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The article presents a calculation method for the shape of the ultrasonic atomizer surface. The parameters influencing the shape of the spray torch and its performance are considered. Ultrasonic emitters are manufactured according to the obtained calculation formulas and their main technical characteristics are obtained. The developed calculation method allows creating multifunctional ultrasonic atomizers capable of solving various technological problems.

In the actual production of ultrasonic atomization, to cater to the consumers’ preference for the appearance of the products, the surface of the ultrasonic atomizer needs to be treated with different machining processes, which tend to affect the surface hardness of the atomizer, and affect the atomization performance of the atomizer. Therefore, the beauty of the appearance and the reduction of atomization performance has become a contradiction in the current industrial production of atomizers. In this study, it is theoretically proved that the hardness is inversely proportional to the atomization rate. Two machining processes are selected among the five common processing techniques for the experiment: (1) mirror polishing treatment of the atomizer, and (2) mirror polishing-sandblasting-plasma spraying treatment of the atomizer. To evaluate various aspects of the atomizer’s performance, several experiments were conducted, focusing on the hardness of the atomizer’s surface, its vibration displacement and the atomization performance. The results indicate that there is an inverse relationship between the atomization rate and the surface hardness, while the atomization rate is directly proportional to the peak vibration displacement. These findings align with the theoretical predictions. Following the process (2) treatment, the atomizer’s surface developed a frosted texture. As a result, its hardness increased by approximately 13.6%, the peak vibration displacement decreased by around 23.46%, and the atomization rate dropped by about 30.59% compared to the untreated atomizer. After the treatment of process (1), the surface of the atomizer had a mirror texture, where the hardness decreased by around 26.8%, the peak vibration displacement increased by approximately 64.2%, and the atomization rate increased by approximately 110.81%, compared with the untreated atomizer. The hardness influences the atomization rate by affecting the vibration displacement of the ultrasonic atomizer.

The following article proposes the design of a bi-centrifugal atomizer that allows the interaction of sprays from two fluids (water and liquid nitrogen). The liquid nitrogen (LN2) is below −195.8 °C, a temperature low enough for the nitrogen, upon contact with the atomized water, to cause heat loss and bring it to its freezing point. The objective is to convert the water droplets present in the spray into ice. Upon falling, the ice particles can be dispersed, covering the largest possible area of the seafood products intended for cold preservation. All these phenomena related to the interaction of two fluids and heat exchange are due to the bi-centrifugal atomizer, which positions the two centrifugal atomizers concentrically, resulting in the inevitable collision of the two sprays. Each of these atomizers will be designed using a mathematical model and CFDs tools. The latter will provide a better study of the flow behavior of both fluids inside and outside the bi-centrifugal atomizer. Hence, the objective revolves around confirming the validity of the mathematical model through a comparison with numerical simulation data. This comparison establishes a strong correlation (with a maximum variance of 1.94% for the water atomizer and 10% for the LN2 atomizer), thereby ensuring precise manufacturing specifications for the atomizers. It is important to highlight that, in order to achieve the enhanced resolution and comprehension of the fluid both inside and outside the duplex atomizer, two types of meshes were utilized, ensuring the utilization of the optimal option. Similarly, the aforementioned meshes were generated using two distinct software platforms, namely ANSYS Meshing (tetrahedral mesh) and ANSYS ICEM (hexahedral mesh), to facilitate a comparative analysis of the mesh quality obtained. This comprehension facilitated the observation of water temperature during its interaction with liquid nitrogen, ultimately ensuring the freezing of water droplets at the atomizer’s outlet. This objective aligns seamlessly with the primary goal of this study, which revolves around the preservation of seafood products through cold techniques. This particular attribute holds potential for various applications, including cooling processes for food products.

