Spray Droplets Research Articles

Field Study to Assess UASS Mosquito Adulticiding: Methods and Data

Highlights Mosquito adulticiding over operationally relevant areas is feasible using UASS. Wind speed plays an important role in the spray landing position, as expected based on previous studies using CASA. Results are based on both passive and active collectors, including flat cards, rotary impingers, and bottle brushes. Over 1900 total samples were collected in 8 trials, and elevated samplers allowed analysis of the descent of the droplet cloud. Abstract. A spatially extensive experiment was designed to evaluate the effectiveness of Uncrewed Aerial Spray Systems (UASS) in mosquito adulticiding. The practice of adulticiding uses very fine droplets (DV0.5 <50µm). The objective is to fill a volume of air with fine droplets that a flying adult mosquito will encounter in flight. A field program was designed with samplers as far as 500 m downwind from the UASS flight line. A total of over 1900 samples were collected over the course of eight trials. Both passive and active collectors were deployed. Tests were conducted in the early morning and were generally successful in terms of meteorological conditions and data collection. Elevated samplers successfully tracked the descent of the spray cloud, and spray was collected from the most distant samplers. The known dependence of spray movement on wind speed that has been widely observed and codified into label language for Crewed Aerial Spray Aircraft (CASA) was observed. Very low wind speed conditions are problematic for adulticiding in general, and undesirable near-field deposition of adulticiding spray was observed in the data presented here under low wind speed conditions. It needs to be emphasized that much more data needs to be collected before statistically robust conclusions can be drawn. Generally, these data show that UASS can be used to disperse very fine spray droplets over areas representative of operational adulticiding. This paper presents and discusses spray movement and deposition, a second paper is in preparation comparing these data to existing models of spray dispersion and deposition from UASS spraying. A third paper examining mortality from UASS adulticiding has been published. Keywords: Adulticiding, Pesticide drift, UASS Spraying, UAV.

CHARACTERIZATION OF FULLY DEVELOPED AIR-ASSISTED SPRAY UNSTEADINESS USING RP-3 JET FUEL

The ideal spray theory of Edwards and Marx was utilized to investigate the dependence of fully developed intermittent air-assisted spray unsteadiness on operational conditions and fluid properties. Time series information of spray droplets was identified by phase Doppler particle analyzer and used for inter-particle arrival time statistics. Results demonstrated that spray unsteadiness along the spray axis and in proximity to the nozzle exit area is more pronounced than far-nozzle field and spray periphery. The unsteadiness on the spray axis exhibits a decreasing function with the fuel injection durations, whereas an increase of air injection duration significantly elongates the unstable region along the spray axis. The properties of test liquid fuels show a moderate effect on the unsteadiness of the air-assisted spray, potentially due to their inconspicuous influences on spray atomization characteristics. Chi-square method is generally the preferred method for quantifying the global spray unsteadiness when compared to the deviation of the first time gap of experimental and theoretical inter-particle time distribution. Unsteadiness results observed during high-velocity droplet spray stage are relatively distinct compared to droplet deceleration and suspension stages. This distinction can be attributed to the continuous energy input during the initial nozzle opening, emphasizing the significance of droplet velocity in determining spray unsteadiness.

不同喷雾参数对流体动力式超声雾化喷嘴的沉积性能研究

In order to study the spraying effect of hydrodynamic ultrasonic atomizing nozzle under different spraying methods, and to investigate the practical application effect of hydrodynamic ultrasonic atomizing nozzle in agriculture, the atomization angle test and droplet size test under different spraying conditions were designed. Different spraying conditions atomization angle test and droplet size test were designed, the test results data were recorded, the pattern of change of the data was observed, and the data were fit to give the data changes in line with the functional equation; different spraying conditions and different corn leaf position droplet deposition coverage test were designed and the value of the deposition coverage of each position was recorded. The results showed that: the maximum value of the variation of atomization angle under different spraying conditions was 75.49°, and the minimum value was 14.49°; the maximum value of the variation of droplet size was 18.23 μm, and the minimum value was 4.78 μm; and the droplet deposition coverage was the highest in the mid-leaf position of the upper and lower leaves of the maize when the input air pressure was 0.3 MPa, which was 86.98% and 46.97%, respectively. Fitting the atomization angle data and droplet size data, the R2 of the binomial fit was 0.85 and 0.94, respectively, and the Adjusted R2 was 0.87 and 0.88, respectively, which made the fitting function meaningful and the fitting accuracy high. The hydrodynamic ultrasonic atomizing nozzle has a great advantage in generating small droplet sizes and performs well in deposition effect, and the experimental results can provide a reference for the research of hydrodynamic nozzles in the application technology.

Experimental Study on the Smoke-Logging Phenomenon Owing to Sprinkler Operation During Initial Fire

This study establishes basic data for the reasonable evaluation of evacuation safety and investigates the smoke-logging phenomenon owing to the operation of sprinklers during the initial fire. The spray droplet characteristics of a sprinkler and water mist head were examined, and the descending air current of the smoke layer was analyzed according to the type of fire source (ethanol, polyurethane) and head. A regression equation based on the findings was derived using the prediction equation for the descending air current of the smoke layer presented in a previous study.

Experimental Investigation of Electrospraying Properties Based on Ring Electrode Modification.

Electrospraying uses a high-voltage potential difference to create fine droplets. This study conducts a comparative analysis of the spray pattern and droplet properties using ring electrode parameters. The spray pattern and droplet characteristics are analyzed based on the experimental parameters of the ring electrode. The results show that the cone-jet mode forms quickly for the ring electrode. In addition, as the ring diameter decreases, the ring voltage increases and an increase in the distance between the ring and the nozzle in the bottom direction decreases the Sauter mean diameter and its standard deviation. The optimal conditions for the formation of fine and uniform droplets include a ring diameter of 15 mm, a ring voltage of 7 kV, and a nozzle-to-ring distance of (+) 20 mm.

Study on reactivity characteristic of TDA droplet group with gaseous phosgene for preparing TDI

Toluene diisocyanate stands as a pivotal chemical, predominantly synthesized through the phosgenation reaction between toluene diamine and phosgene. To address the inherent limitations of existing phosgenation methods, we pioneered a novel phosgenation reaction based on flash atomization and confirmed its feasibility with preliminary theoretical calculations. This manuscript delves deeper into the superiority of this method and refines its reaction parameters. By integrating the discrete phase model with the Eulerian model, we studied the reaction dynamics of droplet sprays, exploring the effects of spray velocity, droplet size, phosgene temperature, and particle size distribution on the reaction. Our results highlight that, with a mean droplet diameter of 70 μm and a spray velocity of 40 m/s, an impressive reaction yield of 97.4 % can be achieved. This research enriches our understanding of the gas–liquid two-phase phosgenation method, setting the stage for its future exploration and potential applications in Toluene diisocyanate and other isocyanate industry.

Distribution function and atomization parameters of petroleum fuels sprays: An experimental and numerical study

Heavy fuels are difficult to spray. To investigate the burning of this fuel and create an appropriate combustion chamber, one must first understand the atomization process and spray properties of petroleum fuels. The Diesel spray behavior compared to Mazut fuel spray gives us an understanding of the atomization phenomenon of fuels. The most crucial fuel atomization characteristics include droplet diameter, spray angle, breakdown length, and droplet distribution. The shadowgraphy technique is used to capture images of fuel spray, which are then processed using image analysis software. The size and speed of the fuel spray droplets are predicted using the maximum entropy method. From a pressure difference of 15 bar onwards, the rate of mass flow remains almost constant. The fuels spray cone angle initially increases, and after the flow approaches full atomization, it reaches approximately a constant value. The breakup length and droplets diameter decrease with increasing fuel temperature and pressure, and with the full development of the flow, they tend to almost zero. By raising the fluid's viscosity, the diameter size distribution of the droplets becomes more uniform and smooth (unlike velocity distribution). In this research, an attempt has been made to develop experimental and numerical methods to measure the powdering parameters of a heavy non-Newtonian oil fuel called Mazut and a light petroleum fuel called diesel, as well as to investigate the spray behavior of these fuels.

Evaluating Ink Structure Using Ultrasonic Spray Coating for PEMFC MEA

From the standpoint of improving manufacturing productivity and performance/durability of PEMFC MEAs, there is an increasing interest in ink. Ink research is centered on comprehending the interplay between the components of the ink, including catalysts, ionomers, and solvents, to control the ink structure and evaluate its influence on ink properties, catalyst layer microstructure, and fuel cell performance. As a facet of this ink research, the current study proposes ultrasonic spray coating as a methodology to indirectly evaluate the ink structure.50 wt% Pt/C catalysts loaded on Ketjenblack (KB) and Vulcan carbon (VC) were separately incorporated to produce sprayable inks with a solid content of 4 wt% using an Aquivion ionomer (EW 720) and a mixture solvent composed of a 1:1 weight ratio of 1-propanol and water. The structural differences between the two catalyst inks were compared by quantifying the amount of adsorbed and free ionomers, as well as their rheological properties. Additionally, the advantages of ultrasonic spray coating, such as the formation of small droplets on the order of tens of micrometers and rapid drying, were utilized to coat each ink onto a silicon substrate. The structural characteristics of the resulting catalyst layers were compared through SEM images, as well as the distribution of constituent elements using EDS and Auger spectroscopy. The Pt/KB catalyst ink forms a gel-like structure due to its relatively high amount of adsorbed ionomer, resulting in a relatively uniform distribution of catalyst particles and ionomers in the catalyst layer formed from ultrasonic spray droplets. In contrast, the Pt/VC catalyst ink behaves as a liquid-like, mainly existing in the form of free ionomer, regardless of ionomer content. During the drying process of each droplet, they merge to form larger unit catalyst layers, which exhibit an uneven distribution where free ionomers tend to concentrate at the edges of the catalyst layer due to the coffee-ring effect. As a result, the catalyst and ionomers exist in a non-uniform distribution, which is observed to affect the performance and electrochemical characteristics of fuel cells. In this presentation, we will discuss in detail the series of characteristics of ink-catalyst layer-fuel cell performance that vary according to catalyst properties.

Macroscopic and microscopic spray characterisation of Low-Octane blends for gasoline compression ignition engines

Gasoline compression ignition is an advanced combustion technology that controls harmful emissions from low-octane fuels used in compression ignition engines. Fuel’s physical properties and injection strategy influence the fuel–air mixture formation and combustion. High volatile fuel and fuel injection pressure improve the spray atomisation and fuel–air mixture formation. Gasoline-diesel blends are widely investigated for gasoline compression ignition engine applications. This study investigated microscopic and macroscopic spray characteristics of 70 % v/v gasoline and 30 % v/v diesel blend (G70), 80 % v/v gasoline and 20 % v/v diesel blend (G80), and baseline diesel injected at different fuel injection pressures. Parameters such as liquid fuel spray penetration length, spray cone angle, and droplet size and velocity distributions were assessed. The results of these parameters help determine the effect of the fuel injection parameters on combustion. It was found that though the liquid spray penetration length was not significantly different for the three test fuels, G70 exhibited a slightly lower liquid spray penetration length than the other two test fuels. Increasing the diesel fraction in the test blend reduced the spray cone angle and improved the axial dispersion of the fuel spray. The spray droplet diameter reduced with increasing gasoline fraction in the test blend and the fuel injection pressure. Sauter mean diameter decreased by up to 20 % for G80 than baseline diesel and up to 36 % with an increased fuel injection pressure from 300 to 700 bar. This study addressed a significant research gap in the spray characteristics of gasoline-diesel blends and provided a benchmark for simulation based model validation.

Droplet Combustion Behavior and Spray Characteristics of Diesel–Ethanol–Jatropha Oil Ternary Fuel Blends Under High-Pressure Evaporating Conditions

Abstract This study investigates the behavior of a single droplet exposed to high-temperature ambient air and macroscopic spray characteristics of various ternary blends of diesel–ethanol–jatropha oil. The experiments on single droplet are performed at ambient pressure and high temperature. The spray experiments are performed under high-pressure and high-temperature conditions, similar to those of a diesel engine in-cylinder air at the time of fuel injection for three blends. The D50E35J15 has exhibited micro-explosion behavior; D50E30J20, which has shown puffing, and D60E20J20, which has demonstrated both micro-explosion and puffing during single droplet experiments, are selected for spray experiments. A constant volume spray chamber with optical access equipped with an electric heater was used to study evaporating spray characteristics of the blends at 5 MPa and 900 K. The spray experiments have shown that the ternary fuel blends have higher liquid penetration as compared to that of diesel due to the higher boiling point of jatropha oil. The variation in the spray cone angle between the different blends was found to be insignificant and within the measurement’s uncertainty limits. Thus, the blends which have exhibited micro-explosion and puffing in droplet experiments have not affected the macroscopic spray characteristics at higher ambient pressures.

