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The objective of this study was to review representative publications for improved knowledge of spraying dense field crop canopies to augment the current understanding of the interaction between target foliage characteristics, spray practices, and the environment. Emphasis was placed on measured deep-canopy spray deposits made by full-scale sprayers and studies of airflow within and around crop canopies. Airflow could act as a spray droplet carrier and/or indicator of the internal canopy structure that restricts droplet penetration. High variation in natural airflows was noted in several studies. Crop canopy descriptions for spray studies were generally limited to overall canopy/row dimensions, descriptions of individual plant structures, leaf shapes, and leaf area index. Few studies evaluated the internal canopy "openness" with characteristic shape and size of internal volumes that would accommodate spray droplet trajectories. There have been significant increases in available spray tip designs with multiple orifices, discharge configurations, and droplet sizes that offered the applicator many choices. Advanced sprayer technologies ranging from nozzle control to sensor navigation are available, provided that suitable algorithms can be developed in a timely manner that pertain to a wide variety of spray and crop conditions. The air-assist technique provides a dynamic alternative to traditional over-the-top sprays for increasing spray penetration and deposit, advocating that the specifics of air discharge, spray droplet sizes, and canopy structure can be integrated. The complexity of the spraying process needs an extensive collaborative effort of many stakeholders to develop solutions for sprays to penetrate foliage that is subject to diseases and pests. [ABSTRACT FROM AUTHOR]

The objective of this study was to review representative publications for improved knowledge of spraying dense field crop canopies to augment the current understanding of the interaction between target foliage characteristics, spray practices, and the environment. Emphasis was placed on measured deep-canopy spray deposits made by full-scale sprayers and studies of airflow within and around crop canopies. Airflow could act as a spray droplet carrier and/or indicator of the internal canopy structure that restricts droplet penetration. High variation in natural airflows was noted in several studies. Crop canopy descriptions for spray studies were generally limited to overall canopy/row dimensions, descriptions of individual plant structures, leaf shapes, and leaf area index. Few studies evaluated the internal canopy "openness" with characteristic shape and size of internal volumes that would accommodate spray droplet trajectories. There have been significant increases in available spray tip designs with multiple orifices, discharge configurations, and droplet sizes that offered the applicator many choices. Advanced sprayer technologies ranging from nozzle control to sensor navigation are available, provided that suitable algorithms can be developed in a timely manner that pertain to a wide variety of spray and crop conditions. The air-assist technique provides a dynamic alternative to traditional over-the-top sprays for increasing spray penetration and deposit, advocating that the specifics of air discharge, spray droplet sizes, and canopy structure can be integrated. The complexity of the spraying process needs an extensive collaborative effort of many stakeholders to develop solutions for sprays to penetrate foliage that is subject to diseases and pests. [ABSTRACT FROM AUTHOR]

Metal droplet-based 3D printing provides unique advantages for fabricating micro complex parts. Especially, assisted by soluble support, structures with high-quality inner surfaces can be directly printed without post-processing, which is very promising for the fabrication of waveguides and antenna horns. Here, a spatially distributed equidistant helical deposition strategy with only one-step positioning was proposed to improve the inner surface quality of the parts, and a five-axis motion stage was designed for matching its motion planning. The influence mechanisms of key process parameters on the forming quality were investigated. The droplet positioning errors, the aggregation behaviour, and the hole-defects formation on sloping surfaces were analyzed. As a proof-of-concept, a horn-structured tube was directly printed via the proposed printing method, which possessed both high-quality cavity surfaces and high density. This work paves the route towards the efficient additive manufacturing of metal tubes with high-quality inner surfaces. [ABSTRACT FROM AUTHOR]

