Diffusion coefficient of H2, CH4, CO, O2 and CO2 in water near the critical point (600-670K, 250atm) is numerically investigated using Molecular Dynamics (MD) simulation. Main factors determining ...diffusion coefficient are discussed. Arrhenius behavior of temperature can be divided into two separate parts which are subcritical region and supercritical region. The activation energy has a huge difference between two regions. Diffusion coefficient has a negative power relation with density of water through logarithmic plot. Viscosity of water has effects on diffusion coefficient by a combination with temperature that term 1/Tη has a quadratic relation with diffusion coefficient. A new empirical equation to predict diffusion coefficient in water near the critical point is developed in which the effect of solute gas and solvent water is separated to the pre-factor A0 and the second part Fw. A0 is a unique constant for different solutes and Fw considers temperature, density and viscosity of water. It successfully predicts diffusion coefficient near the critical point for all solute gases and average absolute relative deviation is only 7.65%. Compared to other equations, our equation shows the best accuracy and simplicity for extension and modification.
•K&C model is systematically calibrated for generic UHPCs.•Calibrated K&C model is adopted in the numerical simulation of contact explosions on UHPC slabs to demonstrate its validity through a ...comparison to the test results.•Parametric studies are performed to establish a new empirical equation to predict the local damage mode of UHPC slabs under contact explosions.
Karagozian and Case (K&C) concrete model is extensively adopted in the numerical simulations of ultra-high performance concrete (UHPC) structural members subjected to impulsive loads such as impact and blast. In this study, a calibration of the K&C concrete model was conducted for UHPC in terms of three strength surfaces, equation of state, shear dilatancy, damage evolution and strain rate effect to offer simple and general guidelines on the determination of key model parameters for this new class of concrete. With the calibrated concrete model, a single element method was adopted to verify its accuracy through a comparison to the results from the static tests of the uniaxial compression, direct tension and triaxial compression. Furthermore, the numerical simulations of contact explosion tests on the UHPC slabs with the incorporation of the strain rate effect were performed and the numerical results exhibited good predictions regarding the failure mode, crater and scabbing damage as compared to the test results. More importantly, this proposed numerical model and simulation methodology are reasonable to be generally used for structural members constructed of UHPC materials under contact explosions when lacking sufficient static and dynamic test data. Using the calibrated and validated K&C concrete model, parametric studies were conducted to derive a new empirical equation for predicting the local damage mode of UHPC slabs under contact explosions.
•We measured data of 80 blasting operations in Bakhtiari Dam, Iran.•We proposed a SVM model for predicting PPV resulting from blasting.•Empirical equations were also employed to predict PPV.•A ...comparison was made to demonstrate capability of the proposed models.
Mines, quarries, and construction sites face blasting environmental problems due to high level of ground vibrations. This phenomena can cause injury to both human and damage to structures in the blasting environment. To estimate ground vibration, several empirical predictors have been established by various researchers, while these predictors are not commonly enforceable beyond the particular conditions. However, ground vibration prediction is a complicated issue in consequence of the fact that a large number of influential factors are involved. In this study, a support vector machine (SVM) was applied and developed to predict ground vibration in blasting operations of Bakhtiari Dam, Iran. To achieve this aim, 80 blasting works were investigated and results of peak particle velocity (PPV) as a vibration index, distance from the blast-face and maximum charge per delay were measured and monitored to utilize in the modeling. To demonstrate applicability of the SVM model for prediction of PPV, several empirical equations were also employed and the relevant site constants were proposed. In the analyses procedure of this study, 60 datasets were used for model development and remaining 20 datasets were applied to check the performance capacity of the developed model. After comparing the results obtained from SVM and empirical equations, it was found that the SVM method provides higher performance capacity in predicting PPV compared to empirical equations.
•C2OC2mimOAc and C2OC2mimLac were prepared and characterized.•The experimental values of ρ, γ, nD, η and k of samples were measured.•The surface tensions of C2OC2mimOAc and C2OC2mimLac were ...predicted.•The Ek and Eη values of samples were obtained by Arrhenius empirical equation.•The variation trend between η (or κ) and T of samples was investigated by VFT equation.
