Enthalpies Of Mixtures Research Articles

Measurement and Modeling of Excess Molar Enthalpies of Binary Mixtures Involving Hydrocarbon Components of Fuel

Experimental excess molar enthalpies of binary systems that are constituted by different groups of hydrocarbons, which are 1-hexene, methylcyclohexane, cyclohexane, isooctane, and heptane, are repo...

Solid-liquid equilibria and excess enthalpies in binary mixtures of acetophenone with some aliphatic amides

Solid-liquid equilibria for the binary systems of acetophenone and {N-methylformamide, or N,N-dimethylformamide, or N,N-dimethylacetamide, or N-methyl-2-pyrrolidone} were determined by the cloud-point and DSC techniques. For the same systems, excess enthalpies were measured at 293.15 K and 308.15 K by the titration calorimetry. Both types of data were correlated by the Redlich-Kister equation. The description of the solid-liquid equilibria incorporated measured excess enthalpies. The results of the prediction performed by the modified UNIFAC model were compared with the experimental data. The observed trends and differences between systems were discussed.

The potential of statistical RANS to predict knock tendency: Comparison with LES and experiments on a spark-ignition engine

Pollutant regulations and fuel consumption concerns are the driving guidelines for increased thermal efficiency and specific power in current internal combustion engines. The achievement of such challenging tasks in Spark Ignition units is often limited by the onset of knock, which hinders the possibility to operate the engine with the optimal combustion phasing. The sporadic occurrence of individual knocking events is related to cycle-to-cycle variability of turbulent combustion. This is avoidable by only accepting a safety margin from its earliest onset.On one side, the stochastic nature of knock and turbulence-related combustion variability would indicate Large-Eddy Simulation (LES) as the most appropriate technique for CFD analyses. Nevertheless, Large-Eddy Simulation remains a very time- and CPU-demanding approach, hardly integrated in the industrial timeframe for the design exploration and development of new units. Therefore, Reynolds Averaged Navier Stokes (RANS) models representing the average flow are chosen to limit CPU and development times, though they suffer from the intrinsic inability to account for cycle-dependent phenomena (e.g. knock). This is particularly critical at knock-borderline conditions, where far-from-average knocking events may occur. A previously developed statistical RANS-PDF knock model partly overcomes this limitation using equations for mixture fraction and enthalpy variance, ultimately reconstructing log-normal distributions of knock intensity. This allows RANS simulations to be directly compared to the usual statistical knock analysis at the test-bench.In this paper all the mentioned modelling techniques (LES, RANS and RANS-PDF) are applied to simulate combustion and knock in a currently made turbocharged GDI engine under knock-safe, knock-limited and light-knocking conditions. The study relevance lays in the critical comparison of the results. The full potential of the statistical RANS-PDF model for engine development is highlighted on a coherent basis. The possibility to preserve the RANS formalism while enriching the results with knock statistical description is a relevant advancement in the virtual design of high-efficiency engines.

Excess Molar Enthalpies of Binary and Ternary Mixtures Containing Ethyl Acetate, Methanol and 1-Butanol at the Temperature 298.15 K

Experimental excess molar enthalpies of ternary mixtures (ethyl acetate + methanol + 1-butanol) and the corresponding binary mixtures at 298.15 K are reported. An isothermal calorimeter has been used for both binary and ternary system experimental measurement. Endothermic nature for complete range of composition is shown by all the binary and the ternary systems. The experimental results for the binary and ternary system have been correlated using a polynomial equation to predict the coefficients. Roozeboom diagrams shows contours for ternary system at constant enthalpy and smooth representations of the results are described. The least square regression shows good match between calculated and experimental results.

MoDoop: An Automated Computational Approach for COSMO-RS Prediction of Biopolymer Solubilities in Ionic Liquids.

