Hydrocarbon Droplets Research Articles

Measurement of evaporation of hydrocarbon droplets by laser absorption spectroscopy

Concentration measurements of evaporated hydrocarbon species by infrared laser absorption spectroscopy at a monodisperse droplet chain are presented. A droplet generator was installed within a flow channel and operated with cyclohexane, iso-octane, n-heptane, n-pentane and 1-butanol. The flow channel was flushed with a laminar flow of air at different temperatures. The absorption of a HeNe laser beam at $$\lambda = 3.39\,\upmu \hbox {m}$$ traversing through the flow channel at varying distances from the droplet chain was exploited to determine the vapor concentrations of the hydrocarbons. Measurements of the absorption cross sections in a heated gas cell ($$T = 300$$–773 K) enabled the quantification of the absorption signals from the droplet chain. Vapor concentrations were determined in planes perpendicular to the droplet chain. From the increase of vapor concentration between the planes, the evaporation rate could be determined. The evaporation rates were measured in dependence of co-flow temperature, droplet velocity, droplet generation frequency and droplet spacing. In the investigated temperature range of the air (313–430 K) the evaporation rates increased linearly with temperature. The order of the fuels with respect to evaporation rates corresponded with the boiling points of the individual fuels. In addition to the presentation of the results, the paper discusses the performance of vapor concentration measurements by laser absorption spectroscopy at droplet chains which has not been tested before in such a configuration. Particular attention was paid to the spatial resolution of the measurement. The results are well suited to validate models and numerical simulations.

Estimation curvature in PLIC-VOF method for interface advection

Heat and mass transfers’ equations of hydrocarbon liquid droplet are solved numerically by using a semi-implicit method based on the finite volume scheme (VOF). The Piece-wise Linear Interface Calculation (PLIC) is used in our modeling. A curvature estimation technique based on PLIC-VOF method is developed. The determination of the normal vector based on the calculation of the curvature is presented. Then, our numerical calculation is performed for hydrocarbon droplets by realizing several static and dynamic tests. These tests are compared to other techniques. Good agreement between the results of our method and the ones of the other techniques is observed. The deformation of the liquid droplet interface, the ascension of the liquid droplet and the liquid droplet surface regression are observed by taking into consideration the effect of the surface tension force and the drag force. Finally, instead of using smoothed color function, our curvature estimation hugely decreases the spurious current and reconstructs smoothed shape.

An Immersed Boundary Method for flows with evaporating droplets

We present a new Immersed Boundary Method (IBM) for the interface resolved simulation of spherical droplet evaporation in gas flow. The method is based on the direct numerical simulation of the coupled momentum, energy and species transport in the gas phase, while the exchange of these quantities with the liquid phase is handled through global mass, energy and momentum balances for each droplet. This approach, applicable in the limit of small spherical droplets, allows for accurate and efficient phase coupling without direct solution of the liquid phase fields, thus saving computational cost. We provide validation results, showing that all the relevant physical phenomena and their interactions are correctly captured, both for laminar and turbulent gas flow. Test cases include fixed rate and free evaporation of a static droplet, displacement of a droplet by Stefan flow, and evaporation of a hydrocarbon droplet in homogeneous isotropic turbulence. The latter case is validated against experimental data, showing the feasibility of the method towards the treatment of conditions representative of real life spray fuel applications.