1-(2-Ethoxyethyl)-3-methylimidazolium acetic acid (C2OC2mimOAc) and 1-(2-ethoxyethyl)-3-methylimidazolium lactic acid (C2OC2mimLac) ether-functionalized ionic liquids (ILs) were prepared. In terms of the standard addition method, the experimental data of density, surface tension, refractive index, viscosity and electrical conductivity of two pure ILs were obtained. Using the definition of the molar surface Gibbs energy with Lorentz-Lorenz empirical equation, the surface tensions of ether-functionalized ILs were estimated, and their predicted values were in good agreement with the experimental values. According to the Vogel-Fulcher-Tamman (VFT) equation, the variation tendency between viscosity (or electrical conductivity) and temperature of C2OC2mimOAc and C2OC2mimLac was studied. The variation trend of the viscosity was opposite to electrical conductivity. Namely, the viscosity gradually decreased and electrical conductivity gradually increased with increasing temperature. The results indicated that VFT equation had an enormous application range for fitting the viscosity and electrical conductivity of ether-functionalized ILs. The activation energies of C2OC2mimOAc and C2OC2mimLac were estimated by Arrhenius empirical equation. The calculated results indicated that C2OC2mimLac (Eη means the activation energy, Eη = 41.24 kJ·mol−1) was larger than C2OC2mimOAc (Eη = 33.57 kJ·mol−1). This result may be related to physical size or stronger interactions.
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•Electrochemical active surface area is affected by humidity and temperature.•A fitting equation of electrochemical active surface area has been proposed.•The equation can be ...universally applied in different catalyst layer compositions.•Validations are completed on data measured in low humidity operations.•Including the equation in models helps predict more accurate cell performances.
The electrochemical active surface area has a vital influence on the performance of proton exchange membrane fuel cells. In this study, a universal semi-empirical equation of the electrochemical active surface area in the catalyst layer of fuel cells is proposed based on self-designed experiments, aiming to improve the predictive accuracy of numerical models under low humidity conditions. The generalization of this equation is also verified with the other nine catalyst layers of different compositions. At very low water content corresponding to low inlet humidification operations, the electrochemical active surface area is generally low and increases sharply with the increment of water content. When the water content exceeds a certain threshold value, the electrochemical active surface area becomes independent of water content. In addition, the electrochemical active surface area significantly decreases as the operating temperature increases. Consequently, including this newly proposed electrochemical active surface area equation in conventional full-cell models is of significant importance to accurately predict the activation loss and performance of fuel cells under both cold-start and normal operation conditions, especially at low humidification, which is validated against experimental data. In contrast with the conventional constant electrochemical active surface area assumption, this equation improves the model accuracy from about 70% to be higher than 90% under low humidity conditions.
With the effects of global warming, the Arctic is presenting a new environment where numerous ice floes are floating on the open sea surface. Whilst this has improved Arctic shipping navigability in ...an unprecedented way, the interaction of such floes with ships is yet to be understood to aid the designing of ships and route planning for this region. To further explore this topic, the present work develops a procedure to derive an empirical equation that can predict the effects of such floes on ship resistance. Based on a validated computational approach, extensive data are extracted from simulations of three different ships with varying operational and environmental conditions. The ice-floe resistance is shown to strongly correlate with ship beam, ship buttock angle, ship waterline angle, ship speed, ice concentration, ice thickness and floe diameter, and the regression powers of each of the parameters on resistance are ascertained. This leads to a generic empirical equation that can swiftly predict ice-floe resistance for a given ship in a given condition. Subsequently, demonstrations are given on the incorporation of the derived equation into a set of real-time Arctic ship performance model and voyage planning tool, which can predict a ship's fuel consumption in ice-infested seas and dynamically suggest a route with the least safety concern and fuel consumption. Moreover, the equation is validated by providing ice resistance prediction for experimental and full-scale conditions from multiple sources, showing high accuracy. In conclusion, the empirical equation is shown to give valid and rapid estimates for ice-floe resistance, providing valuable insights into ship designs for the region, as well as facilitating practical applications for polar navigation.
