Extension of the Neoclassical Theory of Capillarity to Advanced Cubic Equations of State

The neoclassical Redlich–Kwong (RK) theory of capillarity is extended to the Soave–Redlich–Kwong (SRK) and Peng–Robinson (PR) equations of state. Use of the SRK and PR fluid models results in poorer predictions of interfacial tension compared to the RK model because the RK overpredicts vapor densities to a greater extent than SRK or PR, reducing the corresponding RK interfacial tension predictions to be in better agreement with accepted values. The limits of the theory applied to cubic equations are reached by proposing modified SRK and PR fluid models based on a known interfacial tension datum and knowledge of the fluid molecular structure. These modified fluid models provide improved accuracy in interfacial tension predictions of 6% (SRK) and 10% (PR) for the fluid set in this study when compared to applying the RK model (17%). These modified fluid models also provide improved predictions of bulk liquid density, but sacrifice accuracy in pressure and vapor density predictions.     

A mesh-independent finite element formulation for modeling crack growth in saturated porous media based on an enriched-FEM technique

In this paper, the crack growth simulation is presented in saturated porous media using the extended finite element method. The mass balance equation of fluid phase and the momentum balance of bulk and fluid phases are employed to obtain the fully coupled set of equations in the framework of \(u{-}p\) formulation. The fluid flow within the fracture is modeled using the Darcy law, in which the fracture permeability is assumed according to the well-known cubic law. The spatial discritization is performed using the extended finite element method, the time domain discritization is performed based on the generalized Newmark scheme, and the non-linear system of equations is solved using the Newton–Raphson iterative procedure. In the context of the X-FEM, the discontinuity in the displacement field is modeled by enhancing the standard piecewise polynomial basis with the Heaviside and crack-tip asymptotic functions, and the discontinuity in the fluid flow normal to the fracture is modeled by enhancing the pressure approximation field with the modified level-set function, which is commonly used for weak discontinuities. Two alternative computational algorithms are employed to compute the interfacial forces due to fluid pressure exerted on the fracture faces based on a ‘partitioned solution algorithm’ and a ‘time-dependent constant pressure algorithm’ that are mostly applicable to impermeable media, and the results are compared with the coupling X-FEM model. Finally, several benchmark problems are solved numerically to illustrate the performance of the X-FEM method for hydraulic fracture propagation in saturated porous media.     

Classification and general derivation of interfacial forces, acting on phases, situated in the bulk, or at the interface of other phases

In the present paper the general equation and algorithm to derive interfacial forces, acting on phases, situated in the bulk, or at the interface of other phases are given. Based on that, interfacial forces are classified into the following six major types: (i) the “curvature induced interfacial force” (due to Laplace), (ii) the “interfacial gradient force”, acting on particles in inhomogeneous fluid phases, due to composition-, temperature- and electrical potential gradient (known as Marangoni force, or thermocapillary force), (iii) the “interfacial capillary force”, acting on a phase at an interface of two large phases, including the behaviour of solid particles at the liquid/gas, fluid/fluid and solid/solid interfaces (known as the capillary force, and as the Zener pinning force), (iv) the “interfacial meniscus force,” acting between two, solid phases, situated at a curved fluid/fluid or solid/solid interface, the curvature being due to the gravitational or electric fields (known also as the lateral capillary force, or electrodipping force), (v) the “liquid bridge induced interfacial force,” acting between two, solid particles, due to the liquid bridge of small volume between them, and (vi) the “interfacial adhesion force,” acting between two particles in a homogeneous fluid phase (with the phenomenological Derjaguin- and Hamaker constants, re-visited).     

Measurement of the surface tensions and the interfacial tensions of n-pentane-water and R 113-water systems

The surface and the interfacial tensions of mutually immiscible liquid systems were experimentally studied. The measured systems are n-pentane-water and R 113-water, which are proposed as heat transfer fluids for a direct-contact heat exchanger to be used for geothermal and waste heat recovery plants. The experimental apparatus was constructed based on the principle of the pendant drop method. Measurements were performed in the temperature range from 20 to 150°C. Based on the correlation of the surface and the interfacial tensions, the temperature dependences of the spreading coefficient, the film pressure, and the work of adhesion in each system were calculated.     