Numerical simulations of the spray coating process with an electrostatically supported high-speed rotary bell with internal charging were carried out, focusing on the effects of droplet charge on the spray formation, the film thickness distribution on the target and the transfer efficiency. From simulation results of the electrohydrodynamics (EHD) atomization process close to the bell edge, droplet size-to-charge relationships and initial droplet velocities were derived and used in the present coating simulation. Three different droplet charge models were applied and the resulting electric fields were analysed. It was found that the droplet size-to-charge relationship plays an important role for the spray-painting performance. Despite a relatively low influence of the charging model on the transfer efficiencies (TE), varying between 89 % and 94 % at an experimental TE of 94 %, significantly different film thickness distributions on the target were found. The best agreement between measured and simulated film thickness distributions was obtained using the proportionality between charge and droplet volume as indicated by the EHD-breakup simulations. Furthermore, effects of the initial droplet positions and velocities were analysed, comparing simulative and experimental results with respect to film thickness distributions on the target and droplet velocity profiles downstream the bell. • Simulation of spray coating process with an electrostatically supported high-speed rotary bell with internal charging. • Comparison of electric field using three different droplet charge-to-diameter models. • Very good results were obtained for the droplet charge model based on the EHD-breakup simulation. • Effects of the initial droplet positions and velocities were analysed here please another bullet: ° Comparison between simulation and experiment for film thickness distributions and the transfer efficiencies. [ABSTRACT FROM AUTHOR]

• A measurement model of optical fiber probe is constructed based on wave optics simulation. • The effective field of view for the probe and the detectable interface inclination are revealed. • The sensitivity of the probe to different droplet sizes, eccentricities, and trajectories is investigated. • Characteristics of the pre-signal are verified by simulation and experimental results. Fiber optical reflectometer (FOR) is a novel technique for dense droplet detection that combines conventional phase detection with non-invasive velocity measurement capabilities. In this study, the mechanism of FOR technique and its sensitivity to droplet trajectory are investigated by wave optics simulation and experiment. This paper first describes the simulation method and analyzes the dynamic response of probe during the droplet piercing process. Next, an exploration is conducted on the effective field of view for the probe and the detectable interface inclination. Afterwards, by precisely controlling the droplet size, eccentricity, and trajectory, the simulation reveals the sensitivity of FOR technique to droplet parameters and quantifies the accuracy of measurement on droplet velocity, which provides specific guidance for the design and application of FOR technique. Finally, in the static experiment, the measurement error of the droplet axial velocity is controlled within 13 %, which verifies the reliability of the simulation results. [ABSTRACT FROM AUTHOR]

Abstract This study presents the elaboration of controlled microstructure of yttria stabilized zirconia (8YSZ) coatings by using an axial suspension plasma spraying (SPS) system. Several 8YSZ coatings were fabricated from porous to dense by using same starting feedstock powder via adjustment of the suspension concentration and the deposition distance. The microstructure control is strongly related to the flying droplet size and its momentum in front of the substrate surface. Both aspects significantly determine the droplet flattening behavior, the deposit size, and therefore the final coating microstructure. Graphical abstract Unlabelled Image Highlights • Axial suspension plasma spraying and controlling the coating microstructure • Suspension solid-load content, spraying distance and droplet size • Droplet trajectory, momentum, and impacting on substrate • 8YSZ coatings from porous to dense microstructure by same system [ABSTRACT FROM AUTHOR]

In this paper, a theoretical predictive model is developed to investigate the heat and mass transfer from saline water droplets in cold seas and ocean regions. Also, the trajectory and cooling process of saline water droplets during flight over marine platforms are analyzed. The predictive model considers convection, evaporation, and radiation heat transfer from the droplet's surface to the ambient air. The results show that droplets with medium sizes can reach their maximum heights and horizontal positions at the moment of impact on the deck during flight over marine platforms. For small water droplets of approximately up to 1.1 mm, a uniform temperature within the droplet is found to be a reasonable approximation. The temperature gradient inside the droplet is small for larger droplets, because the Biot number is less than 0.5. The results indicate good agreement between the predicted results and previously published data. A sensitivity analysis is performed to examine the effects of various parameters on the trajectory and cooling process of the droplets as well as a droplet's Biot number. This analysis shows that the parameters of air temperature, droplet size, initial droplet temperature, and droplet flight time have a significant impact on the droplet cooling process, although the size of marine platforms is an important factor. Also, wind velocity plays a considerable role on the trajectory of the droplets. This model is a useful and relatively simple design tool for the analysis of thermal behaviour and prediction of the cooling process of saline water droplets. [ABSTRACT FROM AUTHOR]