Air-blast atomizers are extensively used for a variety of purposes. Due to its complexity, the atomization mechanism has not been elucidated. In this study, a mechanistic model is proposed to predict the droplet diameter distribution based on the atomization process of a planar liquid film with co-current gas flows, and its validity is examined by comparing the estimated and measured droplet diameters using high-speed image analysis and laser measurement. As a result, using high-speed imaging, we clarified that the bag film rupture is caused not by the turbulence of the gas flow but by the impact of floating droplets on the liquid film of the expanding bag when the film is thin enough. The average thickness of the liquid film at the bag breakup is of the order of micrometres and varies greatly, resulting in a dispersed distribution of droplet diameters. After the film ruptures, the bag film shrinks towards its transversal and vertical rims due to surface tension, forming large-diameter ligaments. During the contraction process of the bag film, tiny droplets of the order of micrometers are formed at the edge of the perforation. Finally, the remaining ligaments with large diameters fragment into large droplets with submillimetre diameters. The good agreement between the measured and predicted droplet diameter distributions validated the mechanistic model.

Rotary atomizers are mainly used in agricultural manned aircrafts. Atomization characteristics at high speeds have been studied, but methods to measure the atomization efficiency have not been elucidated. The atomization efficiency of rotary atomizers under high-speed airflow was investigated using an IEA-I high-speed wind tunnel experimental installation, AU5000 rotary atomizer, and a laser diffraction particle size analyzer. Accordingly, a model equation for atomization efficiency measurements was innovatively obtained. When the flow rate, fan blade angle of the atomizer, and wind speed were used as variables, the experimental results showed that the atomization efficiency mainly depended on the fan blade angle. When the fan blade angle was 35°, the atomization efficiency was optimal, regardless of wind speed. In contrast, when the fan blade angle of the atomizer was 65°, it exhibited the worst atomization efficiency, regardless of the wind speed. The experimental data from this study can provide guidance for aerial application in fixed-wing manned aircraft, such as the flow rate, and operating speed.

Measuring the dynamic parameters of liquid fragments generated in the near-field of atomizing sprays poses a significant challenge due to the random nature of the fragments, the instability of the spray, and the limitations of current measuring technology. Precise determination of these parameters can aid in improving the control of the atomization process, which is necessary for providing suitable spray structures with appropriate flow rates and droplet size distributions for various applications such as those used in heat engines. In piston and gas turbine engines, controlling spray characteristics such as penetration, cone angle, particle size, and droplet size distribution is crucial to improve combustion efficiency and decrease exhaust emissions. This can be accomplished by adjusting the structural and/or operating parameters of the fuel supply system. This article aims to measure the breakup length, spray cone angle, axial velocity, breakup time, and liquid sheet film thickness for a swirl air-blast atomizer used in a gas-steam engine. The measurement was conducted using a shadowgraph imaging system developed specifically for this study, consisting of a high-speed camera, a lens, and a light source. While lasers are commonly used as light sources in the literature, this study utilized a special LED high-speed pulse light generator, which is cheaper, easier to handle, and provides a more uniform background. Images were processed using a MATLAB code developed for this study. Although the breakup zone is naturally random and the breakup location significantly varies with time, the novel method developed in this study helps quantify critical parameters under different operating conditions.

The two-phase mixing layer formed between parallel gas and liquid streams is an important fundamental problem in turbulent multiphase flows. The problem is relevant to many industrial applications and natural phenomena, such as air-blast atomizers in fuel injection systems and breaking waves in the ocean. The velocity difference between the gas and liquid streams triggers an interfacial instability which can be convective or absolute depending on the stream properties and injection parameters. In the present study, a direct numerical simulation of a two-phase gas–liquid mixing layer that lie in the absolute instability regime is conducted. A dominant frequency is observed in the simulation and the numerical result agrees well with the prediction from viscous stability theory. As the interfacial wave plays a critical role in turbulence transition and development, the temporal evolution of turbulent fluctuations (such as the enstrophy) also exhibits a similar frequency. To investigate the statistical response of the multiphase turbulence flow, the simulation has been run for a long physical time so that time-averaging can be performed to yield the statistically converged results for Reynolds stresses and the turbulent kinetic energy (TKE) budget. An extensive mesh refinement study using from 8 million to about 4 billions cells has been performed. The turbulent dissipation is shown to be highly demanding on mesh resolution compared with other terms in TKE budget. The results obtained with the finest mesh are shown to be close to converged results of turbulent dissipation which allow us to obtain estimations of the Kolmogorov and Hinze scales. The estimated Kolmogorov scale is found to be similar to the cell size of the finest mesh used here. The computed Hinze scale is significantly larger than the size of droplets observed and does not seem to be a relevant length scale to describe the smallest size of droplets formed in atomization.