Performance of spray nozzles and droplet size on glufosinate deposition and weed biological efficacy

Nozzle type and droplet size are one of the most important factors that affect spray deposition and the efficacy of herbicides. This study focused on evaluating the performance of spray nozzles and droplet sizes on the deposition of glufosinate and its biological efficacy of two weed species. Treatments consisted of spraying glufosinate on Euphorbia heterophylla and Digitaria insularis by five spray nozzles (XR 11002 – fine droplet; TT 11002 – coarse; AIXR 11002 – very coarse; AIXR 110025 – extremely coarse; and TTI 11002 – ultra coarse) assessing the spray deposits and its influence on plant biomass reduction. The spray deposits on E. heterophylla were found to be similar between most of the spray nozzles, except for the TTI 11002 nozzle, which had lower spray deposits. In contrast, for D. insularis, the spray deposits tended to decrease as the droplet size increased. The spray uniformity was lower for the AIXR 11002 nozzle for E. heterophylla and the XR 11002 nozzle for D. insularis. Regarding the efficacy of glufosinate on both weeds, the lower C50 (concentration required for 50% dry weight reduction) were obtained using the XR 11002 nozzle with fine droplets. The TT 11002 nozzle and the AIXR 11002 nozzle showed intermediate C50, making them viable options to reduce spray drift and achieve acceptable weed control. However, the nozzles using extremely coarse (AIXR 110025) and ultra-coarse (TTI 11002) droplet class resulted in higher C50, indicating reduced herbicide efficacy. Our study provided clues on how different spray nozzles and droplet sizes can significantly impact spray deposits and herbicide efficacy on the control of E. heterophylla and D. insularis. Nozzles with fine droplet class generally provided better control, while extremely coarse and ultra-coarse showed reduced efficacy at weed control.

Experimental investigation on a novel external-mixing prefilming atomizer for advanced aircraft engines

As a crucial component of aircraft engine combustors, the external-mixing prefilming atomizer exhibits significant advantages in enhancing combustion efficiency and reducing pollutant emissions. However, the intricate relationship between spray characteristics, droplet breakup mechanisms, flow fields, and geometric parameters of the external-mixing prefilming atomizer remains poorly understood. This paper presents a novel external-mixing prefilming atomizer, aiming to address this knowledge gap. Additionally, particle image velocimetry (PIV), high-speed Schlieren photography, and particle image analysis (PIA) measuring systems were employed to gain insights into the spray characteristics and droplet breakup mechanism of the external-mixing prefilming atomizer under various swirl flow fields. The obtained results reveal the formation of two distinct regions, namely a low-density area and a high-density area. Notably, the number of droplets in the low-density area, located within 0–2 cm from the central axis, is significantly lower compared to the high-density area situated further away from the central axis. The breakup of droplets in the low-density region is primarily attributed to the inner swirl airflow, while the outer swirl airflow induces droplet breakup in the high-density region. As the Reynolds number of the incoming flow increases, the air-liquid ratio (ALR) and Weber number also increase, thereby enhancing the fuel breakup effect. The Schlieren results reveal a two-stage spray development process. The initial stage is characterized by the dominant momentum of the dense spray, with the spray tip penetration (STP) exhibiting a relatively slow increase. The aerodynamic force of airflow plays a crucial role in governing the breakup and transport of droplets, leading to a linear variation of STP over time. As the swirl number increases, there is an enhanced momentum exchange between droplets and airflow, resulting in accelerated spray penetration and droplet breakup.

Enhanced dosage delivery of pesticide under unmanned aerial vehicle condition for peanut plant protection: tank-mix adjuvants and formulation improvement.

