Impingement Process Research Articles

Prediction of interface morphology formed by the oblique gas jet impinging on a liquid surface

This study presents a theoretical analysis of the oblique gas jet impingement process on a liquid surface, elucidating the evolution of the flow field distribution and the influence of jet parameters on cavity shape dynamics. By integrating surface tension effects, the existing Blanks and Chandrasekhara model was refined to develop an advanced predictive model for cavity morphology. The theoretical framework was substantiated through numerical simulations and corroborated with experimental measurements of cavity dimensions, captured using state-of-the-art machine vision technology. The findings reveal a consistent trend in cavity dimension variations: an increase in the cavity surface width with the elevation of the impinging angle from the vertical and an escalation in gas jet velocity. Conversely, a reduction in the impinging angle coupled with an increase in jet velocity leads to a deeper cavity. To enhance the predictive accuracy, the model underwent iterative optimization, incorporating experimental data and accounting for jet parameters. The refined model demonstrated achieved a maximum error of 0.135 mm and a minimum error of 0.03 mm, providing reliable forecasts of cavity depth, which is pivotal for applications in fluid dynamics and related engineering fields.

Morphology and heat transfer of a train of microdroplets impinging on the heated surface for spray cooling

Owing to the superior cooling performance of the droplet impingement process, the spray cooling is widely used in various industries including aerospace, e-motors, data centres and so on. In the present study, the morphological evolution and heat transfer characteristics of vertical and oblique impacts on the heated surface were investigated experimentally and numerically. A droplet generation system and a substrate heating system were designed to observe continuous vertical and oblique droplets impinging on the hot surface by a high-speed camera. The coupled Level Set and VOF (CLS-VOF) model and adaptive mesh refinement technique were used to establish a mathematical model for a train of micro-sized droplets impinging on the heated surface, which was validated by experimental data. The film that spreads on the surface exhibits asymmetry due to the horizontal velocity of the droplets. When continuous droplets impinge vertically on the heated wall, the evolution of the crown and the wall temperature appear periodic. The effects of impingement angles on morphological patterns and heat transfer of a train of micro-sized monodispersed droplets with the same Weber numbers were analyzed further. The results indicated that with a smaller angle of impingement, the crown is more likely to splash, and the crown asymmetry is less obvious.

Numerical Simulation and Consequence Analysis of Full-Scale Jet Fires for Pipelines Transporting Pure Hydrogen or Hydrogen Blended with Natural Gas

The use of existing natural gas pipelines for the transport of hydrogen/natural gas mixtures can achieve large-scale, long-distance and low-cost hydrogen transportation. A jet fire induced by the leakage of high-pressure pure hydrogen and hydrogen-blended natural gas pipelines may pose a severe threat to life and property. Based on the Abel–Nobel equation of state and a notional nozzle model, an equivalent pipe leakage model is established to simulate high-pressure pipeline gas leakage jet fire accidents. Large-scale high-pressure hydrogen and natural gas/hydrogen mixture jet fires are simulated, showing the jet impingement process and obtaining an accurate and effective simulation framework. This framework is validated by comparing the simulated and experimental measured results of flame height, flame appearance and thermal radiation. Several combustion models are compared, and the simulated data show that the non-premixed chemical equilibrium combustion model is superior to other combustion models. The influence of the pipe pressure and the hydrogen blending ratio on the consequences of natural gas/hydrogen mixture pipeline leakage jet fire accidents is explored. It is found that when the hydrogen blending ratio is lower than 22%, the increase in the hydrogen blending ratio has little effect on the decrease in the thermal radiation hazard distance.

Experimental and numerical studies of the evaporation and combustion characteristics of large-angle impinging sprays

