Spray Jet Research Articles

Experiments on the water entry of curved wedges: High speed imaging and particle image velocimetry

In this work, we experimentally study the water entry of curved rigid wedges. Experiments are performed on two groups of rigid wedges comprising five specimens each. Each group has a fixed mean deadrise angle (25° and 35°) and varying radius of curvature. Drop tests are conducted in free-fall, and the drop height is parametrically varied to investigate the effect of the entry velocity on the pile-up evolution, the impact dynamics, and the energy transferred to the fluid. Specifically, high speed imaging is utilized to simultaneously measure the penetration depth of the wedge and its wetted surface. Experimental results are used to compute the pile-up coefficient, which is found to be largely independent of both the wedge geometry and the entry velocity, while exhibiting modest variations as a function of the penetration depth. In addition, particle image velocimetry is used to investigate the flow physics generated by the water entry, and especially dissect the energy absorbed by the risen water during impact. Results show that between 60 and 80% of the impact energy is consistently transferred to the risen water, which accounts for the formation of the pile-up and the spray jets.

Effect of interaction between spray and attrition jets in a high temperature fluidized bed

A high temperature fluidized bed unit was used with simultaneous liquid injection and jet attrition, using separate nozzles that were located to allow for interactions between the jet cavities they created in the fluidized bed. The effect of jet interactions on liquid–solid contact and particle attrition was studied. When the attrition nozzle was located and inclined so that its jet would interact with the spray jet, there was a large reduction in the formation of large liquid–solid agglomerates, but particle attrition was reduced and the formation of fines was increased. The best results were obtained when the attrition jet hits the spray jet at its base, just downstream of its nozzle tip.

Effect of Viscosity and Heating Temperature on an Intermittent Spray Jet of Starch Dispersion

In this paper, an attempt was made to integrate the effect of jet injection time, load pressure and solution physical properties on jet breakup parameters. A starch-urea-borax complex solution was prepared and tested with an axi-symmetric full cone nozzle. The jet injection time was set to 100, 200, 300 and 400, the solution heating temperature was set to 20°C and 80°C ms, the load pressure was set to 1, 2, 3, 4, and 5 bar, and corresponding spray patterns were imaged by using a high speed camera. The imaging study of the developing spray patterns revealed that the unheated solution forms only spinning jets for all used load pressures. No jet breakup was seen in the near and far-nozzle imaged regions except at 5 bar load pressure, where minor spreading in the jet was seen after 80 mm downstream of the nozzle exit. At 80°C temperature and 5 bar load pressure, very dense spray patterns with an increased spray cone angle were emerging from the nozzle. After 300 ms of injection time, these developing spray jets were changed into fine spray patterns.

Effect of turbulence non-isotropy modeling on spray dynamics for an evaporating Acetone spray jet

The effect of turbulence closure on spray dynamics is studied for three dilute Acetone spray jets using an Eulerian–Lagrangian approach with two-way coupling. A stochastic random walk algorithm is employed to model the droplets’ dispersion. Simulations using different turbulence closure models (i.e. the isotropic SST-k-ω, and the k-∊ realizable models, and the non-isotropic Reynolds Stress Model (RSM)) are compared with the Sydney spray measurements for SP2,SP6, and SP7 spray conditions (Gounder et al., 2012). The experimental mass flow rate, spray mean and rms data are injected for each available size bin during the numerical simulations. Overall, the simulations show good comparisons with the mean and rms spray measurements. The turbulence closure non-isotropy modeling shows relatively weak effect on the spray mean velocity and size profiles predictions, where the RSM predictions was slightly better at the centerline at x/D=10 and x/D=20 for the SP2 mean axial velocity, with similar predictions to the k models for the SP6 and SP7. The RSM, however, consistently predicts better rms axial and radial spray velocity distribution, which indicates more realistic droplet dispersion than the isotropic SST-k-ω and the k-∊. The RSM gas phase shear stresses show that close to the nozzle (i.e. at x/D=5 and x/D=10) the turbulence non-isotropy increases as we approach the centerline and is maximum at the shear layer location at x/D=5. On the other hand, at the downstream locations at x/D=30 the turbulence field non-isotropy increases at the jet edge. A conical region of large size mean droplets (D10>26μm) is observed around the SP2 jet edge. This region disappears quickly for the SP6 and SP7 after the inflow section. The data analysis exhibits that the RSM predicts higher Stokes number than the SST-k-ω due to faster mixing time scales. For the impact on dynamics, at the centerline the SST-k-ω and k-∊ models, predict higher droplets’ slip velocity, higher drag force, and faster droplet’s response than the RSM. The droplets’ tendency for cross-stream dispersion is also found to vary with the turbulence model. The fan spreading phenomenon is observed at the down stream locations away from the nozzle. The results show that the spray turbulence is non-isotropic and lags the gas phase rms values, especially at the centerline. This discrepancy decreases downstream and towards the jet edge. The study shows the importance of non-isotropy modeling on the droplets dispersion and spray dynamics predictions.