Vibrational Coupling and Kapitza Resistance at a Solid–Liquid Interface

The rapid development and application of nanotechnologies have promoted an increasing interest in research on heat transfer across the solid/liquid interface. In this study, molecular dynamics simulations are carried out to elucidate the effect of vibrational coupling between the solid and the liquid phases on the Kapitza thermal resistance. This is accomplished by altering the atomic mass and interatomic interaction strength in the solid phase (thus, the vibrational properties), while keeping the solid–liquid interfacial interaction unchanged. In this way, the Kapitza resistance can be altered with a constant work of adhesion between the solid and the liquid phases. The simulation results show that the overlap degree between the vibrational density of states profiles of the interfacial liquid layer and the outermost solid layer, which measures the degree of interfacial vibrational coupling, increases with larger atomic mass and weaker inter-atomic interaction in the solid phase. An inverse relation exists between the Kapitza resistance and the overlap degree of the vibrational density of states profiles. It means that the Kapitza resistance decreases with better interfacial vibrational coupling. The simulations show that the Kapitza resistance is not only affected by the interfacial bonding strength but also the vibrational coupling between the solid and the liquid atoms. The interfaces with better thermal transport efficiency should be the ones with stronger interfacial interaction and preferable vibrational coupling between solid and liquid phases.     

Comparison of a mixture formulation with a similarity solution for binary alloy solidification

Motivated by a principal interest in the continuous casting of alloys, an application of a mixture theory has been proposed for examining problems involving solidification of a multicomponent system. The formulation provides a basis for studying the solidification of a binary alloy in which the two phases may be present in arbitrary amounts. Balance laws for mass, momentum and energy for each phase are written which account for interactions between the mixture components. The present work describes methods for modeling the rate of growth of solid in terms of a mass exchange: incorporates drag, buoyancy and interfacial pressure forces in the momentum exchange: and includes the latent heat and dissipation in the energy exchange. For unidirectional solidification under equilibrium cooling conditions, the thermal field is resolved and compared with a classical similarity solution.     

凝固时的扩散效应

具有明确边界条件的多组元体系在凝固时, 溶液内的热量和质量输运方程的严格求解非常困难, 因此简化方程是十分必要的. 本文在普适流体力学方程的基础上, 采用表征流体特征的无量纲参数和适当的边界条件, 简化了扩散方程. 证实了简化后的质量扩散模型在凝固现象中的物理有效性. 指出由扩散引起的整体流的实质是微对流, 它环绕着固液界面流动, 并限制在质量边界层内, 即固液界面溶液一侧溶质浓度有显著变化的区域内. 我们的氧化物晶体生长实验结果已经证实了上述结论的正确性. 为了强调质量流的物理概念, 讨论采用了二维双组元模型.     

Zum Einfluss von in Flüssigkeiten unter Druck gelösten Gasen auf Grenzflächenspannungen und Benetzungseigenschaften

Measurements of interfacial tensions of water and ethanol in dense carbon dioxide up to 10 MPa and 373 K were performed. Also, in order to predict the wettability of these liquids on teflon and glass surfaces in the presence of carbon dioxide, contact angles between these liquids and both surfaces were determined under the same conditions of pressure and temperature. The interfacial tension were measured according to the pendant drop method. A mathematical derivation for the evaluation of the interfacial tension according to the geometry of the pendant drop and the difference of the density between the phases is presented. The contact angle determinations were performed using both the static and the dynamic method. The results show that because of the solubility of carbon dioxide in the liquids, the measured interfacial tensions are much lower than the interfacial tension of the pure substances. The interfacial tension appears as a function of only the density of CO₂ above its critical temperature [1]. Even though the solubility of carbon dioxide in the liquid phase affects the interfacial tension, such a clear relation between these variables, like the one between the interfacial tension and the density of carbon dioxide, cannot be observed. The excess concentration on the interphase, as a measurement of adsorption according to Gibbs, was calculated for both systems. The contact angle of water on teflon surface increases with pressure until total non wetting is reached. On the other hand, the contact angle of ethanol decreases with the increasing pressure until spreading occurs. The same phenomena was noted for the wetting characteristic of water on glass surface. The contact angle of water increases as pressure increases. Ethanol spreads totally on the surface of glass at all evaluated pressures. With the dynamic method, contact anglesgreater than the ones obtained with the static method were measured.     

3D CFD-PBM modeling of the gas–solid flow field in a polydisperse polymerization FBR: The effect of drag model

This work investigated a coupled computational fluid dynamics and population balance modeling (CFD-PBM) approach to predict the hydrodynamic behavior of the complex gas–solid two-phase flow in a three-dimensional (3-D) polydisperse propylene polymerization fluidized bed reactors (FBRs). Four different drag models, namely Syamlal–O’Brien, Gidaspow, McKeen and EMMS, were incorporated into the CFD-PBM model for evaluating the different effect of drag force between the gas and solid phases. Simulation results revealed a significant effect of the drag model on gas–solid flow in polydisperse polymerization FBRs. It was found that (1) compared to Syamlal–O’Brien and Gidaspow drag models, McKeen and EMMS drag models could predict a lower bed height, a higher temperature and an obvious core-annulus structure in polymerization FBRs; (2) EMMS drag model outperforms the other three drag models with respect to pressure drop prediction; and (3) the drag coefficient had little influence on the evolution of Sauter number and particle-size distribution.     

