Spray Flow Research Articles

A study on droplets dispersion and deposition characteristics under supersonic spray flow for nanomaterial coating applications

Supersonic spray coating of nanomaterials, owing to high impact velocity of particles, offers significant potential to improve the physical and mechanical properties of target surfaces. Rather than handling individual light nano-scale particles directly with a number of limitations, aqueous nanomaterial colloids and suspensions can be supersonically deposited onto surfaces by converting these complex liquid mixtures into the form of atomized micro-scale droplets. Dispersion and deposition characteristics of these droplets play a vital role in the quality and efficacy of the resultant nanomaterial coating. In the present study, comprising numerical modeling and experimental validation, we investigate details of the dispersion and deposition characteristics of droplets under supersonic flow conditions. In the numerical study, a two-way coupled discrete phase modeling is used to track the discrete phase (i.e., droplets) and to investigate the interaction of droplets with the continuous gas phase (i.e., high-velocity driving gas) in regard to their properties and conditions. The results through computational fluid dynamics (CFD) show that driving gas properties (i.e., temperature, pressure, gas type) and droplet size play a prominent role in droplets dispersion and deposition phenomena. In particular, smaller droplets (≤2 μm) are observed to be more susceptible to turbulent dispersion and evaporation. In the experimental study, an atomization-based supersonic spray system is developed for model validation and a case example of nano-coating applications. The CFD modeling results are validated by particle image velocimetry (PIV) measurements. A case study of titanium dioxide (TiO2) nanomaterial coating on a polymer substrate (ITO/PET film) is performed to demonstrate the suitability of the present spray deposition system, which also addresses the current challenges of TiO2 coating onto ITO/PET surface.

Study on Thermal Stratification of Marine Reactor Surge Line Based on Operating Data

The thermal stratification of marine reactor surge line is divided into four types of typical transient based on the operating data: power increase, power decrease, off-design conditions, and small spray flow. The dimensionless Richardson number (Ri) analysis and the numerical simulation calculation of transient conditions are performed separately for these typical transients, generating the thermal stratification section length, duration and maximum temperature difference along the horizontal line section of the surge line under these typical transients. As indicated by the results, the thermal stratification under power increase and decrease transient conditions extends through the surge line just once, and the surge line safety may be affected by the circulating thermal fluctuation at the joint under the power increase transient condition, the thermal stratification of long section, long time and large temperature difference in the horizontal section under the small spray flow transient condition, and the thermal stress fluctuation caused by the off-design conditions. The method of study on thermal stratification of surge line based on operating data, proposed in this paper, lays a foundation for the subsequent thermal stress and thermal fatigue analyses, and also provides reference for the thermal stratification studies of other volumetric equipment.

AN EFFECT OF SPRAY CONFIGURATION AND ADSORBENT MATERIAL ON PERFORMANCE OF THE SPRAY SCRUBBER IN THE DOWNDRAFT GASIFIER-ENGINE SYSTEM

The work aims to investigate an effect of spray configuration and adsorbent material on performance of wet scrubber in removing tar gravimetric in producer gas. The scrubber is installed at small scale downdraft gasifier-engine system and the tests are conducted in two sections. Firstly, the scrubber is tested using water adsorbent at various spray flow configurations to the producer gas flow (cross flow, counter flow, mixed flow). Secondly, the scrubber is tested using adsorbent of cooking oil and waste of engine lubricant at cross flow spray configuration. The performance of the scrubber investigated are temperature profile, log mean temperature difference, heat transfer rate, and tar removal effectiveness. For spray configuration test, the result shows that cross spray configuration (CrS) has the optimum performance. The CsS scrubber has the highest LMTD, heat transfer rate, and tar removal efficiency among others. The values are 29.8°C, 7.84 kW, and 0.43, accordingly. Meanwhile, the test using different adsorbent indicates adsorption property of the adsorbent plays an important rules in tar removal effectiveness of the scrubber. The removal effectiveness of the scrubber for using adsorbent of water, cooking oil, and engine lubricant are 0.43, 0.12, and 0.60, respectively.