Impacts of acetone on the spray combustion of Acetone–Butanol–Ethanol (ABE)-Diesel blends under low ambient temperature

Acetone–Butanol–Ethanol (ABE), an intermediate product in the ABE fermentation process for producing bio-butanol, is considered a promising alternative fuel because it not only preserves the advantages of oxygenated fuels which present lower soot emissions compared to diesel, but also lowers the cost of fuel recovery for individual component during fermentation. The advantageous characteristics of ABE–Diesel include higher oxygen content which promotes soot oxidation; longer ignition delay and flame lift-off length allowing more air entrainment upstream of the spray jet thus providing better air–fuel mixing. With the development of advanced ABE fermentation technology, the volumetric percentage of acetone, butanol and ethanol in the bio-solvents can be precisely controlled. In this respect, it is desirable to estimate the performance of different ABE blends to determine the best blend and optimize the production process accordingly. In this paper, ABE fuels with different component volumetric ratio (A:B:E of 6:3:1; 3:6:1; 0:10:0), were blended with 80% vol. diesel and injected into a constant volume chamber. The combustion characteristics of these blends were experimentally investigated under LTC conditions (ambient temperature of 800K with varying ambient oxygen content). Time-resolved broadband luminosities from the combustion process were captured by a high speed camera and flame lift-off lengths were also acquired. The impacts of acetone and butanol content on the combustion characteristics of the blends were addressed in detail. ABE20(6:3:1) displayed combustion characteristics very similar to those of pure diesel, displaying a much shorter ignition delay than that of the other ABE–Diesel blends due to a high fraction of acetone. At the same time, ABE20(6:3:1) presented a much lower natural flame luminosity (lower soot formation) compared to diesel, owing to its shorter combustion duration and stronger premixed combustion.

Characterization of atomization and combustion in moderately dense turbulent spray flames

This paper presents a study of spray jets and flames where the liquid fuel loading in the carrier air is such that there are substantial liquid–liquid interactions close to the exit plane. The burner consists of an air-blast atomizer located within a wide hot co-flow used to stabilize turbulent auto-igniting spray flames. Laser/phase Doppler anemometry, microscopic backlit imaging coupled with advanced image processing, broadband chemiluminescence and OH-PLIF imaging are utilized. A key focus here is on a novel characterization of the spray boundary condition in terms of non-spherical shapes of fluid fragments. Three different classes of shapes, namely: ligaments, droplets, and large, generally irregular objects are examined. Statistics for each of these fragments are computed in a range of sprays and it is found that their size and probability of occurence depends on the initial Weber number and fuel/air mass ratio (F/A). The change in chemiluminescence emission that is measured as a function of the F/A ratio trends in the same manner as the change in the size of the largest non-spherical objects in the spray. In addition, it is found that changes in the growth of reaction zone width occur as estimated from OH images of laser induced fluorescence, and this is also controlled by the F/A ratio. Therefore, the spray structure at the exit plane may partly dictate the downstream flame characteristics; and this could be largely due to the presence of non-spherical fragments and hence the different rates of atomization and vapourization amongst the different sprays. The burner, as well as the classification of the spray introduced here, while complex, can form a platform for the improvement of models for moderately dense reacting sprays.

