Spray Dispersion Research Articles

Modeling simple-jet mode electrohydrodynamic-atomization droplets' trajectories and spray pattern for a single nozzle system

Electrohydrodynamic atomization (EHDA), or simply Electrospraying is the process of influencing the breakup of a liquid into droplets by using a strong electric field. There can be different modes of Electrospraying depending, basically, on the created electric field strength and the liquid flowrate, for a specified liquid. Among these modes, the so-called cone-jet mode is the most explored one. This is due to its ability to produce highly charged monodisperse droplets in the nano- to micro-meter size range. Another mode of interest, which can also produce monodisperse droplets is the simple-jet mode. This mode is less explored when compared to the former. Within the papers that were explored by the authors, Agostinho et al. (2012) were the first authors to carefully investigate and characterize this mode. In their work, the authors reported about the influence of the electric field and the liquid flowrate on the droplets' size and spray dispersion. They also pointed out that the charge on these droplets can be expressed as a certain percentage of their Rayleigh limit.So far, there has been no model proposed to describe the droplets' trajectories in the simple-jet mode. This paper describes the design and the implementation of a physical model for determining the droplet trajectories in this mode. The model is done, specifically, for a single nozzle/ring-up configuration. It is a two-dimensional model, which solves the force balance equation for each droplet breaking up from the jet. It takes into consideration; the initial droplet velocity, the force of gravity, the electric field force, the inter-droplet coulombic force and the drag force. The droplets' deformation and reorientation were hypothesized, from observations, to play a major role in initiating the droplets' dispersion. They were simulated by implementing periodic displacements on the droplets' center of charge from its center of mass. The calculated droplets' trajectories' envelope angle was fitted to the experimental envelope angle by adjusting the droplet charge around the values that were reported by Agostinho et al. (2012). The model was validated by comparing the shapes of the theoretical and experimental sprays.The model offers new possibilities of modeling the droplets' trajectories in complex geometries, and of introducing additional forces to manipulate their trajectories in the simple-jet mode.

Optimization of spray break-up CFD simulations by combining Σ-Y Eulerian atomization model with a response surface methodology under diesel engine-like conditions (ECN Spray A)

This work evaluates the performance of the Σ-Y Eulerian atomization model at reproducing the internal structure of a diesel spray with a special focus on Sauter Mean Diameter (SMD) predictions. Modeling results have been compared to x-ray radiography measurements [21,24,38] which provided unique data within dense spray region. The first step corresponds to accurately reproduce the large scale spray dispersion. Among different RANS turbulence models, the standard k-ε with the round jet corrected C1ϵ value (1.60), has shown the best performance, as shown in [12]. Then, the study is devoted to the application and optimization of the predicted interphase surface density (Σ). In this work, a combination of CFD modeling and the statistical Design of Experiments (DOE) technique known as Response Surface Method (RSM) is applied in order to improve Sauter Mean Diameter (SMD) predictions from Σ equation compared to experimental measurements. In the investigation, two different optimizations are conducted for the three modeling parameters involved in the equation, following a Central Composite Design (CCD), leading to 15 simulations for each one. After that, both optimum sets of values are validated to assure the accuracy of the method and it is decided the best choice. Finally, different injection and ambient conditions are simulated, with those selected values, providing a remarkable improvement in the modeling performance.

Spatially-resolved spray measurements and their implications

Fire sprinkler manufacturers have developed a great variety of application specific sprinkler designs. Advances in product development practices, performance based design, risk analysis, and fire suppression research have increased stakeholder interest in quantifying the spray produced by these devices. These sprinkler spray patterns consist of complex spatio-stochastic features originating near the sprinkler head. A Spatially-resolved Spray Scanning System (4S) has been developed to capture the complete spatio-stochastic nature of the spray at its point of origin for documentation and analysis. The 4S synthesizes spray measurements, transport analysis, and statistical representation frameworks providing high-fidelity spray characteristics suitable for evaluation of component-level performance (e.g. sprinkler spray pattern uniformity) or system-level performance (e.g. fire suppression system simulations). Each sprinkler's unique spray pattern is captured through optical and mechanical probing of the spray over a measurement (or initialization) surface close to the sprinkler head (0.4−0.8m) and analyzing local drop characteristics (e.g. drop size, velocity, and volume flux). These high-fidelity 4S spray measurements consisting of terabyte scale data densities present remarkable challenges with regard to data management, test repeatability, and test timing. These challenges are addressed through integration of automation, flow control, data acquisition, and data analysis systems. Spatially-resolved sprinkler spray measurements are presented providing insight into the sprinkler spray patterns and their connection with deflector geometry. Comparisons between far-field spray dispersion measurements and simulations initialized with 4S measurements demonstrate unprecedented agreement further highlighting the value of spatially-resolved sprinkler measurements for modern suppression analysis.