Thermal management strategy for electronic chips based on combination of a flat-plate heat pipe and spray cooling

With the rapid development of electronic technology, the required heat dissipation capacities of electronic chips are increasing. In this study, a thermal management strategy for electronic chips based on a combination of a flat-plate heat pipe (FPHP) and spray cooling was designed to improve the heat dissipation performance of the condensation section of the heat pipes. Experiments were conducted to investigate the start-up characteristics of the FPHP, as well as the effects of the inlet temperature and the spray flow rate on the overall heat transfer performance. The best comprehensive performance of the FPHP and spray cooling was obtained when the heat flux was 20–40 W/cm2. In this heat-flux range, the heat pipe had the lowest thermal resistance and the highest thermal conductivity, and the corresponding spray heat transfer coefficient was 168.4 kW/(m2•K), which was significantly higher than those for traditional air-cooled (0.02∼0.1 kW/(m2•K)) and water-cooled radiators (1∼10 kW/(m2•K)). Within a certain range, a higher inlet temperature corresponded to a shorter start-up time of the heat pipe, and the effect of inlet temperature on the heat transfer uniformity of the heat pipe was negligible. Moreover, when the heat flux was less than 30 W/cm2, increasing the inlet temperature would help increase the temperature difference between the evaporation surface and the condensation surface of the heat pipe, and improved the heat transfer performance of FPHP. But when the heat flux was greater than 30 W/cm2, the higher the inlet temperature, the higher the amount of steam in the vapor chamber, the greater the thermal resistance, and the worse the heat transfer performance of FPHP. Increasing the inlet temperature of the cooling medium caused the droplets to vaporise at the entrance of the nozzle in advance, weakening the dissipation effect of the spray cooling. The combination of the heat pipe and spray cooling provides a novel idea for electronic thermal management technology, that is, using two or more cooling technologies to adapt to diverse applications.

Numerical and experimental investigations of the early injection process of Spray G in a constant volume chamber and an optically accessible DISI engine

In this work, the Engine Combustion Network Spray G injector was mounted in the Darmstadt optical-accessible engine to study phenomena typical of multi-hole, early direct-injection events in spark-ignition engines characterized by tumble flow charge motion. Dedicated experimental measurements of both in-cylinder spray morphology and flow velocities before and after the injection process were carried out to assess the adopted numerical setup under real engine conditions. A dynamic secondary breakup model from the literature was coupled with an atomization multi-motion regime model. The model was validated against state-of-the-art ECN Spray G experiments for a constant-volume chamber under low evaporating condition. Then, the simulation of the spray injection in the engine was carried out and the achieved results were compared against the experimental data. Overall, good agreement between experiments and simulations was observed for the spray morphology and velocity fields in both cases. With reference to engine calculations the intake flow was seen to induce spray asymmetry. A partial vortex generated during the intake phase on the tumble plane interacts with the spray, developing into a full vortex which induces an upward flow that stabilizes the spray. The upward flows below the intake valve increase the dilution of the plume outside the tumble plane, which therefore exhibits reduced penetration. Moreover, the intake valves protect from the energetic intake flow the recirculation vortex generated at the tip of the plumes that lie outside the tumble plane. The intake flow helps fuse the vapor fuel clouds of the individual plumes near the injector tip, obtaining a vapor fuel with a shape like that generated by a horseshoe multi-hole injector. Finally, a phenomenological model of the interaction between the multi-hole injector jets and the engine intake flow was introduced to describe the spray evolution in a typical DISI engine.

Dynamic Characteristic Analysis of a Gas–Liquid Swirl Injector Using Planar Laser Imaging

The oscillation of the mass flow rate of the input propellant in liquid rocket engines may induce a periodic heat energy release within the combustion chamber, resulting in operational instability. Since propellant components are discharged from the injector head, the injectors can play a role as a source of oscillation in the dynamic system of a liquid rocket engine. Prior studies confirmed that if the liquid spray and gas flow intersect by using gas-centered dual-swirl injector with tangential inlet in the gas flow path, droplets are generated with periodicity (fracture frequency). In this study, the characteristics and mechanisms of this periodicity were analyzed using longitudinal cross-section spray images. Since the multiple scattering signal that inhibits clarity is non-modulated components, it can be removed by using two modulated images with a phase difference of 180 deg (two-phase structured laser illumination planar imaging technique). And the dynamic characteristics of the gas–liquid spray were analyzed by applying the fast Fourier transform method. It was confirmed by this method that the fracture frequency was related to the impinging velocity of gas and hydrodynamic feature of liquid film. That is, it can be said that fracture frequency of the liquid film is dependent on the liquid Weber number and gas Weber number as the entrainment effect and impact force by gas flow are applied to the liquid film.

