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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]

An Air-cooled condenser (ACC), which finds popularity in a steam power plant in arid areas, is usually less efficient as film condensation occurs inside the condenser tube. Recent research is directed towards eliminating the thermally insulating liquid film with the application of novel superhydrophobic surfaces. The self-cleaning property of such surfaces facilitates easy condensate drainage in the form of jumping droplets exposing favourable nucleation sites, thereby significantly promoting dropwise condensation. The present study explores the characteristics of jumping droplet condensation in finite condenser tubes using computational fluid dynamics (CFD). The wall-heat-flux for condensation is modelled here by a uniform suction boundary condition. The strength of suction is quantified by a suction Reynolds number Re s . We mainly focus on the zone corresponding to 2.3 < Re s < 10, where no previous solution exists. In a long horizontal tube, the progressive realization of a self-similar region starting from the developing regions is demonstrated. We examine the characteristics of the developing region based on the sign of the pressure gradient. The results of three-dimensional CFD simulations illustrate the variations of droplet trajectories with the inception size and coordinates of jumping droplets determined locally by the relative contributions of various force components, viz. gravity, axial drag in the vapour core, suction induced radial drag and Saffman lift. The present study also predicts the effect of pipeline inclination on condensate drainage. Ultimately, considering multiple jumps, we found that the maximum condensate emission can be obtained for small droplets (5−15 μm), while medium-sized droplets (20−50 μm) are most advantageous for isolated jumps. [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.

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]

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]

High‐pressure homogenization is a commonly used process to produce emulsions with a droplet size of less than 1 μm. During the process, a pre‐emulsion is pumped with a pressure of several mega Pascal through a disruption unit, where the droplets are deformed and subsequently broken up in the turbulent area of the disruption unit. The scope of this investigation is to determine the influence of the droplet trajectory on the droplet size distribution of emulsions of different viscosity ratios or interfacial tension. Measurements of the droplet deformation prior to the droplet breakup using image‐processing tools complemented the observations. In addition, computational fluid dynamics simulations were performed to determine the stress history on the droplet trajectories. It was found that droplets on a trajectory close to the wall are more deformed when leaving the disruption unit compared to droplets on the centreline. The deformation of droplets at the edge of the jet increases downstream the disruption unit until it is finally disrupted. The simulation results support the experimental data, as it can be shown that shear and strain stresses on the trajectories close to the wall significantly exceed the stresses on the trajectories on the centreline. For an emulsion with a viscosity ratio greater than 3, droplets on a trajectory close to the wall resulted in smaller droplets and narrower droplet size distribution, while no significant influence was found for smaller viscosity ratios. Lowering the interfacial tension results in a stronger deformation, which was more pronounced for lower viscosity ratios (λ ≈ 3). [ABSTRACT FROM AUTHOR]

The study of air velocity inside the cooling tower gives an overview of the process of heat or mass transfer. This study developed mathematical modelling based on the principle of continuity and statistical thermodynamics to track changes in radius, velocity, density, and temperature of droplets and air along with the droplet trajectory or tower height. Before that, the droplet radius range is predicted in advance to get the accuracy of the calculation. Also, water capacity and fan rotation are varied to determine their effect on cooling tower performance. The calculation results showed that 18 Lpm capacity gives efficiencies above 50%, while for 0.5 Lpm capacity, it produces efficiencies in between 25% to 40%. The highest efficiency indicates that the evaporation process occurs most efficiently. Mathematical modelling in calculations can also describe the increase in air temperature, which usually uses numerical simulations. [ABSTRACT FROM AUTHOR]

This study provides a fast analysis of pesticide spray trails and dispersion influenced by crosswind, headwind, velocity field and the wake of an agricultural aircraft approaching the ground, to improve operational efficiency and reduce environmental impact. The lifting line-wingtip vortices mixture model is proposed to calculate induced velocity field around a monoplane far to 190 wingspans downstream, and N-vortex system based on point vortex dynamics is applied to simulate vortex rebound and vortex motion on considering extreme ground effect. The droplet trajectories governed by wake vortices and their induced velocity field are therefore determined under the Lagrangian framework. According to the ground deposition of typical droplets, the Gaussian mixture model is employed to predict droplet drift or dispersal for the whole spectrum of droplets in the spanwise direction. The fast analysis is compared to AGDISP and computational fluid dynamics (CFD) simulation for Thrush 510G aircraft, which runs on a common personal computer (CPU 2 GHz, memory 2 GB) within 3.2 s, faster than AGDISP and CFD, and does not rely on swath width input needed by AGDISP. The results suggest crosswind speed and droplet size are two leading factors affecting the drift and ground deposition. To increase droplet size or reduce the portion of fine droplets, the pesticide drift can be suppressed in some degrees.

The study of air velocity inside the cooling tower gives an overview of the process of heat or mass transfer. This study developed mathematical modelling based on the principle of continuity and statistical thermodynamics to track changes in radius, velocity, density, and temperature of droplets and air along with the droplet trajectory or tower height. Before that, the droplet radius range is predicted in advance to get the accuracy of the calculation. Also, water capacity and fan rotation are varied to determine their effect on cooling tower performance. The calculation results showed that 18 Lpm capacity gives efficiencies above 50%, while for 0.5 Lpm capacity, it produces efficiencies in between 25% to 40%. The highest efficiency indicates that the evaporation process occurs most efficiently. Mathematical modelling in calculations can also describe the increase in air temperature, which usually uses numerical simulations. [ABSTRACT FROM AUTHOR]

