Calculation of thermodynamic properties of lubricant + refrigerant mixtures using GMA equation of state

In this work, we have used a simple equation of state (EoS) to calculate the density of five lubricant/refrigerant mixtures including octane/dimethyl carbonate, TriEGDME/HFC-134a, TEGDME/HFC-134a, heptane/TEGDME, and decane/dimethyl carbonate at different temperatures, pressures, and compositions. The excess molar volumes of these mixtures have been calculated using this equation of state. Also, we have computed other thermodynamic properties such as isobaric expansion coefficient, isothermal compressibility, and internal pressure, for octane/dimethyl carbonate system for which the corresponding experimental values are available. A wide comparison with experimental data has been made for each thermodynamic property. The values of statistical parameters between experimental and calculated properties show the ability of this equation of state in reproducing and calculating of different thermodynamic properties for studied mixtures.     

Comparative Analysis of Some Representative Models of Viscosity Versus Pressure in the Case of Various Hydrocarbons and Their Mixtures

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Empirical method for selecting working pairs for sorption heat pumps and for estimating isobaric bubble temperatures

By the use of the integral enthalpy of evaporation of binary mixtures obtained from the linearized Clapeyron diagram (In P against 1/T plot) an expression was derived which may be useful for screening purposes when new working pairs are to be selected. For the construction of the Clapeyron diagram, the knowledge of isobaric bubble temperatures of binary mixtures is required. Suitable mixtures for heat pumping consist of polar components and exhibit normally strong negative deviations from Raoult's law. A method for the estimation of isobaric bubble temperatures of binary organic and organic/water mixtures was derived and tested. The method was based on an empirical generalization of Clapeyron's and Raoult's law for dilute solutions, certain symmetry properties of the linearized Clapeyron diagram and the knowledge of pure component properties. For 35 test mixtures, a total average deviation of 1·42% of estimated thermodynamic bubble temperatures was calculated.     

Phase equilibria of benzene–cyclohexane binary mixtures using a solid–liquid–vapor equation-of-state

Based on our previously developed solid–liquid–vapor equation of state (EOS), we have calculated phase equilibria of benzene, cyclohexane, and their mixtures. The model predictions for phase behaviors of pure compounds and vapor–liquid phase equilibria of the binary system have been straightforward and agreed well with the reported data. However, solid–liquid phase equilibria of the binary system are not well correlated to the experimental data with the present unified EOS model. Then, from this fact, we have found that the coexisting solid phases in the present binary system exist in two different solid structures (or two different Gibbs free-energy curves). We have developed a model to overcome such a problem within the present unified EOS model and successfully correlated the experimental data for wide ranges of temperatures and pressures.     

Thermodynamic properties of lithium nitrate-ammonia mixtures

In this paper, the thermodynamic properties of lithium nitrate-ammonia mixtures are presented. The vapour pressure-temperature correlations are developed by fitting the experimental P-T-x data. The enthalpy of solution, the latent heat of vaporization, the integral heat of solution and the differential heat of solution are presented in appropriate tabular and graphical forms.     

A new modification on RK EOS for gaseous CO2 and gaseous mixtures of CO2 and H2O

To develop an equation of state with simple structure and reasonable accuracy for engineering application, Redlich–Kwong equation of state was modified for gaseous CO₂ and CO₂–H₂O mixtures. In the new modification, parameter ‘a’ of gaseous CO₂ was regressed as a function of temperature and pressure from recent reliable experimental data in the range: 220–750 K and 0.1–400 MPa. Moreover, a new mixing rule was proposed for gaseous CO₂–H₂O mixtures. To verify the accuracy of the new modification, densities were calculated and compared with experimental data. The average error is 1.68% for gaseous CO₂ and 0.93% for gaseous mixtures of CO₂ and H₂O. Other thermodynamic properties, such as enthalpy and heat capacities of CO₂ and excess enthalpy of gaseous CO₂–H₂O mixtures, were also calculated; results fit experimental data well, except for the critical region. Copyright © 2005 John Wiley & Sons, Ltd.     

