Monodisperse monocomponent fuel droplet heating and evaporation

The results of numerical and experimental studies of heating and evaporation of monodisperse acetone, ethanol, 3-pentanone, n-heptane, n-decane and n-dodecane droplets in an ambient air of fixed temperature and atmospheric pressure are reported. The numerical model took into account the finite thermal conductivity of droplets and recirculation inside them based on the effective thermal conductivity model and the analytical solution to the heat conduction equation inside droplets. The effects of interaction between droplets are taken into account based on the experimentally determined corrections to Nusselt and Sherwood numbers. It is pointed out that the interactions between droplets lead to noticeable reduction of their heating in the case of ethanol, 3-pentanone, n-heptane, n-decane and n-dodecane droplets, and reduction of their cooling in the case of acetone. Although the trends of experimentally observed droplet temperatures and radii are the same as predicted by the model taking into account the interaction between droplets, the actual values of the predicted droplet temperatures can differ from the observed ones by up to about 8 K, and the actual values of the predicted droplet radii can differ from the observed ones by up to about 2%. It is concluded that the effective thermal conductivity model, based on the analytical solution to the heat conduction equation inside droplets, can predict the observed average temperature of droplets with possible errors not exceeding several K, and observed droplet radii with possible errors not exceeding 2% in most cases. These results allow us to recommend the implementation of this model into CFD codes and to use it for multidimensional modelling of spray heating and evaporation based on these codes.     

Effects of oxygenate concentration on species mole fractions in premixed n-heptane flames

Atmospheric pressure, laminar, premixed, fuel-rich flames of n-heptane/oxygen/argon and n-heptane/oxygenate/oxygen/argon were studied at an equivalence ratio of 1.97 to determine the effects of oxygenate concentration on species mole fractions. The oxygen weight percents in n-heptane/oxygenate mixtures were 2.7 and 3.4. Three different fuel oxygenates (i.e. MTBE, methanol, and ethanol) were tested. A heated quartz micro-probe coupled to an on-line gas chromatography/mass spectrometry has been used to establish the identities and absolute concentrations of stable major, minor, and trace species by the direct analysis of samples, withdrawn from the flames. The oxygenate addition has increased the maximum flame temperatures and reduced the mole fractions of CO, low-molecular-weight hydrocarbons, aromatics, and polycyclic aromatic hydrocarbons. The reduction in mole fractions of aromatic and polycyclic aromatic hydrocarbon species by an increase in oxygenate concentration was more significant.     

Hydrogen pressure dependence in the ring-opening reactions of propylcyclobutane over Pd/SiO2 catalyst

Temperature dependence and the effects of hydrogen pressure on the rate and regioselectivity were studied in the ring opening of propylcyclobutane over a low-dispersion Pd/SiO₂ catalyst. At a certain composition (1.33 kPa of propylcyclobutane and 20 kPa of H₂) the reaction rate versus temperature curve was found to pass through a maximum. At each temperature the ring opened selectively (or exclusively at 423 K) in the sterically more hindered direction over the clean surface as well as over the steady-state catalyst, yieldingn-heptane as the major product. The hydrogen pressure versus turnover frequency curves were of saturation type for both products over the initial surface at 523 K. Over the steady-state surface, however, the reaction mechanism changed: ring-opening rate versus hydrogen pressure curve passed through a maximum forn-heptane, while it remained of saturation type for 3-methylhexane. For rationalizing the high regioselectivity towardn-heptane formation, the anchoring effect of the propyl side-chain was suggested.     

Evaluation of lipase from Burkholderia cepacia immobilized in alginate beads and application in the synthesis of banana flavor (isoamyl acetate)

The alginate in bead forms was used to immobilize Burkholderia cepacia lipase. The microencapsulation technique for lipase entrapment was a 2% (w/v) of sodium alginate concentration prepared by ionic gelation using calcium chloride as the cross-linking agent in a gelling solution. The beads were tested in different solvents as acetone, chloroform, toluene, n-hexane, and n-heptane. Over a 5-day period (120?h), the n-heptane maintained the reasonable (excellent) residual activity of the immobilized lipase. Morphological studies on reused beads and new beads were performed. All beads for isoamyl acetate yield were tested. The reused bead leaches substantially, with a maximum ester yield of 92%. With modifications in the molar ratios, the synthesis of banana flavor (isoamyl acetate) was performed in both the alcohol per acid and acid per alcohol excesses.     

