了ＰＺＮ基陶瓷在烧结时的相变过程。     

溴化锂第二类吸收式热泵热力过程的Yong分析

通过计算机模拟，对溴化锂第二类吸收式热泵热力过程和热泵系统各部件进行了详细计算，提出了循环倍数、工作液浓溶液浓度、蒸发温度、冷却温度对Yong效率的影响程度。指出了Yong损失的分布，计算了Yong损系数和Yong效率。     

EXERGY ANALYSIS OF DISTILLATION STAGES BY NON-EQUILIBRIUM THERMODYNAMICS

An exergy balance equation which relates to heat and mass transfer on distillation stages was derived from the theory of non-equilibrium thermodynamics. This equation was used to analyze an ethylene distillation column, and the result checked satisfactorily with that of equilibrium thermodynamic exergy analysis.In a multiphase discontinuous system, each phase may be considered as a subsystem, and all subsystems are separated by interfaces. With appropriate hypotheses, the equation of exergy loss relating to energy and mass transfer through interfaces may be expressed as follows:D=T_o[J_q·Δ(1/T)-sum from k to n J_k·Δ(μ_k/T)] Thus, profound insight into distillation process could be gained to provide ideas for further improvement of the distillation scheme.