TO THE QUESTION OF LOW-TEMPERATURE SEPARATION TECHNOLOGY EFFICIENCY

Currently, natural gas is widely used in the energy and chemical indus- tries. It is as an inexpensive high efficiency fuel. For gas transportation pipeline transport is mainly used, which has high productivity and efficiency. However, in the process of transportation there are various complications. They are: corrosion of the pipeline and equipment, formation and deposition of hydrocarbon liquid, water con- densate and gas hydrates. In order to avoid these problems, it is necessary to carry out field treatment of the extracted raw materials. Gas and gas condensate fields are specified by high pressures within the reservoir at early stages of development. In the process of extraction, gas leaves the well with a significant pressure, of 10-15 MPa and higher. With this feature, it is advisable to treat the gas by low-temperature separation method. By throttling the flow, it is possible to obtain cold practically free due to the energy contained in the high-pressure gas streams themselves. This method is widely used and it requires a minimum of capital invest- ment. Simple service and maintenance of the equipment is also a positive factor. This article considers one of the possible options for gas and gas conden- sate treatment plans, namely the three-stage low-temperature separation used in the gas condensate field of the Urengoy field. For this technologi- cal chain, the main stages of raw materials treatment are considered and the designs of the equipment used are described. In order to evaluate the efficiency of the method and the quality of the products being treated, the results of the gas sample and gas condensate tests are presented, followed by a comparison of the required criteria (characteristic and composition of commercial gas and unstable gas condensate, dew-point temperature, heavy hydrocarbon droplet entrainment) with acceptable values. These data show that with the use of low-temperature separation technology, it is possible to achieve the required quality standards of the products being treated, but thanks to the use of energy from gas streams, the process of purification of petroleum raw materials occurs at a much lower cost.

Modeling hydrocarbon droplet dissolution in near-critical or supercritical water using GCA-EOS and non-ideal diffusional driving force in binary mixtures

In this work, the mixing of a hydrocarbon droplet in near- and super-critical water (NCW/SCW) is mathematically modeled, coupling thermodynamic properties calculation with transport processes. In non-ideal systems, mass transfer is captured using the generalized Maxwell-Stefan equations with the driving force expressed in terms of the fugacity gradients. The GCA-EOS is used to predict the thermodynamic properties and phase equilibrium compositions. We select n-decane, n-triacontane, benzene, naphthalene and 1-decylnaphthalene as representative hydrocarbons. Our simulations show delayed mixing processes as the temperature approaches the upper critical solution temperature (UCST) of the mixture, consistent with the impact of non-ideal diffusional driving forces evaluated from pure thermodynamic calculations. Results also show that the phase behavior notably affects the non-ideal driving forces near the UCST, which confirms the importance of coupling accurate thermodynamic models in predictive mixing studies.

Self-faceting of emulsion droplets as a route to solid icosahedra and other polyhedra

HypothesisTemperature-controlled self-faceting of liquid droplets has been recently discovered in surfactant-stabilized alkane-in-water emulsions. We hypothesize that similar self-faceting may occur in emulsion droplets of UV-polymerizable linear hydrocarbons. We further hypothesize that the faceted droplet shapes can be fixed by UV-initiated polymerization, thus providing a new route towards the production of solid polyhedra. ExperimentsTemperature-induced shape variations were studied by optical microscopy in micron-size emulsion droplets of UV-polymerizable alkyl acrylate. When polymerized, the resultant solid particles’ 3D shape and internal structure were determined by combined scanning electron microscopy (SEM) and focused ion beam (FIB) slicing. The SEM and FIB nanoscale resolution provided a far greater detail imaging than that achievable for the liquid droplets, which could only be studied by optical microscopy, severely limiting their 3D shape determination. FindingsWe demonstrate the formation of solid icosahedra, polyhedral platelets, and rods of hitherto-unreported sizes, well below the 3D-printing resolution (∼20μm). The presence of icosahedral shapes and the absence of any resolvable internal structure at sub-μm length scales, are in line with the surface-freezing-driven mechanism proposed for the faceting phenomenon. Further development of the method presented here may allow large-quantity production of shaped micron- to nano- sized colloidal building blocks for 3D metamaterials and other applications.