Numerical study of flame spread in an <Emphasis Type="Italic">n</Emphasis>-heptane droplet array in different ambient temperature and microgravity conditions

Flame spread in an n-heptane droplet array under conditions of microgravity, different ambient temperatures, and droplet spacing is studied numerically. The dimensionless distance, fuel type, and ambient temperature are characteristic parameters that could change the flame spread modes. Variations of the droplet spacing change the amount of the gas fuel on the centerline of droplets, and the flame can either appear between the droplets or pass above this space. A high-temperature environment causes an increase in the flame spread rate. Good qualitative agreement in the flame spread behavior between numerical results and microgravity experiments is obtained. Flame spread rates are obtained for different droplet spacings. This curve has a maximum, similar to experimental result.     

Numerical investigation of the evaporation of two-component droplets

A numerical model for the complete thermo-fluid-dynamic and phase-change transport processes of two-component hydrocarbon liquid droplets consisting of n-heptane, n-decane and mixture of the two in various compositions is presented and validated against experimental data. The Navier-Stokes equations are solved numerically together with the VOF methodology for tracking the droplet interface, using an adaptive local grid refinement technique. The energy and concentration equations inside the liquid and the gaseous phases for both liquid species and their vapor components are additionally solved, coupled together with a model predicting the local vaporization rate at the cells forming the interface between the liquid and the surrounding gas. The model is validated against experimental data available for droplets suspended on a small diameter pipe in a hot air environment under convective flow conditions; these refer to droplet’s surface temperature and size regression with time. An extended investigation of the flow field is presented along with the temperature and concentration fields. The equilibrium position of droplets is estimated together with the deformation process of the droplet. Finally, extensive parametric studies are presented revealing the nature of multi-component droplet evaporation on the details of the flow, the temperature and concentration fields.     

Partition coefficient calculation of selected terpenes and low molecular weight solvents between tall oil fatty acid and air and polydimethyl siloxane oil and air

Headspace gas chromatography-mass spectrometry (GC-MS) has been applied to the analysis of the temperature-dependent tall oil fatty acid (TOFA)/air partition coefficient (k ₁) and the polydimethyl siloxane oil/air partition coefficient (k ₂) of selected terpenes and low molecular weight solvents. As expected, both the TOFA and the silicone oil are effective trapping media for the nonpolar terpenes, but they are also efficient traps for acetone, methanol, n-propanol, and n-butanol. However, several species of low and moderate molecular weight (less than 150 amu) aldehydes, ketones, and organic acids that might adversely affect its trapping capacity were detected in the TOFA. This article will report the empirically gathered data and the subsequent calculation of the partition coefficients for the terpenes: α- and β-pinene, limonene, and α-terpineol and the solvents: acetone, methanol, n-propanol, and n-butanol between 50 and 130°C.     

Synthesis of polymeric microspheres employing SPG emulsification technique

Relatively uniform polymeric microspheres, the coefficients of variation being close to 10%, were obtained by the BPO-initiated suspension polymerization of styrenic monomers. Unlike the conventional stirred-tank system, a particular microporous glass membrane (SPG) provided uniform monomer droplets continuously when monomer was allowed to permeate through the micropores. The monomer droplets were suspended in an aqueous solution containing the stabilizing agents, transferred to a stirred vessel, and polymerized. Up to 10μm spheres, of a far narrower size distribution than those obtained by conventional microsuspension polymerization spheres, were obtained. The initial droplet size and distribution were retained with the successful suppression of secondary particle nucleation by the addition of hydroquinone in the aueous phase. Crosslinked polystyrene spheres were also synthesized in the presence of various low-molecular-weight diluents. While a good solvent, toluene, was not so effective; poor solvents, n-heptane and n-heptane, easily yielded the microporous structure, the specific surface area being as high as 160 m²/g. © 1994 John Wiley & Sons, Inc.     