Spray characterization of DMC and MeFo on multi-hole injectors for highly boosted DISI combustion engines

In the future, synthetic fuels could replace fossil fuels to minimize the CO2 emissions of combustion engines. Dimethyl carbonate (DMC) and methyl formate (MeFo) represent not only possible synthetic fuels but, due to their oxygen content, also have properties to reduce the pollutant emissions. For a good combustion process, the spray targeting and evaporation properties are important. Due to the less known injection behavior of DMC and MeFo, the spray characteristics were examined in a pressure chamber. The penetration depth, projected spray area, and spray angle were investigated at injection pressures of 100 and 200 bar, chamber pressures of 1 and 2.5 bar, and a temperature variation of up to 90°C for two different injector spray angles and flow rates in comparison with gasoline E5. The spray was recorded with a high-speed camera in a constant-volume chamber with a N2 environment. Both fuels showed a faster evaporation than E5 even with a higher injection mass due to their lower LHV. MeFo showed extreme spray collapse and flash boiling effects, which lead to even faster evaporation rates and higher penetration velocities.

Determination of adhesion of the coating deposited by arc spraying with pulsation of atomizing air flow

During electric arc spraying, during the transfer of molten metal by air flow, there is a significant burnout of alloying elements with the formation of a large amount of oxides, which negatively affects the adhesion of the coating to the base. A solution to the problem of increasing the adhesion strength by using pulsation of the atomizing air flow is proposed. At the optimal frequency of the pulsed flow shut-off, the time of formation of liquid metal droplets at the ends of the electrodes coincides with the frequency of pulses of the spraying flow. As a result, the droplets acquire an optimal size, they are transported by an air flow with conservation of energy, a lower mass of oxygen and, as a consequence, a significant decrease in the oxidation of alloying elements in the sprayed material. The existing test methods of sprayed coatings for adhesion strength to the base are analyzed. The design of a modernized device for determining the adhesion strength is developed and described, which provides complex loading of the coating with a combination of tear-off and shear. The tests revealed a significant (up to two times) increase in the adhesion strength of aluminum, zinc-aluminum and steel (Sv08A) coatings applied with air pulsation. This is achieved by increasing the number of fusion zones of the coating particles between themselves and with the base. It is shown that the effect of the pulsation frequency on the adhesion strength changes along a curve with a maximum corresponding to a frequency of 70–80 Hz, regardless of the coating material. It has been established that the aluminum coating has an increased tendency to oxidation, as a result of which it is 15–20 % inferior to the zinc-aluminum coating in adhesion strength. The data obtained substantiate the use of the proposed spraying technology in production

Use of pulsed spray airflow for electric arc spraying of different types of wires

The object of research is the control of the process of formation of a spraying air flow and the transfer of particles of liquid metal from electrodes during arc spraying. One of the problem areas of the arc spraying process is the oxidation of the sprayed metal particles by the oxygen of the air flow during their transportation to the sprayed surface. This leads to the formation of a sufficiently large amount of oxides of chemical elements, which significantly deteriorate the adhesion strength and burn out alloying elements that are necessary to obtain a wear-resistant and corrosion-resistant coating. The suitability and durability of coatings during use depends on the strength of adhesion to the substrate. In the course of the study, methods were used to determine the adhesion strength of the coating to the base – the Steffens method and methods for studying the microstructure of coatings were taken as the basis. The data was processed and dependencies were plotted. The proposed method makes it possible to improve the quality of the resulting coating in terms of such an indicator as improvements in chemical composition. And also to influence the chemical composition by controlling the process of transfer of molten metal using a pulsating air flow. The obtained results of approbation of the method allow us to consider it effective, as evidenced by the quality of the obtained coatings. This is due to the fact that the correctness of the formulation and solution of the problem provided adequate results. In contrast to the existing methods, the proposed one makes it possible to significantly influence the amount of harmful oxygen involved in the formation of a sprayed coating, which makes it possible to obtain a sprayed layer with the required performance characteristics. And also allows to improve its quality without significant capital costs. In addition, the issues of resource and energy saving are being addressed, since the burnout of chemical elements decreases and the air consumption during arc metallization decreases. To solve this problem, a simple design of the pulsator is proposed, which provides the ability to control the spray flow by adjusting the level of overlapping of the holes.

