Full-cone Spray Research Articles

Experimental investigation on fluid structure and full-cone spray characteristics of a jet-swirl atomizer using shadowgraph technique

Full-cone spray is quite important in spray cooling and catalytic combustion applications; however, it is not extensively studied. Besides, the liquid spray is relatively a non-uniform structure especially along longitudinal axis which includes different sizes and distribution of droplets. The few published experimental studies are limited to calculate some of the spray characteristics on a certain plane located downstream of the nozzle exit. Therefore, the spray parameters representing fluid structure, droplets mean diameter, and their distribution in different cross sections from nozzle exit are considered in this study. Accordingly, a jet-swirl atomizer with pressure-swirl full-cone spray is investigated where all important full-cone spray characteristics are considered at different planes from nozzle exit. The spray images are obtained with a shadowgraph technique and are analyzed to obtain the Sauter mean diameter (SMD), D10, and droplet size distribution along with the spray structure, spray cone angle, and discharge coefficient. The experimental results are verified based on the pre-published numerical studies on the same atomizer. The experimental and numerical results show good agreement. Moreover, the results show that the SMD is increased by moving away from center of spray to its edges, and the droplets number density is increased in central regions. The increased droplets number density leads to the greater external forces which create smaller droplets. In contrast, larger particles exist in peripheral parts due to the less droplets concentration. Furthermore, and far away from the exit nozzle, the SMD values are decreased due to the increased aerodynamic forces and oscillations. The droplets dispersion including spray density in radial and axial directions is also observed using spray density images.

Analysis of the Impact of Typical Severe Thermal Hydraulic Condition on the Evolution of Droplet Characteristics in a Spray: the Numerical Simulation

Numerical simulation has been widely applied in the research of spray systems during a severe nuclear plant accident. In order to improve the predictive accuracy of the calculation, the impact of the thermal hydraulic conditions on the development of the spray have been examined by the researchers. The current study presents the influence of the initial droplet distribution at the injection point of a full cone spray. By comparing the velocity of the droplets of different sizes with the experimental results, a reasonable initial droplet size distribution is suggested. Discussions are also performed to explain the divergence between the experiments and the numerical simulation.

STUDY OF METHODS FOR NEUTRALIZING BIODIESEL WITH AQUEOUS SOLUTION OF CITRIC ACID

The production of methyl esters of fatty acids, also called biodiesel, by traditional technology occurs in the presence of an alkaline homogeneous catalyst, which does not react, but only accelerates it, remaining in the manufactured methyl ester of fatty acids and causing engine corrosion. Purification of methyl esters of fatty acids from a homogeneous catalyst must be preceded by its neutralization. An aqueous solution of inorganic (hydrochloric, sulfuric, phosphoric, etc.) and organic (acetic, citric) acids is used for this purpose. The aim of the study is to determine the establishment of optimal and rational parameters for the neutralization of methyl esters of fatty acids. Studies of the effectiveness of neutralization of methyl esters of fatty acids were performed by mixing it with an aqueous solution of citric acid (volumetric method) and by spraying an aqueous solution of citric acid over a layer of methyl ester of fatty acids (aerosol method). Investigations of the influence of the stirrer parameters on the alkalinity of the neutralized methyl ester of fatty acids were performed at temperatures of 20°C, 40°C, 60°C and 80°C and stirrer shaft speeds of 200, 350, 500 and 650 rpm. The stirring time was 5 minutes The study of the effect of nebulizer parameters on the alkalinity of fatty acid methyl ester was performed by spraying 6 ml of an aqueous solution of 1% citric acid per 100 ml of fatty acid methyl ester through a centrifugal full-cone spray "Dis and Core". The spraying time was 1.5-3 s at a pressure of 0.15-0.25 at. It is experimentally established that the neutralization of biodiesel should be carried out in a three-dimensional way at a temperature of 40°C and a rational speed of the stirrer shaft 240-410 rpm/min., While the optimal speed of the stirrer shaft is 323 rpm/min.

