Explore the vast range of titles available.

Minimum quantity lubrication (MQL) is a relatively efficient and clean alternative to flooding workpiece machining. Electrostatic atomization has the merits of small droplet diameter, high uniformity of droplet size, and strong coating, hence its superiority to pneumatic atomization. However, as the current research hotspot, the influence of jet parameters and electrical parameters on the average diameter of droplets is not clear. First, by observing the shape of the liquid film at the nozzle outlet, the influence law of air pressure and voltage on liquid film thickness ( h ) and transverse and longitudinal fluctuations are determined. Then, the mathematical model of charged droplet volume average diameter (VAD) is constructed based on three dimensions of the liquid film, namely its thickness, transverse wavelength ( λ h ), and longitudinal wavelength ( λ z ). The model results under different working conditions are obtained by numerical simulation. Comparisons of the model results with the experimental VAD of the droplet confirm the error of the mathematical model to be less than 10%. The droplet diameter distribution span value Rosin-Rammler distribution span (R.S) and percentage concentrations of PM10 (particle size of less than 10 µm)/PM2.5 (particle size of less than 2.5 µm) under different working conditions are further analyzed. The results show that electrostatic atomization not only reduces the diameter distribution span of atomized droplets but also significantly inhibits the formation of PM10 and PM2.5 fine-suspension droplets. When the air pressure is 0.3 MPa, and the voltage is 40 kV, the percentage concentrations of PM10 and PM2.5 can be reduced by 80.72% and 92.05%, respectively, compared with that under the pure pneumatic atomization condition at 0.3 MPa.

The spray atomization of an injector significantly influences the performance and working life span of a bipropellant thruster of a spacecraft. Deep space exploration requires the thruster to be able to operate reliably at a low temperature range from −40 °C to 0 °C, so the effect of low temperature conditions on the atomization characteristics of injector spray is motivated to be comprehensively investigated. To study the swirl atomization characteristics of MMH (methylhydrazine), which is more difficult to atomize than NTO (nitrogen tetroxide), numerical simulations were conducted, employing the methods of VOF (volume of fluid) and LES (large eddy simulation) under low temperature conditions. The physical model with a nozzle size of 0.5 mm and boundary conditions with a velocity inlet of 3.89 m/s both follow the actual operation of thrusters. The development of spray atomization at low temperatures was observed through parametric comparisons, such as spray velocity, liquid total surface area, droplet particle size distribution, spray cone angle and breakup distance. When the temperature decreased from 20 °C to −40 °C at the same condition of flowrate inlet, those atomization characteristics of MMH propellant vary following these rules: the spray ejection velocity of MMH is significantly reduced by 7.7%, and gas-liquid disturbance sequentially decreases; the liquid film development is more stable, with a negative influence on atomization quality, causing difficulties for primary and secondary breakup, so the total surface area of droplets also decreases by 6.4%; the spatial distribution characteristics, spray cone angle and breakup distance vary less than 5%. Therefore, the low temperature condition can directly lower the combustion efficiency of thrusters with obvious performance degradation, but there are no significant changes in the propellant mixing and liquid film cooling. It is concluded that the bipropellant thruster can reliably work at low temperatures around −40 °C for deep space probe operation.

To further improve the dust removal efficiency of water spray, the influence of key structure parameters of nozzle on atomization characteristic (droplet size, atomization angle, flow rate, effective spray distance, wind disturbance resistance) was studied. The results showed that the nozzle had good atomization performance when the outlet diameter was 1.5 mm. The internal structure of the nozzle had an obvious influence on the atomization characteristics. The shrinkage angle had a prominent effect on the droplet size and atomization angle. When the shrinkage angle was increased from 60 to 120°, the droplet size and atomization angle were improved by 29.2% and 45.5%, respectively, while the increased shrinkage angle from 120 to 150° only improved by 9.1% and 4.2%, respectively. In addition, the diameter of the center hole had a strong correlation with the effective spray distance. When the diameter of the center hole increased from 1 to 2 mm, the effective spray distance increased by 60.9% (to 7.4 m) at the pressure of 4 MPa, while the effective spray distance without change increased when the diameter of the center hole increased from 2 to 2.5 mm. It was determined that the nozzle with the outlet aperture of 1.5 mm, the shrinkage angle of 120°, and the diameter of the center hole of 2 mm had good atomization and dust control characteristics. Additionally, it was verified that the optimized nozzle had a substantial improvement in controlling respirable dust, and the dust removal efficiencies for PM2.5 and PM5 were increased by 14.29% and 16.52%, respectively, compared to the original nozzle. This study provided guidance for choosing the nozzle of hydraulic support to form the effective dust control spray.

