Condensation Of Mixture Research Articles

Influence of an admixture of H2 molecules on the structure and parameters of a Ne lattice

X-Ray investigations of solid solutions formed by condensation of mixtures of normal hydrogen and neon gases are performed for concentrations ranging from 2 to 60 mol.% nH2 and temperatures ranging from 5 K to the melting temperature of the sample. The structure of the vacuum condensates Ne-nH2 immediately after the samples are obtained is investigated. The boundary of single-phase solutions of hydrogen in neon is established to be 2 mol.%. At high H2 concentrations a hexagonal hcp2 phase forms in addition to a cubic fcc phase. The lattice volumes of these phases are somewhat larger but close to the volume of a pure-neon cell. The hexagonal hcp2 phase vanishes when the condensates are heated to a temperature of the order of the melting temperature of neon. This metastable hexagonal phase in the neon-rich mixtures studied is probably identical in nature to the previously observed hcp2 phase in hydrogen-rich solid mixtures. Both phases have one symmetry and the same cell volume. Information on the phase composition of the condensates is obtained from data on the concentration and temperature variations of the x-ray reflection intensities. It is shown that as the concentration of hydrogen molecules in the initial gas mixtures increases, the amount of the fcc phase in the condensates decreases almost linearly and the amount of the hcp2 phase increases. A combined analysis of the data obtained in the present work and previous measurements established the phase boundaries in the entire concentration range of the condensates. Evidently, because the molecular parameters of the components are close the Ne-nH2 mixtures do not form gel-like states, which are characteristic for quench-condensed Kr–H2 condensates.

Surprising effects of combined vapour and liquid mass transfer resistances when condensing a mixture outside tube banks

Detailed calculations are carried out for condensation of a binary zeotropic mixture outside a tube bank to investigate combined effects of mass transfer resistances in the liquid and vapour phases. The question is how a change in mass transfer resistance in the vapour phase can influence the heat flux. The surprising result is that a decrease in resistance in the vapour phase by reducing the tube pitch, and thus increasing the vapour velocity, reduces the heat flux between 20% and 50% for the conditions studied. This is due to a combination of mass transfer resistance, depletion of the heavy volatile component, and a reduction of the phase interface temperature.

Capillary condensation of a model binary mixture in slit-like pores with differently adsorbing walls

We investigate capillary condensation of symmetric binary fluid mixtures confined in slit-like pores with differently adsorbing walls. The interactions between adsorbate particles are modeled by Lennard–Jones (12, 6) potentials and the adsorbing potentials are of the Lennard–Jones (9, 3) type. We concentrate on the evaluation of the phase diagrams for the mixture of different compositions placed in pores of different adsorption potentials. The calculations were performed by means of a density functional theory. Our investigations indicate that a binary mixture may exhibit rich phase behavior.

The Simulation of Multicomponent Mixtures Condensation in Plate Condensers

The application of plate heat exchangers for the condensation of multicomponent mixtures requires reliable, well-grounded methods of calculation. A numerical simulation using semi-empirical equations of heat and mass transfer performance along the surface of plate condensers was carried out for different multicomponent mixtures with noncondensable components. The plates with cross-corrugated patterns for plate condensers were used. The simulation was done for four different types of corrugated plates of industrially manufactured plate heat exchangers. The results of the simulation are in a good accordance with experimental data obtained during long-time experiments for a pilot plant at the pharmaceutical factory in Kharkiv. It is shown that the enhancement of heat and mass transfer in a plate condenser for the case of a four-component mixture gives the possibility of decreasing by 1.8–2 times the necessary heat transfer surface area comparatively with shell-and-tube unit for the same process parameters.

Characteristic curves and the promotion effect of ethanol addition on steam condensation heat transfer

Although most previous studies concerning the condensation of binary vapor mixtures report the condensation rates to be less than that for pure vapor, heat transfer enhancement can be realized by using additives to form a positive system (solutal Marangoni condensation). The objective of the present study was to clarify the effect of mixing ethanol into steam on condensation heat transfer. Precise measurements of the ethanol concentration in the vapor of water–ethanol mixtures were performed over a wide range of ethanol concentrations, and the condensation behavior was observed. The maximum heat transfer coefficients in the condensation characteristic curves were determined to be 0.12 and 0.18 MW/m 2 K for vapor velocities of 0.4 and 1.5 m/s, respectively, and appeared at an ethanol vapor mass fraction of approximately 1%. The mixing was demonstrated to be extremely effective, particularly in the low-ethanol concentration range. The condensation heat transfer was enhanced approximately 2–8 times compared to pure steam.

