Wall Impingement Research Articles

Investigation of cross-stream spray injection and wall impingement in a circular channel for SCR application

A parametric study of cross-stream pulsed spray injection and wall impingement characteristics in a circular channel has been carried out with an objective to investigate performance improvement in selective catalytic reduction (SCR) systems for exhaust gas after-treatment in diesel engines. The spray computations are performed based on a combined Eulerian and Lagrangian based modeling approach for the continuous and the discrete phases respectively. The simulation results are validated using the in-house experimental data for water injection in both open atmospheric and channel flow conditions. The spray structure, penetration, and droplet size are compared and good agreement between the experiments and simulations is demonstrated. Though the focus of the present work is on studying the influence of liquid preheating on post-impingement spray and wall-film characteristics as well as evolution of species mass fraction, the effect of air mass flow rates, and temperature, and the choice of the working liquid (water or Urea Water Solution (UWS)) are also investigated. While the mass flow rate of air and the selection of the above liquids for spray injection are found to have marginal influence on the results, the liquid preheating is shown to strongly affect the droplet evaporation and thus, the spray impact process. Especially, the liquid injection temperature that leads to flash evaporation results in reduced wall filming, higher ammonia generation rate and spatial uniformity of NH 3 across the channel. This paper demonstrates preheating as a promising approach for the improvement of SCR performance. • Spray injection and wall impingement in a duct air flow relevant to SCR systems is numerically investigated. • The predicted post-impingement droplet size and spatial distribution compared well against the in-house experiments. • Marginal influence of air mass flow rate and choice of the liquid (water or UWS) is observed. • Preheating the injected liquid is a viable alternate for performance optimization of the SCR systems. • Especially, the flash evaporation condition ensures reduced wall filming and, higher rate of NH 3 and its spatial uniformity.

Detailed evaluation of drug powder deposition in swirl-type dry powder inhalers

Based on numerical simulations by the Euler/Lagrange approach in combination with the RNG-k-ε turbulence model flow field and particle transport through inhaler devices are studied. Since one major problem in inhaler performance and drug powder release is their deposition on the inhaler walls this issue is analysed in more detail. For computing fine particle motion through the stationary flow field all relevant particle forces and turbulent dispersion are considered. A potential deposition of fine particles is governed by two elementary processes, namely the transport of the fine drug particles towards the walls and their possible wall adhesion. Wall impingement of particles is induced by fluid transport and particle inertia as well as turbulence and for very fine particles also Brownian random motion. The possibility of particle sticking on the inhaler walls is modelled by considering the van der Waals adhesion force. Based on an energy balance for an oblique elastic-plastic wall impingement, a critical impact velocity is derived below which the particles are depositing. This approach accounts for the mechanical properties of wall and particle materials. First, the performance of different deposition models was analysed and the results were compared with literature experiments. The local and global deposition of particles in the considered swirl-type inhalers is determined in dependence of particle size, stationary flow rates (between15 l/min and 90 l/min) and particle release location. The range of particle sizes considered is between 0.05 μm and 10 μm, representing a typical spectrum for fine drug powders in use. Additionally, the spatial distribution of the deposits within the two inhaler types is evaluated for allowing inhaler optimisation and the predicted emitted fraction of fine particles is compared with experimental observations.

Experimental Investigation on Spray Evaporation and Dispersion Characteristics of Impinged Biodiesel-Butanol Blends

Abstract The objective of the investigation is to explore the spray evaporation and dispersion characteristics of impinged biodiesel-butanol blends at various n-butanol ratios (0, 10%, 30%, 50%) and ambient conditions. A total of 180 experimental cases were performed in a constant-volume combustion chamber. The liquid- and vapor-phase sprays were captured by backlight imaging technique and Schlieren imaging technique, respectively. Several macroscopic parameters were measured and discussed, including impinged spray structure, width, height, and area. Some novel parameters are derived to analyze spray evaporation and dispersion. Results show that biodiesel blended with 30% n-butanol transits better from liquid-phase to vapor-phase compared with other blends, displaying rapid liquid-phase evaporation an steady vapor-phase dispersion. After wall impingement, an increase in the ambient pressure or temperature hinders the liquid-phase dispersion in the vertical direction significantly, leading to a rapid decrease in the height of the impinged spray. The vapor-phase diffusion rate in the horizontal direction is about four times the rate in the vertical direction, and the rate ratio is slightly affected by ambient conditions and injection pressure. Compared with the free jet, the impinged spray is not beneficial for liquid-phase evaporation and vapor-phase dispersion, presenting larger liquid-phase area and smaller vapor-phase area. However, impinged biodiesel blended with 30% n-butanol displays better spray evaporation and dispersion.

An investigation of the effect of plateau environment on the soot generation and oxidation in diesel engines

The plateau environment deteriorates the combustion quality inside the heavy duty diesel engine, bringing difficulties in controlling soot emissions. To study the causes of soot increase is the basis for optimizing highland engines and achieving clean operation. A multidimensional CFD model based on a 6V150 engine was developed in this study to investigate the effect of altitude on soot formation and oxidation processes. The comparison between experimental data and numerical results showed that the model was deemed to be able to predict in-cylinder activities at various altitudes. The simulation results showed that when the diesel engine was operated at high altitude, the mismatch between fuel and air led to more soot formation but less oxidized. The wall impingement of fuel droplets occurred at altitudes above 3000 m and soot emissions rose sharply when the altitude exceeded 4000 m. It can be concluded that the engine recalibration strategy may mitigate the increase in soot at altitudes below 3000 m, but may not be very effective when the engine is operating at 4000 m. In addition, the application of oxygenated fuels that can provide more hydroxyl radicals may be an alternative solution to mitigate soot emissions from diesel engines operating in very high altitude regions.

Effects of face shield on an emitter during a cough process: A large-eddy simulation study

Face shield is a common personal protection equipment for pandemic. In the present work, three-dimensional computational fluid dynamic (CFD) method is used to simulate a cough jet from an emitter who wears a face shield. A realistic manikin model with a simplified mouth cavity is employed. A large eddy simulation with a dynamic structure subgrid scale model is applied to model the turbulence. An Eulerian-Lagrangian approach is adopted to model the two-phase flows, with which the droplets are represented by a cloud of particles. The droplet breakup, evaporation, dispersion, drag force, and wall impingement are considered in this model. An inlet velocity profile that is based on a variable mouth opening area is considered. Special attentions have been put the vortex structure and droplet re-distribution induced by the face shield. It is found that the multiple vortices are formed when the cough jet impinges on the face shield. Some droplets move backward and others move downward after the impinging. It is also found that a small modification of the face shield significantly modifies the flow field and droplet distribution. We conclude that face shield significantly reduces the risk factor in the front of the emitter, meanwhile the risk factor in the back of the emitter increases. When the receiver standing in front of the emitter is shorter than the emitter, the risk is still very high. More attentions should be paid on the design of the face field, clothes cleaning and floor cleaning of the emitters with face shields. