Evaporation of single droplets of ethanol-fuel oil mixtures

Measurements of droplet evaporation behaviour are reported for mixtures of pure and denatured ethanol with No. 2 fuel oil. A model for the evaporation of droplets of these mixtures is presented which uses continuous thermodynamics to describe the fuel oil fraction. Activity coefficients were used to describe non-ideal phase equilibrium behaviour. Distribution function parameters for the fuel oil were fitted from a continuous thermodynamics simulation of the ASTM distillation test; this simulation was also used to test the accuracy of the phase equilibrium model. The model is shown to give very good agreement with the measurements. Internal boiling of the liquid is seen to take place during evaporation of the alcohol, but is not sufficiently violent to eject mass from the droplet.     

The role of liquid mixing in evaporation of complex multicomponent mixtures: modelling using continuous thermodynamics

This paper investigates the part played by internal mixing in the evaporation of droplets of mixtures with large numbers of components. Continuous thermodynamics—the use of probability density functions rather than discrete components to represent composition—is applied as the mixture model, and continuous mixture formulations of the liquid phase transport equations and diffusivities are developed. Sample calculations are presented for a mixture with a single distribution function as well as for mixtures with two widely separated distributions (“dumbbell” mixtures, composed of very light and very heavy fractions). The calculations show that internal mixing generally has a smaller influence on droplet behaviour for a mixture with a large number of components than it does for a binary mixture, and give some guidance as to when a well-mixed droplet model may—or may not—be a good approximation for practical work.     

A model for the evaporation of biomass pyrolysis oil droplets

This paper presents a numerical model for the evaporation and pyrolysis of a single droplet of pyrolysis oil derived from biomass. Continuous thermodynamics theory for multi-component droplet evaporation is used, with the fuel being represented by four fractions: organic acids, aldehydes/ketones, water, and pyrolytic lignin, each of which is described by a separate distribution function. Pyrolysis of the lignin fraction is included, and detailed properties for all fractions are presented. The model is compared with the results of suspended droplet experiments, and is shown to give good predictions of the times of the major events in the lifetime of a droplet.     

Pilot plant studies of biodiesel production using Brassica carinata as raw material

In recent years, the development of alternative fuels from renewable resources, like biomass, has received considerable attention. Biodiesel is defined as fatty acid methyl or ethyl esters from vegetable oils, when it is used as fuel in diesel engines and heating systems.

In this context, the cultivation of Brassica carinata as oilseed crop for biodiesel production in the south of Europe (Spain and Italy) and north of Africa has gained special interest, since it allows the use of set-aside lands, giving higher yields per hectare than the traditional Spanish crops.

Methyl or ethyl esters are the product of transesterification of vegetable oils with alcohol (methanol/ethanol) using an alkaline catalyst. In addition, the process yields glycerol, which has large applications in the pharmaceutical, food and plastics industries.

In the present work, the process of biodiesel production for pilot plant using B. Carinata oil as raw materials with methanol and using potassium hydroxide as catalyst has been studied.

The biodiesel quality meets European specifications defined by pr EN 14214:2002 (E). The obtained results have been used for industrial scale up of the process.     

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.     

Evaporation of pure liquid droplets: Comparison of droplet evaporation in an acoustic field versus glass-filament

The rate of heat and mass transfer to droplets in sprays is a critical issue in the design of many industrial spray systems. Applications like fuel injection in internal combustion engines or spray drying stimulate interest in studying the processes related to the evaporation of droplets. In this study an acoustic levitator and the glass filament method are used to observe single droplets during evaporation. The introduction of a droplet into the acoustic field leads to the formation of two steady toroidal vortices close to the droplet surface, known as outer acoustic streaming. The results of this study illustrate how this “outer acoustic streaming” affects the heat and mass transfer. The elimination of these vortices has been achieved through applying a ventilating air flow. Particle Image Velocimetry has been used to characterize the flow field and the interfacial transfer. Furthermore, the resulting evaporation rates have been verified by comparing them with existing model predictions. A comparison of these results to those obtained with the glass-filament method revealed good agreement when the air flow was increased to a limit where the inner acoustic streaming is eliminated, i.e. when forced convection was the primary mechanism in determining the evaporation rate of the liquid droplet. For other air-flow regimes no direct comparisons between results obtained with the two techniques were permissable, as confirmed by the differing Sherwood numbers obtained in the experiments.     

Assessment on the use of biodiesel in cold weather: Pour point determination using a piezoelectric quartz crystal

In order to use biodiesel safely, as an alternative fuel for diesel engines, without fear of cold weather, the pour point of the blends needs to be estimated. This paper is aimed to propose an alternative and easy to use methodology, based on a piezoelectric quartz crystal, to determine the pour point of biodiesels and blended fuels.Impedance and phase of impedance vs. frequency of the piezoelectric quartz crystal change significantly during cooling of biodiesel and biodiesel blended fuels and allows to confirm the role of ethanol as a cold flow improver for biodiesel. Pour point is readily determined by finding the minimum series or parallel frequencies of a barred piezoelectric quartz crystal in contact with the biodiesel blended fuel along cooling. This new methodology only needs the measurement of series frequency, which can be accomplished with high precision by connecting a frequencymeter to a home made oscillator that drives the piezoelectric quartz crystal. Although inexpensive, this new methodology is no more based on visual inspection as the ASTM D97 method, and allows data to be acquired more frequently than the 3 °C intervals recommended by the time consuming standard methodology. In the new proposed methodology, data is acquired while the fuel is at the controlled temperature, which is not possible with the ASTM method, where the test jar needs to be removed from the thermostatic bath for visual inspection.Pour points of biodiesel blends with a commercial diesel fuel determined by this new methodology were compared with the ones obtained by the official ASTM methodology. For samples with pour points ranging from 2.3 °C (pure biodiesel) to −15.0 °C (pure commercial fuel diesel), median pour point values obtained for replicate measurements performed by the two methodologies were not statistically different (α = 0.05), although the results obtained by the new methodology were more precise.     

多种类型液滴蒸发综述

液滴蒸发过程是伴随着复杂变化但又没有统一且充分认知的的过程,是目前一个重要的研究热点,在许多科学应用中起到关键作用。本文介绍了液滴蒸发的历史研究过程,综述了3种不同类型液滴,即纯液滴、二元混合溶液液滴和聚合物溶液液滴蒸发过程的研究成果,分析了液滴蒸发过程中和蒸发结束后沉积物的影响因素,简述了液滴的研究成果在实际生活中的应用。现有研究表明,不同类型液滴的蒸发过程受到多种因素的影响,比如溶液中的纳米粒子、环境温度和压力等。这些因素还会影响到沉积物的图案和大小。目前,研究人员已经研究出典型的液滴蒸发过程（接触线固定和接触角固定模式）,讨论出液滴蒸发基本理论。对一些常见的二元及多元溶液,研究人员已经发现它们与纯溶液蒸发过程的不同之处,并且已经在科学界进行了大量的研究及讨论,建立出数学模型。最后重点介绍了液滴蒸发在医学领域的研究成果、应用和未来发展的方向,比如通过生物液滴蒸发后的沉积物的纳米层,跟正常沉积物对比结果来检测疾病等。最后对液滴蒸发理论的现状、潜力和未来发展需求进行了总结和展望。     

Towards continuous sustainable processes for enzymatic synthesis of biodiesel in hydrophobic ionic liquids/supercritical carbon dioxide biphasic systems

The excellent suitability of immobilized Candida antarctica lipase B (Novozym 435) catalyst to carry out the synthesis of methyl oleate (biodiesel) by methanolysis of triolein in ILs based on imidazolium cations with large alkyl side chain (from C₁₂ to C₁₈) has been demonstrated at 60 and 85 °C. The phase behaviour of IL/triolein/methanol and IL/methyl oleate mixtures were studied at different concentrations and temperatures, the best results (up to 98.6% biodiesel yield after 6 h) being obtained for ILs able to provide monophasic reaction systems, i.e. 1-methyl-3-octadecylimidazolium bis(trifluoromethylsulfonyl)imide). A continuous enzymatic reactor, based on biocatalysts particles coated with hydrophobic ILs, for biodiesel synthesis in supercritical carbon dioxide was studied at 60 °C and 180 bar. The operational stability of the immobilized lipase was improved by its coating with ILs, i.e. 1-methyl-3-octadecylimidazolium hexafluorophosphate, leading to a two-phase systems with respect to the biodiesel product, which showed an excellent catalytic behaviour in continuous operation under supercritical conditions (up to 82% biodiesel yield after 12 cycles of 4 h).     

Nature of some insoluble materials recovered from biodiesel samples

This paper summarises the work carried out over the last few years on the identification of the insoluble material that may affect quality and performance of biodiesel. The correct isolation and purification procedure is important for sediment identification. The main objective is FTIR analysis of the purified materials. In the present report the FTIR technique was used to provide some preliminary information about the nature of the isolated solid product. In every case, starting from this information, several other tests (carried out by TLC, GC, GC/MS and HPLC) were used to identify the real structure of contaminants. Interesting case studies, such as the recovery and identification of waxes, lysophosphatides, filter aids, citric acid salts, steryl glucosides and other contaminating molecules are presented and discussed. For each case, the logical path for the solution of problem is presented, starting from the purification step, through the FTIR spectrum until specific chemical tests.     