•A procedure is developed to derive an empirical equation to rapidly predict ship resistance induced by floating ice floes.•Multiple sources of model tests and full-scale measurements are used to validate the empirical equation.•The derived equation is incorporated into a set of new tools - Arctic ship performance model and voyage planning tool.•The tools can inform a ship's fuel consumption in ice-infested seas and perform route planning on a real-time basis.
Fibre reinforced concrete (FRC) has gained increasing interest in recent years due to its superior mechanical properties compared to normal concrete. To apply FRC in civilian and strategically ...important buildings and other infrastructures, fire resistance is an inevitable matter of concern. According to the existing test results, different fibre types, fibre dosages and cementitious matrix designs would affect the fire resistance of FRC. This paper presents a comprehensive review of the recent research works on the fire resistance of FRC. In particular, the temperature-dependent mechanical properties of steel fibre reinforced concrete, polypropylene fibre reinforced concrete and hybrid fibre reinforced concrete are discussed, including permeability, spalling, compressive strength, tensile strength, elastic modulus, toughness and mass loss. In addition, the currently available predicting equations for FRC residual properties are summarised and compared.
•Studies on the effect of elevated temperatures on FRC properties are reviewed.•Influencing factors on the temperature-dependent FRC properties are discussed.•The effects of reinforcing fibres are compared in detail.•The existing predicting equations are discussed.
•Triple emulsion droplet generation in a flow-focusing device is numerically studied.•The hydrodynamic behaviors of the dripping, jetting and threading regime are elucidated.•Effects of flow ...conditions and fluid properties on the droplet generation performance are examined.•Role of hierarchy levels of the droplet on the generation regime is recognized by a regime diagram.•An empirical equation is proposed to predict the critical threshold between different flow regimes.
A numerical research is conducted to investigate the triple emulsion droplet generation in a three-dimensional axisymmetric flow-focusing device. The simulation predicts three flow regimes: dripping, jetting, and threading. The hydrodynamics underlying the droplet generation and effects of operation conditions on the droplet generation are clarified. An increase in flow rate of one dispersed phase results in the larger droplet enclosing this phase and smaller droplet enclosed by this phase. As the interfacial tension between any two phases increases or viscosity of any phases decrease, the flow regime transits from jetting to dripping, accompanied by a decrease in the droplet size. Increasing the interfacial tension coefficient or decreasing the viscosity under both two regimes can increase the droplet size. Additionally, regime diagrams for single, middle, and triple emulsion droplet generation are compared, and an empirical equation is proposed to predict the flow regime transition.
•COC4mimGly, COC4mimAla and COC4mimThr were prepared.•The physicochemical properties of all binary mixtures were measured.•The correlation between VE (or gsE or ΔG≠r) and x1 was investigated.•The ...predicted surface tensions of ILs + DMSO binary mixtures were obtained.•The activation properties for viscous flow of binary mixture were studied.
In the full molar fraction range, the density, surface tension and viscosity of 1-(4-methoxybutyl)-3-methylimidazolium glycine (COC4mimGly), 1-(4-methoxybutyl)-3-methylimidazolium alanine (COC4mimAla) and 1-(4-methoxybutyl)-3-methylimidazolium threonine (COC4mimThr) with DMSO binary mixtures were determined. The variation trends of excess molar volume (VE), excess molar surface Gibbs energy (gsE), Gibbs energy of activation for viscous flow of the relative viscosity (ΔG≠r) and x1 of binary system mixture were systematically studied, and the interaction between ether-functionalized ionic liquids (ILs) and solvent molecules in binary system mixtures was studied. According to the molar surface Gibbs energy definition, excess molar surface Gibbs energy definition and Redlich-Kister empirical equation, the correlation between the predicted and experimental surface tension values of ILs + DMSO binary system mixtures was investigated. Furthermore, using the improved Eötvös empirical equation and thermodynamic formula, molar surface entropy and molar surface enthalpy of binary system mixture were calculated. The molar surface enthalpy of binary mixture was independent of temperature. This fact indicated that the process from the bulk to the surface of binary system mixture was an isocoulombic reaction.
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