Droplet Velocity Distributions Research Articles

Ultrasonic-assisted radial jet reattachment atomizer

Ultrasonic atomization, a powerful method using high-frequency sound waves, has gained notable significance across diverse industries due to its capacity to disintegrate liquids into very fine droplets. The use of ultrasonic vibrations for spray formation can effectively address the challenges associated with conventional methods, including the requirement for high temperatures and high-pressure fluids. Compared to conventional methods, ultrasonic atomizers can deliver a spray with lower velocity, operate at lower temperatures, produce smaller particle sizes, achieve high evaporation rates, and impose low mechanical stress. The radial jet reattachment (RJR) nozzle is a unique design to modify a jet’s flow and improve its transport characteristics, especially in air drying and cooling processes. In this paper, a novel technology is utilized with the combination of an RJR nozzle and ultrasonic atomization to atomize most liquids. The corresponding atomization rate, mist droplet size distribution, and mist droplet velocity distribution, influenced by liquid properties, temperature change, transducer mesh pore size, and applied voltage have been investigated in this paper. The energy consumption ratios, defined as the ratio of thermal energy required to evaporate liquid divided by ultrasonic energy, are analyzed based on atomization rate and applied power, showing very promising results among atomizing methods. Furthermore, the results in terms of the droplet average diameter and mean velocity as well as the resultant volumetric flow rate under different operating conditions and for all working fluids considered have been correlated with the aid of non-dimensional parameters. In addition, certain potential applications based on the remarkable characteristics of the ultrasonic-assisted RJR atomizer such as misting liquids and spray drying are highlighted.

Movement Characteristics of Droplet Deposition in Flat Spray Nozzle for Agricultural UAVs

At present, research on aerial spraying operations with UAVs mainly focuses on the deposition outcomes of droplets, with insufficient depth in the exploration of the movement process of droplet deposition. The movement characteristics of droplet deposition as the most fundamental factors affecting the effectiveness of pesticide application by UAVs are of great significance for improving droplet deposition. This study takes flat spray nozzles as the research object, uses the Particle Image Velocimetry (PIV) technique to obtain movement data of water droplet deposition under the influence of rotor flow fields, and investigates the variation characteristics of droplet deposition speed under different influencing factors. The results show that the deposition speed and the distribution area of high-speed (>12 m/s) particles increase with the increase of rotor speed, spraying pressure, and nozzle size. When the rotor speed increases from 0 r/min to 1800 r/min, the average increase in maximum droplet deposition speed for nozzle models LU120-02, LU120-03 and LU120-04 is 33.26%, 19.02%, and 7.62%, respectively. The rotor flow field significantly increases the number of high-speed droplets, making the dispersed droplet velocity distribution more concentrated. When the rotor speed is 0, 1000, 1500, and 1800 r/min, the average decay rates of droplet deposition speed are 36.72%, 20.00%, 15.47%, and 13.21%, respectively, indicating that the rotor flow field helps to reduce the decrease in droplet deposition speed, enabling droplets to deposit on the target area at a higher speed, reducing drift risk and evaporation loss. This study’s results are beneficial for revealing the mechanism of droplet deposition movement in aerial spraying by plant protection UAVs, improving the understanding of droplet movement, and providing data support and guidance for precise spraying operations.

Impact and spread dynamics of a viscoelastic droplet on an inclined hydrophilic surface