Measurements of spray-plume interactions for model validation

Fire suppression using automatic fire sprinklers is tremendously successful in reducing loss of life and property in the event of a fire. With the increasing computing power available, as well as the spread of performance-based design methods, the ability to accurately model spray dispersion and suppression is desirable. In this study, experiments were conducted to quantify spray dispersion and spray-plume interactions for model validation. Numerical simulations of these spray interactions were performed using FireFOAM. These simulations were distinguished by the use of comprehensive highly-resolved initial spray measurements to generate the numerical spray. The experimental Sprinkler Array Facility (SAF) used in this study consisted of a centrally located, well-characterized, forced air jet (simulating the updraft from a real fire plume) providing a challenge to the spray. Reliable model boundary conditions were established from detailed measurements of the air jet injection velocities and detailed measurements of the initial spray using the Spatially-resolved Spray Scanning System (4S). Measurements of volume flux as well as optical measurements of drop size and velocity were obtained at various locations within the air jet. Four flow conditions were investigated with the intent of providing model validation data; close and far sprinkler spacing, each with quiescent air and strong jet conditions. The strong jet was capable of overwhelming the smallest drops within the spray, reversing their direction, and reducing the volume flux at the floor. Computational simulations (informed by detailed initial spray measurements) demonstrated good agreement with the spray dispersion and plume penetration experiments.

The Evolution of a Dispersant Spraying Platform from Turboprop to Jet Engine Aircraft

ABSTRACT Abstract 2017-370.As a result of a successful modification to an Oil Spill Response Limited Boeing 727 aircraft (registration G-OSRA) to enable aerial dispersant spraying, a paper has been written, aiming to provide an insight into the introduction of a turbine aircraft dispersant-application platform and the implications of the evolution from turboprop to jet engine aircraft. Furthermore, Oil Spill Response Limited has recently commissioned and introduced a second aircraft of the same modification specification (registration G-OSRB).As a response technique, dispersant application can have a significant impact on tackling large quantities of oil at sea; however, much of its effectiveness relies on targeting the oil during the window of opportunity in which dispersant will work successfully, in the early stages of the weathering processes.Time is, therefore, a critical factor and it is this key aspect, as well as others explored in detail throughout the paper, that led to the development of a pioneering system, specifically designed to respond to oil spills, that will undoubtedly prove to have a positive impact in terms of response times to incident sites.The paper also presents the reasons supporting the choice of a Boeing 727-2S2F (RE) aircraft as the chosen platform for dispersant spraying operations, such as the power to weight ratio, cargo capacity, and rearward mounted engine positions, to name but a few.It is also important to analyse the benefits of the Boeing 727-2S2F (RE) and the dispersant spraying system it contains during the different stages of the incident life cycle, be it during the preparation phase or the response phase. In the preparation phase, one of the advantages to highlight is the resilience of having two aircraft operated under a back to back schedule of maintenance as envisioned by a maintenance program specially designed to ensure continuous operational availability. During the response phase, aircraft such as G-OSRA and G-OSRB benefit from reduced transit times to incident sites due to the higher speed through the air that is possible with jet aircraft. Also, the paper also compares some key performance indicators such as range and speed between the turboprop aircraft of choice, Hercules L-382 and the Boeing 727-2S2F (RE).

Effect of microbubble-induced cavitation on the dispersion of sprays

An experimental investigation into the effect of cavitation, created from seeded microbubbles, on the dispersion of sprays is presented. The dispersion, determined through laser-induced phosphorescence, shows no significant difference between cavitating and noncavitating conditions.