Experimental study on the auto-ignition and combustion characteristics in the homogeneous charge compression ignition (HCCI) combustion operation with ethanol/n-heptane blend fuels by port injection

This article investigates the auto-ignition, combustion, and emission characteristics of homogeneous charge compression ignition (HCCI) combustion engines fuelled with n-heptane and ethanol/n-heptane blend fuels. The experiments were conducted on a single-cylinder HCCI engine using neat n-heptane, and 10%, 20%, 30%, 40%, and 50% ethanol/n-heptane blend fuels (by volume) at a fixed engine speed of 1800 r/min. The results show that, with the introduction of ethanol in n-heptane, the maximum indicated mean effective pressure (IMEP) can be expanded from 3.38 bar of neat n-heptane to 5.1 bar, the indicated thermal efficiency can also be increased up to 50% at large engine loads, but the thermal efficiency deteriorated at light engine load. Due to the much higher octane number of ethanol, the cool-flame reaction delays, the initial temperature corresponding the cool-flame reaction increases, and the peak value of the low-temperature heat release decreases with the increase of ethanol addition in the blend fuels. Furthermore, the low-temperature heat release is indiscernible when the ethanol volume increases up to 50%. In the case of the neat n-heptane and 10% ethanol/n-heptane blends, the combustion duration is very short due to the early ignition timing. For 20–50% ethanol/n-heptane blend fuels, the ignition timing is gradually delayed to the top dead center (TDC) by the ethanol addition. As a result, the combustion duration prolongs obviously at the same engine load when compared to the neat n-heptane fuel. At overall stable operation ranges, the HC emissions for n-heptane and 10–30% ethanol/n-heptane blends are very low, while HC emissions increase substantially for 40% and 50% ethanol/n-heptane blends. CO emissions show another tendency compared to HC emissions. At the engine load of 1.5–2.5 bar, CO emissions are very high for all fuels. Beside this range, CO emissions decrease both for large load and light load. In terms of operation stability of HCCI combustion, for a constant energy input, n-heptane shows an excellent repeatability and light cycle-to-cycle variation, while the cycle-to-cycle variation of the maximum combustion pressure and its corresponding crank angle, and ignition timing deteriorated with the increase of ethanol addition.     

Design and control of transesterification reactive distillation with thermal coupling

In the study, the design and control strategies of a reactive distillation process with partially thermal coupling for the production of methanol and n-butyl acetate by transesterification reaction of methyl acetate and n-butanol are investigated. Since methanol and methyl acetate formed an azeotrope, the products of a reactive distillation column include n-butyl acetate and the mixture of methanol and methyl acetate, which must be separated by an additional column. Partially thermal coupling can be used to eliminate the condenser of the second column. Not only energy reduction but also better operability and controllability can be obtained for the thermally coupled reactive distillation process. Proper selection and pairing of controlled and manipulated variables chosen for three control objectives were determined by using steady-state analysis. A simple control scheme with three temperature control loops is sufficient to maintain product purities and stoichiometric balance between the reactant feeds.     

Selective Liquid Phase Adsorption and Separation of ortho-Xylene with the Microporous MIL-53(Al)

Metal-organic framework MIL-53(Al) pellets were tested for the selective adsorption and separation of xylene isomers, in liquid phase and using n-heptane as eluent. The objective of this work is to assess relevant data for a posterior xylene isomers separation process design. In order to complete this study, single and multi-component breakthrough experiments were performed at 313 K, in the presence of n-heptane. MIL-53(Al) presented a preference for o-xylene over m-xylene and p-xylene in all experiments. The selectivities of 2.0 were obtained for o-xylene over m-xylene and over p-xylene. It is concluded that MIL-53(Al) may be used for separating o-xylene from the other xylene isomers, using n-heptane as desorbent. Supplemental materials are available for this article. Go to the publisher's online edition of Separation Science & Technology to view the free supplemental file.     

The enantiomers of 7aH-cyclopenta[b]pyran-7-ones and their thermal racemization

The separation of the enantiomers of 7aH-cyclo-penta[b]pyran-7-ones 1 was performed by enantioselective liquid chromatography with the sorbent/solvent systems triacetylcellulose/methanol, tribenzoylcellulose/methanol, and (+)-poly(trityl methacrylate)/silica gel/n-heptane/isopropanol. Barriers to ring opening were determined for two 7a-methyl and two 7a-phenyl substituted 2,4,5-triaryl derivatives by thermal racemization of the enantiomers. Substituted cyclopentadienones 2 are discussed as intermediates in the thermal electrocyclic ring opening/ring closure reactions.     