To achieve a large fuel injection mass per cycle, using one injector will need a large nozzle, which may lead to combustion deterioration in high power density (HPD) engines. Therefore, two-injector method was adopted and then impinging sprays by two injectors were developed to promote the air/fuel mixing and combustion performance. This study investigated the spray, evaporation, ignition and soot emission characteristics of twin injectors at different impinging angles (90°, 120°, 150°, and 180°) using various high-speed imaging techniques in a constant volume chamber. Further, CFD simulations were performed to analyze the impinging sprays under HPD condition. Innovatively, a kinetic energy loss model for impinging sprays was proposed to quantify the effect of spray impingement. The results showed that the turbulent kinetic energy increased with the impinging angle, and the kinetic energy loss at any angle could be predicted by the kinetic energy loss of 180° impinging spray. The kinetic energy loss model better characterized the spray impingement process, and then more accurately predicted the atomization quality and mixing capacity compared with spray volume. Spray impingement changed fuel and soot distributions, the peak soot mass decreased with the impinging angle, which was reduced by 36.8 %, 39.8 %, 44.4 % and 45.9 % at 90 ∼ 180° impinging sprays, respectively, comparing to the single spray. These findings recommended that using a large impinging spray angle in real HPD engines can promote spray atomization and reduce soot formation.

Effect of flow on heat transfer between a translating plate and gas discharged from multiple inclined slot nozzles

The presented study aims to reveal flow and heat transfer characteristics as a translating aluminum plate is impinged by high-temperature gas discharged from inclined slot nozzles. The computational fluid dynamics (CFD) and the fluid-solid interaction (FSI) techniques were used to simulate the impingement process. A comprehensive comparison of flow, heat transfer, and structural parameters was implemented. The results indicate that twin vortices are produced between the two inclined nozzles. When the velocity ratio increases from 0.1 to 1.0, the vortex at the left expands, while the right one is compressed. Meanwhile, average Nusselt number and the pressure coefficient exhibit opposite variation tendencies. The highest average pressure coefficient of 0.45 arises at a velocity ratio of 0.5. As the plate-nozzle distance increases, characteristic flow structures are developed, and the distributions of temperature and the pressure coefficient are uniformized. The maximum Nusselt number decreases from 473 to 266 when the nondimensional plate-nozzle distance increases from 4 to 8. Large deformation occurs at the middle part of the plate. High equivalent stress is concentrated at the front and rear ends of the plate, which is insensitive to the velocity ratio and the plate-nozzle distance.

The morphology regulation mechanism of microdroplet printing based on heterogeneous wettability surfaces

Microdroplet printing technology can effectively realize the precision preparation of complex electronic devices at the micro-scale, relying on the mutual interaction between the tiny micro-droplets, which can improve the organizational microstructure of the fabricated parts and effectively enhancement the mechanical properties of the fabricated parts. In this paper, the interaction process between micro-droplets and patterned wetted modified surfaces during the microdroplet printed process is studied based on the coupled level collective integral number method (CLSVOF) and equivalent heat capacity method. The influence of patterned schemes for non-uniform surface wetting modification, regional wetting differences and impingement process parameters on the impingement spreading flow of metal droplets and their heat transfer cooling process is investigated. The evolution mechanisms of the droplet geometry and the distribution characteristic of the droplet internal temperature and heat flow density during the impingement spreading process are discussed. The optimization mechanism of heterogeneous wetting modified surfaces for molten droplet forming is revealed. The results show that the four-way homogeneous pattern modification scheme can effectively improve the microdroplet stabilization rate and enhance the preparation efficiency by ensuring the shape size and positioning accuracy. Four three-phase contact lines morphology patterns for the equilibrium state of droplets, namely, circular, rectangular, concave shape and rhombic, were obtained by adjusting the wetting differences between the areas. A scheme to regulate the surface behavior of printed microdroplets with lyophilic high-adhesion region to anchor the droplets and lyophobic low-adhesion environment to provide a physical barrier to confine the droplet morphology was developed. In addition, the pattern modification scheme has an obvious optimization effect for the droplet forming and its heat exchange process in the process of metal droplet printing. Basis on the ensuring the radial dimensional accuracy and sphericity of the molten droplet molding, the rebound and oscillation behavior of the molten droplet is effectively suppressed. The stabilizing efficiency of droplet printing is greatly enhanced and further improves the heat transfer performance of the droplet. The results further enrich the theory of precise regulation of the dynamic behavior of droplet surfaces. Not only can it be used as a new strategy for universal high-precision printing and droplet control, but it will also promote the application and development of technologies in numerous fields, such as liquid transport and microfluidics.

Wall shear stress and pressure patterns in aortic stenosis patients with and without aortic dilation captured by high-performance image-based computational fluid dynamics.