PVTxy properties of CO2 mixtures relevant for CO2 capture,transport and storage: Review of available experimental data and theoretical models

The knowledge about pressure–volume–temperature–composition (PVTxy) properties plays an important role in the design and operation of many processes involved in CO₂ capture and storage (CCS) systems. A literature survey was conducted on both the available experimental data and the theoretical models associated with the thermodynamic properties of CO₂ mixtures within the operation window of CCS. Some gaps were identified between available experimental data and requirements of the system design and operation. The major concerns are: for the vapour–liquid equilibrium, there are no data about CO₂/COS and few data about the CO₂/N₂O₄ mixture. For the volume property, there are no published experimental data for CO₂/O₂, CO₂/CO, CO₂/N₂O₄, CO₂/COS and CO₂/NH₃ and the liquid volume of CO₂/H₂. The experimental data available for multi-component CO₂ mixtures are also scarce. Many equations of state are available for thermodynamic calculations of CO₂ mixtures. The cubic equations of state have the simplest structure and are capable of giving reasonable results for the PVTxy properties. More complex equations of state such as Lee–Kesler, SAFT and GERG typically give better results for the volume property, but not necessarily for the vapour–liquid equilibrium. None of the equations of state evaluated in the literature show any clear advantage in CCS applications for the calculation of all PVTxy properties. A reference equation of state for CCS should, thus, be a future goal.     

Estimation of thermodynamic properties of the ternary molten salt system, LiF-NaF-BeF2, by the modified Peng-Robinson equation

The molten salt reactor (MSR), which is one of the generation IV reactors, can meet the demand of transmutation and breeding. The thermodynamic properties of the molten salt system like LiF-NaF-BeF₂ influence the design and construction of the fuel salt and coolant in the MSR for the new generation. In this paper, the equation of state of the ternary system 15%LiF-58%NaF-27%BeF₂, over the temperature range from 873.15 to 1 073.15 K at one atmosphere pressure, is described using a modified Peng-Robinson (PR) equation. The densities of the ternary system and its components are estimated by this equation directly, and compared with the experimental data. Based on the equation of state, the other thermodynamic properties such as the enthalpy, entropy and heat capacity at constant pressure are estimated by the residual function method and the fugacity coefficient method respectively. The densities calculated by PR equation are highly in agreement with the experimental data, and the enthalpy, entropy and heat capacity evaluated by the two different methods are consistent with each other. It can be concluded that the modified PR equation can be applied to evaluate the density of the molten salt system, and it is recommended that it be used as the basis to estimate the enthalpy, entropy and heat capacity of the molten salt system.     

天然气物性的LKP方程求解

对于流程中的天然气和混合制冷剂,用LKP方程求解其焓熵等物性参数,对LKP方程的求解展开讨论,给出了一个收敛性极好的LKP方程求解方法,并计算了混合制冷剂天然气液化流程中天然气和混合制冷剂焓值与温度,压力和组分的关系,所给出的解法同样适用于其它类型的物质。     

Second stage porous media burner for syngas enrichment

The syngas production from hydrocarbons by porous media combustion (or conventional gasification) processes has been intensively and extensively studied due its calorific value and its applications in the energy sector. However, the syngas produced in a first stage gasifier can still have concentrations of light hydrocarbons (e.g., methane) which can be post-processing for further enrichment of hydrogen and carbon monoxide. The present work numerically investigates the performance of a second stage porous media burner to enrich the syngas content, mainly hydrogen and carbon monoxide. A one-dimensional model based on a two-temperature approximation is implemented, based on the PREMIX code, and supported by CHEMKIN and GRI-MECH 3.0 database and routines. From hybrid porous bed reactor experiments, five types of mixtures in the equivalence ratio range between 0.4 and 2.4 are tested: pure methane as baseline, pure Eucalyptus nitens syngas, pure Pinus radiata syngas, and two mixtures of methane with each of the biomass syngas in equal volume quantities, as transition points. The results obtained show that in the enriched syngas, in comparison to the first content after the first stage reactor, the concentrations of hydrogen and carbon monoxide increase, due to the partial oxidation of methane, however part of the hydrogen is consumed in the process. The intermediate species present in methane processing for pure syngas mixtures have broader reaction zones and in lower concentrations compared to the use of pure methane. For equivalence ratios greater than 1.9, pure syngas mixtures show higher conversion efficiencies compared to the baseline. At the equivalence ratio of 2.4, the pure syngas from Eucalyptus nitens and Pinus radiata has an energy return over energy invested (EROI) of 58.27% and 53.95%, respectively, and a maximum hydrogen and carbon monoxide yields of 31.66% and 48.40%, respectively. In the case of the Pinus radiata, the outlet syngas concentrations of the hydrogen and carbon monoxide on dry basis expose an increment about two times in comparison to the initial concentrations.     