An automated computational framework (MoDoop) was developed to predict the biopolymer solubilities in ionic liquids (ILs) on the basis of conductor-like screening model for real solvents calculations of two thermodynamic properties: logarithmic activity coefficient (ln γ) at infinite dilution and excess enthalpy (HE) of mixture. The calculation was based on the optimized two-dimensional structures of biopolymer models and ILs by searching the lowest-energy conformer and optimizing molecular geometry. Three lignin models together with one IL dataset were used to evaluate the prediction ability of the developed method. The evaluation results show that ln γ is a more reliable property to predict lignin solubilities in ILs and the p-coumaryl alcohol model is considered as the best model to represent lignin molecules. The developed MoDoop approach is efficient for rapid in silico screening of suitable ionic liquids to dissolve biopolymers.

Demarcation of reaction effects on laminar burning velocities of diluted syngas–air mixtures at elevated temperatures

AbstractLaminar burning velocities of CO2/N2 (60%, 70%) diluted H2/CO/air mixtures were measured at elevated temperatures using the externally heated diverging channel method. The computed burning velocities using the two reaction mechanisms (Davis et al., Proc. Combust. Inst. 2005;30(1):1283–1292; FFCM‐1, http://nanoenergy.stanford.edu/ffcm1) are compared with the experimentally determined burning velocities. The accuracy of the chemical kinetic mechanisms at high dilution rates and elevated temperatures was investigated for various hydrogen fractions in the fuel composition. The burning velocity is observed to increase at high temperatures due to higher mixture enthalpy. The dilution effect on the variation of laminar burning velocity was stronger for the CO2 dilution case compared to N2 dilution. A comparison between the FFCM‐1 mechanism and experimental measurements shows an accurate depiction of the reaction chemistry regarding the prediction of laminar burning velocities. The role of third‐body reactions and direct inhibiting effect of N2 and CO2 molecules on burning velocity of diluted syngas–air mixtures is analyzed in detail. Detailed kinetic analysis revealed that the use of GRI 3.0 collision efficiency factors in the Davis mechanism helps in accurately predicting the burning velocities at elevated temperatures and high CO2 dilution rates. The thermal effect dominates the reduction in laminar burning velocity for N2 dilution case. The FFCM‐1 mechanism agrees well with the experiments for syngas flames diluted with N2 compared to the Davis mechanism. The addition of third‐body efficiency of N2 in the FFCM‐1 mechanism improved the predictions of laminar burning velocities for the N2 dilution case.

Large Eddy Simulation with tabulated chemistry of an experimental sidewall quenching burner

The flame-wall interaction (FWI) is an important aspect of the combustion inside gas turbines or internal combustion engines since it can have a strong effect on pollutant formation, fuel consumption and heat losses. In FWI one distinguishes between head on quenching, where the whole flame, and sidewall quenching (SWQ), where only the flame tip is quenched at a wall. The present work focuses on the second aspect. In this context, a new laboratory scale turbulent SWQ burner is examined. It features a rod stabilized, stoichiometric methane/air V-shaped flame under atmospheric conditions that interacts with an actively cooled wall. Highly resolved Large Eddy Simulations (LES) are employed and the chemistry is treated by means of a three-dimensional FGM chemistry tabulation using mixture fraction, enthalpy and reaction progress variable. To avoid any inaccuracies in the boundary conditions being often detrimental to LES, an additional isothermal LES of the entire burner geometry was conducted to obtain realistic inflow data for the reactive simulation and to characterize the upstream turbulence. Within the overall numerical study, physical processes in the burner are examined, numerical results are compared with available experimental data and an analysis of the flame-wall interaction is carried out based on the three-dimensional transient data. The comparison with measurements demonstrates, that the utilization of realistic turbulent inflow data combined with a highly resolved LES based on tabulated chemistry represents a promising approach to simulate SWQ processes. Furthermore, it is shown that the simulation can provide a database that helps to understand the relevant physics in complex combustors.