In this work, the impact of a three-dimensional viscoelastic droplet on an inclined hydrophilic surface is investigated by means of direct numerical simulations. The volume-of-fluid method is adopted to capture the interface, and the Oldroyd-B model is used to describe the rheological behavior of the viscoelastic droplet. The effects of the Weissenberg number (Wi) and the Weber number (We) on the impacting and spreading processes are studied, including the viscoelastic droplet shape, velocity, energy transformation, and stress distribution. Our results are in good agreement with the experimental data in the literature. In particular, the elastic force markedly influences droplet deformation at intermediate Wi values, although this trend diminishes at higher or lower Wi values. With increasing We, the impacting viscoelastic droplet reaches its maximum deformation more rapidly, while the nonmonotonic peak of kinetic energy indicates that the droplet elasticity plays significant role at moderate We. Additionally, the inclination of the surface has a pronounced effect on the droplet spreading process, and the elongated viscoelastic droplet at larger inclination angle is likely to experience a stronger oscillation. According to further analyses, We exerts a modest influence on the change rates of the droplet potential energy and spreading length in the flow direction. However, a larger inclination angle reduces stress concentration and accelerates the change rates. Due to the oscillation dynamics, Wi exhibits a non-monotonic effect on the spreading process and induces a monotonous increase in potential energy of viscoelastic droplets. The above analyses provide insights into the impact mechanism of droplets on an inclined hydrophilic wall and, therefore, will guide the applications in the future.

Hydraulic performance assessment on dynamic fluidic and complete fluidic sprinklers under indoor and outdoor conditions

Since Complete Fluidic Sprinklers (CFS) cannot function well in low-pressure environments, Dynamic Fluidic Sprinkler (DFS) were developed to address this issue. In 2021, research in the field and laboratory were conducted to examine how well DFS and CFS performed hydraulically in both indoor and outdoor conditions. In this investigation, a Thiess Clima laser precipitation monitor was used to evaluate the droplet size and velocity distribution of two different types of sprinklers indoors. From the findings, DFS velocities ranged from 0.1 to 4 m/s whereas CFS ranged from 0.1 to 5.3 m/s. The maximum frequency value was obtained at velocities of 1 m/s for each combination. The DFS had a slightly greater discharge coefficient and spray pattern than the CFS. The DFS's maximum spray range was 12.2 m, while the CFS's maximum spray range was 10.8 m, with standard deviations of 1.07 and 1.66, respectively. Under high wind speed conditions, the maximum combined Coefficient of Uniformity (CU) of DFS and CFS were 81.1% and 78%, respectively. For a given pressure and sprinkler spacing, DFS delivered higher CU values than CFS, especially while running at low pressure, demonstrating that DFS offered a more favoured water distribution pattern at low pressure. At different distances from the sprinkler, the highest application rates for DFS and CFS were 6.7 mm h−1 at 7 m and 6.5 mm h−1 at 7 m, respectively. A comparison of DFS and CFS under hydraulic performance indicated that DFS had a better performance than CFS. The study can serve as a guide for how to conserve water in sprinkler-irrigated fields.

Liquid and aerated jets behind different pylon configurations in supersonic crossflow

Effects of different pylon configurations on the liquid and aerated jets injected in supersonic crossflow of Mach number 1.65 were investigated experimentally. Pylon configurations with different bottom curvatures at the trailing edge were explored. Two liquid jets with momentum flux ratio of 0.1 and 0.4, and two aerated jets with gas-to-liquid mass ratio of 2% and 4% were selected in the current study. Acetone and air were used as the secondary liquid jet and the aeration gas, respectively. For the atomization quality of the jet, the droplet velocity field was obtained using fluorescence-based particle image velocimetry. The high-speed shadowgraph and cross-sectional planar laser-induced fluorescence experiments were performed for the mixing characteristics, such as penetration height and spreading area. The high-speed images were also used for the dynamic mode decomposition, which revealed dominant structures and their associated frequencies. Curved pylons with 45°and 60°trailing edge curvatures produced higher droplet velocity distribution than the other cases for liquid and aerated jets, respectively. The penetration height of the liquid jet at low momentum flux ratio tends to traverse towards the wall downstream of the injection. Aeration substantially improves the penetration height for the same liquid flow rate due to the annular nature of the aerated jet with a gas-to-liquid mass ratio of 2%. Cross-sectional planar laser-induced fluorescence results revealed a considerable increase in the spreading of the jet for the aerated jets as compared with the low momentum flux ratio liquid jet. This was due to the higher shear layer interaction of the aerated jet than that of the liquid jet. The aerated jets produced 60% higher spreading area than the liquid jet with the same mass flow rate. The curved pylons exhibited at least 10% increment in the spreading area as compared to the standard pylon cases for all the liquid and aerated jets. Three distinct modes were observed in the DMD analysis. The convective mode was the typical first and second modes of all the cases. The shear layer flapping and shear-induced entrainment breakup modes have also been observed with frequencies around 5 kHz.