Survey of experimental data and assessment of calculation methods of properties for the air–water mixture

Thermodynamic properties of the air–water mixture at elevated temperatures and pressures are of importance in the design and simulation of the advanced gas turbine systems with water addition. In this paper, comprehensive available experimental data and calculation methods for the air–water mixture were reviewed. It is found that the available experimental data are limited, and the determined temperature is within 75 °C. New experimental data are needed to supply in order to verify the model further. Three kinds of models (ideal model, ideal mixing model and real model) were used to calculate saturated vapor composition and enthalpy for the air–water mixture, and the calculated results of these models were compared with experimental data and each other. The comparison shows that for the calculation of saturated vapor composition, the reliable range of the ideal model and ideal mixing model is up to 10 bar. The real model is reliable over a wide temperature and pressure range, and the model proposed by Hyland and Wexler is the best one of today. However, the reliability of the Hyland and Wexler model approved by experimental data is only up to 75 °C and 50 bar, and it is necessary to propose a new predictive model based on the available experimental data to be used up to elevated temperatures and pressures. In the calculation of enthalpy, compared to the ideal model, the calculated results of the ideal mixing model are closer to those of real model.     

Optimization of laminar pipe flow using nanoparticle liquid suspensions for cooling applications

Heat transfer of nanoparticle suspensions in laminar pipe flow is studied theoretically. The main idea upon which this work is based is that nanofluids behave more like single-phase fluids than like conventional solid?liquid mixtures. This assumption implies that all the heat transfer and friction factor correlations available in the literature for single-phase flows can be extended to nanoparticle suspensions, provided that the thermophysical properties appearing in them are the nanofluid effective properties calculated at the reference temperature. In this regard, two empirical equations, based on a wide variety of experimental data reported in the literature, are used for the evaluation of the nanofluid effective thermal conductivity and dynamic viscosity. Conversely, the other effective properties are computed by the traditional mixing theory. The novelty of the present study is that the merits of nanofluids with respect to the corresponding base liquid are evaluated in terms of global energetic performance, and not simply by the common point of view of the heat transfer enhancement. Both cases of constant pumping power and constant heat transfer rate are investigated for different operating conditions, nanoparticle diameters, and solid?liquid combinations. The fundamental result obtained is the existence of an optimal particle loading for either maximum heat transfer at constant driving power or minimum cost of operation at constant heat transfer rate. In particular, for any assigned combination of solid and liquid phases, it is found that the optimal concentration of suspended nanoparticles for maximum heat transfer is only slightly higher than that for minimum cost of operation. These optimal concentrations increase as the nanofluid bulk temperature is increased, the length-to-diameter ratio of the pipe is decreased, and the Reynolds number of the base fluid is increased. Moreover, the optimal concentrations increase with increasing the nanoparticle average size at high bulk temperatures, whilst they are practically independent of the nanoparticle diameter at lower bulk temperatures.     