Heat flux correlation models for spray evaporative cooling of vibrating surfaces in the nucleate boiling region

New empirical correlation models are constructed to characterise heat transfer associated with spray evaporative cooling of vibrating surfaces - a process involving complex two-phase physics well beyond current numerical simulation capabilities. The proposed correlation models, which account for dynamic, rather than just static surface conditions as in existing models, are constructed using dimensional analysis involving the Generalized Buckingham Π-Theorem. Experimentally-measured spray evaporative cooling data is used to fit the model using the Vibrational Reynolds number and a dimensionless acceleration number which better correlate the influence of surface frequency and amplitude in the nucleate boiling regime. Different coolant flow-rates through a full-cone spray nozzle are used to cool a flat circular test-piece acting as a horizontal surface. The test-piece surface is excited by a shaker through a range of low and high vibration frequencies and amplitudes. The results show that surface dynamic effects certainly influence nucleate boiling, but they also show that surface vibration does not have the same effect for all excess temperatures - dynamic effects can either increase or decrease heat transfer depending on the heat transfer mechanism. These new models are important for thermal management in several areas, particularly involving batteries, power electronics, and electrical machines in automotive and aerospace applications.

Performance of a Monofiber Optical Probe in Determining the Droplet Size and Velocity in Spray Systems Compared with a High-Speed Camera

Optical fiber probe has been recently developed for characterizing the liquid dispersed in gas in droplet form, but its performance has yet been identified for an actual spray system. This work aims to compare the performance of a monofiber optical probe in characterizing the hydrodynamics in spray systems with that of a high-speed camera. Initially, both techniques determined the same series of droplets produced by a syringe. The droplet velocities and sizes obtained from the optical probe were in accordance with the high-speed camera when the droplet coalescence was filtered out from the data. Second, a full-cone spray nozzle was used and the average velocities from the two techniques were close, but the off-center collision on the probe and the difference in size limits caused the discrepancy in the size determination. However, the probe is still beneficial to determine the droplet hydrodynamics and local liquid fraction, the essential characteristics of a spray system.

Experimental and mathematical investigations of spray angle and droplet sizes of a flash evaporation desalination system

This research experimentally studied the effect of operational parameters on spray characteristics of flash evaporation system which is the key component of the discharge thermal energy combined desalination (DTECD) system. For this purpose, initially the effect of superheat degree, inlet pressure, and inlet temperature on the spray angle of three different types of full cone spray nozzles was investigated using a high speed camera. Moreover, a force balanced mathematical model was developed to calculate droplet sizes and the results were compared with experimentally measured values using shadowgraph technique. The results show that the spray angle was largely affected by the superheat degree regardless of nozzle type. In addition, an empirical equation was suggested to correlate inlet pressure, saturation pressure, and spray angle. Further, a model was proposed to estimate the variation of droplet sizes along the spray centreline and concluded that the spray capacity significantly influenced the droplets' lifetime.

Numerical investigation of the full-cone spray structure and characteristics provided by a jet-swirl atomizer

Jet-swirl atomizers are one of the pressure-swirl atomizers that produce full-cone spray. Although many hollow-cone pressure-swirl sprays have been studied, characteristic investigation of pressure-swirl full-cone sprays are limited to a few experimental, analytical, and numerical works where each of them investigate some of the main spray parameters. The few existing numerical studies are limited to calculate the coefficient of discharge and spray cone angle. Current numerical study investigate a newly developed jet-swirl atomizer with pressure-swirl full-cone spray, which considers other important full-cone spray characteristics including Sauter mean diameter, D10, and spray tip penetration along with the spray structure. In this study, a full-cone spray based on a newly developed jet-swirl injector is numerically simulated and analyzed using sprayFoam solver in the OpenFOAM 4.1 software. The existing code of the solver is developed and its dictionary is modified. The C+ + Sauter mean diameter and D10 codes on the cross-sectional surface are developed and this feature is added to the sprayFoam solver. The pre-published experimental and current work numerical results were in good agreement. In the simulation process, blob sheet model is used for the spray primary breakup. Two models including Taylor analogy breakup and Reitz–Diwakar have been used for the secondary breakup of the developed jet-swirl atomizer. This work shows that the results of the Reitz–Diwakar model are close to that of the Taylor analogy breakup model. The time-varying results of Sauter mean diameter, D10, and spray tip penetration are found to be in good agreement in both models. The results show that the Reitz–Diwakar model is stabilized somewhat later than the Taylor analogy breakup model. The simulated spray structure shows that the density of droplets is higher in the spray center region and this density is gradually reduced through the radial direction. The results along the radius show that the diameter of the droplets becomes larger while moving away from the center of the spray.