Gas–liquid coaxial atomization with swirl in high-pressure environments

We present recent experimental results on the dynamics of atomization of a liquid column by a coaxial turbulent gas jet, under varying air angular momentum (swirl) conditions and densities. We compare between atomization under atmospheric conditions and in a pressurized environment where the atomizing and ambient air density is 5 times the atmospheric level. For both conditions, the parameter space includes a gas-to-liquid momentum ratio in the range of M=25−56 and swirl ratios of SR=0−1. High-speed shadowgraphy images in the spray near-field are used to quantify the spatial and temporal evolution of the liquid–gas interface. In the mid-field, Phase Doppler Interferometry, collected radially across the spray, quantify droplet size, velocity, and number density distributions. At high pressure and with increasing M, we observe a decrease in spray angle when SR=0 but a spray angle increase when SR>0.5 (critical swirl). We reconcile these observations with the crown de-wetting mechanism, first observed in X-ray shadowgraphs of the spray. Crown de-wetting depends on gas inertia relative to the liquid, which increases linearly with atomization environment pressure, leading to this switch in behavior. This mechanism also explains the modified droplet radial distribution in the mid-field, with critical transition from concave to convex-shaped trends in the mean droplet size profile. Finally, we reconstruct the full spray droplet population from radial measurements, showing that swirl not only modifies the transport of droplets in the spray cross-section, but also enhances break-up and reduces the Sauter Mean Diameter globally, for all momentum ratios and pressure conditions tested.

Review of atomization characteristics of liquid jets in crossflow

The atomization process of liquid fuels is vital in scramjet engines. The level of atomization directly impacts the subsequent evaporation, mixing, and combustion processes. Therefore, understanding the atomization mechanism of liquid jets in crossflow is necessary to promote the mixing process of scramjet engines and improve the combustion efficiency. This article overviews the atomization process of liquid jets in transverse airflow based on the breakup mechanism, atomization characteristics, and factors affecting atomization. The deformation and fragmentation of droplets are influenced primarily by the Weber number and have little correlation with the Reynolds number. There are similarities in the properties between the primary fragmentation of liquid jets and the breakup of liquid droplets in crossflow. The primary breakup of liquid jets in crossflow is characterized primarily by continuous jet column breakup. The Rayleigh–Taylor instability causes columnar breakup, while the Kelvin–Helmholtz instability causes surface breakup in the jet. The size distribution of droplets follows C-, I-, or S-shaped distributions, while the velocity distribution of droplets follows an inverse C-shape. Finally, the shortcomings of current research are pointed out, namely, the lack of research on the jet breakup mechanism in crossflow under actual scramjet engine configurations and inflow conditions. In the future, it can be combined with artificial intelligence to reveal the jet breakup mechanism under actual working conditions and establish a wide range of theoretical prediction models.

Hydraulic Characterization of the External Flow Field of a Pressure-Self-Controlled Water-Pesticide Integrated Sprinkler