电场作用下液滴的变形及库仑分裂模式

基于高速成像技术,本文对电场作用下甲醇液滴的显微形貌特征进行了可视化研究,精确捕捉了两相流体系中不同生长阶段的荷电液滴基于时间分辨特性的变形及库仑分裂演变行为,得到不同工况下荷电液滴的变形分裂过程及行为演化细节。基于液滴所受库仑力和介电泳力与周围流域的耦合作用,揭示了电场作用下不同生长阶段的液滴库仑分裂形成机理。结果表明,电场强度和液滴粒径是决定液滴变形及库仑分裂模式的主要因素,荷电液滴的变形及库仑分裂模式可以分为推压变形、顶部破碎、顶部-边端破碎、伞状破碎。结合量纲为1参数对液滴的变形及破碎特征进行了定量分析,随着电场强度的增大及液滴粒径的减小,液滴变形及顶部破碎的程度更加剧烈,液滴临界伞状破碎长度减小。     

Interfacial Composition,Structural and Thermodynamic Parameters of Water/(Surfactant+<Emphasis Type="Italic">n</Emphasis>-Butanol)/<Emphasis Type="Italic">n</Emphasis>-Heptane Water-in-Oil Microemulsion Formation in Relation to the Surfactant Chain Length

Interfacial behavior, structural and thermodynamic parameters of a water/(surfactant+n-butanol)/n-heptane water-in-oil (w/o) microemulsion have been investigated using the dilution technique at different temperatures, and [water]/[surfactant] mole ratios. The cationic surfactants used were alkyltrimethyl ammonium bromides (CnTAB, n = 10, 14 and 16) while the nonionic surfactants were polyoxyethylene (20) sorbitan monoalkanoates (polysorbate), viz., palmitate (PS 40), stearate (PS 60) and oleate (PS 80). The distribution of cosurfactant between the oil–water interface and the bulk oil at the threshold level of stability, and the thermodynamics of transfer of the cosurfactant from the bulk oil to the interface were evaluated. Structural parameters such as the dimensions, population density and effective water pool radius of the dispersed water droplets in the oil phase and the interfacial population of the surfactant and cosurfactant have been evaluated in terms of the surfactant chain length.     

Enthalpies of mixing and heat capacities of mixtures containing alcohols and <Emphasis Type="Italic">n</Emphasis>-alkanes with corn oil at 298.15 K

Enthalpies of mixing for mixtures containing alcohols (methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, and 2-butanol) plus corn oil or n-alkanes (n-hexane, n-heptane, and n-octane) plus corn oil were measured at 298.15 K and atmospheric conditions. The enthalpy was measured in the range of concentrations in which alcohols were miscible with the vegetable oil. Results were correlated by the Redlich-Kister equation. The mixing of alcohols with corn oil was strongly endothermic, whereas values obtained for the binaries containing n-alkanes were slightly endothermic. Thus, heat capacities were calculated for all the systems studied.     

Controllably crazed polystyrene: Morphology and permeability

The effects of n-heptane and heat treatment on the structural and transport properties of polystyrene films (biaxially oriented and unoriented) were studied to determine whether these treatments improve the film as selective barriers for separation of molecules differing only slightly in size and shape. n-Heptane treatment of biaxially oriented polystyrene produces a sandwich structure composed of expanded, crazed, surface layers surrounding an apparently unaffected central core. The crazed layers contain a continuous network of interconnected channels. The core provides the total resistance to gas permeation, hence, the overall effect of n-heptane treatment is fabrication of a thinner more permeable membrane. By restricting the stress-cracking treatment to one face of the film, it should be possible to make high flux, anisotropic membranes—a type of membrane which is required for successful development of membrane separation processes. n-Heptane treatment of cast, annealed polystyrene results also in a crazed polymer, but the crazing is in the form of spherical voids, and the films, even with a residual uncrazed core, are too weak to be useful as separation membranes. The crazing process in both types of polymer specimens is characteristic of case II non-Fickian diffusion in which the kinetics are apparently controlled by polymer relaxation processes. Sorption of isopentane into cast, annealed polystyrene does not cause visible crazing but the kinetics are again non-Fickian. Desorption of isopentane into n-heptane-treated polystyrene releases the appreciable residual n-heptane in the film which could not be removed by long-term exposure to vacuum. Analysis of D(0) values for isopentane in n-heptane treated films indicates that the polymer surrounding the visible voids in the film is essentially unaltered polystyrene with only a small fraction of the voids being interconnected by open channels.     