A study on the effect of the cushion pressure on a planing surface

The study of a planing flat plate may be considered as a topic of wide interest for academic and industrial applications. From experimental and numerical studies, flow separation occurs near the stagnation point and a thin jet sprays forward along the plate, while a clear wave pattern develops downstream. In the present study, the effect on the jet-root position caused by a cushion pressure applied on the downstream free surface is considered and the consequent variation in lift and drag coefficients is studied. This canonical problem is important in the design of Surface Effects Ships (SES), the bow seal of which may be assumed as a planing deformable surface with a cushion pressure behind it. This study focuses on the hydrodynamic interaction between the plate and the cushion pressure; as such, the plate geometry is prescribed. A two-dimensional numerical study of this problem has been performed in the present work using a finite-volume Chimera-overlapping-grids approach to numerically solve the Navier–Stokes equations; the free surface is handled by means of two-phase level-set method. Validity of the results is assessed by the comparison with theoretical and numerical results available in the literature.

The role of separation of scales in the description of spray combustion

The present paper deals with the description of the interacting multiscale processes governing spray vaporization and combustion downstream from the near-injector atomization region in liquid-fueled burners. One of the main objectives is to emphasize the progress made in the mathematical description and understanding of reactive spray flows by incorporation of rationally derived simplifications based on the disparity of length and time scales present in the problem. In particular, we aim to show how the disparity of the scales that correspond – with increasing values of their orders of magnitude – to the droplet size, interdroplet spacing, and width of the spray jets, ensures the validity of their homogenized description. The two-way coupling associated with exchanges of mass, momentum, and energy between the gas and the liquid phases is dominated by the homogenized exchanges with the gas provided collectively by the droplets, and not by the direct interaction between neighboring droplets. The formulation is used as a basis to address nonpremixed spray diffusion flames in the Burke-Schumann limit of infinitely fast chemical reactions, with the conservation equations written in terms of chemistry-free coupling functions that allow for general nonunity Lewis numbers of the fuel vapor. Laminar canonical problems that have been used in the past to shed light on different aspects of spray-combustion phenomena are also discussed, including spherical spray clouds and structures of counterflow spray flames in mixing layers. The presentation ends with a brief account of some open problems and modeling challenges.

Effect of Nozzle Distance and Fluid Flow Rate in Jet Spray Wafer Cleaning Process

Recently the reduction of the devise sizes causing the semiconductor processes more complicated and becoming more and more sensitive to the particle contamination [1]. Numerous studies have been carried out to improve the device yield with high particle removal efficiency (PRE) and Wet cleaning process along with megasonic is one of the well-established techniques used for particle removal in the semiconductor industry [1, 2]. However as the pattern size is reduced bellow 60 nm this method is not effective to improve the PRE. Recently, two-flow jet spray cleaning process became popular in semiconductor manufacturing processes due to its many advantages [2]. In this process, micron size water droplets are jetted onto a wafer surface at high velocity, which can remove the particles which are on the wafer surface. It consists of two separate nozzles for liquids and carrier gases which are concurrently delivered on the wafer surface during cleaning process. However, there is still lot of scope to improve the PRE during jet spray wet cleaning process by optimizing the process parametrs. Hence in the present study we focused on the jet spray wet cleaning parameters such as nozzle distance from the wafer and the flow rate of the carrier gas to improve the PRE with minimum pattern damage.

Research on Jet Flame Extinguishing Process

The flame used in combustion flame spraying is typical of a high-temperature free jet. The flow fields of free jets are multi-phase flows that couple the mass and heat transfer. This work develops an analytical method to describe free combustion spray jets. The aim of the research is to develop a fully understanding of the characteristics of free-flame jets. Experimental measurements were carried by a unique high-speed continuous CCD camera.