Observations of the cellular structure of fuel–air detonations

Detonation cell widths, which provide a measure of detonability of a mixture, were measured for hydrocarbon–air and hydrogen–air–diluent mixtures. Results were obtained from a 0.43-m-diameter, 13.1-m-long heated detonation tube with an initial pressure of 101 kPa and an initial temperature between 25 and 100 °C. The cell widths of simple cyclic hydrocarbons are somewhat smaller than those of comparable straight-chain alkanes. Cyclic hydrocarbons tested generally had similar cell sizes despite differences in degree of bond saturation, bond strain energy, oxygen substitution, and chemical structure. There was a significant reduction in the cell width of octane, a straight-chain alkane, when it was mixed with small quantities of hexyl nitrate. The effect of a diluent, such as steam and carbon dioxide, on the cell width of a hydrogen–air mixture is shown over a wide range of mixture stoichiometries. The data illustrate the effects of initial temperature and pressure on the cell width when compared to previous studies. Not only is carbon dioxide more effective than steam at increasing the mixture cell width, but also its effectiveness increases relative to that of steam with increasing concentrations. The detonability limits, which are dependent on the facility geometry and type of initiator used in this study, were measured for fuel-lean and fuel-rich hydrogen–air mixtures and stoichiometric hydrogen–air mixtures diluted with steam. The detonability limits are nominally at the flammability limits for hydrogen–air mixtures. The subcellular structure within a fuel-lean hydrogen–air detonation cell was recorded using a sooted foil. The uniform fine structure of the self-sustained transverse wave and the irregular structure of the overdriven lead shock wave are shown at the triple point path that marks the boundary between detonation cells.     

Numerical investigation for the calculation of TiO2–water nanofluids' pressure drop in plain and enhanced pipes

In this investigation, a numerical model having two-dimensional equations was obtained by a CFD program and authors' experimental data were evaluated for the verification procedure of the numerical outputs. The experimental case study includes the single-phase flow of pure water in plain and micro-fin pipes whereas the numerical one has the simulated results of TiO₂ particles suspended in single phase water flow in equivalent pipes at a constant heat flux. Hydrodynamics and thermal behaviors of the water–TiO₂ flow were calculated by constant heat flux and temperature-dependent settings. Physical specifications of nanofluids were calculated by means of the results of authors' previous ANN analyses. This study illustrates local and average values of temperature, pressure, and velocity distributions in the tested pipes; furthermore, comparisons of pressure drop characteristics are given in terms of nanoparticle concentrations and tube types.     

A two-phase flow model for geothermal wells in the presence of non-condensable gas

Quantitative information on the phenomena occuring during the upward flow of a geothermal fluid in water-dominated wells is a requisite for designing the wellhead system and optimizing resource exploitation. The geothermal fluid consists, for the most part, of a two-phase mixture of water containing dissolved salts, steam and non-condensable gases. Various, closely interrelated effects must therefore be taken into consideration: pressure drop of the rising fluid; heat and mass transfer between the phases (due to evaporation and desorption); heat exchange with rock formations. Simultaneous application of the mass, energy and momentum equations results in a rather complex model that can be solved by a numerical computer program. The model described here accounts for the effects of: the presence of salts, when computing all the thermodynamic properties of the fluids, especially enthalpy, density, vapour pressure of the brine and superheated steam enthalpy; the presence of non-condensable gases, considering their deviations from ideal behaviour and their contribution to density; the heat exchange with the surrounding rock formations; variation in salt concentration along the flow-path; possible variation in pipe diameter and surface roughness with height. The simplified hypotheses adopted are: fluid flow is stationary; thermodynamic equilibrium conditions exist between the phases in each point along the well; the non-condensable gases are assumed to be CO₂; Henry's law is assumed valid and the quantity dissolved chemically is assumed negligible; the salts are assumed to be NaCl; the activity coefficients are unitary; liquid surface tension and viscosity values are assumed equal to those of pure water. Comparison of the results of the computer program and the experimental pressure and temperature profiles shows that these are in satisfactory agreement within a rather wide range of operative conditions. The noncondensable gases, even in very low concentrations, were shown to be of importance to these calculations. Once the experimental temperature and pressure profiles are known, the model will also permit calculation of the concentration of non-condensable gases. The most efficient of the two correlations used to compute pressure drop in two-phase regimes seems to be that devised by CISE^‡, which is based on global parameters not correlated to the different flow regimes.     