This paper aims to discuss the internal flow and cavitation characteristics of petal bionic nozzle holes under different injection pressures to improve the atomization effect of methanol. The FLUENT (v2022 R1) software is used for simulation. The Schnerr-Sauer cavitation model in the Mixture multiphase flow model is adopted, considering the evaporation and condensation processes of methanol fuel to accurately simulate cavitation and internal flow performance. The new nozzle hole is compared with the ordinary circular nozzle hole for analysis to ensure research reliability. The results show that the cavitation of the petal bionic nozzle hole mainly occurs at the outlet, which can enhance the atomization effect. In terms of turbulent kinetic energy, the internal turbulent kinetic energy of the petal bionic nozzle hole is greater under the same pressure. At 1 MPa, its outlet turbulent kinetic energy is 38.37 m2/s2, which is about 2.3 times that of the ordinary circular nozzle hole. When the injection pressure is from 0.2 MPa to 1 MPa, the maximum temperature of the ordinary circular nozzle hole increases by about 33.4%, while that of the petal bionic nozzle hole only increases by 12.3%. The intensity of internal convection and vortex is significantly reduced. The outlet velocity and turbulent kinetic energy distribution of the petal bionic nozzle hole are more uniform. In general, the internal flow performance of the petal bionic nozzle hole is more stable, which is beneficial to the collision and fragmentation of droplets and has better uniformity of droplet distribution. It has a positive effect on improving the atomization effect of methanol injection in the intake port of methanol-diesel dual-fuel engines.

The dust pollution at the fully mechanized heading face has seriously threatened the health of the miners. As the main technical means, the outer spray of a roadheader has the problems of small coverage of the fog field and low dust removal efficiency. Based on the multiscale swirl atomization model of LES-VOF, this study simulated and analyzed the atomization process of the nozzle. The influence law of the diameter, the length and the circulation area ratio of the swirl chamber, and the swirl core angle on the swirl number and atomization effect were determined, and the nonlinear function relationship between variables was obtained. With the help of the BP neural network model, a new type of swirl nozzle is developed which is suitable for the outside spray system at the fully mechanized heading face. The experimental results show that the error between the predicted results of the new swirl nozzle and BP network model is less than 15%, the atomization angle θ c is 24.2°, the average particle size D 32 is 64.43 µm, and the effective range R eff is about 2.1 m. At the same time, the total dust removal efficiency and respirable dust removal efficiency of the new swirl nozzle at the driver’s place are 61.10% and 63.85%, respectively, which are 21.69% and 20.92% higher than the original nozzle. Graphical abstract

This study addresses the issues of prolonged testing cycles and high costs associated with traditional sprayers. Using Computational Fluid Dynamics method, a simulation model of the gas-liquid coupling flow field for multi-duct sprayer was established, and the effects of operational parameters, the air outlet opening angle, interval, and air velocity on droplet deposition and atomization characteristics were systematically investigated. A multi-factor simulation test was conducted by constructing a CFD simulation model, performing multi-polyhedron meshing, and applying the RNG k - ϵ turbulence model along with the Discrete Phase Model. The results demonstrate that as the flow rate increases from 0.03 kg/s to 0.06 kg/s, the mean thickness of the liquid film and the uniformity index of its distribution both increased, from 197.3 μm and 0.7521 to 340.71 μm and 0.8465 respectively. Medium spray angles and small inner diameter nozzles optimize the uniformity of liquid film distribution, indirectly revealing the effects of each parameter on droplet deposition and its distribution uniformity. When the air outlet opening angle increases from 70° to 80° and then to 90°, the effective working height of the airflow field increases by 0.2 m and 0.1 m, respectively. However, increasing the interval leads to a decrease in the uniformity of the end velocity. The droplets undergo two atomization events within the airflow field. Following the first atomization, the particle size increases due to collisions and merging. The secondary atomization, occurring at a distance of 1.2 m from the air outlet, reduces the particle size and enhances deposition efficiency. Furthermore, as the initial air velocity decreases, the particle size of the droplets within the airflow field tends to increase. The reliability of the CFD simulation model developed in this study were validated through a droplet particle size measurement test. The test results demonstrated that the trend of the measurement values aligned with the simulation values, with the relative error ranging from 11.4% to 15.3%. This research reveals the gas-liquid coupling mechanism within the multi-duct spray flow field, providing a theoretical foundation for the further optimization and modification of this sprayer, thereby significantly reducing costs and improving efficiency.