Intermittent Fasting Primes the Tumor Microenvironment and Improves Nanomedicine Delivery in Hepatocellular Carcinoma

Fasting has many health benefits, including reduced chemotherapy toxicity and improved efficacy. It is unclear how fasting affects the tumor microenvironment (TME) and tumor-targeted drug delivery. Here the effects of intermittent (IF) and short-term (STF) fasting are investigated on tumor growth, TME composition, and liposome delivery in allogeneic hepatocellular carcinoma (HCC) mouse models. To this end, mice are inoculated either subcutaneously or intrahepatically with Hep-55.1C cells and subjected to IF for 24 d or to STF for 1 d. IF but not STF significantly slows down tumor growth. IF increases tumor vascularization and decreases collagen density, resulting in improved liposome delivery. In vitro, fasting furthermore promotes the tumor cell uptake of liposomes. These results demonstrate that IF shapes the TME in HCC towards enhanced drug delivery. Finally, when combining IF with liposomal doxorubicin treatment, the antitumor efficacy of nanochemotherapy is found to be increased, while systemic side effects are reduced. Altogether, these findings exemplify that the beneficial effects of fasting on anticancer therapy outcomes go beyond modulating metabolism at the molecular level.     

Intermetallic growth study on SnAgCu/Cu solder joint interface during thermal aging

The intermetallic compound (IMC) growth behavior at SnAgCu/Cu solder joint interface under different thermal aging conditions was investigated, in order to develop a framework for correlating IMC layer growth behavior between isothermal and thermomechanical cycling (TMC) effects. Based upon an analysis of displacements for actual flip-chip solder joint during temperature cycling, a special bimetallic loading frame with single joint-shear sample as well as TMC tests were designed and used to research the interfacial IMC growth behavior in SnAgCu/Cu solder joint, with a focus on the influence of stress–strain cycling on the growth kinetics. An equivalent model for IMC growth was derived to describe the interfacial Cu-Sn IMC growth behavior subjected to TMC aging as well as isothermal aging based on the proposed “equivalent aging time” and “effective aging time”. Isothermal aging, thermal cycling (TC) and TMC tests were conducted for parameter determination of the IMC growth model as well as the growth kinetic analysis. The SnAgCu/Cu solder joints were isothermally aged at 125, 150 and 175 °C, while the TC and TMC tests were performed within the temperature range from ?40 to 125 °C. The statistical results of IMC layer thickness showed that the IMC growth for TMC was accelerated compared to that of isothermal aging based on the same “effective aging time”. The IMC growth model proposed here is fit for predicting the IMC layer thickness for SnAgCu/Cu solder joint after any isothermal aging time or thermomechanical cycles. In addition, the results of microstructure evolution observation of SnAgCu/Cu solder joint subjected to TMC revealed that the interfacial zone was the weak link of the solder joint, and the interfacial IMC growth had important influence on the thermomechanical fatigue fracture of the solder joint.     

Effect of a hard coat layer on buckle delamination of thin ITO layers on a compliant elasto-plastic substrate: An experimental–numerical approach

Layer buckling and delamination is a common interfacial failure phenomenon in thin film multi-layer structures that are used in flexible display applications. Typically, the substrate is coated on both sides with a hybrid coating, called a hard coat (HC), which acts as a gas barrier and also increases the scratch resistance. In this paper 250 nm thick indium tin oxide (ITO) layers have been deposited on a 200 μm thick high temperature aromatic polyester substrate (Arylite^TM), with and without a 3 μm HC. In order to study the influence of this HC layer on delamination phenomena, two-point bending experiments are performed from which buckle width and height values are measured after straightening of the sample. An analytical model and a finite element (FE) model are developed to estimate the adhesion properties from the measured buckle geometries. In the numerical model, the initiation and propagation of the delamination process is described by cohesive zone elements, of which the parameters are extracted from response surface model (RSM) results. Furthermore, the numerical model is used to illustrate the significant change in buckle geometry upon load reversal, i.e. from loaded to straightened state, which is governed by the elasto-plastic behavior of the substrate material. It is concluded that the addition of a HC layer significantly decreases the adhesion of the ITO layer. The latter is determined as function of the actual mode angle.     

Study on interfacial adhesion strength of single glass fibre/polypropylene model composites by altering the nature of the surface of sized glass fibres

Polypropylene (PP) compatibly sized glass fibres (GFs) were treated with boiling water and toluene, respectively, to reveal the interactions of water and toluene with different components in the sizing of sized GF and their influences on the interfacial adhesion strength of GF/PP model composites. Compared to control GF/PP model composites, about 30% increase of interfacial adhesion strength was achieved for composites with water-treated GF, whereas a small decrease of interfacial adhesion strength was revealed for composites with toluene-treated GF. X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Zeta-potential measurement, and water contact angle measurement demonstrated that the boiling water-treated GFs posses a more polar and hydrophilic surface with homogeneously distributed derivatives of 3-aminopropyltriethoxysilane, which is related to a higher interfacial adhesion strength for water-treated GF/PP model composites. In contrast, hot toluene-treated GFs led to a more hydrophobic surface with low molar mass PP and surfactants enriching on the outermost surface.     