Measurements and Modeling of Excess Molar Enthalpy of Binary Mixtures of Oxygenate and Hydrocarbons

Measurements and Modeling of Excess Molar Enthalpy of Binary Mixtures of Oxygenate and Hydrocarbons

Vapor pressure, vapor-liquid equilibria, liquid-liquid equilibria and excess enthalpy of the system consisting of isophorone, furfural, acetic acid and water

In this work, the phase equilibria of the system comprised of isophorone, furfural, water and acetic acid were studied from the viewpoint of the extraction process. Equilibrium vapor pressure of pure isophorone was measured at sub-atmospheric pressure. Isobaric (at 40 kPa) isophorone-furfural vapor-liquid equilibria, the excess enthalpy of isophorone-furfural mixture (at 323 K) and isophorone-acetic acid vapor-liquid equilibria (from 322 K to 342 K) were investigated and compared to the available literature data. Liquid-liquid equilibria of systems comprised of isophorone-furfural-water (from 303 K to 343 K) were measured for the first time. The experimental results of this study and the literature values were utilized for optimizing the parameters for UNIQUAC model. The model was validated against the measured liquid-liquid equilibrium of the quaternary system isophorone-furfural-acetic acid-water (from 298 K to 343 K). Isophorone was found to be a favorable solvent for furfural extraction from its aqueous solutions.

Excess Molar Enthalpies for Binary and Ternary Mixtures Containing Cyclic Ethers, Lactam and Cyclic Ketones

Excess molar enthalpies $$ H_{{}}^{\text{E}} $$ for binary 1,3-dioxolane (1) + 1,4-dioxane (2) or N-methylpyrrolidin-2-one (2) + cyclohexanone or cycloheptanone (3) and $$ H_{123}^{\text{E}} $$ for ternary 1,3-dioxolane (1) + N-methylpyrrolidin-2-one or 1,4-dioxane (2) + cyclohexanone or cycloheptanone (3) mixtures have been measured over the entire mole fraction range at 308.15 K and atmospheric pressure using a micro differential calorimeter (Model-l DSC 7 Evo). The $$ H_{{}}^{\text{E}} $$ and $$ H_{123}^{\text{E}} $$ data have been correlated with composition by fitting of the corresponding data to the Redlich–Kister equation. The topology of the constituent molecules (Graph theory) has been utilized to predict $$ H_{123}^{\text{E}} $$ values of the present mixtures. It is observed that the $$ H_{123}^{\text{E}} $$ values calculated by Graph theory compare well with their corresponding experimental values. The $$ H_{123}^{\text{E}} $$ data have also been tested in terms of the Prigogine–Flory–Patterson (PFP) theory.

A RANS knock model to predict the statistical occurrence of engine knock

In the recent past engine knock emerged as one of the main limiting aspects for the achievement of higher efficiency targets in modern spark-ignition (SI) engines. To attain these requirements, engine operating points must be moved as close as possible to the onset of abnormal combustions, although the turbulent nature of flow field and SI combustion leads to possibly ample fluctuations between consecutive engine cycles. This forces engine designers to distance the target condition from its theoretical optimum in order to prevent abnormal combustion, which can potentially damage engine components because of few individual heavy-knocking cycles.A statistically based RANS knock model is presented in this study, whose aim is the prediction not only of the ensemble average knock occurrence, poorly meaningful in such a stochastic event, but also of a knock probability. The model is based on look-up tables of autoignition times from detailed chemistry, coupled with transport equations for the variance of mixture fraction and enthalpy. The transported perturbations around the ensemble average value are based on variable gradients and on a local turbulent time scale. A multi-variate cell-based Gaussian-PDF model is proposed for the unburnt mixture, resulting in a statistical distribution for the in-cell reaction rate. An average knock precursor and its variance are independently calculated and transported; this results in the prediction of an earliest knock probability preceding the ensemble average knock onset, as confirmed by the experimental evidence. The proposed model estimates not only the regions where the average knock is promoted, but also where and when the first knock is more likely to be encountered.The application of the model to a RANS simulation of a modern turbocharged direct injection (DI) SI engine with optical access is presented and the analysis of the knock statistical occurrence obtained by the proposed model adds an innovative contribution to overcome the limitation of consolidated “average knock” analyses typical of a RANS approach.

Excess Enthalpies of Binary Mixtures in Liquid State, near the Critical Points and Gas State

Excess Enthalpies of Binary Mixtures in Liquid State, near the Critical Points and Gas State

Lattice model for water-solute mixtures.