The effect of ambient pressure on the heat transfer of a water spray

The present work is aimed at quantifying the effects of ambient pressure in the heat transfer at single injections of a full cone spray over a hot metal surface. The experimental configuration is that of a spray impinging down perpendicularly onto a flat surface located at 55mm inside an injection chamber. The experiments were conducted for prescribed initial wall temperatures ranging from single phase to local nucleate boiling and transition regimes of heat transfer. Ambient pressures ranged from atmospheric to 30bar. The analysis is based on spatial resolved measurements of the instantaneous surface temperature during the injection period. The measurements are then processed in order to obtain estimates of the time-averaged values of the local heat flux. The overall cooling rate is also obtained by integrating the local values within the total area of the spray impact. Results show that the amount of heat extracted by the impinging spray increases 3.4 times when ambient pressure is increased from atmospheric to 20bar at the same superheating degree at the wall of 45°C. This corresponds to an increase from 13.3% to 47.7% in the ratio between the actual cooling and the theoretical maximum cooling, defined here as cooling efficiency. This is a result of a better spreading of the liquid film at the wall, covering a larger footprint upon impact. Instantaneous peak heat flux is also increased, as a clear indication of the improved heat transfer between the impinging droplets and the wall.The work presented herein derives from a broader research program devised to develop a system for in-cylinder cooling of internal combustion engines using high pressure water sprays produced by gasoline direct injectors.

Multiphase computational fluid dynamics–conjugate heat transfer for spray cooling in the non-boiling regime

A numerical study is described to predict, in the non-boiling regime, the heat transfer from a circular flat surface cooled by a full-cone spray of water at atmospheric pressure. Simulations based on coupled Computational Fluid Dynamics and Conjugate Heat Transfer are used to predict the detailed features of the fluid flow and heat transfer for three different spray conditions involving three mass fluxes between 3.5 and 9.43 kg/m2s corresponding to spray Reynolds numbers between 82 and 220, based on a 20 mm diameter target surface. A two-phase Lagrange-Eulerian modelling approach is adopted to resolve the spray-film flow dynamics. Simultaneous evaporation and condensation within the fluid film is modelled by solving the mass conservation equation at the film-continuum interface. Predicted heat transfer coefficients on the cooled surface are compared with published experimental data showing good agreement. The spray mass flux is confirmed to be the dominant factor for heat transfer in spray cooling, where single-phase convection within the thin fluid film on the flat surface is identified as the primary heat transfer mechanism. This enhancement of heat transfer, via single-phase convection, is identified to be the result of the discrete random nature of the droplets disrupting the surface thin film.

Analysis of Water Mist Fire Suppression System Applied on Cellulose Fire

Shophouse (Rumah Toko) is a type of building that provides a combined functions for residential and business purposes. Fire risk of shophouse building depends upon the type and volume of the materials stored in the premises. Fire safety improvement for shophouses can be achieved by providing fast response and effective fire supression system such as water mist system. Water mist is a fire supression system that minimizes the risk of material damage by cooling the surface of fuel material. Wood, cellulose material, is one of the most common materials that can be found in shophouse building, thus it is used as fuel material in this experiment. The experimental work was performed in laboratory scale using a single full cone spray with various water pressures of 3, 5 and 7 bar and various fuel placement ((1) center of the room; (2) one corner of the room; (3) all 4 corners of the room). Comparison with numerical simulation using Fire Dynamics Simulator version 6.0 in 1:1 scale with the real test experiment was also performed. Wood crib of 12 cm x 12 cm x 27 cm sizes with an estimated heat release rate of 126 kW/m2 was applied in this work. The water mist nozzle was placed at 2.5 m height above the floor. The water was supplied by a stand alone pump. The results showed that water mist spray can extinguish the fire effectively under 5 minutes, with 7 bar system pressure as the fastest. Droplet coverage area measured from discharge nozzle, increased in accordance with the increase of water pressure. At higher water pressure, water mist can cover larger fuel surface and perform cooling action, to prevent fuel vapor from reacting with oxygen. Water usage calculated for water mist (NFPA 750) for each system pressure of 3, 5 and 7 bar was 0.15, 0.19, and 0.23 LPM/m3,respectively. It shows that water mist system requires far less water consumption than the calculated water requirements for sprinkler system (NFPA 13) of 0.79 LPM/m3 which uses the nozzle's K factor.