The Condensation of Ammonia-Water Mixtures in a Horizontal Shell and Tube Condenser

Abstract The heat transfer rates that develop when ammonia water mixtures condense within a small, un-vented, horizontal, shell and tube condenser are examined. The vapor flow within the condenser was constrained by baffles and the condensate created formed a pool that flowed along the base of the condenser. During the test program the inlet ammonia vapor concentration to the condenser varied from 0 to 10 wt % and the maximum local vapor concentration measured was 26 wt %. The experimental results demonstrate that the condensation heat transfer rates generally decrease with increasing ammonia concentration, however at low ammonia concentrations (<2 wt %) the local and overall heat transfer rates for the condenser were enhanced. When the ammonia concentration was 0.9 wt %, the vapor heat transfer rate was 34 percent greater than that predicted by the Nusselt analysis for steam at the same conditions. This enhancement is attributed to the disturbed morphology of the condensate film, created by Marangoni instabilities.

Research on convective condensation heat transfer for a gas mixture in a vertical tube

AbstractThis paper discusses the convective condensation of a gas mixture in a vertical tube. A mathematical model was derived by combining a modified film model and Nusselt's condensation theory. The effect of wall temperature on film thickness and interfacial temperature was predicted and film thickness was calculated. When compared with the gas phase resistance method, the film model is better. The phenomenon of SO2 absorption into condensate is illustrated and discussed. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(4): 219–228, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20011

Coordination complexes of molybdenum with 3,6-di-tert-butylcatechol. Addition products of DMSO, pyridine N-oxide, and triphenylarsine oxide to the putative [MoVIO(3,6-DBCat)2] monomer and self-assembly of the chiral [(MoVIO(3,6-DBCat)2)4] square.

Molybdenum complexes of 3,6-di-tert-butylcatechol have been prepared from the reaction between [Mo(CO)(6)] and 3,6-di-tert-butyl-1,2-benzoquinone. A putative "[MoO(3,6-DBCat)(2)]" monomer is assumed to form initially by reaction with trace quantities of oxygen. Condensation of the reaction mixture leads to the formation of oligomeric products, including the [(MoO(3,6-DBCat)(2))(4)] chiral square isolated by chromatographic separation. Molybdenum centers at the corner of the square are bridged by oxo ligands centered along edges. Four-fold and inversion crystallographic symmetry gives tetramers as either LambdaLambdaLambdaLambda or DeltaDeltaDeltaDelta isomers, and the crystal structure consists of parallel columns of squares with the same chirality. Addition of O-Subst (O-Subst = dmso, pyridine N-oxide, triphenylarsine oxide) ligands to [MoO(3,6-DBCat)(2)] occurs selectively to give cis-[MoO(O-Subst)(3,6-DBCat)(2)] products. All three addition complexes are fluxional in solution. The temperature-dependent stereodymanic behavior of [MoO(dmso)(3,6-DBCat)(2)] has been shown to occur via a trigonal prismatic intermediate (Bailar twist) that conserves the cis disposition of oxo and dmso ligands. Electrochemical and chemical reduction reactions have been investigated for [MoO(dmso)(3,6-DBCat)(2)] with interest in displacement of SMe(2) with formation of cis-[MoO(2)(3,6-DBCat)(2)](2-). Cyclic voltammetry shows an irreversible two-electron reduction for the complex at -0.852 V (vs Fc/Fc(+)). Chemical reduction using CoCp(2) was observed to give a product with an electronic spectrum that is generally associated with cis-[MoO(2)(Cat)(2)](2-) complexes. Structural characterization revealed that the product was [CoCp(2)][MoO(3,6-DBCat)(2)], possibly formed as the product of dmso displacement upon one-electron reduction of [MoO(dmso)(3,6-DBCat)(2)].

平面凝縮相における2成分混合蒸気の蒸発・凝縮 : 線形化ボルツマン方程式の数値解析(S27-2 熱流体現象に対する分子気体力学および分子動力学法の応用(2),S27 熱流体現象に対する分子気体力学および分子動力学法の応用)

Half-space problem of evaporation and condensation of a binary mixture of vapors is investigated on the basis of the linearized Boltzmann equation for hard-sphere molecules with the complete condensation condition. The problem is analyzed numerically by a finite-difference method, in which the complicated collision integrals are computed by the extension of the method proposed by Sone, Ohwada, and Aoki [Phys. Fluids A 1, 363 (1989)] to the case of a gas mixture. As a result, the behavior of the mixture is clarified not only at the level of the macroscopic quantities but also at the level of the velocity distribution function. In addition, accurate formulas of the temperature, pressure, and concentration jumps caused by the evaporation or condensation are constructed for arbitrary values of the concentration of a component gas by the use of the Chebyshev polynomial approximation.