Investigation of Grinding Fluid Supply Parameters on Workpiece Surface Integrity

The grinding heat directly affected workpiece surface in the grinding process and it might produce some defects such as crack and burn. Meanwhile wear debris generated in the grinding process could easily embed grinding wheel blowhole and caused clogging and passivation. So it was particular important to avoid defects and improve the grinding workpiece surface integrity effectively. This paper established an incompressible turbulent fluid spray model based on the study of the existing airflow and the grinding fluid distribution in the grinding zone. Then according to different grinding fluid supply parameters established the two-phase gas liquid spray flow model by using CFD(computational fluid dynamics), simulated and calculated the model, compared the mass flow rate of the grinding fluid flow field with different spray distances, heights, speeds and spray angles in the grinding zone and determined the most reasonable spraying jet position. At the last, through researching on the workpiece surface integrity experiment, it provided an experimental basis to determine the most suitable spray jet position and verify the rationality of supply parameters selection.

High-Temperature Jet Spray Reactor for the Preparation of Rare Earth Oxides by Pyrolysis: Computer Simulation

A new type of high-temperature jet spray pyrolysis (SP) reactor is investigated in this article as part of studies on the preparation of rare earth oxides at Northeastern University (NEU), Shenyang, China. The jet spray reactor examined here is a horizontal, tubular reactor conveying the hot products of the combustion of methane and oxygen with a converging–diverging jet section in an arrangement that provides for inspiration of LaCl3 solution to pyrolyze to La2O3 with the hot gas. The present article is concerned with a computer simulation using a computational fluid dynamic model to develop the velocity, temperature, and pressure profiles in the jet reactor since direct measurement is difficult. The article includes brief comments on a room-temperature model designed to examine the flow characteristics of the jet SP reactor. It was found that the velocity decreased at first, and then it increased near the jet throat. The highest velocity occurred at the throat of jet SP reactor where the LaCl3 enters the unit. Along the reactor axis, the temperature decreases with distance from the gas inlet. The lowest temperature zone was near the wall before the throat of the reactor due to wall heat losses. The temperature was estimated to be close to 1700 K at the throat of the reactor, and it was about 1300 K toward the exit of the reactor. It was shown that a reaction would take place mainly in the throat and in the vicinity of first contact between gas and induced spray. A negative pressure was produced as gas passes through the converging–diverging throat of the jet SP reactor that causes the LaCl3 solution to enter the throat of the reactor. While the investigations of this type of reactor are at an early stage, the results look promising. NEU continues to investigate this approach for the preparation of La2O3 based on high-temperature testwork and physical modeling techniques.

Prevalence and potential factors associated with probable sleep or awake bruxism and dentin hypersensitivity in undergraduate students

OBJECTIVE: To measure the prevalence of probable sleep or awake bruxism and cervical dentin hypersensitivity of undergraduate students and to determine the symptoms associated with these conditions.METHODOLOGY: This was a cross-sectional study. A diagnosis of probable bruxism was reached when students reported clenching or grinding of the teeth during sleep and/or wakefulness, and when they also presented some of the signs and symptoms of bruxism and masseter muscle pain on palpation. Cervical dentinal hypersensitivity was diagnosed by testing for sensitivity to pain in the cervical region of the teeth. Pain was triggered either by touch (using a #5 probe) or by an air jet spray. The sample consisted of 306 university students aged between 19 and 35 years old. The data were stored and analysed using SPSS software, version 15.0 for Windows.RESULT: The prevalence of probable bruxism was 34.3%, with no predominance regarding sex. Probable awake bruxism was more prevalent (61.9%), mostly occurring when the individual reported being in a state of mental concentration (63.1%). There was no association between probable sleep or awake bruxism and dentin hypersensitivity (p = 0.195). Individuals with probable sleep bruxism had increased odds of having muscular pain in the face upon waking (OR = 14.14, 95% CI 5.06-39.55), and those with probable awake bruxism had a increased odds of having facial muscle fatigue when chewing or talking for a long time (OR = 2.88, 95% CI 1.53-5.43) and muscular pain in the face upon waking (OR = 5.31, 95% CI 1.93-14.62).CONCLUSION: The prevalence of probable bruxism was 34.3% and that of HDC was 57.8%, with 22.2% of these subjects also showing probable bruxism. Individuals with probable bruxism tended to have a higher odds of facial pain when they awakened and when chewing or talking for long periods. There were no associations between probable sleep and awake bruxism and cervical dentin hypersensitivity.