Spatial patterns of elevated wall shear stress and pressure due to blood flow past aortic stenosis (AS) are studied using GPU-accelerated patient-specific computational fluid dynamics. Three cases of moderate to severe AS, one with a dilated ascending aorta and two within the normal range (root diameter less than 4cm) are simulated for physiological waveforms obtained from echocardiography. The computational framework is built based on sharp-interface Immersed Boundary Method, where aortic geometries segmented from CT angiograms are integrated into a high-order incompressible Navier-Stokes solver. The key question addressed here is, given the presence of turbulence due to AS which increases wall shear stress (WSS) levels, why some AS patients undergo much less aortic dilation. Recent case studies of AS have linked the existence of an elevated WSS hotspot (due to impingement of AS on the aortic wall) to the dilation process. Herein we further investigate the WSS distribution for cases with and without dilation to understand the possible hemodynamics which may impact the dilation process. We show that the spatial distribution of elevated WSS is significantly more focused for the case with dilation than those without dilation. We further show that this focal area accommodates a persistent pocket of high pressure, which may have contributed to the dilation process through an increased wall-normal forcing. The cases without dilation, on the contrary, showed a rather oscillatory pressure behaviour, with no persistent pressure "buildup" effect. We further argue that a more proximal branching of the aortic arch could explain the lack of a focal area of elevated WSS and pressure, because it interferes with the impingement process due to fluid suction effects. These phenomena are further illustrated using an idealized aortic geometry. We finally show that a restored inflow eliminates the focal area of elevated WSS and pressure zone from the ascending aorta.

Numerical simulation of jet impact process with different jet velocities in a negative pressure ambient

The effect of jet velocity on jet impingement process was of great importance. However, the process of jet impingement and fragmentation is highly complex and involves various physical and thermal phenomena. Therefore, our current work primarily focuses on using computational fluid dynamics (CFD) method to investigate the effect of jet velocity on the characteristics of jet impingement in a negative pressure ambient. The Realizable k-ε model is employed to simulate the turbulent flow process, and an improved Mixture model is used to describe the distribution behavior of the gas-liquid phases. The characteristics of flow field, pressure distribution, velocity distribution, turbulence kinetic energy distribution and vortex behavior were analyzed under different jet velocities at a negative pressure of 31.6 kPa. The results indicate that as the jet velocity increases, the core of jet impingement pressure also increases. The above situation resulted in fragment effect enhancement and an increased number of atomized droplets. These findings provide a theoretical basis for further research on the jet impingement-negative pressure deamination reactor (JI-NPDR).

Insights into the spray impingement process from a gasoline direct injection fuel system fuelled with gasoline and ethanol

Particulate Matter (PM) emissions have a negative impact on both climate change and human health. To control PM emissions emitted by vehicles with the Gasoline Direct Injection (GDI) fuel system, increasing fuel injection pressure is being developed as a practical approach. In this paper, an experimental and numerical study was presented to thoroughly explore the entire development process of gasoline and ethanol impingement spray from a GDI injector under injection pressure of 10 MPa and 50 MPa. The results demonstrate that more droplets are predicted to distribute in the splash region with the increase of injection pressure (PI) from 10 MPa to 50 MPa, which helps improve air-fuel mixing quality and reduce PM emissions. The splash probability of gasoline droplets is about two percent higher than ethanol. By increasing PI from 10 MPa to 50 MPa, droplets with higher absolute normal velocity would promote the growth of impingement spray. The probability curves of droplet diameter are more concentrated in the smaller size range. Besides, the probability of relatively large droplets of gasoline is slightly lower than that of ethanol. Regarding the fuel film distribution, more folds and bulges can be seen at the boundary of fuel film with the PI increase to 50 MPa. Meantime, the film distribution becomes more scattered, which would benefit the homogeneity of air-fuel mixture. The film distribution area and boundary irregularity of gasoline are greater than those of ethanol, further promoting a homogeneous air-fuel mixture.