A study of mass transfer from single large oscillating drops

A study was made of mass trasfer rates from single large oscillating drops of pure liquid-liquid systems, in the size range of 5 to 10 mm. A thrermostatically-controlled, 50 mm in diameter, 1000 mm long, rising drop column was used, in which mirrors in the jacket enabled front and side views of drops to be photographed simultaneously. The systems studied were (1) toluene and acetone (dispersed)-water (continuous), and (2) n-heptane and acetone (dispersed)-water (continuous). High concentrations of acetone (up to 3.75 kmol/m³) were used to examine the effect of different parameters on the mass transfer rate, frequency and amplitude of oscillation in countercurrent operation. Previous theories and empirical correlations [2–6, 12, 13, 15] for the prediction of overall mass transfer coefficients showed large deviations from measured values. These may have aarisen because the models do not represent droplet oscillation accurately, and/or apply only to oscillations of small droplets. Fair agreement was obtained for small oscillating droplets as low solute concentrations. The oscillations of a travelling drop were asymmetrical; the period of oscillation was uniform for mutually-saturated systems but changed when mass transfer was taking place. The periods were longer than those predicted by the Lamb [7] and Shroeder and Kintner [37] correlations. Terminal velocities predicted from literature correlations [32, 34] did not give reasonable agreement with experimental data when there was mass transfer of solute. The drag coefficient increased with increasing mass transfer rate from the drop. Correlation of the results and the dispersed phase mass trasfer coefficients by dimensional analysis resulted in the correlation

1 List of symbols at the end of the paper.

with a mean deviation of ±23%, by insertion of experimental oscillation frequency data. This will facilitate more accurate prediction of the dispersed phase mass transfer coefficients relating to equipment containing droplets in the oscillating regime, e.g. pulsed columns or agitated tanks.     

Influence de la concentration des agents tensio-actifs sur la vitesse terminale d'ascension des gouttes

The rising of droplets in water contaminated with two surfactants, sodium salt dodecylhydrogenosulphate (L.S.S.) and Teepol, in the range 200 < N_Rep < 1000 was studied. The dispersed phases used were cyclohexane, benzene, toluene, and n-heptane. Experiences were conducted at a constant temperature of 30°C. It was shown that the presence of the two agents decreases the final rising rate of the droplets with an increasing surfactant concentration and droplet diameter. For the same interfacial tension values, this phenomenon is enhanced in the case of Teepol. An equation is proposed for the computation of the critical droplet diameter as well as the droplet rising rate. These equations demonstrate the effect of the chemical nature of the surface agent and reproduce the experimental results with variations less than 10%.     

Extraction of Mn(II) from NaCl solution by NaCl/sodium oleate/n-pentanol/n-heptane microemulsion system

A microemulsion (ME) consisting of sodium oleate, n-pentanol, n-heptane and sodium chloride (NaCl) solution was used for Mn(II) extraction. The cation exchange mechanism of Mn(II) extraction by sodium oleate (NaOL) was confirmed by the analysis of continuous variation of the NaOL concentration and the infrared spectrum. The effect of the extraction time, the cosurfactant type and volume fraction, the volume ratio of aqueous to ME (R), the initial concentration of Mn(II), temperature, pH and the NaCl concentration in aqueous phase on the extraction yield of Mn(II) were investigated. The extraction percentage of Mn(II) was up to 99% when R = 1. Both the extraction and re-extraction had good extraction efficiency. Therefore, the extraction of Mn(II) by NaCl/sodium oleate/n-pentanol/n-heptane ME is an effective approach.     

Measurement of the PVTx properties of n-heptane in supercritical water

By means of a constant-volume piezometer, measurements have been made of the PVTx properties of water-n-heptane mixtures at supercritical conditions. The measurements cover the temperature range from 573 to 673 K and pressures from 2 to 30 MPa. Values of excess, partial, and apparent molar volumes were obtained from these measurements. Tests on the piezometer and consistency tests on the measurements suggest that the results are free from significant ‘dead volume’ error. The PVT data for the pure components (water and n-heptane) obtained using the piezometer are in excellent agreement with results obtained by other investigators. The overall accuracy of the pressure, density, temperature, and mole fraction are ± 0.15%, ± 0.5%, ± 10 mK and ± 0.002, respectively.Analysis of the results for dilute water-n-heptane mixtures show that the partial molar volume of n-heptane (solute) and the excess molar volume of the mixture near the critical point of pure water (solvent) exhibit remarkable anomalies. Our results contribute to the formulation of supercritical solubility in near-critical fluids.