Highlights A pressure-self-controlled water-pesticide integrated sprinkler was developed for trellis crops. The dual-flow channel design integrates both water and pesticides and allows simultaneous downward irrigation of grape roots and upward spraying of grape branches and leaves. The comprehensive scoring method was employed to evaluate the spraying performance of the water-pesticide integrated sprinkler for both irrigation and spraying modes. Abstract. To ensure optimal growth of plants, including for trellis-style grape cultivation, it is essential to provide water to plant roots, branches, and leaves. Unfortunately, existing sprinkler systems are not designed to accommodate irrigation and spraying at the same time. To address this issue, a pressure-self-controlled water-pesticide integrated sprinkler was developed for trellis crops in this research. To assess the performances of irrigation and spraying modes, several factors, including the droplet diameter, droplet velocity, droplet striking kinetic energy, spray uniformity, and velocity distribution, were evaluated. Advanced measurement tools such as a two-dimensional video disdrometer (2DVD) and a particle image velocimeter (PIV) were employed to experimentally study the hydraulic features of different working modes. This study provides precise working parameters, including pressure and installation height, for the sprinkler system under different conditions. These parameters offer valuable engineering guidance. Notably, during irrigation, the sprinkler dispersed water toward the ground to irrigate the roots. Furthermore, the spray droplet diameter and velocity decreased with increasing pressure. Based on an analysis of the parameters affecting the droplet striking kinetic energy, the recommended optimal working pressure is 250 kPa. The high-pressure water produced by the sprinkler in the spraying mode effectively covered the crop leaves at an optimal working pressure of 400 kPa, as determined by the spray distribution pattern at different heights. In this study, for the water-pesticide integrated sprinkler, we recommend an installation height of 1.4 m for optimal operation. These findings could promote the practical application of this system. Keywords: Hydraulic performance, Spray characteristics, Spraying, Sprinkler irrigation, Water-pesticide integrated systems.

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.

Experimental investigation on droplet evolutions in co-flow around the bluff body

Annular mist flow widely exists in natural gas and other engineering fields. Vortex flowmeter has gradually become an effective means of wet gas measurement. However, the droplets in the flow field will influence the stability of the vortex. In this paper, the interaction between droplets and vortex was studied by experiments. A novel in-focus criterion was proposed to improve the accuracy of droplet measurement. Simultaneous acquisition of droplet size, velocity, and concentration was achieved. The spatial evolution of droplet parameters was obtained to determine the position where the droplets were evenly distributed. The bidirectional coupling mechanism between droplets and vortex was studied. Firstly, the influence of the vortex flow field on droplets was reflected by the characteristics of droplet distribution around the bluff body. Secondly, the effect of droplets on the vortex signal in the flow field was analyzed based on Stokes number Stp and liquid-phase load φl. When φl < 0.03, the probability distribution of droplet velocity downstream of the bluff body presents double peaks. The exchange momentum between the small droplets and the vortex is stronger, and vice versa for the larger droplets. Finally, the quality factor of vortex signals decreases from -2.09 to -2.18 with the increase in the volume concentration of droplets. It is further demonstrated that the increase in volume concentration of droplets will destroy the vortex structure and degrade the quality of the vortex signal.

Integrating properties and conditions to predict spray performance of alternative aviation fuel by ANN model

Alternative aviation fuel has been confirmed benefits for GHGs reduction and energy saving. Alternative fuel use should meet drop-in fuel requirement, and one of the important factors to ensure combustion completeness is to achieve spray requirement in the whole envelop of flight. Alternative fuels are characterized different fuel properties at low temperature comparison with traditional jet fuel. For understanding fuel properties and spray-related processes under different conditions, alternative aviation fuel, including Fischer Tropsch (FT), cellulose hydrotreating jet fuel (CHJ) and traditional jet fuel (RP-3), were investigated spray performance. According to empirical equation deduced from experiment data (283 K-343 K), deviations to RP-3 enhanced significantly on surface tension and viscosity at low temperature aera (243 K-273 K). As the complex and discontinuous interaction between nozzle structure and fuel properties with temperature, and thus it is difficult to obtain appropriate empirical equation or simulation results at low temperature. Moreover, non-drop-in fuel like pure FT fuel cannot comply with the same spray mechanism as drop-in fuel. The artificial neural network (ANN) approaches have been involved to solve the complex relationship of properties with spray performance. ANN-spray model coupling with ANN-mass flow can predict not only cone angle and liquid length but also SMD and velocity in liquid zone and droplet zone with above 0.99 total correlation coefficient. Coupling simulation results of mass flow and spray performance, FT and CHJ as well as blend fuels present more obvious difference to RP-3 in droplet size distribution and velocity distribution at low temperature.