Impact of Surface Roughness on the Impingement of Urea–Water Solution Droplets

The understanding of impingement processes is crucial for optimizing automotive selective catalytic reduction (SCR) systems. An accurate description of this behavior helps design exhaust systems and increases the validity of modeling approaches. A component test bench was set up, featuring a droplet chain generator for producing droplet sizes typically found in the urea–water solution sprays of SCR systems. A heatable impingement plate with an interchangeable surface enabled investigation of the influence of surface roughness. Data were acquired using a high-speed camera and image postprocessing. The droplet–wall interaction could be described using different regimes. An approach to characterizing impingement behavior based on weighted-regime superposition enabled gradual transitions between regimes, instead of step-like changes. It was observed that the surface roughness increased the droplet–solid contact area and generated thermal-induced secondary droplets at lower temperatures. A region of enhanced mechanical disintegration of the droplet was found, caused by peaks of the surface shearing off parts of the droplet. The probability of a droplet rebounding from the wall was reduced on a rough surface, due to the interference of the surface spikes with the droplet’s spreading and contracting motion. Additionally, the influence of surface topography was investigated using a shot-peened surface. Caused by this surface’s reduced root mean square slope, the aforementioned enhancement of mechanical disintegration was not observed.

Directional droplet bouncing on a moving superhydrophobic surface

Droplets directionally bouncing off moving superhydrophobic solid surfaces are universal in nature and are crucial in many biological, sustainable, environmental, and engineering applications. However, their underlying physics and regulation strategies remain relatively unknown. This paper demonstrates that the maximum directional acceleration of a post-impact droplet mainly occurs in the spreading stage and that the orientational velocity of the droplet mainly originates in the early impingement process. Furthermore, it clarifies the underlying physics based on momentum transfer process imposed by the boundary layer of impacts and proposes a strategy for regulating the directional droplet velocity using a comprehensive formula. Finally, it shows that directional bouncing reduces the flight momentum of a small flying device by 10%-22%, and the experimental values agree closely with the predicted values. This study reveals the droplet bounce orientation mechanism imposed by moving substrates, provides manipulation methods, and makes positive and meaningful discussions of practical applications.

Modeling the impingement deformation and solidification of a hollow zirconia droplet onto a dry substrate and solidified layer

Despite the numerous research studies involving the solidification of continuous molten metal droplet impingement on dry substrates during the process of plasma spraying, the impingement between a hollow molten metal droplet and a solidified layer has, to date, not yet been thoroughly explored. A liquid shell enclosing the air cavity forms a hollow droplet. The coupled level set and volume of fluid method is used to track the air–liquid interface, and the enthalpy–porosity method is used to track the liquid–solid interface. A two-dimensional axis symmetric model is adopted to describe the impingement and solidification process. This study includes a detailed investigation of transient impact deformation and solidification. The heat transfer characteristics of the solidification of a continuous dense and hollow molten droplet impacting on a dry substrate and solidified layer are studied and compared. A thin solidified layer appears and develops between the droplet and the substrate, and the impacting droplet finally pins to the surface with mainly the liquid solidified. For a hollow droplet impact on the solidified layer, a splashed crown liquid sheet forms from the drop-solidified layer neck area. Various temperatures of the solidified layer induce a different development of the crown, spreading, and rebound counter-jet. The deterioration of local heat transfer is attributed to a strong fluctuation of the rebound counter-jet and the existence of an annular cavity (formed by the crown sheet falling back). Attention should be paid to this phenomenon in industrial applications involving droplet impact.

Spreading dynamics of the viscous droplet impacting on a spherical particle

The dynamic behavior of droplets in the impingement process with particles has attracted extensive interest due to its widespread industrial applications. In this study, collision experimentation was carried out to investigate the spatial and temporal variation of droplets on a target particle surface by utilizing high-speed photography. Energy conversion and force analysis were conducted through theoretical analysis. Moreover, we captured the microscopic and evolutionary features of droplets in detail by image processing. The dimensionless liquid film thickness in the maximum spreading state is primarily determined by its spreading area. The Weber number can be used to calculate the maximum spreading area of droplets for liquids with a specific viscosity and droplet-to-particle size ratio. The time-evolved liquid film morphology and spreading area of a highly viscous liquid show a different trend compared to that of the low-viscous liquid. When the liquid film is not broken, the maximum dimensionless spreading area is linearly related to the Weber number. At low Weber numbers and high Reynolds numbers, droplets exhibit more pronounced oscillation characteristics. The oscillation period of the collision is related to the droplet-to-particle size. The liquid film thickness decreases as the Weber and Reynolds numbers rise. As for the low-viscous liquid, a low Weber number leads to a periodic change in the dynamic contact angle. A decrease in the Reynolds number for the highly viscous droplets generates a greater dynamic contact angle. The recoiling of the liquid film results in a more significant reduction in the dynamic contact angle.