Investigation of Cycle-to-Cycle Variation of In-Cylinder Engine Swirl Flow Fields Using Quadruple Proper Orthogonal Decomposition

It has been observed that the swirl characteristics of in-cylinder air flow in a spark ignition direct injection (SIDI) engine affect the fuel spray dispersion and flame propagation speed, impacting the fuel mixture formation and combustion process under high swirl conditions. In addition, the cycle-to-cycle variations (CCVs) of swirl flow often degrade the air–fuel mixing and combustion quality in the cylinder. In this study, the 2D flow structure along a swirl plane at 30 mm below the injector tip was recorded using high-speed particle image velocimetry (PIV) in a four-valve optical SIDI engine under high swirl condition. Quadruple proper orthogonal decomposition (POD) was used to investigate the cycle-to-cycle variations of 200 consecutive cycles. The flow fields were analyzed by dividing the swirl plane into four zones along the measured swirl plane according to the positions of intake and exhaust valves in the cylinder head. Experimental results revealed that the coefficient of variation (COV) of the quadruple POD mode coefficients could be used to estimate the cycle-to-cycle variations at a specific crank angle. The dominant structure was represented by the first POD mode in which its kinetic energy could be correlated with the motions of the intake valves. Moreover, higher order flow variations were closely related to the flow stability at different zones. In summary, quadruple POD provides another meaningful way to understand the intake swirl impact on the cycle-to-cycle variations of the in-cylinder flow characteristics in SIDI engine.

Computational sensitivity study of spray dispersion and mixing on the fuel properties in a gas turbine combustor

A swirl stabilized gas turbine burner has been simulated in order to assess the effects of the fuel properties on spray dispersion and fuel–air mixing. The properties under consideration include fuel surface tension, viscosity and density. The turbulence of the gas phase is modeled applying the methodology of large eddy simulation whereas the dispersed liquid phase is described by Lagrangian particle tracking. The exchange of mass, momentum and energy between the two phases is accounted for by two-way coupling. Bag and stripping breakup regimes are considered for secondary droplet breakup, using the Reitz–Diwakar and the Taylor analogy breakup models. Moreover, a model for droplet evaporation is included. The results reveal a high sensitivity of the spray structure to variations of all investigated parameters. In particular, a decrease in the surface tension or the fuel viscosity, or an increase in the fuel density, lead to less stable liquid structures. As a consequence, smaller droplets are generated and the overall spray surface area increases, leading to faster evaporation and mixing. Furthermore, with the trajectories of the small droplets being strongly influenced by aerodynamic forces (and less by their own inertia), the spray is more affected by the turbulent structures of the gaseous phase and the spray dispersion is enhanced.

Spray dispersion measurements of a sprinkler array

A careful measurement methodology has been developed for highly resolved spray dispersion measurements. These measurements are used to establish spatial resolution requirements for evaluation of sprinkler spray patterns and to provide a comprehensive data set for computer model validation. For this study, four nozzles were arranged in a square configuration typical of fire sprinkler system installations. Volume flux of water delivered to the floor was measured 1.5m below the array at locations on a 50mm grid. The detailed measurements accurately portray the spatial variations existing in the spray and indicate that each sprinkler contributes a unique spray pattern. The total mean volume flux was 5.9mm/min, with local measurements ranging from 25% to nearly 400% of the mean value. A spatial averaging analysis suggests that at least 25 measurements should be taken across the reach (i.e. extent) of the spray to resolve gradients in the spray pattern. Fewer measurements provide limited insight beyond the overall mean flux (due to resolution errors), while more measurements become increasingly expensive and less accurate (due to repeatability errors). To quantify the significant spray pattern variations, a meticulous measurement and alignment routine is described to ensure results are sufficiently comprehensive, detailed, and accurate for use in computational model validation.