Higher-alcohols biorefinery: improvement of catalyst for ethanol conversion.

The concept of a biorefinery for higher-alcohol production is to integrate ethanol and methanol formation via fermentation and biomass gasification, respectively, with conversion of these simple alcohol intermediates into higher alcohols via the Guerbet reaction. 1-Butanol results from the self-condensation of ethanol in this multistep reaction occurring on a single catalytic bed. Combining methanol with ethanol gives a mixture of propanol, isobutanol, and 2-methyl-1-butanol. All of these higher alcohols are useful as solvents, chemical intermediates, and fuel additives and, consequently, have higher market values than the simple alcohol intermediates. Several new catalysts for the condensation of ethanol and alcohol mixtures to higher alcohols were designed and tested under a variety of conditions. Reactions of methanol-ethanol mixtures gave as high as 100% conversion of the ethanol to form high yields of isobutanol with smaller amounts of 1-propanol, the amounts in the mixture depending on the starting mixture. The most successful catalysts are multifunctional with basic and hydrogen transfer components.

Capillary condensation and interface structure of a model colloid-polymer mixture in a porous medium.

We consider the Asakura-Oosawa model of hard sphere colloids and ideal polymers in contact with a porous matrix modeled by immobilized configurations of hard spheres. For this ternary mixture a fundamental measure density functional theory is employed, where the matrix particles are quenched and the colloids and polymers are annealed, i.e., allowed to equilibrate. We study capillary condensation of the mixture in a small sample of matrix as well as demixing and the fluid-fluid interface inside a bulk matrix. Density profiles normal to the interface and surface tensions are calculated and compared to the case without matrix. Two kinds of matrices are considered: (i) colloid-sized matrix particles at low packing fractions and (ii) large matrix particles at high packing fractions. These two cases show fundamentally different behavior and should both be experimentally realizable. Furthermore, we argue that capillary condensation of a colloidal suspension could be experimentally accessible. We find that in case (ii), even at high packing fractions, the main effect of the matrix is to exclude volume and, to high accuracy, the results can be mapped onto those of the same system without matrix via a simple rescaling.

Synthesis of meso-substituted cationic porphyrins as potential photodynamic agents

Novel meso-substituted cationic porphyrins have been synthesized as potential photodynamic agents. 5,10-bis(4-Acetamidophenyl)-15,20-bis(4-methylphenyl)porphyrin 1 was prepared using a modification of the Alder-Longo procedure. However, two different approaches were compared in the synthesis of 5-(4-trifluorophenyl)-10,15,20-tris(4-acetamidophenyl)porphyrin 2. One involved a condensation of binary mixture of aldehydes and pyrrole under equilibrium conditions and the other a binary mixture of aldehydes and meso-(4acetamidophenyl)dipyrromethane 3. The last synthetic pathway was advantageous mainly for an easier reaction work up and a higher yield. Both amido porphyrin 1 and 2 were hydrolyzed in basic media and treated with methyl iodide to form 5,10-di(4-methylphenyl)-15,20-di(4trimethylammonium phenyl)porphyrin iodide 4 and 5-(4-trifluorophenyl)-10,15,20-tris(4trimethyl ammoniumphenyl)porphyrin iodide 5, respectively. Porphyrin 5 bears a highly lipophilic trifluoromethyl group, which increases the amphiphilic character of the structure. On the other hand, the photodynamic properties of porphyrin 5 were changed forming metal complex with Pd(II), porphyrin 6. Absorption and fluorescence spectroscopic studies of these porphyrins were compared in different solvents. These amphiphilic cationic porphyrins are promising photosensitizers with potential applications in bacteria inactivation by photodynamic therapy.

Condensation and Freezing of a Binary Gas Mixture Adsorbed in Mesoporous Vycor Glass

The phase behavior of Ar−Kr gas mixtures adsorbed in porous Vycor glass and in bulk have been investigated using positron annihilation spectroscopy. For the bulk mixtures, we have determined the li...

Capillary condensation of a model binary mixture in slit-like pores

We study capillary condensation of symmetric binary fluid mixtures in slit like pores. The interactions between adsorbate particles are modeled by Lennard–Jones (LJ) (12,6) potentials and the adsorbing potentials are of the LJ (9,3) type. The parameters were set to induce the demixing in a bulk phase. The calculations were performed for different pore widths and at different concentrations of a bulk gas, by means of a density functional theory. On the base of the calculations, the capillary phase diagrams were evaluated and discussed.