Printing with inkjet technology has found new forms of application in the industry and in this article we study this technology focused on printing on non-flat surfaces. Since there is no print history over distances greater than 1 mm due to the rupture phenomenon, an initial quality standard is defined to measure achievements in a relative manner. An interactive method is used that requires the user to approach the machine in multiple analyzes of different types. The first approach is a mathematical model this model was constructed to predict the drop distance of the drop in the non-planar substrate with respect to the planned one in the flat substrate, taking into account that most of the drops fall to different heights presenting a greater or lesser state of development the phenomena present in the flight. The results allow to initiate a process of compensation that avoids the distortion of the figure to improve the printing resolution. The results are validated using a relative quality through industrial ink-jet printer with heads capable of injecting functional fluids. The initial result indicates that in standard surface printing with print relative quality already defined, it can be used only for low resolution formats with thick lines, and the result can be improved when the original figure is treated by compensating the distance between the numerical prediction and the initial objective. [ABSTRACT FROM AUTHOR]

The motion mechanism of the single droplet during wing cleaning of aeroengine is studied, and the force acting on the droplet entering the fan at low speed is analysed, and the motion model of a single droplet in swirl field is established. The influence of the main parameters such as droplet diameter, incident velocity and incidence angle on the droplet trajectory is analysed. The mechanism of droplet movement in the fan is described qualitatively.

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]

Wind-driven rain (WDR) in the built environment is a complex multiscale phenomenon. Wind flows in complex urban environment and rain events of various intensities may lead to very different rain deposition distributions within the city. Proper modeling of WDR is required as moisture is a main cause of material degradation in the built environment but also as understanding the water cycle in the urban environment is essential to provide solutions for the urban heat island, amongst others. What are the main aspects to be taken into account to predict wind-driven rain? How should such aspects be considered and modeled? Is it possible and relevant to predict in detail the moisture loads due to rain in complex systems as cities? This paper answers these questions from a multiscale perspective combining modeling and experimental work. The different scales relevant for accurate estimation of wind-driven rain in the built environment are presented. Rain deposition on complex geometries can be modeled by CFD, taking into account turbulent dispersion. Such modeling provides the impact velocity and angle of attack for each droplet size at any location on the urban surfaces. Using this information and the structure of the surface, the fate of the rain droplets can be predicted, namely whether it splashes, bounces or simply spreads. [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 5μm 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”.

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 use of swirling gas jets for more effective application of refractory coatings on the converter lining is considered. Numerical modeling is employed to analyze the aerodynamics of the working space and the motion of converter-slag droplets, in the case where neutral gas is supplied through a special lance with swirling elements. The description of slag-droplet motion to the converter lining is refined; the relation between the parameters of droplet motion and the characteristics of the swirling jet is established. The swirling of the jet mainly determines the trajectory of the slag droplets, regardless of their size. According to theoretical analysis, the use of swirling gas jets will permit more flexible slag-coating application to the converter lining. [ABSTRACT FROM AUTHOR]

This study provides a fast analysis of pesticide spray trails and dispersion influenced by crosswind, headwind, velocity field and the wake of an agricultural aircraft approaching the ground, to improve operational efficiency and reduce environmental impact. The lifting line-wingtip vortices mixture model is proposed to calculate induced velocity field around a monoplane far to 190 wingspans downstream, and N-vortex system based on point vortex dynamics is applied to simulate vortex rebound and vortex motion on considering extreme ground effect. The droplet trajectories governed by wake vortices and their induced velocity field are therefore determined under the Lagrangian framework. According to the ground deposition of typical droplets, the Gaussian mixture model is employed to predict droplet drift or dispersal for the whole spectrum of droplets in the spanwise direction. The fast analysis is compared to AGDISP and computational fluid dynamics (CFD) simulation for Thrush 510G aircraft, which runs on a common personal computer (CPU 2 GHz, memory 2 GB) within 3.2 s, faster than AGDISP and CFD, and does not rely on swath width input needed by AGDISP. The results suggest crosswind speed and droplet size are two leading factors affecting the drift and ground deposition. To increase droplet size or reduce the portion of fine droplets, the pesticide drift can be suppressed in some degrees. [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]

The recent pandemic of COVID-19 has brought about tremendous impact on every aspect of human activities all over the world. The main route of transmission is believed to be through coronavirus-bearing respiratory droplets. The respiratory droplets have a wide spectrum in droplet size, ranging from very small droplets (aerosol droplets) to large droplets of tens and even hundreds of μm in size. The large droplets are expected to move like projectiles under the action of gravity force, buoyancy force and air resistance. Droplet motion is complicated by droplet evaporation, which reduces droplet size in its trajectory and affects the force acting on it. The present work attempts to determine the trajectories of the large droplets by using a simplified single-droplet approach. It aims at providing a clear physical picture to elucidate the mechanics involved in single droplet motion and the various factors affecting the range. Assuming an indoor environment with an air temperature of 18 °C and relative humidity of 50%, the horizontal range L x of large respiratory droplets (diameter 120 μm–200 μm) in common respiratory activities are as follows: Speaking, L x ≈ 0.16 m–0.68 m, coughing, L x ≈ 0.58 m–1.09 m, and sneezing, L x ≈ 1.34 m–2.76 m. For the smaller droplets (diameter < 100 μm), the droplets are reduced to aerosol droplets (≤5 μm) due to evaporation, and will remain suspended in the air instead of falling onto the ground like a projectile. • Trajectories of droplets (initial dia. 40–200 μm, vel. 2–50 m/s) are studied. • Air resistance is the most important factor in affecting droplet motion. • Relative humidity and evaporation also play a significant role. • Smaller droplets (diam. ≤ 100 μm) are reduced to aerosol droplets in the air. • The range is 0.16–0.68, 0.58–1.09, 1.34–2.76 m in speaking, coughing, sneezing. [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]