As-Applied Estimation of Volumetric Flow Rate from a Single Sprayer Nozzle Series Using Water-Sensitive Spray Cards

<abstract> The objective of this study was to test the feasibility of using coverage measurements from water-sensitive spray cards to estimate the volumetric flow rate at an individual sprayer nozzle. TeeJet VisiFlow Even Flat Spray Tips were selected due to their uniform distribution of coverage. Spray distribution for each nozzle was validated using a spray patternator table with 2.5 cm sampling widths. A rotary test fixture translated water-sensitive spray cards through the spray dispersion (water at ambient conditions) at a constant angular velocity and a radius of 1.2 m. The test fixture measured volumetric flow and pressure at the nozzle and recorded data at a rate of 10 Hz. A helical gear pump and a piston-type pressure regulating valve were used to provide constant pressure. The first experiment fixed the test fixture speed at 3.14 rad s-1 and used varying pressures from 70 to 552 kPa (10 to 80 psi) in 70 kPa (10 psi) increments. First-order and second-order regression models were developed for the nozzle series, and validation data were collected at intermediate pressures to test the ability of the model to predict volumetric flow rates. The second experiment fixed the system pressure at 310 kPa (45 psi) and varied the speed of the test fixture at seven increments between 2.0 and 3.8 rad s-1. Spray cards were digitized using a scanner and processed for coverage using the MATLAB image processing toolbox. Results showed that the accuracy of the spray card method was within 1% full-scale of a commercial impeller flowmeter for a single series of nozzles moving at constant speed. Varying speed could be accounted for but required knowledge of the individual nozzle model.

Three-dimensional numerical investigation on wall film formation and evaporation in port fuel injection engines

ABSTRACTWall film formation and evaporation were studied on a flat wall inside a constant-volume vessel using a three-dimensional numerical method. The computation was based on the discrete phase model (DPM) of spray dispersion, a spray–wall interaction model coupled with an enhanced wall film evaporation sub-model, in which the operating conditions of cold wall are considered for port fuel injection (PFI) engines. The influence of impacting parameters including injection pressure, the impingement distance from the injector and the impinged wall, injection duration, impingement angle, and wall temperature was discussed.

STUDY OF ELECTROSTATIC DISPERSION

The article deals with the problems of studying the process of dispersing liquid fuel and water-fuel emulsions, in particular the characteristics of the dispersed spray in high-potential electrostatic fields. The paper deals with the development of a research method for disperse characteristics of liquid fuels, in particular, the changes in the diameter of the spray particles of liquid fuels and water-fuel emulsions based on them, depending on the intensity of high-grade electrostatic field. These studies are relevant in the creation of new devices based on new dispersion, which are not currently used for fuel atomization and combustion devices, in particular based on the electrostatic dispersion. The currently available methods for assessing dispersion are based on the evaluation of the particle diameter, which are formed by dispersing (particle breakage) of the liquid fuel. The views expressed in the course of the study suggest that the dependence of the particle diameter from the electrostatic field can be estimated not only in case of the destruction of the particles (dispersion), but also in case of the formation (growth) of drops during the expiration of the capillary. In order to confirm the provisions the authors developed the installation and technique to study the changes in the dispersion in dependence with the voltage value of high potential electrostatic field. The results of experimental studies are presented and experimental graphics are built for F5 bunker fuel and water-oil emulsions with different concentrations based on it. On the basis of the experimental data processed by correlation analysis method the authors obtained the mathematical model of diameter changes of the particles under the influence of an electrostatic field, which corresponds to the theory of electrostatic dispersion. The developed technique greatly simplifies the determination of the disperse characteristics of liquid fuel in case of electro-static dispersion.

Parametric study on spray cooling system for optimising nozzle design with pre-cooling application in natural draft dry cooling towers

Pre-cooling of inlet air with water spray is proposed for performance enhancement of natural draft dry cooling towers (NDDCTs) during high ambient temperature periods. Previous experiments showed promising results on cooling enhancement using spray cooling. Spray nozzles characteristics are an essential element for designing spray cooling systems. A parametric analysis is conducted on the effect of different spray characteristics parameters and various hollow-cone droplet size distribution patterns on a spray cooling system performance for nozzle design optimisation. A validated Eulerian–Lagrangian 3-D model with a novel nozzle representation method for hollow-cone nozzles was used to perform the analysis. The results can help prepare design principles of effective spray nozzles for spray cooling systems. The results showed a clear trend of increasing spray cooling efficiency as droplet velocity increases due to better spray dispersion. 15% improvement in cooling performance was achieved by increasing droplet velocity from 20 to 80 m/s. A spray nozzle with high injection velocity, small droplet size distribution, large cone angle and a droplet size pattern of mean droplet size increasing towards the spray periphery was found to be the best for sprays with Dv90 ≤ 50 μm. Complete evaporation was successively achieved within 5 m distance using a spray with droplet size distribution of Dv90 = 20 μm and droplet velocity of 120 m/s at an air velocity of 1 m/s.