A lattice model for the study of mixtures of associating liquids is proposed. Solvent and solute are modeled by adapting the associating lattice gas (ALG) model. The nature of interaction of solute/solvent is controlled by tuning the energy interactions between the patches of ALG model. We have studied three set of parameters, resulting in, hydrophilic, inert, and hydrophobic interactions. Extensive Monte Carlo simulations were carried out, and the behavior of pure components and the excess properties of the mixtures have been studied. The pure components, water (solvent) and solute, have quite similar phase diagrams, presenting gas, low density liquid, and high density liquid phases. In the case of solute, the regions of coexistence are substantially reduced when compared with both the water and the standard ALG models. A numerical procedure has been developed in order to attain series of results at constant pressure from simulations of the lattice gas model in the grand canonical ensemble. The excess properties of the mixtures, volume and enthalpy as the function of the solute fraction, have been studied for different interaction parameters of the model. Our model is able to reproduce qualitatively well the excess volume and enthalpy for different aqueous solutions. For the hydrophilic case, we show that the model is able to reproduce the excess volume and enthalpy of mixtures of small alcohols and amines. The inert case reproduces the behavior of large alcohols such as propanol, butanol, and pentanol. For the last case (hydrophobic), the excess properties reproduce the behavior of ionic liquids in aqueous solution.

Excess enthalpies of ternary mixtures of (oxygenated additives + cycloalkane) in fuels and bio-fuels: (dibutyl ether + 1-propanol + cyclohexane), or methylcyclohexane, at T = (298.15 and 313.15) K

New experimental excess molar enthalpy data of the ternary systems (dibutyl ether+1-propanol+cyclohexane), or methylcyclohexane, and the corresponding binary systems at T=(298.15 and 313.15)K at atmospheric pressure are reported. A quasi-isothermal flow calorimeter has been used to make the measurements. All the binary and ternary systems show endothermic character at both temperatures. The experimental data for the systems have been fitted using the Redlich–Kister rational equation and the UNIQUAC model.

Flamelet LES of a semi-industrial pulverized coal furnace

The goal of this work is to introduce the flamelet model into large eddy simulation (LES) of realistic coal furnaces. A flamelet table based on two mixture fractions (for volatile and char off-gases) and enthalpy is generated and used in a massively parallel LES of the semi-industrial IFRF coal furnace (Weber et al. 1992 [1, 2]) for which comprehensive experimental data is available enabling the validation of the flamelet model under realistic conditions. Comparison between experiment and simulation is shown by means of averaged quantities of velocities, species concentrations and temperature. Overall good agreement between experiment and simulation could be obtained, giving evidence for the suitability of the flamelet model. The results of the LES are further analyzed, focussing on instantaneous particle and gas phase data to gain additional insight into the coal conversion process inside the furnace.

INFLUENCE OF THE ADDITIVES OF THE THIRD ELEMENT IN ALLOY Cu-Ti ON ENERGY OF THE SEGREGATION OF THE IMPURITY DURING CELLULAR PRECIPITATION OF THE SOLID SOLUTION

The mathematical analysis of influence of additives of the third component (Cr, Mn, Fe, Co, Ni, Ga, Zr, In, Sn) on quantities of energies of a segregation of impurities in volume and on boundaries of grains of alloy Cu-4,35 at. % Ti is made during aging on the cellular mechanism. Calculation of enthalpies of a segregation is spent with the account of energies of interatomic and elastic interaction of atoms of a different grade. Effects of experimental researches testify, in particular, to effective accelerating influence Ni on development of cellular decay in alloy Cu-4,35 ат. % Ti and essential inhibiting action of the given process by an additive Co. On the basis of modelling calculations of enthalpies of mixture in volume and on boundaries of grains it is erected that for the specified additives distinctions in quantities of an enthalpy of mixture in volume of grains appear considerable. The carried out analysis can be taken as a principle build-ups of model of a dynamic segregation and its influence on velocity of cellular decay in threefold metal systems.