Implementation of the NCN pathway of prompt-NO formation in the detailed reaction mechanism

This work presents revised detailed reaction mechanism for small hydrocarbons combustion with possibly full implementation of available kinetic data related to the prompt NO route via NCN. It was demonstrated that model predictions with the rate constant of reaction CH + N₂ = NCN + H measured by Vasudevan and co-workers are much higher than experimental concentrations of NO in rich premixed flames at atmospheric pressure. Analysis of the correlations of NO formation with calculated concentrations of C₂O radicals strongly supports the inclusion of reaction between C₂O and N₂ and reduction of the rate constant of reaction between CH and N₂. Rate constants of the reactions of NCN consumption were mostly taken from the works of Lin and co-workers. Some of these reactions affect calculated profiles of NCN in flames. Proposed modifications allow accurate prediction of NO formation in lean and rich flames of methane, ethylene, ethane and propane. Agreement of the experiments and the modeling was much improved as compared to the previous Release 0.5 of the Konnov mechanism. Satisfactory agreement with available measurements of NCN radicals in low pressure flames was also demonstrated.     

Experimental exploration and theoretical certainty of thermal conductivity and viscosity of MgO-therminol 55 nanofluid

In this study, a combination of thermal conductivity, viscosity, and density characteristics are experimentally probed for attaining maximum heat transfer using MgO-Therminol 55 as nanofluid is reported. Recent studies proved that nanofluids have miserable properties that make them feasibly useful in many applications in heat transfer compared to base fluid.MgO-Therminol 55 nanofluid is synthesized by diffusion of MgO nanoparticles of size 160–190 nm in Therminol 55 at different concentrations (0.05%–0.3%). Thermal conductivity and viscosity are calculated at a temperature range of 30–60°C using kd₂ analyzer and Fenske viscometer. Data obtained from the experimental results reveals that when volume concentration is increased with respect to that thermal conductivity increases, viscosity decreases and density decreases at different temperatures. The proposed models were supportive to the experimental data.     

Numerical study of turbulent forced convection flow of nanofluids in a long horizontal duct considering variable properties

The turbulent flow of nanofluids with different volume concentrations of nanoparticles flowing through a two-dimensional duct under constant heat flux condition is analyzed numerically. The nanofluids considered are mixtures of copper oxide (CuO), alumina (Al₂O₃) and oxide titanium (TiO₂) nanoparticles and water as the base fluid. All the thermophysical properties of nanofluids are temperature-dependent. The viscosity of nanofluids is obtained on basis of experimental data. The predicted Nusselt numbers exhibit good agreement with Gnielinski's correlation. The results show that by increasing the volume concentration, the wall shear stress and heat transfer rates increase. For a constant volume concentration and Reynolds number, the effect of CuO nanoparticles to enhance the Nusselt number is better than Al₂O₃ and TiO₂ nanoparticles.     

Effect of the degree of hydrogenation on the viscosity,surface tension,and density of the liquid organic hydrogen carrier system based on diphenylmethane

For the efficient design of hydrogenation and dehydrogenation processes, a comprehensive database for the viscosity, surface tension, and density of mixtures of the diphenylmethane-based liquid organic hydrogen carrier system and the pure intermediate cyclohexylphenylmethane measured by complementary optical and conventional methods and calculated by molecular dynamics simulations at process-relevant temperatures up to 623 K is presented. The simulations employ self-developed force fields including a new one for cyclohexylphenylmethane and reveal surface enrichment and orientation effects influencing the surface tension. Relatively simple correlation and prediction approaches yield accurate representations as function of temperature and degree of hydrogenation (DoH) of the mixtures with average absolute relative deviations (AARD) of 0.07% for the density and 2.9% for the surface tension. Application of the extended hard-sphere theory considering the presented accurate density data allows capturing the highly nonlinear DoH-dependent behavior of the dynamic viscosity with an AARD of 2.9%.