Optimization Design of Spray Cooling Fan Based on CFD Simulation and Field Experiment for Horticultural Crops

In recent years, horticultural plants have frequently suffered significant heat damage due to excessive temperatures. In this study, a horticultural spray cooling system was designed, consisting mainly of a jet fan and spraying system. CFD simulation technology and response surface methodology were used to optimize the design of the jet fan, which improved the thrust of the fan. The length of the inlet section was 300 mm, the length of the outlet section was 300 mm, the length of the cone section was 450 mm, and the diameter of the outlet was 950 mm, where the thrust of the jet fan was 225.06 N. By establishing the CFD model of spray cooling in a tea field and designing a L9 (34) orthogonal experiment, the effect of the spray parameters on the maximum temperature drop and effective cooling distance was studied, and the best parameters were selected. The simulation results show that the optimum parameters are a spray flow rate of 4.5 kg/s, a droplet diameter of 15–45 μm, a droplet temperature of 298.15 K, and a nozzle double circle layout. Based on the simulation results of the optimized jet fan and spray parameters selected, a spray cooling test bench was established. Field test results show that when the initial ambient temperature was 310.05 K–310.95 K, the maximum temperature drop of the spray cooling fan was 9.1 K, and the cooling distance was approximately 36.0 m. The temperature drop decreased with increasing distance from the fan. This study is of great significance to protect horticultural plants from extremely high temperatures.

Cherry Tree Crown Extraction from Natural Orchard Images with Complex Backgrounds

Highly effective pesticide applications require a continual adjustment of the pesticide spray flow rate that attends to different canopy characterizations. Real-time image processing with rapid target detection and data-processing technologies is vital for precision pesticide application. However, the extant studies do not provide an efficient and reliable method of extracting individual trees with irregular tree-crown shapes and complicated backgrounds. This paper on our study proposes a Mahalanobis distance and conditional random field (CRF)-based segmentation model to extract cherry trees accurately in a natural orchard environment. This study computed Mahalanobis distance from the image’s color, brightness and location features to acquire an initial classification of the canopy and background. A CRF was then created by using the Mahalanobis distance calculations as unary potential energy and the Gaussian kernel function based on the image color and pixels distance as binary potential energy. Finally, the study completed image segmentation using mean-field approximation. The results show that the proposed method displays a higher accuracy rate than the traditional algorithms K-means and GrabCut algorithms and lower labeling and training costs than the deep learning algorithm DeepLabv3+, with 92.1%, 94.5% and 93.3% of the average P, R and F1-score, respectively. Moreover, experiments on datasets with different overlap conditions and image acquisition times, as well as in different years and seasons, show that this method performs well under complex background conditions, with an average F1-score higher than 87.7%.

Sea Spray Icing: The Physical Process and Review of Prediction Models and Winterization Techniques