This study utilized experimental and numerical simulation methods to investigate and analyze the atomization characteristics of three internal air–water mixed atomizers under different operating conditions. By comparing the research results, the effective dust control working parameters for the application of the selected atomizer in the engineering field were determined. Firstly, the atomization characteristics of the three atomizers were studied using a customized experimental system. The results indicated that nozzle 2 had a wide atomization range, a small atomization distance, and small droplet size; nozzle 3 had a narrow atomization range, large droplet size, and fast atomization speed; and nozzle 1 not only had a large atomization range but also could produce droplets of dry mist size with fast atomization speed, meeting the dust reduction requirements of the Majiliang Coal Preparation Plant. Secondly, Fluent software was used to simulate the atomization process and particle size distribution of the three internal mixed atomizers, determining the working conditions of the atomizers, the required number of atomizers, and the application angle of the atomizers in the internal mixed dust removal system. Finally, the atomized dust control system was applied on-site, achieving a total dust removal efficiency of 90.72% and a respirable dust removal efficiency of 89.75%.

Pressure nozzle is commonly used in the dust-reduction techniques by spraying of underground coal mines. Based on the internal structure, the pressure nozzle can be divided into the following types: spiral channel nozzle, tangential flow-guided nozzle and X-swirl nozzle. In order to provide better guidance on the selection of nozzles for the coal mine dust-reduction systems by spraying, we designed comparing experiments to study the atomization characteristics and dust-reduction performance of four commonly used nozzles in the coal mine underground with different internal structures. From the experimental results on the atomization characteristics, both the tangential flow-guided nozzle and the X-swirl nozzle have high flow coefficients. The atomization angle is the largest in the spiral non-porous nozzle, and smallest in both the X-swirl nozzle and the spiral porous nozzle. The spraying range and the droplet velocity are inversely proportional to the atomization angle. When the water pressure is low, the atomization performance of the spiral non-porous nozzle is the best among the four types of nozzles. The atomization performance of the X-swirl nozzle is superior to other types when the water pressure is high. Under the high water pressure, the particle size of the atomized droplets is smallest in the X-swirl nozzle. Through the experiments on the dust-reduction performance of the four types of nozzles and the comprehensive analysis, the X-swirl nozzle is recommended for the coal mine application site with low water pressure in the dust-reduction system, while at the sites with high water pressure, the spiral non-porous nozzle is recommended, which has the lowest water consumption and obvious economic advantages.

Gelled fuels have promising applications in the aerospace field. Higher density and calorific value can be achieved with the addition of energetic metal particles to gelled fuels, which can also effectively improve the combustion efficiency of the fuel and thus enhance the engine performance. However, the addition of metal particles can also make the rheological properties of gelled fuels more complex, which introduces difficulties regarding their atomization and combustion. In order to investigate the effect of the concentration of metal particles on the rheological and atomization characteristics of gelled fuels, the gelled fuel was prepared with three metal particle concentrations of 0%, 15%, and 30%. In this paper, the rheological properties of the gelled fuel were tested by a rotational rheometer, and the atomization properties (spray cone angle, Sauter mean diameter (SMD), and droplet size distribution) of the gelled fuel were measured experimentally. In this paper, three nozzle structures were designed, including a DC nozzle, a swirl nozzle, and a self-excited oscillation nozzle. The effects of different nozzle structures and metal particle concentrations on the atomization of gelled fuels are compared and discussed.

Single-fluid nozzles and dual-fluid nozzles are the two typical jet crushing methods used in spray dust reduction. To distinguish the atomization mechanism of single-fluid and dual-fluid nozzles and improve dust control efficiency at the coal mining faces, the atomization characteristics and dust reduction performance of the two nozzles were quantitatively compared. Results of experiments show that, as water supply pressure increased, the atomization angle of the swirl pressure nozzle reaches a maximum of 62° at 6 MPa and then decreases, but its droplet size shows an opposite trend with a minimum of 41.7 μm. The water supply pressure helps to improve the droplet size and the atomization angle of the internal mixing air–liquid nozzle, while the air supply pressure has a suppressive effect for them. When the water supply pressure is 0.2 MPa and the air supply pressure reaches 0.4 MPa, the nozzle obtains the smallest droplet size which is 10% smaller than the swirl pressure nozzle. Combined with the dust reduction experimental results, when the water consumption at the working surface is not limited, using the swirl pressure nozzle will achieve a better dust reduction effect. However, the internal mixing air–liquid nozzle can achieve better and more economical dust reduction performance in working environments where water consumption is limited.