Breakup of water in wave-impact sea spray is examined in this paper. The formation of a spray cloud, caused by high energy striking of a sea wave on the bow or hull of a marine vessel, is dependent on the water breakup phenomena and droplet trajectories. The Weber and Reynolds numbers are key parameters defining the thresholds at which breakup begins. The model uses “stripping breakup” and “bag breakup” characteristics to demonstrate the breakup phenomena. A combined breakup model with droplet trajectories is developed in this paper to predict the extent of the breakup phenomena. The governing equations of breakup and trajectories of droplets are solved numerically. Stripping breakup occurs from the beginning of the breakup phenomenon and finishes in front of the vessel. Bag breakup completes the stripping breakup to create stable droplets with constant diameters. A sensitivity analysis evaluates the response of the model to various ranges of initial conditions. Numerical results have reasonable agreement with the size-velocity dependence characteristics at the tip of the bow. The extent of the spray as well as wet heights, obtained by the numerical solutions, are consistent with field observations reported for a Medium-sized Fishing Vessel (MFV). [ABSTRACT FROM AUTHOR]

The spatial distribution of droplets in a spray cloud created by wave-impact sea spray and the distribution of their sizes and velocities over a vessel deck are investigated. Existing mono-size and mono-velocity models of sea spray are not accurate enough for modelling marine icing phenomena. Wave-impact sea spray creates numerous droplets in front of and around a vessel. Droplets are the result of sheet and droplet breakup of sea water. The velocity-size dependence of the resultant droplets causes the creation of various sizes and velocities of droplets. A droplet trajectory method employs the velocity-size dependence of the droplets to find their spatial distributions in the cloud of spray over the vessel deck. Drag and body forces overcome the initial velocities of the droplets, and consequently, they follow the wind and gravitational directions. The motion of the droplets affects the shape and extent of the spray cloud over the vessel. A numerical scheme is used to find the distribution of sizes and velocities of the droplets over a vessel. Results show that neither the smallest nor the largest droplets reach the maximum height. The medium-sized droplets can reach the maximum height of the spray cloud. As the spray cloud travels over the deck, the droplet velocities become almost the same. Comparing the numerical results with field observations shows that the predicted results are consistent and have reasonable agreement with the field measurements. [ABSTRACT FROM AUTHOR]

A theoretical model is presented to predict water droplet trajectories in the flow past an airfoil. The model considers droplet deformation and includes a drag coefficient that accounts for the influence of flow acceleration. This is because, as seen from the reference frame of the droplet, the flow accelerates as the airfoil approaches, even if the airfoil moves at constant velocity. To validate the theoretical model, a series of experimental tests have been carried out in a rotating arm facility. Three parameters were changed in the experiments: 1) the size of the model airfoil (radius of curvature 0.103 m, 0.070 m, and 0.030 m), 2) its velocity (50 m/s, 60 m/s, 70 m/s, 80 m/s, and 90 m/s), and 3) the droplets' initial diameters (in the range from 550 μm to 1050 μm). Comparison between the results obtained using the theoretical model and those collected in the experimental tests (droplet tracking was carried out using a high speed imaging system) showed a good agreement. This suggests that, within the range of parameters that has been tested, the proposed theoretical model could be confidently used for trajectory prediction purposes. [ABSTRACT FROM AUTHOR]

Marine icing phenomena are strongly dependent on the rate of water impact to marine vessels. The most important source of this incoming water is wave-impact sea spray. There is limited understanding of droplet size and velocity distributions of wave-impact sea spray. Initial distributions of the size and velocity of droplets are crucial for the calculation of the droplet path and consequently for determining the water impact to every individual place on marine vessels. This paper develops a new model of wave-impact sea spray using a distribution of the size and velocity of droplets at the edge of the vessel. The concepts of water-sheet breakup and droplet breakup lead to an inverse dependence between the size and velocity of droplets after the breakup process. Droplets take different paths and form a spray cloud in front of the vessel. The liquid water content in front of the vessel can be calculated by considering the arrangement, sizes, and velocities of a set of droplets in the spray cloud. The response of the droplet trajectory model to various initial conditions with different sets of droplet sizes and velocities is examined. The numerical results are compared to real data from field observations. Droplet sizes are inversely proportional to droplet velocities, as verified by liquid water content data obtained by the field observations. This paper proposes the use of this inverse relationship based on physics of the breakup process as the initial data for calculating the wave-impact sea spray trajectory in front of a vessel. [ABSTRACT FROM AUTHOR]