Facile Method to Synthesis of Golf Ball-Like Particles via Early-Ceased Seeded Dispersion Polymerization

Golf ball-like poly(methyl methacrylate) particles were produced via seeded dispersion polymerization of 2-ethylhexyl methacrylate with poly(methyl methacrylate) seed beads in the presence of saturated hydrocarbon droplets and evaporation of the hydrocarbon after the polymerization. It was observed that the particles are acquired in the form of a stable dispersion if the reaction is ceased around 42% of monomer conversion. Moreover, the effect of different reaction conditions (e.g. hydrocarbon and stabilizer type, initiator and monomer content, and polarity of the medium) on the shape and stability of the produced particles was investigated. It was revealed that the number and size of the dents on the surface of the golf ball-like particles could be manipulated easily with a simple change in each one of the parameters referred to above. In addition, the experimental results showed that some of the particles become unstable and diffuse into each other during polymerization, resulting in the formation of huge golf ball-like objects. The production of disk-like poly(methyl methacrylate) particles via fully developed seeded dispersion polymerization in the presence of a hydrocarbon which owns lengthy alkyl chain was another interesting finding of this study.

Multi-scale simulation of droplet–droplet interaction and coalescence

In this work, droplet–droplet interaction is modelled using a multi-scale approach which couples multiphase flow simulation using a volume of fluid method to a surface thin film model operating on the sub-grid scale. The volume of fluid model is based on a multiple marker method with a smoothed surface tension calculation, and a thin film model is derived to simulate film drainage using a Reynolds equation approach. A novel method of coupling the two allows for the prediction of coalescence or rebound of colliding droplets essentially from first principles, relying only on a critical film thickness parameter. The model is implemented using the open source tool set OpenFOAM and tested against experimental results of colliding hydrocarbon droplets from the literature. It is found to produce accurate interface deformation results for the duration of the collision, and to consistently predict the outcome of the collision process.

Optimal operation of refrigeration oriented supersonic separators for natural gas dehydration via heterogeneous condensation

Refrigerative supersonic separators (3S's) have found extensive applications in natural gas industry, especially for dew point corrections of water vapor and heavier hydrocarbons. Previous studies indicated that even at heavy refrigeration duties and staggering radial acceleration values (>500,000 g) generated inside 3S units, the condensed water (or hydrocarbon) droplets should have a minimum diameter of 2 µm to provide sufficiently large dehydration efficiencies. To promote the overall condensation rate and facilitate the separation of condensed phase from natural gas streams, certain rates of edible salt particles are assumed in the present article to be injected into the gas flow at the 3S unit entrance. The plenum chamber static vanes are also positioned after the throat location to enjoy the full swirling effect. Our simulation results indicate that by using the optimal structure of the 3S unit for a typical case study, the minimum solid particle injection rate is around 2.4 wt% to achieve almost complete overall separation efficiency of the condensed water droplets. Moreover, the overall pressure recovery of the entire 3S unit can be boosted up to 83% for such optimal structure.

Evaporation and combustion characteristics of hydrocarbon fuel droplet in sub- and super-critical environments

An experimental study on evaporation and combustion phenomena of single suspended hydrocarbon droplets was conducted in sub- and super-critical pressure environments under normal gravity. Droplet temperature and photographs were obtained by utilizing embedded thermocouple and high-speed video camera respectively. Experimental results show equilibrium vaporization stage exists during droplet combustion in sub-critical pressure environments, which accords with quasi-steady assumption. However, the equilibrium vaporization stage disappears during droplet combustion in super-critical pressure environments, quasi-steady assumption is not applicable. Droplet combustion time decreases rapidly with the increase of ambient pressure at sub-critical conditions and phase equilibrium controls the droplet burning rate. In super-critical conditions, the interface between droplet and ambient gas becomes ambiguous, droplet combustion time does not decrease and approaches a stable value; phase change disappears and diffusion coefficient starts to affect the droplet burning rate. The trend change of combustion time variation at critical pressure indicates that the critical pressure point is an important basis for judging whether the droplet enters the super-critical combustion or not. The ratio of droplet evaporation time to droplet combustion time has little change in sub-critical pressure environments, but it decreases rapidly in super-critical pressure environments, this indicates droplet evaporation process completes earlier in super-critical pressure environments.