Combined three-color LIF-PDA measurements and infrared thermography applied to the study of the spray impingement on a heated surface above the Leidenfrost regime

This experimental study deals with the impingement of sprays on a heated wall in close to semi-industrial conditions. Therefore, an experimental set-up was specifically designed: high liquid mass flux (up to 8kg/m2/s), large droplets (up to 300μm) and high surface temperature widely above the Leidenfrost point (up to 800°C). The surface to be cooled is a 175mm diameter nickel disk with 5mm thickness heated by electromagnetic induction. The spraying devices consist in full cone sprays. Several studies, performed under these particular conditions, has allowed characterizing the heat flux removed by the spray by using techniques based on thermocouples or infrared thermography (IRT). However, to investigate more finely the heat transfer mechanism, it is necessary to measure the droplet temperature but, to date, no measurement for sprays are available in the literature. Therefore, the objective of the present work is to demonstrate the ability of the three-color Laser Induced Fluorescence (3cLIF) to meet this challenge. The combination of the 3cLIF with a Phase Doppler system allows also determining the droplet temperature per size class before and after impact. By adding the IRT measurements combined to an inverse heat conduction model, an energy balance is done in order to estimate the evaporated liquid mass. The influence of the normal Weber number on the liquid vaporization is investigated by using three sprays (Normal Weber numbers up to about 1500). Thereby, main results show that the droplets temperature after impact increases with the incident Weber number before to reach a plateau, attributed to the apparition of the splashing regime. The analysis of the energy balance shows that the mass of evaporated liquid decreases with the incident Weber number and the droplet heating. These first results are in well agreement with previous works conducted with single calibrated droplets, validating as the same time the use of combined 3cLIF-PDA measurements in the case of sprays.

Experimental investigation of spray impingement hydrodynamic on a hot surface at high flow rates using phase Doppler analysis and infrared thermography

Large panels of studies have been performed in order to investigate the dynamic behavior of a droplet during the impingement onto a rigid wall. Most of them are dealing with single droplets and only fewer are devoted to sprays, for which several diagnostics were implemented. Moreover, when sprays are involved, the liquid mass flux is generally quite low (on the order of several kg/m2/s) and the case of a cold surface was mainly considered. Therefore, the present experimental work aims at investigating the impingement of sprays onto hot surfaces (up to 800°C) with liquid mass flux up to 13kg/m2/s. Specifically, the main objective is to characterize the secondary droplets as a function of the surface temperature, starting from the Leidenfrost regime. To that purpose, a 2D phase Doppler analyzer (PDA) is synchronized with an infrared camera in order to measure simultaneously the time evolution of the local droplets size and velocity distributions with the surface temperature. Six full cone sprays were used in order to obtain a wide range of impingement conditions (normal incident Weber and liquid mass flux). A comparison of the impingement characteristics is also performed when the surface remains at room temperature. Another important point concerns also the effect on the spray flow of the presence of the surface. Results show clearly that the incident droplet trajectories are modified by the presence of the solid wall itself and depend strongly on the temperature surface. The in-depth investigation of the impingement characteristics of the spray is mainly focused on the description of the statistical mean diameter and the mass flux after the impingement. The main results highlight that the mean diameter value of the secondary droplets does not change during the Leidenfrost regime and increases for lower surface temperature. This behavior is strongly correlated to the liquid film formation for temperatures lower than the Leidenfrost point. The expelled mass flux exhibits a similar behavior but a decrease is observed after a given temperature, which can be attributed to the deepening of the liquid, leading to a reduction of the number of expelled droplets.