• Constructed oil collecting pipe to enhance oil phase enrichment. • Analyzed the hydrocyclone separation mechanism around the oil collecting pipe by the swirl number. • Achieved efficient and rapid separation of large oil–water ratio mixtures. In many offshore fields, water takes up 90 % of the produced fluid. The compact and efficient centrifugal pre-separation method is expected to replace the traditional sedimentation separator, which takes up a large area and is low in efficiency. The centrifugal separator can achieve rapid separation of produced fluids in the compact space of offshore platforms. However, conventional tangential inlet or axial hydrocyclone is poor-performed for high water content mixture due to droplet breakage caused by tangential inlet and unstable oil core in outlet section caused by axial inlet. In this paper, based on experiment and numerical simulation, a new type of efficient oil–water separator of high separation accuracy is constructed by the structural innovation of adding oil collecting pipe. In the treatment of 10 % oil mixture, when the inlet flow rate was 0.5 m/s, the volume fraction of oil at the oil outlet can reach 45 % and the volume fraction of oil at the water outlet can be reduced to 0.0724 %. According to the laboratory-scale tests, the novel separator shows great potential in oil field with high water content or offshore platforms. [ABSTRACT FROM AUTHOR]

The trajectory and adhesion behavior of droplets in air-assisted pesticide spraying in greenhouse are closely related with several factors: the velocity field and pressure field of the airflow, the droplets properties (such as droplet size, initial velocity), the spraying angle, as well as the target parameters (such as shape, size and position). This study explored the conditions that influenced the droplets carried by airflow, with a keen emphasis on whether it could touch, instead of going around, and stay on the target. A CFD (computational fluid dynamics) model was introduced for droplet trajectory simulation in an airflow field, in which droplets were traced by discrete phase particle tracking method. A computation region of 1600, 720 and 1000 mm respectively in streamwise, spanwise and normalwise was established. A target with the dimension of 120 mm x 120 mm x 30 mm was placed 400 mm above ground and 840 mm away from the left boundary of the computational domain. To simplify computational complexity, only half of the computational region (1600 mm x 360 mm x 1000 mm) was computed since the whole region was symmetric on both sides of the sprayer in streamwise. The grid number of the actual computation domain was about 0.36 million. A local mesh encryption method was applied around the target in order to increase the resolution of the simulation. The particle diameters involved in this simulation were 10, 30, 40, 50, 60, 70, 80 and 100 µm; and the injection angles were adjusted to 90°, 75°, 60°, 45°, 30° and 15° respectively. A discrete phase boundary condition was set which trapped the droplets on the ground (wall) or the target surfaces. The rest of boundaries for discrete phase were set to boundary condition of droplet escaping. The influences of droplet velocity, droplet size and injection angle on deposition rate were evaluated by the CFD simulation and the experiments proved that: the condition of a droplet touching and adhering on target was that the maximum moving time of droplets in x and y direction should be simultaneously longer than the maximum moving time of droplets in z direction in the region around the target. There was a region below the target where droplets could not reach while spraying, and the length of the region was related to spraying angle. The adhesion behavior of droplets was affected by air velocity and droplet size. When the droplet size was 50 µm and spraying angle was 60°, the larger the spraying velocity, the lower the deposition rate. The comparison of the deposition rates from simulations and experiments proves that the experiment data agree well with the data from simulation, so the simulation can be taken as reliable and valid measure in droplet deposition evaluation under greenhouse condition. [ABSTRACT FROM AUTHOR]

Abstract: A simple experimental arrangement was used to study the trajectories of droplets ejected by an ink-jet printer. Droplets with an average diameter of were ejected from a nozzle with an orifice of . The recorded flight path was used to find the drag force, deceleration and hence the loss of height when the droplets were ejected horizontally. Using various approaches for semi-turbulent flow, good fits for trajectory were obtained. A model was developed to include the effect of the change in droplet shape from cylinder to sphere during flight but this did not improve trajectory fit. Methods for calculation of exit velocity produced deviations of 4–15% from the value measured by high-speed photography. [Copyright &y& Elsevier]