Modelling the effect of variable density and diffusion coefficient on heat and mass transfer from a single component spherical drop evaporating in high temperature air streams

Species, energy and momentum conservation equations are solved in spherical symmetry and under ideal gas approximation, to yield an analytical model capable to evaluate the heat transfer and the evaporation rate from a single component spherical drop under quasi-steady conditions, accounting for the temperature dependence of mixture density and diffusion coefficient. The model is applied to predict the evaporation rate from water, acetone, ethanol and three hydrocarbon droplets under temperature conditions of interest for applicative fields, like fire control and combustion. The results from the proposed model are compared with those obtained by the classical model where mass diffusion coefficient and gas density are kept constant to an average value. The proposed model is validated against experimental data from the open literature of transient drop evaporation in high temperature air streams.

An analytical membrane‐polarization model to predict the complex conductivity signature of immiscible liquid hydrocarbon contaminants

ABSTRACTAn analytical membrane‐polarization model is developed to predict the frequency‐dependent complex conductivity of hydrocarbon‐contaminated sediments. In the absence of hydrocarbon contaminants, the effect of membrane polarization can be approximated using a recently developed analytical model, which describes the pore space as a sequence of two cylindrical pores of different lengths and radii. Different cation and anion concentrations in the electrical double layer at the pore wall lead to an ion‐selective behaviour causing the membrane‐polarization effect. This model can readily be adjusted to account for a wetting liquid hydrocarbon covering the pore wall. To model the effect of non‐wetting hydrocarbon, we extend the analytical model by introducing a second cylindrical body into the cylindrical pores that represents a discrete droplet of the contaminant phase. In order to account for the high electrical resistivity of liquid hydrocarbons, the corresponding volumes are assumed to be electrically insulating. Because most liquid hydrocarbon surfaces are negatively charged when in contact with an electrolyte, they are covered by a second electrical double layer, which can easily be incorporated into the analytical model. We use our extended model to study the effect of varying saturations of wetting and non‐wetting hydrocarbon on the complex electrical conductivity of the pore system. Our results predict that conductivity magnitude and conductivity phase generally decrease with hydrocarbon saturation. However, if the surface potential at the surface of non‐wetting hydrocarbon droplets is larger than the one at the pore wall, we can observe an increase in the conductivity magnitude with the hydrocarbon saturation and a slight increase in the conductivity phase at intermediate hydrocarbon concentrations. This finding is particularly interesting as it offers a possible explanation for the relation between complex conductivity and hydrocarbon saturation observed in different field and laboratory experiments.

Detection and characterization of hydrocarbon droplets using broadband echosounders

Investigation of the fate and transport of liquid hydrocarbons is limited by the small field of view of current instrumentation. Mass spectrometers, fluorometers, and megahertz sonars—the typical instrumentation for detection and classification of liquid hydrocarbons in the marine environment are limited to detections are ranges of less than a few tens of meters. Lower frequency (80–500 kHz) broadband acoustic backscattering from weakly scattering liquid hydrocarbon targets has been investigated using a novel droplet making device. Results show that such instrumentation should be capable of detections at significantly greater ranges than current instrumentation. The results are compared to a variety of models of acoustic scattering from spherical targets to determine the most accurate model for predicting the frequency response of weakly scattering spheres. The frequency response can be used to characterize the liquid hydrocarbon droplets, as long as the acoustic impedance of the hydrocarbon is well known for the range of temperatures and pressures affecting the droplet.