Convection from multiple air jet impingement - A review

• For S/D ≥ 3 and H/D = 2, the staggered pattern enhances Nu when compared with. • inline; • Wall motion is a topic of interest since even low velocities seem to enhance Nu; • Compressibility effects are important and Ma > 0.7 induces stronger instabilities; • SST k-ω model presents the best compromise between computational costs and. • accuracy. Multiple jet impingement is widely implemented in several industrial processes. The efficacy of this convective process depends on various parameters from the geometrical variables of the system, to the impinging surface roughness and the jet’s flow parameters. The study of this complex flow is challenging and increases with the confinement of the impinging domain. This work focus on a detailed analysis of confined and submerged multiple air jet impingement. To understand the physics under this process and the influence of the different variables on heat transfer performance, a review of the jet’s flow dynamics and heat transfer characteristics of submerged multiple air jet impingement systems is presented in this work. In this review, the parameters that affect the convective process are analyzed and special attention is given to less explored variables such as the surface configuration and motion, jet inclination and high jet temperature, and Mach number. The conclusions and relevant statements presented by several authors through their numerical and experimental works are presented and compared, to identify the values of each variable that enhance the heat transfer over the impinging surface. The numerical methods applied for the modeling of impinging jets are also analyzed. The advantages and disadvantages of each turbulence model discussed in the literature are presented and characterized in terms of their computational time and costs, in order to identify the most accurate for the multiple jet impingement process modeling. Finally, relevant correlations for the average Nusselt number, to characterize the heat transfer of single and multiple jet impingement are summarized.

Cooling performance enhancement study of single droplet impingement on heated hole-patterned surfaces using improved GQPSO algorithm

A droplet impingement on solid surfaces plays a critical role in various spray and heat transfer applications. The main objective of this study is to investigate how to enhance the cooling performance of the single droplet impingement process on the heated hole-patterned surfaces by finding desired conditions using optimization techniques. The cooling effectiveness and total contact area at the maximum droplet spread were chosen for objective functions to be maximized. To estimate the optimal values of the unknown variables efficiently, the improved Gaussian-behaved particle swarm optimization (GQPSO) algorithm with a modified local attractor using Gaussian distributed random numbers was newly proposed and applied to the single droplet impingement problem. To verify the improved search performance of the proposed GQPSO approach, the optimization results were compared with the standard particle swarm optimization (PSO) and original GQPSO methods with the same conditions. By comparing the estimated maximum values of given objective functions, calculation times and numbers of penalty particles, we verified that the proposed GQPSO approach could search for more optimal solutions quickly and efficiently due to its improved local fine-tuning capability with the modified local attractor.

Thermal performance and flow pattern of an immersion spray array cooling vapor chamber

An immersion spray array cooling vapor chamber (ISVC) is proposed for high-power electronic devices. Experimental and numerical studies on thermal performance and flow pattern have been conducted. It is shown that increasing the inlet temperature of the coolant facilitates the heat transfer performance and temperature uniformity of the ISVC within the safe working temperature range of electronic devices. The immersed spray impingement process includes a stage of velocity reduction from the nozzle exit to the target surface, a process of velocity boundary layer formation on the target surface, and a flow collision region formation process of adjacent sprays. As the inlet flow rate increases, the effect of the spray on the target surface is enhanced and the interaction between adjacent sprays is stronger. The perturbation effect of the spray on the fluid in the impingement cavity is positively influenced by the inlet flow rate. The spray array has a strong stirring effect on the water in the spray chamber in the XY, XZ and YZ planes. The heat transfer capacity of the ISVC is enhanced with a larger inlet flow rate due to the enhanced spray effect and larger spray coverage area. The temperature uniformity of the ISVC is improved with an increase of flow rate. The ISVC operating limit heating powers of 2.0 L/min, 4.0 L/min and 7.0 L/min flow rates are 531 W, 575 W and 600 W. Compared to the existing integrated heat sink combined vapor chamber and array jet impingement, the operating limit heating power of ISVC is increased by at least 68%.