Al2O3纳米流体液滴蒸发特性的数值模拟研究

纳米流体液滴蒸发现象在电子设备冷却、喷墨打印以及医学检测等领域都有广泛应用。为了研究水基Al₂O₃纳米流体液滴的蒸发特性,建立了纳米流体液滴蒸发的二维瞬态模型,考虑了纳米颗粒输运行为以及液滴内部流动的影响,并采用任意拉格朗日-欧拉法（ALE）捕捉气液运动界面。基于所建立的模型,分析了水基Al₂O₃纳米流体液滴内部Marangoni流、纳米颗粒初始浓度以及基板温度对纳米流体液滴蒸发特性的影响规律。结果表明,液滴内部Marangoni流会影响气液界面温度分布和蒸发速率。由于液滴内部纳米颗粒浓度分布和气液界面温度发生变化,纳米流体液滴的蒸发速率随着纳米颗粒初始浓度和基板温度升高而增加。     

Phase equilibria of crude oils using the continuous thermodynamics approach

This paper deals with the application of continuous thermodynamics to light and heavy oil systems using the Peng- Robinson equation of state. The composition of the high molar mass components in a reservoir oil is described by a continuous distribution function of some characterizing quantity, e.g. molar mass or boiling temperature. Numerical Gaussian quadrature methods are used to generate pseudo-components and their mole fractions from distribution data. Several examples are presented for phase equilibria of solvent/crude oil systems. The results showed that semi-infinite distribution functions, such as the Γ function, cannot be applied to all cases, e.g. dew point calculations. The Gauss- Legendre quadrature method coupled with spline fitting worked best for heavy oil systems.     

连续化条件下超临界甲醇法制备生物柴油

在连续操作的管式反应器中,以大豆油为原料在压力11～19MPa,温度240～400℃的超临界甲醇条件下进行连续化制备生物柴油的研究。考察了在连续反应条件下醇油摩尔比、压力、温度、停留时间及共溶剂对大豆油转化率的影响。实验结果表明:较高的醇油摩尔比有利于油脂转化率的提高,但当醇油摩尔比超过40:1后提高醇油摩尔比对提高油脂转化率的影响不大;在11～15MPa范围内,压力升高对油脂转化率影响很大,但高于15MPa后压力对转化率的影响减弱;反应温度对油脂转化率有着重要影响,在300℃以上随着温度的升高,油脂转化率有较大幅度的上升,但温度太高油脂会发生分解反应;醇油摩尔比40:1,温度350℃,压力15MPa,停留时间1000s是该实验获得的最佳反应条件,在该条件下油脂转化率可达89%。实验还研究了添加共溶剂四氢呋喃对油脂转化率的影响。     

尿素水溶液液滴的蒸发特性

在石英管式炉上通过挂滴法来观察单个尿素水溶液（urea-aqueous-solution,UAS）液滴的具体蒸发过程,比较了不同环境温度以及不同初始直径大小下液滴的蒸发特性。结果表明,尿素溶液液滴在100～1300 ℃的温度范围内呈现出了不同的蒸发行为。在较高的温度下,液滴的蒸发行为较为复杂,如气泡的产生、液滴的变形以及发生微爆的现象;但是,随着环境温度的降低,这些现象就变得非常微弱甚至消失。同时,还定量分析了稳态蒸发常数与温度、液滴初始直径之间的变化关系,发现在初始直径为2.5 mm、温度在100～600 ℃之间变化的情况下,稳态蒸发常数从0.02075 mm2/s增加到了0.23953 mm2/s,增大了10倍左右。此外,还对气流流速为0.25～1.25 m/s范围内的液滴蒸发特性作了实验研究。当液滴周围有强迫气流存在时,液滴与气体间的换热方式由导热转变为对流换热,从而增强了液滴表面的传热传质能力,促进了液滴的蒸发。     

Continuous screening of base-catalysed biodiesel production using New designs of mesoscale oscillatory baffled reactors

Base-catalysed biodiesel production was continuously screened using new designs of mesoscale oscillatory baffled reactors. Experiments were carried out at very low flow rates, less than 2 ml/min, which would be in the laminar flow regime in non oscillatory, steady state. Initially central disc baffles and helically wound wires were used, but provided insufficient mixing at this scale as demonstrated by glycerol settling. A new design of sharp-edged, helically baffled reactor was developed specifically for this application, which exhibited homogeneous mixing in the two-phase liquid reaction even at these low flow rates and low oscillatory Reynolds numbers. Methyl ester (biodiesel) was produced at a consistent quality and there were clear responses to variations in input conditions. A clear step-change between various steady state molar ratios of methanol to oil and dynamic screening was observed in these mesoscale oscillatory baffled reactors. Rapid screening technique such as this has the potential to significantly reduce process development, operating costs and environmental impact.     