Suspension concentrate (SC) is one of the most widely used formulations for agricultural plant protection. With the rapid development of unmanned aerial vehicle (UAV) plant protection, the problems of spray drift, droplet rebound and poor wettability in the application of SC from UAVs have attracted wide attention. Although some tank-mix adjuvants have been used to enhance dosage delivery for UAV, their effects and mechanisms are not fully clear, and few formulations are specifically designed for UAV. The type and concentration of tank-mix adjuvant affect the dosage delivery of SC. MO501 can significantly reduce DV<100μm , and inhibit droplet rebound on peanut leaves at concentrations ≥0.5%. Silwet 408 can achieve complete wetting and superspreading after adding ≥0.2% concentrations, but only ≥0.5% can inhibit rebound. XL-70 shows excellent regulation ability even at low concentration, and 0.2% concentration can simultaneously suppress impact and promote spreading. Besides, the formulation oil dispersion (OD) can significantly reduce the driftable fine fraction and inhibit rebound at dilution ratios of ≤250-fold, thus enhancing dosage delivery. SC is prone to rebound on hydrophobic leaf surfaces and shows poor wetting and spreading properties. Appropriate types and concentrations of tank-mix adjuvants and formulation improvement are two effective strategies for improving the dosage delivery of pesticides, whereas the addition of inappropriate adjuvants may cause potential risks instead. These findings provide guidance for the rational selection of tank-mix adjuvants and potential applications of OD for UAV plant protection. © 2023 Society of Chemical Industry.

The analytical and numerical study of alternative fuel injectors for the purpose of reducing chemical pollution in aviation sector

In this paper, both analytical and numerical analyses are conducted to study the behavior of a simplex time injector with a swirl chamber represented by a pin, designed to operate with kerosene. In an effort to reduce chemical pollution, the injector's performance when operating with alternative fuels such as biofuel and ethanol is investigated. Calculations have been performed to analyze the use of these three fuels at various pressures up to 100 bar. Analytical calculations were used to determine parameters such as spray angle, droplet size, fuel film thickness, and more. For a better visualization of the phenomena occurring during the injector's operation with these three fuels, numerical simulations were carried out using ANSYS, and the spray of droplets at various pressures at the injector inlet was presented. The study revealed that among the liquids studied, ethanol is the most optimal fuel. Ethanol has low viscosity and low density, making it easier to atomize by our injector compared to pure biofuel, which has higher density and viscosity values. The calculations demonstrated the qualities of ethanol following atomization, including a thin liquid film, a wide spray angle consisting of small-sized droplets, at any pressure difference, compared to the other studied fuels. It was observed that pressure difference has a significant impact on the atomization of a liquid. The best atomization qualities and optimal values were achieved when the pressure difference is high.

Antibacterial activity of solid surfaces is critically dependent on relative humidity, inoculum volume, and organic soiling.

Antimicrobial surface materials potentially prevent pathogen transfer from contaminated surfaces. Efficacy of such surfaces is assessed by standard methods using wet exposure conditions known to overestimate antimicrobial activity compared to dry exposure. Some dry test formats have been proposed but semi-dry exposure scenarios e.g. oral spray or water droplets exposed to ambient environment, are less studied. We aimed to determine the impact of environmental test conditions on antibacterial activity against the model species Escherichia coli and Staphylococcus aureus. Surfaces based on copper, silver, and quaternary ammonium with known or claimed antimicrobial properties were tested in conditions mimicking microdroplet spray or larger water droplets exposed to variable relative air humidity in the presence or absence of organic soiling. All the environmental parameters critically affected antibacterial activity of the tested surfaces from no effect in high-organic dry conditions to higher effect in low-organic humid conditions but not reaching the effect size demonstrated in the ISO 22169 wet format. Copper was the most efficient antibacterial surface followed by silver and quaternary ammonium based coating. Antimicrobial testing of surfaces using small droplet contamination in application-relevant conditions could therefore be considered as one of the worst-case exposure scenarios relevant to dry use surfaces.