Stochastic Eulerian field method for radiative heat transfer in a propane oxygen-enhanced turbulent diffusion flame

The stochastic Eulerian field (SEF) method is applied to solve the transport equation of the joint probability density function (PDF) of mixture fraction, enthalpy defect, scalar dissipation rate and soot quantities in order to predict radiative heat transfer from sooting turbulent jet diffusion flames. The flow field is computed by solving the Favre-averaged Navier–Stokes equation coupled with the standard k-ϵ model and a steady laminar flamelet (SLF) model. The modelling of soot production is carried out by using a flamelet-based semi-empirical acetylene/benzene soot model. Radiative heat transfer is modelled by using a wide-band correlated-k model and turbulent radiation interactions (TRIs) are accounted for by using the optically thin fluctuation approximation (OTFA). The model is applied to simulate an oxygen-enhanced jet turbulent diffusion flame fuelled by propane. Predicted soot volume fraction, radiant wall heat flux distributions and radiant fraction are in good agreement with the experimental data. A special emphasis was put on the evolution of the cross correlations between soot volume fraction and temperature and mixture fraction and enthalpy defect over the flame. Model results show that the former is strongly negative in regions where soot radiation is significant, which may affect turbulence–radiation interaction. The analysis of the latter showed that mixture fraction and enthalpy defect are strongly correlated over the flame. Propane flames with the same injection characteristics and different oxygen index were considered, showing that the conclusions drawn for these correlations can be generalised to flames with different sooting propensity.

Application of the UNIFAC models for prediction and description of excess molar enthalpies for binary mixtures of n-propanol, acetic acid, n-propyl acetate, and water

In this paper the ability of the UNIFAC methods (original UNIFAC and modified UNIFAC (Dortmund)) to predict the excess molar enthalpies, HE, is considered. The predicted and the obtained earlier experimental values of the excess molar enthalpies for 5 binary systems of n-propanol, acetic acid, n-propyl acetate, and water were compared. Since the both methods represent the HE unsatisfactorily, new set of group interaction parameters of the UNIFAC (Dortmund) method for mentioned above compounds was evaluated.

The NRTL-PRA group contribution EoS for the simultaneous prediction of LLE, VLE and hE of hydrocarbon mixtures with associating compounds

The goal of this study is to propose a modification of the NRTL-PR EoS for the prediction of phase equilibria and excess enthalpies in mixtures containing methanol with hydrocarbons; indeed, with these systems, the original equation is confronted to many difficulties arising from the simultaneous prediction of liquid-liquid equilibria together with vapor-liquid and enthalpy data. For this purpose, an additional term is included in the EoS excess Gibbs energy, gEoSE, of the Peng-Robinson equation to account for the self-association of methanol. The resulting NRTL-PRA EoS is successfully used for the prediction of both liquid-liquid and vapor-liquid equilibria, as well as excess enthalpies, in mixtures of methanol with hydrocarbons, light gases and associating compounds. Results are comparable to those obtained with other predictive EoS (VTPR and SAFT), but with the main advantage to predict all thermodynamic properties with a simple cubic equation.

Mixing Enthalpy for Binary Mixtures Containing Ionic Liquids.

A complete review of the published data on the mixing enthalpies of mixtures containing ionic liquids, measured directly using calorimetric techniques, is presented in this paper. The field of ionic liquids is very active and a number of research groups in the world are dealing with different applications of these fluids in the fields of chemistry, chemical engineering, energy, gas storage and separation or materials science. In all these fields, the knowledge of the energetics of mixing is capital both to understand the interactions between these fluids and the different substrates and also to establish the energy and environmental cost of possible applications. Due to the relative novelty of the field, the published data is sometimes controversial and recent reviews are fragmentary and do not represent a set of reliable data. This fact can be attributed to different reasons: (i) difficulties in controlling the purity and stability of the ionic liquid samples; (ii) availability of accurate experimental techniques, appropriate for the measurement of viscous, charged, complex fluids; and (iii) choice of an appropriate clear thermodynamic formalism to be used by an interdisciplinary scientific community. In this paper, we address all these points and propose a critical review of the published data, advise on the most appropriate apparatus and experimental procedure to measure this type of physical-chemical data in ionic liquids as well as the way to treat the information obtained by an appropriate thermodynamic formalism.