Secondary atomization of small hydrocarbon droplet by fourth harmonic generation of Nd:YAG pulsed laser

Atomization of small fuel droplets using a UV laser is considered experimentally under atmospheric conditions. The droplet diameters in the experiments are 30µm, 20µm, and 15µm. The maximum spatial resolution is 232nm/pixel. The temporal resolution is 100ns. The fuels under test are diesel oil (JIS K2204, No. 1), hexadecane (99.5%) and o-Xylene (98%). A Nd:YAG pulse laser operating at 266nm is used in the experiments. The maximum laser energy is 10mJ. The laser beam diameter is 5mm, and the flash time is 7ns. As a result, the diesel oil droplets of all diameters are atomized using 10mJ of laser energy. The 15-µm-diameter hexadecane droplets are not atomized. The laser energy threshold for atomization of the 30-µm-diameter o-Xylene droplets is 4.5mJ, and the calculated laser intensity is 450J/m2 under the assumption of a Gaussian distribution. The atomization delay time is almost 8µs. Moisture is observed just before atomization occurs. The moisture indicates that this phenomenon can be explained based on the heat transfer process of the laser energy.

On the role of droplet bouncing in modeling impinging sprays under elevated pressures

Impingement of multiple diesel sprays under an elevated pressure of 30atm is investigated numerically and experimentally, with the particular interest in illustrating the importance of taking into account of the ambient pressure effects in modeling binary droplet collisions. Specifically, a practical while simplified droplet collision model was proposed by modifying the widely-used Estrade et al.’s model to account for the previous experimental observation that hydrocarbon droplets tend to bounce back upon collision at elevated ambient pressures. The KIVA-3V program code implemented with the model was used to simulate the impinging sprays from the previous and the present experiments. The results show that the present model can produce qualitatively satisfactory predictions to the shape, the penetration length, and the Sauter mean diameter (SMD) of the impinging sprays because it accounts for the increased propensity of droplet bouncing at elevated pressures, which however was not considered in any previous models. Due to the limited experimental data on binary droplet collision at elevated pressures, the present model can be treated as a practical approximation for predicting droplet collision outcomes in sprays under high-pressure engine conditions.

Thermal Fouling of Heat Exchanger Tubes due to Heavy Hydrocarbon Droplets Impingement

ABSTRACTThis work discusses fouling in the vapor–steam mixture overheater in the convection section of an industrial steam cracker due to the thermal degradation of heavy hydrocarbon droplets deposited on the tube wall. A spray of heavy hydrocarbon multicomponent droplets is injected in a tube of the vapor–steam mixture overheater and the path of the droplets through the tube is followed by an Eulerian–Lagrangian computational fluid dynamics simulation. To study tube fouling, the droplet impingement behavior on the wall, the evaporation of the deposited liquid, and a coking model describing thermal coke formation due to degradation of heavy hydrocarbons are required. To describe the droplet impingement behavior, a regime map for single component millimeter-sized droplets is taken from the literature. Two simulations are performed to study fouling problems in a vapor-mixture overheater tube. Simulation results are found to be grid sensitive. By analyzing and comparing simulation results it is concluded that reliable fouling data require a regime map for the impingement of multicomponent heavy hydrocarbon micron-sized droplets.

A mechanism for shattering microexplosions and dispersive boiling phenomena in aluminum–lithium alloy based solid propellant

The microexplosive nature of multicomponent liquid fuels has been both studied and fielded to decrease droplet residence times and increase completeness of combustion. However, little work has focused on investigating microexplosive metal fuels to enhance the metal fuel combustion efficiency in traditional energetic material formulations. Microscopic surface videography was performed on two solid propellant formulations, one using aluminum (baseline) and the other with 80/20wt% Al–Li alloy as fuel additives. It was observed that the propellant combustion with neat aluminum formed large molten droplets at the surface as aluminum particles agglomerate, which is a well-known problem with aluminized propellants. In contrast, the Al–Li propellant formed an Al–Li melt-layer on the propellant surface during combustion. Droplets were ejected from the surface melt-layer through dispersive boiling. Above the surface, further dispersive boiling is observed from the ejected droplets and droplet-shattering microexplosions are also observed. These dynamics are thought to be a result of a large disparity in volatility (i.e., boiling points) between the metals in the molten alloy and the large Lewis number in the droplet, so that superheating occurs before the more volatile component (here Li) can diffuse to the surface. A Lewis number of 7440 was estimated for molten 80/20wt% Al–Li alloy, which is nearly three orders of magnitude larger than typical multicomponent liquid hydrocarbon droplets that microexplode, suggesting a higher propensity for molten droplet microexplosions. This would also indicate that a smaller amount of the volatile component might be necessary for microexplosions and dispersive boiling than observed for liquid hydrocarbon fuels. These dynamics are important for metal fuel applications, because injectors cannot be used to decrease droplet size in a metallized energetic material formulation.