Effect of cross-flow velocity on spray evolution and impingement characteristics of a multi-hole port fuel injector

The location and orientation of the injector play a crucial role in determining engine performance and emissions from spark ignition and dual-fuel compression ignition engines. This study focuses on the spray atomization and downstream mixing of gasoline injected from a multi-hole port fuel injector in a crossflow. This study employed the phase Doppler interferometry technique to extract the droplet size and velocity distributions for the flow confined in a circular duct with a diameter similar to the intake port of the dual-fuel compression ignition engine. The flow velocity was maintained at 10 m/s at 1 atm pressure and 299 K temperature. The spray characteristics were compared for the quiescent and crossflow cases. The spray evolution was analyzed using a high-speed imaging technique. Near wall impingement analysis has been carried out using the spray impingement models. The early stage spray evolution was similar for the quiescent and crossflow cases. The horizontal velocity of the spray was found to be ∼12 m/s at 20 mm downstream of the injector. The velocity remained similar for the flow and no-flow cases, as drag force was found to have an insignificant effect. The drag force was estimated to be one order of magnitude higher for the 15-μm droplet than the 50-μm droplet. The maximum Sauter mean diameter observed for the flow case inside the spray was 53 μm, which was 18% higher than the maximum Sauter mean diameter of the no-flow case. The droplet Sauter mean diameter increased along the spray due to the coalescence of slow-moving droplets. The droplet breakup was found to be insignificant downstream of the spray. The flow entrained the droplets smaller than 30 μm. The spray-wall impingement criterion estimated around 42% of droplets to bounce off the surface at 50 mm, compared to 22% without flow.

Categorization of iso-pentane flashing spray based on morphology, thermodynamical and mechanical effects

Accidental release of superheated liquids is typically accompanied with hazardous flashing jets. Indeed, flashing jets undergo fragmentation into massive fine droplets, thus forming ideal circumstances for fires and explosion. To gain a deeper understanding of depressurized release, we studied the dynamics of iso-pentane at superheats of 40–80 °C and injection pressures of 0.6–3.0 MPa. The internal flow pattern and external spray morphology are visualized at quasi-steady stage using a high-speed camera. Results show that the flashing patterns can be classified into non-flashing, transitional flashing, and flare flashing arising from the interaction between thermodynamic and mechanical effects. The contribution of thermodynamic effect decreases as mechanical effect intensifies, due to the suppression of bubble nucleation and burst. We propose the index k, based on JaRp = k(WevOh)−1/7, to identify different flashing regions, i.e., k below 211 for non-flashing, k between 212 and 425 for transitional flashing, and k above 425 for flare flashing. Besides, the microscopic characteristics involving droplet velocity and diameter distribution are investigated and a new correlation for drop size is proposed, which is dependent on factors such as nozzle aspect ratio, mechanical force, and thermodynamic force. These findings should help to define policies to decrease the risk associate with flashing jets.

Material characterization and inter/intra-particle validation for DEM simulation of urea coating process

Particle coating is a common operation in the controlled-release fertilizer (CRF) industry, where a coating layer is appliedto the urea cores. A discrete element method (DEM) computer simulation was applied to model the coating process for the urea granules using measured model parameters. The accuracy of DEM input parameters for the coating material properties and the physical and mechanical characterizations of urea granules are crucial to the study of particle coating processes. Thus, to enhance the simulation accuracy, information on the material properties (urea granules) is required. In this study, the elasticity parameters, shear modulus, coefficient of restitution (CoR), and coefficient of rolling and static friction (CoRF) and (CoSF) of urea granules are estimated experimentally in addition to the physical characteristics. The sensitivity of the angle of repose of the urea bed was investigated at different coefficients of friction. According to the obtained experimental value of the angle of repose, values of 0.2 and 0.3 for CoRF and CoSF, respectively, were adjusted to obtain consistent urea granules’ motion for simulation and the experiment. Moreover, the spray droplet sizes and velocity distributions were estimated using the video-imaging process technique. Based on this experimental characterization, elasticity parameters and spray properties were integrated into DEM simulation software as input data to perform numerical analysis of the coating process to compare simulation and experimental results, which show uniformity at three different pan speeds with a maximum deviation of 0.033 at 5 rpm. Also, consistency between DEM and experiment results was achieved in terms of average coating thickness (μm) of the selected samples and average intra-particle thickness variation (CoVintra). These results revealed that the coating film thickness is proportional to the rotation speed for the experiment and simulation. To enhance the inter-particle coating uniformity, the effects of the most significant parameters such as pan speed, filling ratio, particle size, spray rate, and spray angle, were examined. A low spray rate, filling ratio, and high pan speed improved the coating uniformity. The particle size and spray angle show considerable influence on the coating uniformity, where larger particle sizes and spray angles tend to reduce the inter-particle coating uniformity.