THE SECONDARY DAMAGE TO BIOLOGICAL OBJECTS IN REMOTE PERIOD (100 DAYS) AFTER THE GAS WEAPON APPLICATION

The objective of the present research was a clarification of possibility of secondary damage to biological objects in a remote period (100 days) after application of irritants chloracetophenone, ortochlorbenzylidenmalonodinitrile, dibenzoxazepine and morpholide of pelargonic acid as components of the gas weapon. In a model experiment, irritants were applied to a fabric target in a quantity corresponding to an estimated concentration arising at the dispersion of a gas spray from a distance of 0.5 meters and 1.5 meters. Data are submitted on a remaining irritant in the target object after 100 days at an open way of storage The toxicity assessment of irritants to a biological test object zoohydrobiont Daphnia magna Straus was carried out. The concentration of irritants extracted from the target object were compared to their toxicity to Daphnia. It was established that chloracetophenone, dibenzoxazepine, and pelargonic acid morphodine preserved their activity and possibility to affect an ecosystem more than 100 days after their application . At the maximum extraction from the target, ortokhlorbenzylidenmalonodinitrile does not preserve its biological activity 100 days after application.

A moments-based algorithm for optimizing the information mined in post-processing spray images

The Moments-algorithm was developed to post-process images of sprays with the aim of characterizing the sprays’ complex features (e.g., trajectory, dispersions and dynamics) in terms of simple curves, which can be used for developing correlation models and design tools. To achieve this objective, the algorithm calculates the first moments of pixel intensity values in instantaneous images of the spray to determine its center-of-gravity (CG) trajectory (i.e., the spray density-weighted centerline trajectory). Thereafter, the second moments (i.e., standard-deviations, σ) of intensities are calculated to describe the dispersion of spray materials around the CG. After the instantaneous CG's and σ's for the instantaneous images have been obtained, they are arithmetically averaged to produce the average spray trajectories and dispersions. Additionally, the second moments of instantaneous CG's are used to characterize the spray’s fluctuation magnitude. The Moments-algorithm has three main advantages over threshold-based edge-tracking and other conventional post-processing approaches: (1) It simultaneously describes the spray’s instantaneous and average trajectories, dispersions and fluctuations, instead of just the outer/inner-edges, (2) the use of moments to define these spray characteristics is more physically meaningful because they reflect the statistical distribution of droplets within the spray plume instead of relying on an artificially interpreted “edge”, and (3) the use of moments decreases the uncertainties of the post-processed results because moments are mathematically defined and do not depend upon user-adjustments/interpretations.

Characteristics of spray angle for effervescent-swirl atomizers

This paper draws a link between the liquid viscosity and the spray angle for effervescent and effervescent-swirl atomizers. The spray angle determines the dispersion and coverage area of the resultant sprays. The swirling the gas–liquid mixture in atomizer led to a significant increase of the spray cone angle at low gas to liquid ratio by mass. Additionally, the orifice shape plays an important role in obtaining the spray angle. The highest values of spray angle has occurred during atomization using profiled orifice. Mathematical analysis shows that spray angle depends on the liquid viscosity, the gas and liquid flow rates and the construction of the atomizer. The data obtained are very important from point of view of the design of atomizers and coverage area of spray.