Dual-seeded dispersion polymerization: Effect of different polymerization conditions on the shape of the produced particles

Dual-seeded dispersion polymerization (DSDP) of 2-ethylhexyl methacrylate with polystyrene (PS) and poly(methyl methacrylate) (PMMA) seed beads in the presence of saturated hydrocarbon droplets followed by evaporation of the hydrocarbon was studied. The effect of various polymerization conditions including initiator type and content, stabilizer type and concentration, and different hydrocarbon’s content on the shape of the obtained particles was investigated. The increase of concentration of 2,2'-azobis(isobutyronitrile) (AIBN) had no effect on the shape of the produced almond-shell-like PS particles, although it contributes in the formation of associated composite particles along with larger poly(2-ethylhexyl methacrylate) (PEHMA) beads produced by secondary nucleation. The experimental results showed that other initiators led to the formation of stable golf-ball-like PMMA particles as well as PS ones with symmetric shape. The type of stabilizer did not affect the shape of the particles. This observation suggests that unique almond-shelllike PS particles can be produced through a stabilizer-free DSDP process. The lowering of the concentration of hydrocarbons with long alkyl chains yielded stable disc-like PMMA particles. The formation of functional almond-shell-like particles by using light hydrocarbons was another interesting finding of this research.

An evaluation of the frequency response of hydrocarbon droplets

Development of instrumentation to detect and quantify submerged oil droplets would provide researchers and oil spill responders with crucial information about the fate and movement of oil in the environment. By detecting oil droplets in the watercolumn it should be possible to trace surface sheens to their source and to determine the location and extent of plumes of oil at depth. Methods of detecting oil currently exist, for example, mass spectrometers and fluorometers; however, they are limited to detecting oil that is submeter range from the instrument. Using broadband high frequency (30–300 kHz) acoustic echosounders, it is possible to not only detect oil droplets from a greater distance (10s of meters for individual droplets, depending on the background noise) but to quantify the physical properties of the oil, including the size of droplets. Droplet size is an important factor in determining the likely location of submerged plumes and surface sheens, the rate of biodegradation and rise rate of oil. L...

Combustion characteristics of diesel and Jet-A droplets blended with polymeric additive

Recent experimental research has shown that the addition of long chain polymers to hydrocarbon fuel imparts non-Newtonian characteristics to the fuel which results in suppressed splashing behavior upon spilling over a surface and consequently improves fire safety. In this study, combustion of stationary fuel droplets of Diesel and Jet-A doped with different percentages of a long chain polymer (Polybutadiene) was examined and compared with the normal hydrocarbon behavior. In contrast with hydrocarbon droplets with no polymer addition, several zones of combustion including a slow and steady burning zone, a strong swelling zone and two fast and fairly steady combustion zone were also detected. It was found that combustion of polymer added fuel is controlled by the boiling point of more volatile component, i.e. base fuel. Therefore, initially the base fuel is transported to the droplet surface and evaporates. However, polymer addition turned out to slightly decrease burning rate in this stage. Viscosity was found to be the dominating factor that suppresses diffusion of volatile species to the surface and hence reduces evaporation rate at early stages of combustion. Increasing polymer content also resulted in stronger swelling behaviors as well as reduced burning time for both diesel and jet fuel droplets.