Numerical investigation on spray and flow field characteristics of elliptical nozzle in supersonic crossflow

ABSTRACT It has been suggested that using an elliptical nozzle could enhance the atomization and mixture quality. In order to explore the elliptical liquid jet on spray and flow field characteristics in supersonic airflow, the VOF-Spray one-way coupling model was adopted to study the nozzle exit patterns, size, and velocity distribution of droplets. The research also compared the flow field characteristics in Mach 2.85 air crossflow under the application of different orifices. The numerical results showed that elliptical 4 nozzle (Aspect ratio of 4) had better flow performance than circular nozzle. The cavitation area and turbulent disturbance of elliptical 4 nozzle were mainly concentrated in the major axis direction. The elliptical 4 jet always had a lower penetration depth than circular jet. At the flow range of 0 ~ 50 mm, the penetration depth of elliptical 4 jet is roughly 12% less than that of circular jet. Another finding was that the spanwise extension range of elliptical 4 spray was larger than the circular spray. The spanwise extension range of elliptical 4 spray increased by about 19.4% at most in the flow range of 0 ~ 50 mm. Additionally, the elliptical 4 spray had the smallest Santer Mean Diameter (SMD). The elliptical 4 jet had a 2.9% smaller Santer Mean Diameter than the circular jet. Due to the greater windward surface area of the elliptical 4 orifice, the gas streamwise velocity near the bottom wall was reduced. A reverse vortex pair with distinct characteristics could be observed under the application of elliptical 4 orifice. Furthermore, compared with the circular orifice, the shock wave angle generated by elliptical 4 orifice reduced by 9.7%, and the total pressure recovery coefficient rose by 2.3%.

Cross-infection risk assessment in dental clinic: Numerical investigation of emitted droplets during different atomization procedures

Cross-infection risk induced by the emitted droplets and bioaerosols during dental procedures has challenged service providers and patients alike. The present study aims to investigate the transmission mechanism of emitted droplets during the dental atomization procedures: vibration ultrasonic scaling (vUS) and rotation high-speed drilling (rHSD) and propose the risk assessment. Computational fluid dynamics (CFD) simulation was performed, and the experimentally recorded droplet velocity and diameter distribution during the atomization procedures were defined as initial boundary conditions. The droplet transmission in the dental clinic was analyzed from the final fate (deposition, suspension, and escape) and fallow time (FT) of emitted droplets. The results revealed that the diameter threshold for the droplet deposition and suspension was 60μm, and the fraction of deposited droplets would be stable at 79.5% for rHSD and 85% for vUS. The primary contamination distance was generally within 0.28 m and 0.4 m from the treatment position for the atomization procedures of rHSD and vUS, respectively. An increment of about 2% in the fraction of escaped droplets was noted when conducting the rHSD. The median of estimated FT for the atomization procedure of rHSD, 34 min, was longer than that of vUS, 30.6 min. In general, cross-infection risk during rHSD can be regarded as “higher” than vUS. The contribution of the present study can serve as guidance to decrease the cross-infection risk in dental clinics.