Visual Characterization of Airless Water Spray Jet Breakup and Vortex Clouds Formation at Elevated Temperature and Pressure

Most of the Newtonian fluids when heated close to their boiling points exhibit very complex spray structures where vortex clouds may occur due to turbulence in the flow. The objective of the study was to observe the spray jet dynamics and the vortex cloud formation during the atomization of the water at elevated temperature and pressure. For this purpose, visual and comparative studies were conducted on full cone water spray pattern generated by three axi-symmetric spray nozzles of different exit diameters. Using a high-speed camera, the jet breakup dynamics were visualized as a function of water heating temperature and load pressure. The image analysis confirmed the strong influence of the nozzle orifice diameters and processing parameters on spray structure and characteristics. The spray cone angle and width did not vary significantly with increasing Reynolds and Weber numbers at early injection phases leading to increased macroscopic spray propagation. The discharge coefficient, mean flow rate and mean flow velocity were significantly influenced by the load pressure, but less affected by temperature. The fine-scale image analysis also predicted the formation and decay of the semi-torus-like vortex clouds in the spray structures near the water boiling point. For smallest used orifice diameter, these vortex clouds were seen clearly above 1 bar water pumping pressure and at 90°C heating temperature.

Time-resolved spray, flame, soot quantitative measurement fueling n-butanol and soybean biodiesel in a constant volume chamber under various ambient temperatures

The spray, flame natural luminosity and soot quantitative measurement by fueling n-butanol and soybean biodiesel were investigated on a constant volume chamber using multi laser diagnostics with high temporal resolution of 15,037 frames per second. The ambient temperature ranged from 700K to 1000K was applied to mimic the diesel in-cylinder environment covering both conventional and low temperature combustion conditions. Results demonstrate that the transient liquid penetration lengths gradually decrease with the development of injection in a burning spray. The transient liquid penetration length of n-butanol is less affected by the downstream flame and is shorter than that of biodiesel under similar conditions. The two fuels also present drastically different flame dynamics and emission characteristics during the combustion process. n-Butanol displays higher normalized combustion pressure indicating higher potential thermal efficiency. The flame can be observed at reacting spray jet and near wall region for biodiesel, while the main n-butanol flame is concentrated on reacting spray jet. Compared to biodiesel, the flame luminosity of n-butanol is lower and its propagation and distribution is less sensitive to ambient temperatures. Ambient temperature is confirmed as the dominant impact on the soot emissions as the net soot increases for both tested fuels with elevated ambient temperature. No soot emission is detected for either n-butanol or biodiesel at low ambient temperature of 700K. The soot starts to appear at both downstream of the jet and near wall regions from 800K for biodiesel whereas the soot do not emerge until 900K for n-butanol. The soot concentration of n-butanol is also much lower and restricted within the downstream of the spray jet even at high ambient temperatures. A particular interesting observation is that the normalized time integrated soot mass for B50D50 (50% n-butanol and 50% low-sulfur diesel fuel in volume) is 20–30% lower than that of neat biodiesel fuel at different ambient temperatures even though the oxygen content in both fuels is nearly the same. The higher soot formation for biodiesel is explained by the fact that fuel-bound oxygen is less effective in reducing soot production and that higher viscosity and boiling point results in more local high equivalence-ratio region in mixing process. In this regard, n-butanol is more effective in suppressing the soot formation and shows stronger soot reduction capability than that of biodiesel.

Sonochemical growth of SnO2 hollow nanostructures on cellulose acetate flexible substrates

In this paper, we report for the first time tin oxide hollow nanostructures growth on cellulose acetate flexible substrates by sonochemical spin coating. SnO2 particles formed by microwave irradiation of stannous chloride solution in ethylene glycol, used as starting material. Particles were then dissolved in ethanol and ultrasonicated just before ejecting from the spray jet to the substrates placed on the spin coater. The spin rate was maintained at 5000rpm and the process was repeated for several times. All the samples were annealed at 80°C for 2 to 6h and characterized by structural, morphological and optical studies. All the peaks in the X-ray diffractograms are identified and indexed as tetragonal cassiterite structure. AFM and SEM confirm the formation of porous tube- like growth in vertical direction. Strong photoluminescence peak in the visible region makes these structures suitable for flexible optoelectronic applications.