Abstract Ice accretion on marine vessels and offshore structures is a severe hazard in the Polar regions. There are increasing activities related to oil and gas exploration, tourism, cargo transport, and fishing in the Arctic. Ice accretion can cause vessel instability, excess load on marine structures, and represents a safety risk for outdoor working environment and operations. Freezing sea spray is the main contributor to marine icing. For safe operations in cold climates, it is essential to have verified models for the prediction of icing. Sea spray icing forecast models have improved. Empirical and theoretical models providing icing rates based may be useful as guidelines. For predicting the distribution of icing on a surface at the design stage, computational fluid dynamics has to be applied along with a freezing module. State-of-the-art models for numerical simulation of sea spray icing are still not fully capable of modeling complex ship-sea-wind interactions with spray generation and impact of shipped water. Existing models include a good understanding of spray flow effects and freezing. Further development should focus on developing models for dynamic ship-sea-wind interactions, in particular including spray generation, effects of shipped water, and distribution of icing on the vessel surface. More experimental and full-scale data are needed for the development and verification of new and improved models. Models that estimate ice distribution may improve the winterization design process and reduce the effort required for de-icing. Improved methods for de-icing and anti-icing will reduce the impact of sea spray icing and increase safety for marine operations in cold waters.

Optimization of operational parameters for a photovoltaic panel cooled by spray cooling

This paper presents the optimization of parameters involved in the application of air assisted water spray on the PV panel surface. The effect of spray cooling on panel performance was examined. The increase of cell temperature, hence a decrease of electrical efficiency, was obtained experimentally for a conventional PV panel. In order to prevent a decrease in efficiency, effective parameters were determined. These parameters were examined in 3 levels as spraying time, spray flow rate, nozzle air flow rate, nozzle to panel distance and solar irradiance. Then, 32 experiments were carried out according to the experimental plan obtained using Response Surface Method. As the result, optimum values for highest electrical efficiency were obtained as 49.8990 s for spraying time, 0.0180 m3/h for spray flow rate, 2 m3/h for nozzle air flow rate, 50 cm for nozzle to panel distance and 700 W/m2 for solar irradiance. The most effective parameters were determined to be spray flow rate, spraying time and solar irradiance, respectively. An appropriate correlation with these parameters was proposed for electrical efficiency.

Experimental investigation into the use of emergency spray on suppression of battery thermal runaway

The thermal safety of lithium-ion batteries limits the development of electric vehicles. When the battery heat generation rate exceeds the critical cooling rate of the battery thermal management system, thermal runaway will occur. This article uses spray as an emergency cooling method to suppress battery thermal runaway, which can inhibit the battery heating process when the thermal management system cannot meet the heat dissipation requirements, and ensure thermal safety across the entire temperature range. In this paper, spray is applied to the cooling of battery thermal runaway, and a series of experiments are carried out to study the inhibitory effect of spray cooling on the battery. This experiment explored the influence of spray trigger temperature (Te) and spray duration (ts) on the suppression effect of thermal runaway. In order to achieve a lightweight and economical spray system, whilst ensuring an efficient cooling performance, we tried to analyze the relationship between Te and ts, hoping to quantitatively control spray flow and use the smallest spray flow to achieve suppression.This research provides meaningful results for the application of spray cooling in suppressing battery thermal runaway.

Computational Simulations of Liquid Sprays in Crossflows With an Algorithmic Module for Primary Atomization

Abstract For simulations of liquid jets in crossflows, the primary atomization can be treated with the quadratic formula, which has been derived from integral form of conservation equations of mass and energy in our previous work. This formula relates the drop size with the local kinetic energy state, so that local velocity data from the volume-of-fluid (VOF) simulation prior to the atomization can be used to determine the initial drop size. This initial drop size, along with appropriately sampled local gas velocities, is used as the initial conditions in the dispersed-phase simulation. This procedure has been performed on a coarse-grid platform, with good validation and comparison with available experimental data at realistic Reynolds and Weber numbers, representative of gas-turbine combustor flows. The computational procedure produces all the relevant spray characteristics: spatial distributions of drop size, velocities, and volume fluxes, along with global drop size distributions. The primary atomization module is based on the conservation principles and is generalizable and implementable to any combustor geometries for accurate and efficient computations of spray flows.