This paper proposes the use of mathematical modeling of technological processes as a tool for increasing the efficiency of equipment and solving environmental problems, which contributes to the sustainable development of enterprises in the chemical industry. The results of modeling the process of separating liquids of different densities in a centrifugal field are presented to study the influence of the type of atomizers on the flow rate and the number of contact devices on the separation efficiency. The work shows the importance of using numerical modeling in design to substantiate scientifically decisions made and confirm the effectiveness of developed structures. The results are important to intensify heat and mass transfer processes and to reduce the negative impact of production on the environment.

A bulk of a liquid dispersed into single droplets using the kinetic energy of a high-velocity gas in an air-blast atomizer is frequently employed in technical atomization processes. The atomized liquid is primary situated on a surface (prefilming surface) to form a thin liquid film before being exposed to high-velocity air flow. Moreover, the performance of spray processes is affected by the variation in the atomizer geometry, liquid physical properties and operational conditions. The purpose of this study is to examine and describe the influence of the nozzle geometry and a wide range of test conditions on the spray performance of prefilming air-blast atomizers. In order to evade the commonly complicated internal flow, an important but simple geometry was selected. Liquid break up mechanisms close to the atomizer exit were investigated using shadowgraphy associated with particle tracking. Furthermore, high-resolution local velocity and droplet size measurements were performed using phase Doppler anemometry (PDA). On the whole, the break up mechanism is considerably influenced by either air pressure and liquid flowrates or atomization edge size. Droplet size distribution profile of the different spray parameters in axial and radial directions are studied. The location of the maximum droplet mean velocity and the minimum Sauter mean diameter (SMD) within the spray are determined. The prefilming surface area and atomization edge size were observed to influence the liquid sheet breakup, droplet velocity and droplet size. With an atomization edge length increase of 5.7 mm, the global SMD increased to a maximum of 70% within different operation conditions.

This investigation focuses on the impact of liquid properties—viscosity, surface tension—and air pressure on the Sauter Mean Diameter (SMD) of atomization sprays. Utilizing a twin-fluid atomizer, the study resulted in derived equations that quantify these effects across a spectrum of liquid behaviours, with an emphasis on both viscous and non-viscous liquids. The derivation process for viscous liquids yielded equations showcasing an average deviation of 1.32% from experimentally observed SMD values, validated across a dataset of 250 experimental trials. These trials involved a total of 18,000 droplets analysed, with a standard error of 0.02%, spanning a liquid viscosity range of 3x10-3 to 20x10-3 kg/(m.s), and air pressures from 50 to 300 kPag. For non-viscous liquids, defined by a liquid viscosity threshold of < 3x10-3 kg/(m.s), the equations revealed a higher average deviation of 1.51% from the experimental SMD. These runs included the analysis of 19,600 droplets across liquid surface tensions from 20x10-3 N/m to 72.8x10-3 N/m, with a standard error of 0.03%. This distinction highlights the significant influence of surface tension in shaping the atomization outcomes for these liquids. A quantitative discovery of this research is how a 10% increase in viscosity for viscous liquids correlates to a substantial 33% increase in SMD, impacting around 10,500 droplets per viscosity level, with an observed standard deviation of 0.15% across viscosity measurements. This emphasizes the dominance of viscosity in influencing atomization dynamics for viscous liquids. Conversely, for non-viscous liquids, a 10% increase in surface tension translates to a 45% increase in SMD, affecting approximately 11,200 droplets per surface tension category, with a standard deviation of 0.18% in surface tension measurements. Moreover, this study pioneers the introduction of a particle tracking code, designed for high-speed camera frames, enabling the analysis of over 10,000 droplets per experimental run, summing up to more than 280,000 droplets analysed across all trials, with an overall precision rate of 99.5%. This novel technique enhances system performance by providing highly accurate and real-time droplet size distribution data, which is critical for optimizing atomization processes in industrial applications. In comparison with state-of-the-art studies, this research offers a comprehensive analysis of the combined effects of viscosity, surface tension, and air pressure on SMD, providing new insights and validated predictive models. The contributions of this work lie in its detailed quantitative results and the introduction of advanced measurement techniques, which together represent a significant advancement in the field of atomization.