Effects of ambient pressure and precursors on soot formation in spray flames

The effects of ambient pressure on soot formation in spray jet flames are investigated by means of a two-dimensional direct numerical simulation (DNS). In addition, the effects of precursors on soot formation are also discussed. The inception models considering acetylene and polycyclic aromatic hydrocarbon (PAH) precursors are employed and compared in this study. The extended flamelet/progress-variable approach (EFPV) in which heat transfer between a droplet and the surrounding fluid can be considered is employed as a combustion model. Jet A is used as a liquid fuel with considering the detailed chemistry including 274 chemical species and 1537 elemental reactions by the flamelet library. The evaporating droplets’ motions are tracked by the Lagrangian method and the non-equilibrium Langmuir–Knudsen model is used as an evaporation model. Results show that the spray jet flame structure and the soot formation characteristics are considerably affected by the ambient pressure condition. The soot volume fraction increases with increasing the ambient pressure. It is also revealed that the dominant process to promote the soot formation is different between the acetylene and PAH precursor models. It is essential to model a soot inception process with appropriate precursors in order to understand a detail mechanism of soot formation, since the precursor which plays the important role depends on the type of fuel and the combustion conditions.

Study of the characteristic of diesel spray combustion and soot formation using laser-induced incandescence (LII)

In this paper, the planar images of diesel spray combustion flame and soot formation were measured and analyzed by using LII, in a constant volume combustion vessel. The effects of combustion flame and fuel–air mixing characteristics on soot formation and distribution of soot concentration were studied at different conditions. The result indicates that, with increase in ambient temperature and pressure, the ignition delay of diesel fuel is shorter. The increase of ambient temperature and pressure and the reduction of injection pressure shorten the diesel flame lift-off length. The lower the ambient temperature and pressure, the weaker LII signal intensity. At the same ambient temperature and pressure condition, the higher the diesel injection pressure, the smaller the soot production in diesel jet spray, and soot particles are primarily produced in the relative fuel-rich region, which is encompassed by the flame surface front at the downstream of the diesel jet.

Air jet spray of nylon 6 membrane structures for bone tissue engineering

A novel porous nylon 6 (N6) scaffold with high and low porosity was designed using a facile, one-step approach. The scaffold samples were prepared using air jet spray (AJS) to obtain high production rates as an alternative low cost, effective technique with precise thickness control. The present results show that AJS adequately produced interconnected porous networks ranging from micron to submicron scales that were observed using a scanning electron microscope. The effect of AJS on the secondary structure of N6 was examined to identify and quantify conformational changes that occurred due to processing. The mechanical properties of the fabricated samples were tested. The results of tensile tests indicated higher tensile strength of AJS scaffold than that of electrospun scaffold.

CO2 dry cleaning: Acoustic cavitation and other mechanisms to induce mechanical action

High pressure carbon dioxide (CO2) is a potential solvent for textile dry cleaning. However, the particulate soil (e.g. clay, sand) removal in CO2 is generally insufficient. Since cavitation has been proven to be beneficial in other CO2 cleaning applications, this study aims to investigate the possibility of improving the performance of CO2 textile dry cleaning by using ultrasound or other mechanisms to induce the mechanical action such as bubble spray and jet spray. In the experiments, several types of textiles soiled with a mixture of motor oil and soot were cleaned using 1L and 90L CO2 dry cleaning set-ups. Using either ultrasound, stirring, liquid spray or bubble spray does not give a significant improvement on particulate soil removal from textile. It was also found that the additional use of ClipCOO detergent does not give a significant improvement on particulate soil removal either. The cleaning performance of CO2 is 50% lower than that of PER and thus another method to increase the particulate soil removal in CO2 textile dry cleaning still needs to be developed.