Palmer Amaranth (Amaranthus palmeri) Control in Dicamba-Tolerant Cotton (Gossypium hirsutum) when Applied with Various Dicamba + Insecticide Tank-Mixtures

Postemergence herbicide application timings for Palmer amaranth (Amaranthus palmeri) often coincide with foliar insecticide applications in cotton (Gossypium hirsutum). Combining multiple pesticides into a single application increases efficiency while reducing overall application cost. Multiple foliar insecticides are now labeled for dicamba tank-mixes. However, there is limited literature with respect to efficacy of dicamba on Palmer amaranth control when applied with insecticides. Field experiments were conducted from 2018 to 2020 to evaluate the effect of carrier volume and insecticide on the efficacy of dicamba (XtendiMaxTM with VaporGripTM) to control Palmer amaranth in XtendFlex™ cotton production systems. Dicamba was tank-mixed with acephate and dimethoate to four-leaf cotton and with thiamethoxam and sulfoxaflor just prior to bloom. Applications were made at carrier volumes of 140 and 280 L ha-1 and with a single spray droplet size of 800 µm. Palmer amaranth control 7 d after treatment was negatively impacted when applications included dimethoate; however, no corresponding response in seedcotton yield was observed relative to dicamba applied alone. However, when pooled over carrier volume, applications containing dicamba + acephate resulted in higher seedcotton yield than applications of dicamba + dimethoate. Additionally, pre-bloom applications of dicamba + thiamethoxam or sulfoxaflor increased Palmer amaranth efficacy relative to dicamba applied alone. Although certain insecticides are known to increase herbicidal crop response, the impact of insecticides on herbicide efficacy to control specific weed species is largely unknown. Therefore, we conclude that multiple dicamba + acephate, thiamethoxam, or sulfoxaflor tank-mixtures provide similar control of Palmer amaranth compared to dicamba alone.

Mathematical modelling of evaporation rate and heating of biodiesel blends of a single-component droplets

Biodiesel serve as promising fuel and optimal alternative for mitigating the present issues of fuel scarcity and emission control in compression ignition engines. Several Researches have concluded that engine performance and it’s emission characteristics heavily depends on pa-rameters like fuel droplet spray formation, atomization, evaporation and combustion which in turn depend on thermophysical properties of biodiesel fuel. In this study, the thermophysical properties like normal boiling, critical properties, vapor pressure, latent heat of vaporization, liquid density, liquid viscosity, liquid thermal conductivity, gas diffusion coefficients of two biodiesel fuels sample: Madhuca Indica and Radish oil are determined using standard correla-tion. Accurate mathematical model for estimation of evaporation rate and combustion of sin-gle component biodiesel droplet is framed and validated with single droplet setup experiment result for Jatropa Methyl Ester (JME), Karanjan Methyl Ester (KME), Mahua Methyl Ester (MME), Neem Methyl Ester (NME), Palm Methyl Ester (PME) oil and this model is further extrapolated to predict the evaporation and combustion behaviour of two unexperimented oil, Madhuca and Radish. It is found that Madhuca oil has the higher evaporation constant value of 0.1466 mm2/s and thus lowest lifetime in among the biodiesel fuel studied. This value is attributed to lower mo-lecular weight and higher molecular diffusivity. On the other hand reverse trend is observed in Radish with lower evaporation constant and higher lifetime. This study behaves as compre-hensive methodology for estimating the behaviour of biodiesel based on their composition and chemical structure and also as firm framework for combustion modelling in enhancing engine performance.

Evaluation of the deposition and distribution of spray droplets in citrus orchards by plant protection drones

Plant protection drone spraying technology is widely used to prevent and control crop diseases and pests due to its advantages of being unaffected by crop growth patterns and terrain restrictions, high operational efficiency, and low labor requirements. The operational parameters of plant protection drones significantly impact the distribution of spray droplets, thereby affecting pesticide utilization. In this study, a field experiment was conducted to determine the working modes of two representative plant protection drones and an electric backpack sprayer as a control to explore the characteristics of droplet deposition with different spray volumes in the citrus canopy. The results showed that the spraying volume significantly affected the number of droplets and the spray coverage. The number of droplets and the spray coverage area on the leaf surface were significantly increased by increasing the spray volume from 60 L/ha to 120 L/ha in plant protection drones. Particularly for the DJI T30, the mid-lower canopy showed a spray coverage increase of 52.5%. The droplet density demonstrated the most significant variations in the lower inner canopy, ranging from 18.7 droplets/cm2 to 41.7 droplets/cm2 by XAG V40. From the deposition distribution on fruit trees, the plant protection drones exhibit good penetration ability, as the droplets can achieve a relatively even distribution in different canopy layers of citrus trees. The droplet distribution uniformity inside the canopy is similar for XAG V40 and DJI T30, with a variation coefficient of approximately 50%-100%. Compared to the plant protection drones, the knapsack electric sprayer is suitable for pest and disease control in the mid-lower canopy, but they face challenges of insufficient deposition capability in the upper canopy and overall poor spray uniformity. The distribution of deposition determined in this study provides data support for the selection of spraying agents for fruit trees by plant protection drones and for the control of different pests and diseases.