Spray and deposition characteristics of unsaturated polyester resin applied for impregnating long fiber preform composites

AbstractSpray up is a method intensively applied for short fiber reinforced plastic (FRP) products manufacturing. The current study investigated the application of spray up for impregnation and manufacturing of long fiber FRP products, which can bring major advantages of minimized impregnation time and fewer product defects. Computational fluid dynamics (CFD) modeling was applied to investigate the spray and deposition characteristics of the viscous general‐purpose unsaturated polyester resin on a glass fiber preform. Validation of CFD results was done using phase Doppler anemometer and camera imaging techniques, and errors were calculated. Droplet velocity distributions 30 cm from the nozzle tip showed an average absolute percentage error of 4.3% and root mean square error value of 0.68 m/s, which are minimal. CFD and experimental values of sprayed resin area coverage (main area) after 4 s of spray were 17 and 16.3 cm in diameter, respectively; this is a relatively small error. Resin pool thickness on the target surface was variable, values predicted numerically. Non‐uniformity of pool thickness can be compensated by using appropriate compaction mechanisms. It is also possible to impregnate large size and complex shape products using multiple nozzles of proper arrangement.

Experimental investigation on boiling regime transformation when the binary-droplet impact on the superheated surface

This experimental study focuses on the phenomena induced by thermal effects after a two-component droplet of propylene glycol water impinges on a hot substrate. The visualization experiment revealed that this phenomenon is characterized by a shift in the boiling regime of the droplets, which exhibits different transformation patterns with changes in surface temperature and propanediol concentration. On the basis of high-speed camera sequence images, a temperature-concentration regime map is created. Qualitative analysis is performed on the causes of the boiling transformation, as well as the wall temperatures and concentration intervals at which it might occur. The time at which the boiling regime transformation occurs can be determined by analyzing the secondary droplets. In addition, the effects of various boiling regimes and propylene glycol concentrations on the size and velocity distribution of secondary droplets are briefly investigated.

Probabilistic derivation of droplet velocity using quadrature method of moments

Abstract Accurately prediction of dispersion and polydispersity of droplet flow is not a trivial task due to the complex behavior of the droplet size distribution (DSD) and the strong state of the instantaneous velocity of a droplet on the shape and size of the droplet. Describing the distribution of sizes and velocities of droplets initially formed in sprays is an essential piece of information needed in spray modeling, which is used to define the initial state of the spray droplets in the downstream two-phase flow fields’ predictive computations. The predictive model for the droplet size and velocity distributions in sprays is formulated as the droplet’s velocity magnitude has a power–law relationship with the droplet in this study. The present model incorporates the deterministic and stochastic aspects of the spray formation process. The quadrature method of moments (QMOM) is applied to solve numerically the transport equations of the probability density function coupled with conserved source terms incompressible Navier-Stokes equations for the liquid phase. The sub-models are connected by different source terms signifying the liquid-gas interaction. Equations of transport for spray moments are derived from DSD, and closure is attained using a gamma distribution. The integer spray moments concerning the volume are used to construct the continuous distribution of QMOM. In contrast, the velocity moments are used to determine the droplet velocity as a constant function of the droplet diameter. The model is first applied to simulate a diesel spray tip penetration under nonreactive conditions with different droplet velocity profiles to validate the approach with experimental data. An additional case of a liquid nitrogen spray is applied to show the gamma distribution’s ability to describe spray drop size distribution. The model generally predicts reasonable agreement with the experimental for both cases.

Radial distribution characteristics of droplet size and velocity in annular mist flow around the bluff body

Wet gas is a common gas–liquid flow type in chemical processing. When measuring the gas flow rate and liquid load of wet gas with a vortex flowmeter, the small droplets in the flow can significantly affect the measurement accuracy. The optical shadow method was used to measure the parameters and distribution of droplets around the bluff body in annular mist flow. The experimental results show that the velocity distribution of droplets upstream of the bluff body mainly depends on the gas superficial velocity. After passing through the bluff body, when the liquid loading capacity φl is<0.030, the droplet velocity changes from a concentrated single-peak to an uneven double-peak distribution. However, when φl ≥ 0.041, the droplet velocity distribution recovers to a single-peak distribution. The joint distribution of droplet diameter and velocity indicates that the change in velocity distribution is mainly caused by small droplets within the range of 0 to 20 μm, as large droplets are not easily lifted by vortices but can cause rapid dissipation of vortices. The experimental data quantitatively confirm the momentum transfer and transformation between droplets and the vortex flow field, and describe the motion dynamics of droplets in the flow field through the Stokes number (Stp) to analyze the interaction between droplets and vortices.