Combined experimental and numerical study on fuel deposition characteristics of an impinging PFI spray with different impingement geometries

This paper presents a combined experimental and numerical study on the fuel deposition characteristics during the Port fuel injection (PFI) spray impingement process. The numerical models mainly consisted of a newly developed atomization model, the Senda spray impingement model, and the Bai-Gosman liquid film model. A group of measurement methods were used to hierarchically calibrate and validate the numerical models. It was found that the calibrated models were able to predict the time-resolved morphology of the impinging spray, as well as the shape, area, and thickness distribution of the deposited fuel film with a good reliability. Then the calibrated models were used to study the effects of impingement distance ( Lw) and impingement angle ( θw) on the fuel film deposition. The results showed that as Lw increases, the film area ( Af) and film mass ( mf) rise faster and reach higher final values. As θw increases, Af and mf grow slower, and their final values are hugely reduced. Increasing Lw and decreasing θw can effectively reduce the average film thickness ( hf,a). Af is mainly affected by the contact area between the spray plumes and the impinging wall, while mf is also affected by the dominant droplet-wall interaction regime.

Large-Eddy Simulation of a Water Jet Exhausting into Quiescent Air

This study focuses on a water injection system, typical of those used to inject water in the motor jet plume of rocket engines to reduce noise, and particularly on the destabilization of the liquid jet that leads to a spray system. For that purpose, a large-eddy simulation is conducted for an experimental water jet of the literature. It is a sprinkler whose Reynolds number is and nozzle exit diameter is , similar to injectors used for jet noise reduction studies at a reduced scale. A diffuse interface method is used to calculate the dense liquid phase, and the dispersed phase containing droplets is calculated with an Eulerian solver. Transfers between the dense and the dispersed phases are modeled in the coupling procedure, including the atomization and impingement processes. The jet mean radius and initial instability frequency are consistent with the experimental data, while the position of the jet transition varies with the fluctuation levels at the nozzle exit. The droplets are created in the shear layer and accumulate on the jet center when only the atomization process is considered. When also implemented, the impingement phenomenon, however, is shown to absorb the droplets before they reach the center.

Estimating the number of fingers and size of ejected droplets in droplet impingement processes on solid substrates

The splashing of droplets impinging on solid substrates includes complex behavior that is dependent on numerous factors, including the liquid properties, impingement velocity, and solid surface properties, such as wettability and roughness. Quantitative understanding of the behavior of the unstable liquid film during the splashing process remains elusive. Here we propose new models in which the number of fingers and the size of the ejected secondary droplets can be characterized taking into account the liquid film thickness and the wettability and roughness of the surface. The experimental data regarding the size of the secondary droplet and the number of fingers is found to be in good agreement with the predictions of the proposed model. The results of the present study provide insight into the mechanism behind rim or liquid film fragmentation.

Impact of Gulf Stream Warm-Core Rings on Slope Water Intrusion into the Gulf of Maine

Abstract Intruding slope water is a major source of nutrients to sustain the high biological productivity in the Gulf of Maine (GoM). Slope water intrusion into the GoM is affected by Gulf Stream warm-core rings (WCRs) impinging onto the nearby shelf edge. This study combines long-term mooring measurements, satellite remote sensing data, an idealized numerical ocean model, and a linear coastal-trapped wave (CTW) model to examine the impact of WCRs on slope water intrusion into the GoM through the Northeast Channel. Analysis of satellite sea surface height and temperature data shows that the slope sea region off the GoM is a hotspot of ring activities. A significant linear relationship is found between interannual variations of ring activities in the slope sea region off the GoM and bottom salinity at the Northeast Channel, suggesting the importance of WCRs in modulating variability of intruding slope water. Analysis of the mooring data reveals enhanced slope water intrusion through bottom-intensified along-channel flow following impingements of WCRs on the nearby shelf edge. Numerical simulations qualitatively reproduce the observed WCR impingement processes and associated episodic enhancement of slope water intrusion in the Northeast Channel. Diagnosis of the model result indicates that baroclinic CTWs excited by the ring–topography interaction are responsible for the episodically intensified subsurface along-channel inflow, which carries more slope water into the GoM. A WCR that impinges onto the shelf edge to the northeast of the Northeast Channel tends to generate stronger CTWs and cause stronger enhancement of the slope water intrusion into the GoM.