钛合金化学镀镍层结合力影响因素探讨

钛合金化学镀镍层结合力的大小直接影响到镀件的使用寿命,镀层的结合力受到众多因素的影响.主要研究了浸蚀活化、预镀镍及镀镍后热处理对钛合金TC4与化学镀镍层结合力的影响.结果表明:HF和HCl的比例是影响钛合金表面活化的重要因素,采用26 mL/L HF,58 mL/L HCl活化可以获得新鲜的钛合金表面;浸蚀活化后预镀镍再化学镀镍,可得到结合力良好的镀层;镀层经300℃热处理1 h后与基体的结合力显著提高.     

How can adhesion be determined from micromechanical tests?

The concept of adhesional pressure was proposed to characterise the interfacial bond strength in fibre–matrix systems. The adhesional pressure is the interfacial normal stress produced by the molecular interaction between the fibre surface and the matrix. Using the variational mechanics approach, we calculated the critical normal stress, at which debonding starts in the pull-out and microbond tests. This critical value can be used as a failure criterion. The relationship between “fundamental” (W_A) and “practical” (adhesional pressure) adhesion was investigated. The adhesional pressure appeared to linearly depend on the work of adhesion from the IGC data. This allows to estimate W_A from destructive micromechanical tests. An important advantage of the proposed approach is that it can characterise adhesion for real conditions of the composite formation, including irreversible adhesion.     

表面预处理对钛合金表面低温等离子体氮化的影响

为提高TC4钛合金表面摩擦学性能,探究酸洗及等离子体预处理对TC4钛合金表面低温等离子体氮化进程的影响.首先采用热丝增强等离子体氮化系统分别对表面酸洗及未酸洗TC4钛合金在氩气气氛下进行等离子体预处理,然后对各种表面预处理的TC4钛合金实施低温(500℃)等离子体氮化.采用扫描电子显微镜、能谱仪及X射线衍射仪分别分析了...     

A proposed combination model for predicting surface tension and surface properties of binary refrigerant mixtures

A combination model is proposed to describe the surface tension and surface properties of binary refrigerant mixtures combining the Laaksonen and Kulmala equation with the phase equilibrium between the bulk liquid and surface phases to predict the surface tension, surface composition and surface mole density of the binary refrigerant mixtures. Also, the present model is combined with the volume-translated Peng–Robinson (VTPR) equation of state to describe the fugacity coefficients of the components and molar volumes of the bulk and surface phases. This proposed combination model is subsequently applied for 13 binary refrigerant mixtures and compared with the gradient theory. The results of this model show that the surface tensions predicted by this model agree well with experimental data for these mixtures (overall AAD ∼4.35). Compared with the gradient theory (overall AAD ∼5.67 and 3.94 for density and temperature dependant influence parameter), the proposed combination model performs well.     

Numerical study of gas–solid drag models in a bubbling fluidized bed

Bubbling fluidized beds find application mainly in power conversion industries. For design, dimensioning, and operation of fluidized bed equipment, the understanding of multiphase gas–solid flows is of great importance. The use of computational fluid dynamics in the simulation of gas–solid systems is limited by the complexity of mathematical models, which rely on a series of empirical or theoretical correlations. In the present work, the code Multiphase Flow with Interphase eXchanges (MFIX) was employed to simulate flows in a bubbling fluidized bed and to compare results predicted using different gas–solid drag models. A two-fluid model with kinetic theory of granular flows (TFM-KTGF) was employed, in which gas–solid drag correlations, such as Gidaspow, Hill-Koch-Ladd, or Syamlal and O’Brien, were applied to model momentum transfer between phases. The results predicted were compared with each other and with experimental results from the literature. It was found that the results predicted using each model differ much. The Gidaspow and Hill-Koch-Ladd models yielded bubbles with shapes more similar to the experiments.     

轮轨油污染黏着特性的研究

运用数值算法研究了轮轨在油污染时的黏着特性。以部分弹流理论为基础借助于多重网格作为数值计算工具建立了二维轮轨在油污染状态下考虑表面粗糙度的轮轨黏着计算模型。研究了在有油污染情况下轮轨间接触压力分布以及列车运行速度和接触压力对轮轨黏着系数的影响。给出了轮轨介质接触时的固体承载及液体动压分布。计算结果表明:随着速度的提高,黏着系数逐渐降低,最后基本上趋于稳定;随着接触压力的增大,黏着系数逐渐增大。