Effect of Spraying Pressure on Spray Cooling Enhancement of Beryllium-Copper Alloy Plate

Spray cooling technology relying on phase change mechanism has a notable ability to remove high heat fluxes. Particular problems are experienced when cooling from the high temperature, stable film boiling regime through Leidenfrost to nucleate boiling. The heat transfer characteristics of water spray impingement cooling of stationary flat surface was numerically investigated. Simulations were conducted on a highly heated plate of known dimensions and made of beryllium-copper alloy. The material is subjected to non-stop intensive cooling beneath a full cone spray nozzle. The only controlling parameter taken during the numerical study was water spray pressure. The effect of the controlling parameter on the cooling rates was critically examined during spray impingement cooling. The thermal investigation was achieved through the solution of heat conduction equation. Experimental data are used to study the influence of the dispersion function g(x, y), by varying spraying pressure from 1 bar to 4 bars, on heat transfer enhancement within the metal initially at the temperature of 815°C.

The effects of a spray slurry nozzle on copper CMP for reduction in slurry consumption

The environmental impact of semiconductor manufacturing has been a big social problem, like greenhouse gas emission. Chemical mechanical planarization (CMP), a wet process which consumes chemical slurries, seriously impacts environmental sustainability and cost-effectiveness. This paper demonstrates the superiority of a full-cone spray slurry nozzle to the conventional tube-type slurry nozzle in Cu CMP. It was observed that the spray nozzle made a weak slurry wave at the retaining ring unlike a conventional nozzle, because the slurry was supplied uniformly in broader areas. Experiments were implemented with different slurry flow rates and spray nozzle heights. Spray nozzle performance is controlled by the spray angle and spray height. The process temperature was obtained with an infrared (IR) sensor and an IR thermal imaging camera to investigate the cooling effect of the spray. The results show that the spray nozzle provides a higher Material removal rate (MRR), lower non-uniformity (NU), and lower temperature than the conventional nozzle. Computational fluid dynamics techniques show that the turbulence kinetic energy and slurry velocity of the spray nozzle are much higher than those of the conventional nozzle. Finally, it can be summarized that the spray nozzle plays a significant role in slurry efficiency by theory of Minimum quantity lubrication (MQL).

An investigation on spray cooling using saline water with experimental verification

A natural draft dry cooling tower rejects heat in a power plant. Spray cooling of the inlet air to the cooling tower improves the total efficiency of the power plant. To overcome the scarcity of natural water sources, this research is studying the usage of saline water in spray assisted dry cooling towers. A nozzle is analysed experimentally. It is shown that the CFD model captures the spray well. A full cone spray is simulated in a vertical cylindrical domain representative of cooling tower flows. To investigate the influences of initial and ambient conditions on the spray performance, fourteen different cases are simulated and trends analysed. It is shown that the distances from the nozzle, after which the dry stream starts (wet lengths), are in the range of 4.3–5.25m depending on the test conditions. A dimensionless study is performed on the wet length and cooling efficiency as the two main parameters. Finally, to predict the wet length and cooling efficiency, two dimensionless correlations are presented and their impact on cooling tower operation is discussed.

Electrolyzed Water Spray Scrubber for Removing Ammonia from Air

<abstract> Ammonia (NH₃) emissions from animal feeding operations (AFOs) are the source of a number of environmental issues. Wet spray scrubbers using non-acidic solutions might be a new approach for NH₃ mitigation from AFOs. A lab-scale spray scrubber was built to clean 0.024 m³ s^-1 of an NH₃/air mixture with an average NH₃ concentration of 20 ppmv. Three variables including contact time, nozzle type, and scrubbing solution were investigated to evaluate their effects on the ammonia removal efficiency of the scrubber. The contact times were set to 0.3, 0.6, and 0.9 s, which were achieved by changing the elevation of the spray nozzle. Two types of spray nozzles were studied. The nozzles had full-cone spray patterns with different spray angles and different droplet sizes. Reverse osmosis (RO) NH₃ gas from air. The maximum removal efficiency of 56% was achieved with the ₃ mass ratios lower than 7.6 in order to avoid N₂, Cl₂, and NH₃ gas losses from the scrubbing solution.