• Molecular dynamics simulation is performed to study droplets in rotating gas. • The droplet trajectories in forced vortexes are observed. • A droplet trajectory model based on drag force is proposed. • Droplet collisions in forced vortexes are studied. Molecular dynamics simulations of droplets in gas forced vortexes by applying a virtual rotational potential were presented. The result showed that the flow field scale of the simulation performed can reflect the macroscopic characteristics. The trajectories of water droplets are longer than that of oil droplets within a certain radius of flow field. A droplet trajectory model was proposed to predict droplet behavior. The study continued to investigate droplet collisions. It was observed that the large oil droplet and the downwind small water droplets produced near head-on, highly off-centre and scraping-adhering collisions, forming stable two-phase interfaces. The slight changes of the interfaces between water and oil droplets under the action of rotating flow field can be reflected by van der Waals interaction. The intermolecular hydrogen bonds form when two water droplets collide. Our study provides a new idea for further understanding of droplet collision in gas flow field. [ABSTRACT FROM AUTHOR]

• A 3D mathematical model of spray drying formulated and solved numerically. • Spray drying experiments conducted on a pilot centrifugal spray dryer. • Excellent agreements between experimental and numerical temperatures achieved. • Physical field distributions of gas phase and motion trajectories of droplets visualized. • Influencing factors discussed and mass and heat transfer mechanisms analyzed. Understanding of droplet evaporation and motion is of great value in optimizing the spray drying process. A numerical study based on the Euler-Lagrange approach was performed with experimental verification in a pilot centrifugal spray dryer. Predicted temperatures agreed well with measured values with a maximum relative error of 2.76%. Gas multiphysics distributions and droplet trajectories were visualized. Air backflow phenomena and droplet vortex motions were observed during drying. Increasing inlet air temperature could accelerate the drying rate and increasing disc rotational speed might cause the wall adherence. The results can help guide the future design and operation of spray dryers. [ABSTRACT FROM AUTHOR]

• Theoretical analysis on droplet are investigated. • Effect of initial parameters on lateral motion is studied. • Effect of initial parameters on vertical motion is studied. • Droplet trajectories under inclined condition are studied. • Impact mechanism analysis is done on dynamic characteristics. Theoretical investigations on the dynamic characteristics of spray droplet in air environment subjected to the inclination were performed. The inclined angle ranged from 0° to 30°, and the droplet diameter, initial velocity and injection angle ranged from 0.1 mm to 2 mm, from 1 m/s to 10 m/s and from 15° to 75°, respectively. The results show that the larger droplet initial velocity, diameter and injection angle led to the slower decreasing rate of lateral velocity, the longer lateral distance, and the larger coverage area caused by spray droplet. The larger droplet diameter and initial velocity induce the higher growth rate of vertical distance. The greater difference of droplet diameter and initial velocity result in the shorter chasing time and chasing distance. Increasing the inclined angle will result in the decrease of coverage area and the reduction of the impact of inclined angle on it. In addition, the influence of inclined condition on droplet trajectory heightens with the increase of droplet diameter. For different droplet diameters, the influence of inclined angle on the droplet trajectory located in the same direction with inclination is greater than that of the opposite direction. While the inclined angle has a similar influence on the variation tendency of droplet trajectory located in the same and opposite direction with inclination. Impact mechanism analysis concerns droplet trajectory under inclination are conducted to explain the dynamic characteristics of spray droplet. [ABSTRACT FROM AUTHOR]

In this paper, a CFD model is used to simulate the effect of spray atomization at the compressor inlet on a multistage axial subsonic compressor. Special attention is paid to the change of compressor characteristics with wet compression under different rotating speeds to gain the compressor characteristic lines of wet compression. The effects of pneumatic crushing and blade-wall-collision on water droplets and droplet trajectories are contrasted and analyzed under different spray conditions. Then, the whole/stage-by-stage compressor performances and the flow field are also investigated under dry and wet cases near the design operating condition. The results indicate that multistage compressor performance can be improved with wet compression under the proper water spaying rate and a small droplet size. The influence of pneumatic crushing on the water droplets below 20 μm can be ignored, and the effect of blade collision on water droplets above 5 μm should be considered in the wet compression conditions. Compared to the dry compression, as measured by volume flow, wet compression with proper spaying conditions makes the front stages operate within a relatively high flow range and the back stages operate within a relatively low flow range. Additionally, the operating state with wet compression is opposite to the compressor operating near the surge boundary, which presents the phenomenon of "former surged and back blocking". [ABSTRACT FROM AUTHOR]