Dispersion and vaporization of a dilute spray of electrified droplets injected in a coflowing hot gas – Application to the vaporization chamber of a minicombustor

A numerical model of a dilute spray of electrically charged liquid droplets vaporizing in a hot gas is formulated based on a Eulerian description of the gas and Lagrangian tracking of the droplets. The model is used to simulate the dispersion and vaporization of a spray in a cylindrical chamber where the droplets are axially injected with a coflow of hot gas. The effects of the initial size of the droplets and of the gas-to-liquid mass flux and inlet temperature ratios are analyzed, and the conditions under which the droplets fully vaporize in the chamber without impacting on its walls are determined. The ranges of operation where these requirements are met widen when the flow rate of liquid is split into a number of sources and injected through different orifices, which also improves the uniformity of the temperature and vapor mass fraction distributions at the outlet of the chamber. The effects of satellite droplets and of an applied electric field that pushes the charged droplets in the direction in which they are injected are considered.

Experimental Analysis on the Influence of Nozzle Geometry Over the Dispersion of Liquid N-Dodecane Sprays

Understanding and controlling mixing and combustion processes is fundamental in order to face the challenges set by the ever more demanding pollutant regulations and fuel consumption standards of direct injection diesel engines. The fundamentals of these processes haven been long studied by the diesel spray community from both experimental and numerical perspectives. However, certain topics such as the influence of nozzle geometry over the spray atomization, mixing and combustion process are still not completely well understood and predicted by numerical models. The present study seeks to contribute to the current understanding of this subject, by performing state-of-the-art optical diagnostics to liquid sprays injected through two singe-hole nozzles of different conicity. The experiments were carried out in a nitrogen-filled constant-pressure-flow facility. Back pressures were set to produce the desired engine-like density conditions in the chamber, at room temperature. The experimental setup consists in a diffused back illumination setup with a fast pulsed LED light source and a high-speed camera. The diagnostics focused on detecting the liquid spray contour and evaluating the influence of nozzle geometry over the time-resolved and quasi-steady response of the spray dispersion, at similar injection conditions. Results show a clear influence of nozzle geometry on spray contour fluctuations, where the cylindrical nozzle seems to produce larger dispersion in both time-resolved fluctuations and quasi-steady values, when compared to the conical nozzle. This evidences that the turbulence and radial velocity profiles originated at the cylindrical nozzle geometry are able to affect not only the microscopic scales inside the nozzle, but also macroscopic scales such as the steady spray. Observations from this study indicate that the effects of the flow characteristics within the nozzle are carried on to the first millimeters of the spray, in which the rest of the spray formation downstream is pre-defined.

EFFECT OF GEOMETRICAL PARAMETERS INTERACTION ON SWIRL EFFERVESCENT ATOMIZER SPRAY ANGLE

A wider spray angle produced by an atomizer is often required in providing a better spray dispersion. The formation and wideness of the spray angle were reported to be affected by the changes in geometrical parameters. In the present study, the effect of the interaction between two geometrical parameters (swirl-generating vane angle and discharge orifice diameter) on the swirl effervescent atomizer spray angle was studied. A newly-designed swirl effervescent atomizer was developed with 30°, 45° and 60° swirl-generating vane angle and 1.5, 2.0 and 2.5mm discharge orifice diameter. The atomizer performance tests were carried out using water as the working fluid and nitrogen gas as the atomizing agent. High-speed shadowgraph technique was deployed to record the resultant sprays produced. Video recordings, acquired using a high-speed video camera, were converted to a sequence of images for further analysis using image processing software. It was found that geometrical parameters of the newly designed atomizer have a great impact on the formation and characteristics of the spray angle. The combined effect of both swirl-generating vane angle and discharge orifice diameter has produced an increase in the spray angle. The largest spray angle was observed at the largest dimension of both geometries.

Dispersion of feed spray in a new type of FCC feed injection scheme

A new type of FCC feed injection scheme in which the feed is injected downward into the riser to realize a countercurrent contact of feed oil with catalyst particles is put forward. The dispersion of feed spray and flow behaviors of particles in the new type of feed injection scheme are investigated via a large scale cold‐riser model. Experimental results show that the proposed scheme provides a better contact of feed oil with catalyst particles. Furthermore, the centerline equations of both the feed main flow and the secondary flow in the riser are given by introducing a density correction coefficient. The momentum‐ratio of the secondary flow to the main flow is then obtained and the trajectory of the feed main jets as well as the secondary flow is estimated by the centerline equation. The computed results give a reasonable agreement with the experimental data. © 2015 American Institute of Chemical Engineers AIChE J, 62: 46–61, 2016