Spray cooling heat transfer on microstructured thin film enhanced surfaces

Experiments were performed with FC-72 (only for flow characteristics) and DI water to investigate heat transfer characteristics from enhanced surfaces through spray cooling. Three different enhanced microstructured surfaces of 50μm SiC, 10μm CNT and 50μm diamond thin films were examined. Three full-cone spray nozzles were used with low mass flow rates of 2.92×10−4kg/s to 17.85×10−4kg/s. Three different nozzle-to-surface distances of 20mm, 35mm and 50mm were tested. Both heat transfer data and spray flow characteristics visualization via a high-speed photographic image of droplet evolution impinging the heated surface were presented and discussed. Results indicate that significant cooling performance enhancement can be reached at about 610W/cm2 with a 50μm thin diamond film for the cases under study.

Sub-cavity liquid volume beneath spray droplet impacts into static liquid layers, and initial estimates of the heat flux required to dry out this volume

The time variation of the sub-cavity liquid volume beneath individual droplet impact cavities was measured for ranges of drop Weber and Reynolds numbers that match those for a full cone spray nozzle of interest. Cavity lifetime was also measured. These results will be used in a Monte-Carlo model of the spray cooling process that is currently under development. Droplet Weber numbers were varied between 140 and 1000. Corresponding Reynolds numbers ranged between approximately 1200 and 3600. These ranges matched Phase Doppler results that were obtained for the water spray under study. Thickness of the static liquid layer into which the single droplets impacted was varied between 0.2 and 1.0 times the droplet diameter.The measured sub-cavity liquid volume generally was between 60% and 80% of the original droplet volume over much of the cavity lifetime. Increasing the static liquid layer thickness increased this plateau value of the sub-cavity liquid volume between these lower and upper bounds, for Weber numbers greater than around 400. Sub-cavity liquid volume also increased somewhat as Weber number was increased. The cavity lifetime increased significantly as Weber number increased.The sub-cavity liquid volume and cavity lifetime results were scaled to values for the corresponding spray droplets at equal (We, Re). These were then used in an energy balance between the energy transferred through a heated wall to the sub-cavity liquid and the sum of the sensible heating and latent heat required to dry out the spray drop sub-cavity liquid volume within the cavity lifetime. These computed heat fluxes to dry out the drop impact cavities were then used to estimate the overall average heat flux for a heated surface that would dry out these individual spray droplet impact cavities. The resulting average heat flux values were between 400W/cm2 and 800W/cm2. These predictions are similar to the range of CHF values reported in the literature for water, of 500W/cm2 to 1000W/cm2.

Visual characterization of heated water spray jet breakup induced by full cone spray nozzles

The present work with specific objectives places a greater emphasis on measurements of the breakup lengths and phenomenological analysis of a hot water jet under reduced pumping pressures in still environment. Therefore, visual and comparative studies are conducted on full cone jet disintegration of heated water for low pumping pressures. A further analysis of the grabbed images confirms the strong influence of the input processing parameters on full cone spray patternation. It is also predicted that the heated liquids generate a dispersed spray pattern by utilizing partial evaporation of the spraying medium. The radial spray cone width and angle do not vary significantly with increasing Reynolds and Weber numbers at early injection phases, leading to enhanced macroscopic spray propagation. The discharge coefficient, mean flow rate, and mean flow velocity are significantly influenced by the load pressure, but less affected by the temperature. The fine scale image analysis also predicts toroidal-shaped vortex formation in the spray structure near the water boiling point.

Визуализация распада струи горячего водного аэрозоля, инициированного коническими форсунками

Визуализация распада струи горячего водного аэрозоля, инициированного коническими форсунками