Determination of performance and exhaust emissions properties of B75 in a CI engine application

In this study, performance and exhaust emissions of biodiesel in a compression ignition engine was experimentally investigated. Therefore, biodiesel has been made by transesterification from cotton seed oil and then it was mixed with diesel fuel by 25% volumetrically, called here as B75 fuel. B75 fuel was tested, as alternative fuel, in a single cylinder, four strokes, and air-cooled diesel engine. The effect of B75 and diesel fuels on the engine power, engine torque and break specific fuel consumption were clarified by the performance tests. The influences of B75 fuel on CO, HC, NOx, Smoke opacity, CO₂, and O₂ emissions were investigated by emission tests. The engine torque and power, for B75 fuel, were lower than that of diesel fuel in range of 2-3%. However, for the B75, specific fuel consumption was higher than that of diesel fuel by approximately 3%. CO₂, CO, HC, smoke opacity and NO_x emissions of B75 fuel were lower than that of diesel fuel. The experimental results showed that B75 fuel can be substituted for the diesel fuel without any modifications in diesel engines.     

Transesterification of vegetable oil to biodiesel fuel using alkaline catalyst

Biodiesel is gaining more and more importance as an attractive fuel due to the depleting fossil fuel resources. Chemically biodiesel is monoalkyl esters of long chain fatty acids derived from renewable feed stock like vegetable oils and animal fats. It is produced by transesterification in which, oil or fat is reacted with a monohydric alcohol in presence of a catalyst to give the corresponding monoalkyl esters. This article reports experimental data on the production of fatty acid methyl esters from vegetable oils, soybean and cottonseed oils using sodium hydroxide as alkaline catalyst. The variables affecting the yield and characteristics of the biodiesel produced from these vegetable oils were studied. The variables investigated were reaction time (1-3 h), catalyst concentration (0.5-1.5 w/wt%), and oil-to-methanol molar ratio (1:3-1:9). From the obtained results, the best yield percentage was obtained using a methanol/oil molar ratio of 6:1, sodium hydroxide as catalyst (1%) and 60 ± 1 °C temperature for 1 h. The yield of the fatty acid methyl ester (FAME) was determined according to HPLC. The composition of the FAME was determined according to gas chromatography. The biodiesel samples were physicochemically characterized. From the results it was clear that the produced biodiesel fuel was within the recommended standards of biodiesel fuel.     

The importance of gravity in droplet evaporation: A comparison of pendant and sessile drop evaporation with particles

As a droplet with particles evaporates, the particles deposit on the substrate surface. In this work, we show the extent of gravitational effects on the particle deposition profile and propose a new model for particle tracing in an evaporating droplet which accounts for gravitational effects. Experimentally, we compare pendant and sessile water droplets with 1 and 3 μm polystyrene particles. Numerically, the finite element method was used to create a transport model of the evaporating droplet system and particle deposition. The numerical and experimental results have excellent agreement and show that a pendant water droplet with 1 and 3 μm polystyrene spheres has significant separation of the two particle sizes. Finally, a phase diagaram was created to map different deposition profiles for various gravitational Péclet numbers (Pe_G) and ratios of Péclet number to Damköhler number (Pe/Da). © 2015 American Institute of Chemical Engineers AIChE J, 62: 947–955, 2016     

Modelling of droplet breakage probabilities in an oscillatory baffled reactor

The breakage of droplets dispersed in a continuous aqueous phase determines the performance of many mixing devices and reactors that rely on effective contact between two phases, e.g. emulsion mills, liquid-liquid extraction columns, stirred tank reactors and Oscillatory Baffled Reactors. Quantitative knowledge of the mechanisms involved in the breakage provides parameters for design and prediction. In the work presented here, oil was dispersed in water in a continuous OBR, and a High Speed Camera was used to record the events of breakage of individual oil droplets and probabilities of breakage were estimated. It was confirmed that breakage was more sensitive to changes in the amplitude of oscillation than in the frequency of oscillation. A novel integral model was developed based on an analysis of the total work effected on the deforming droplet in order to interpret the results. The quantitative results from direct observation were compared to the model predictions. The model with fitted parameters was finally extrapolated to smaller diameters, in an attempt to predict the critical drop diameter for breakage.