A note on the influence of droplet interchange on evaporation and condensation of multicomponent mixtures in annular flow

A note on the influence of droplet interchange on evaporation and condensation of multicomponent mixtures in annular flow

Capillary condensation of a binary mixture in slit-like pores

We investigate the capillary condensation of two model fluid mixtures in slit-like pores, which exhibit different demixing properties in the bulk phase. The interactions between adsorbate particles are modeled by using Lennard-Jones (12,6) potentials and the adsorbing potentials are of the Lennard-Jones (9,3) type. The calculations are performed for different pore widths and at different concentrations of the bulk gas, by means of density functional theory. We evaluate the capillary phase diagrams and discuss their dependence on the parameters of the model. Our calculations indicate that a binary mixture confined to a slit-like pore may exhibit rich phase behavior.

Two-dimensional turbulent film condensation of vapours flowing inside a vertical tube and between parallel plates: a numerical approach

Film condensation of vapour flowing inside a vertical tube and between parallel plates is treated. A methodology is presented to determine numerically the heat transfer coefficients, the film thickness and the pressure drop. The analysis is based on the resolution of the full coupled boundary layer equations of the liquid and vapour phases and does not neglect inertia and convection terms in the governing equations. Turbulence in the vapour and condensate film is taken into account using mixing length turbulence models. An explicit method and an implicit finite difference procedures are described. The calculated results for the condensation of steam in a 24 mm diameter tube are compared with those obtained from Chen's correlation. The heat flow rate for the condensation of R123 flowing between parallel plates obtained from numerical solution are compared with experimental values. The mean heat transfer coefficients for the condensation of vapour mixture R123/R134a are also presented.

In-tube condensation of mixture of R134a and ester oil: empirical correlations

This paper presents a comparative study of the condensation heat transfer coefficients in a smooth tube when operating with pure refrigerant R134a and its mixture with lubricant Castrol “icematic sw”. The lubricant is synthetic polyol ester based oil commonly used in lubricating the compressors. Two concentrations of R134a-oil mixtures of 2% and 5% oil (by mass) were analysed for a range of saturation temperatures of refrigerant R134a between 35 °C and 45 °C. The mass flow rate of the refrigerant and the mixtures was carefully maintained at 1 g/s, with a vapour quality varying between 1.0 and 0. The effects of vapour quality, flow rate, saturation temperature and temperature difference between saturation and tube wall on the heat transfer coefficient are investigated by analysing the experimental data. The experimental results were then compared with predictions from earlier models [Int J Heat Mass Transfer (1979), 185; 6th Int Heat Transfer Congress 3 (1974) 309; Int J Refrig 18 (1995) 524; Trans ASME 120 (1998) 193]. Finally two new empirical models were developed to predict the two-phase condensation heat transfer coefficient for pure refrigerant R134a and a mixture of refrigerant R134a with Castrol “icematic sw”.

Influence of the outlet air temperature on the thermohydraulic behaviour of air coolers

The determination of the optimal process conditions for the operation of air coolers demands a detailed analysis of their thermohydraulic behaviour on the one hand, and the estimation of the operating costs, on the other. One of the main parameters of the thermohydraulic behaviour of this type of equipment, is the outlet air temperature. The influence of the outlet air temperature on the performance of air coolers (heat transfer coefficient overall heat transfer coefficient, required surface area for heat transfer air-side pressure drop, fan power consumption and sound pressure level) was investigated in this study. All the computations, using AirCooler software [1], were applied to cooling of the process fluid and the condensation of a multicomponent vapour mixture on two industrial devices of known geometries.

Experimental study and modelling of heat transfer during condensation of pure fluid and binary mixture on a bundle of horizontal finned tubes

An experimental investigation was conducted to measure the local heat transfer coefficient for each row in a trapezoidal finned horizontal tube bundle during condensation of both pure fluid (HFC 134a) and several compositions of the non-azeotropic binary mixture HFC 23/HFC 134a. The test section is a 13×3 (rows × columns) tube bundle and the heat transfer coefficient is measured using the modified Wilson plot method. The inlet vapour temperature is fixed at 40 °C and the water flow rate in each active row ranges from 170 to 600 l/h. The test series cover five different finned tubes all commercially available, K11 (11 fins/inch), K19 (19 fins/inch), K26 (26 fins/inch), K32 (32 fins/inch), K40 (40 fins/inch) and their performances were compared. The experimental results were checked against available models predicting the heat transfer coefficient during condensation of pure fluids on banks of finned tubes. Modelling of heat exchange during condensation of binary mixtures on bundles of finned tubes based on the curve condensation model is presented.