Effects of secondary breakup, collision dynamics, gravity and evaporation on droplet size distribution in a pressure-swirl JET A-1 spray

Size and velocity of droplets in pressure-swirl sprays vary with distance downstream the nozzle. This study aims to explain the phenomena contributing to size-resolved spatial variation of the drop size distribution for Jet A-1 spray from a small pressure swirl atomizer injected into quiescent ambient air at atmospheric conditions. The effects of secondary breakup, droplet collisions, gravity, drag-driven spray dispersion, and evaporation are evaluated. Phase Doppler anemometer (PDA) was used to resolve the velocity and size of the droplets in radial profiles at several axial distances (Z) from the nozzle exit at injection pressures between 0.5 and 1.5 MPa. The droplet motion and collision dynamics were qualitatively characterised by high-speed imaging. The analysis focused on areas along 1) the spray axis and 2) the liquid sheet direction. The first area covers small droplets with marginal evolution, while the mean drop size in the second area significantly increases downstream. The local drop size distribution and its axial evolution results from a combined effect of ballistic filtering (drifting of small droplets from periphery to spray centre and large droplets vice versa), centrifugal and turbulent droplet dispersion, and droplet collisions (increasing drop size with distance). The relative droplet-gas velocity was found at investigated Z positions too small for drag-driven secondary droplet breakup to occur. Evaporation of Jet A-1 sprayed at room temperature and pressure into still atmosphere reduces the drop size marginally. Trajectory of all drop sizes is insignificantly altered by gravity. The smallest droplets are strongly drag-driven to the spray axis, while large ones disperse centrifugally and have sufficient momentum to neglect the gravity. Combining results from imaging and laser diagnostics, various collision outcomes were identified, with a conclusion that these depend on the size and velocity of colliding droplets. Coalescing collisions dominate and strongly increase the mean drop size downstream the spray at off-axis positions while insignificantly contribute along the spray axis. The drop size span factor reduces with Z as separative collisions between large droplets and mixed-type collisions between small and large droplets narrow the drop size distribution. The above effects can be most easily amplified for drop size reduction via modification of physical properties of sprayed liquid by its heating.

Numerical study on spray cooling of aircraft equipment cabin

With the increase in the number of aircraft onboard equipment and the sharp increase in heat dissipation power, the thermal control of cabin equipment has become one of the important issues restricting the development of high-speed aircraft technology. Spray cooling has the advantages of high cooling efficiency, simple cooling system structure, easy adjustment and control, etc. It is one of the most effective methods for thermal control of the aircraft equipment cabin. This work builds a simplified physical model of the aircraft equipment cabin, and improves the simulation method of the spray cooling of the equipment cabin. To test the accuracy of the simulation method, an experimental validation study was carried out. In the three-dimensional numerical simulation of cabin spray cooling, the structure characteristics of multi-nozzle spray droplet field, temperature field and flow field are addressed. It’s found that using multi-nozzle spray cooling for large-area and multi-surface equipment cabins is feasible, which can effectively control the temperature of most surfaces. However, for some slit areas, such as between adjacent equipment and between the equipment and the cabin, the temperature is relatively high due to the ineffective coverage of spray cooling. An improved method was applied to investigate the variation of temperature and pressure of the cabin during spray cooling. The study found that the pressure in the cabin can be flexibly controlled by adjusting the size of the exhaust hole of the cabin. The matching of the heating power of the cabin and the spray cooling capacity is an important guarantee condition for realizing the temperature and pressure control of the cabin. This study provides valuable reference data for engineers to design aircraft cabin cooling schemes.