Numerical analysis of charged droplets size distribution in the electrostatic coating process: Effect of different operational conditions

This paper presents a numerical performance evaluation of the electrostatic rotary bell sprayer (ERBS) with a particular focus on droplet charge, electric field, and ambient conditions through the implementation of a high-voltage control-ring field pattern effect into the fully turbulent airflow and by including the atomized droplets discrete phase. The simulation shows that the inclusion of droplet charging and electric field coupling, with different parametric values, significantly impacts the atomized droplet distribution over the spray plume and the deposition rate. This analysis was conducted using a three-dimensional (3D) Eulerian–Lagrangian model to describe the two-phase spraying flow by extending the base OpenFOAM package. The procedure includes an unsteady compressible Navier–Stokes solver combined with a large Eddy simulation approach to model turbulence effects on the air flowfield. This is coupled to the spray dynamics by including droplet trajectory tracking, wall film dynamics, and electric field charge. The approach is further extended to include the evaporation phenomenon and the transport of its products. Compared to a conventional ERBS, herein, we provide an in-depth analysis of the fluid dynamic characteristics around the ERBS with a control-ring field pattern for vorticity, velocity, and electrical fields. The results indicate that the control-ring operation improves the performance and transfer efficiency of the ERBS, and it also helps to harmonize the direction of the charged paint droplets. For the first time, finding a balance between the effect of the inside bell cup surface and control-ring voltage and charged droplet has been conducted.

Extending the range of back-lit imaging in two-phase flows using an interrogation-window based method

This paper introduces a novel image processing methodology to enable an extension of the range of applicability of the back-lit imaging method to provide the simultaneous measurement of size and velocity in turbulent flows with a high concentration of objects having various shapes and sizes. The new image processing methodology applies an interrogation-window method similar to that used in particle image velocimetry, alongside interface identification as used in backlight imaging. The matching of droplets or particles of arbitrary shape is achieved by dividing the image into several small windows and cross-correlating objects in each window to obtain a coefficient of dissimilarity, extracted using a variety of metrics of droplet or particle morphology. To demonstrate its utility this technique is applied to measurement of velocities from (i) a highly turbulent spray flow and (ii) a swirling particle-laden flow as applicable to dry powder inhalation systems. Results are validated against phase Doppler anemometry data and a sensitivity analysis of the controlling parameters of the image processing methodology demonstrate that the technique is robust for a variety of input conditions. A key advantage of this approach lies in complementing the diagnostics capability of PDA methods to span a broader range of particle sizes irrelevant of shape and particle concentration.

Effectiveness of a built-in air duct desalination machine with absorption process

Because there is no mature potable desalination machine specifically designed to provide a sustainable water supply to vessels, this paper proposes a built-in air duct desalination machine based on humidification and dehumidification processes. The machine is powered by waste heat exhausted from the vessel’s diesel engines. The humidifier and dehumidifier are stacked so that the structure is compact. The dehumidification process is fulfilled based on the freshwater absorption process. The operating principle and structural design of the machine are introduced. A series of steady state experiments are conducted to assess the effects of heating temperature, hot seawater spray flow rate, and cold water spray flow rate on freshwater production and gained output ratio. The results show that the machine can obtain a freshwater productivity of 19.6 kg/h with gained output ratio of 0.53 when the heating temperature is 90 °C, the hot water spray flow rate is 1 t/h, and the cold water spray flow rate is 1.2 t/h. The freshwater production per volume unit per hour can reach up to 10.5 kg/(m3h). Owing to its superimposed structure, the rising driving force of the water vapor can be fully utilized, and 60% of the normal water productivity can be achieved when the fan is turned off.

New Spraying Modelling of Special Surfaces for Environmental Protection

Research on spraying models of special profiles has a great significance on optimizing spraying quality, saving paint and protecting environment and health of workers. This article establishes a paint deposition model including the spray flow field model and impact adhesion model based on the Euler-Euler method. The model is solved by using polyhedral mesh to divide the fluid calculation domain and the coupled SIMPLE algorithm to compute the governing equations. The methods of spraying along the bus bar and circumferential spraying are applied to simulate and test the conical surface and the arc surface successively. Results of the experiments demonstrate the errors of the four cases are all less and confirm that the established paint deposition model is suitable for spraying research on conical outer surface.

O-16 ペレットストーブの排煙除去に及ぼす噴霧流量の影響

O-16 ペレットストーブの排煙除去に及ぼす噴霧流量の影響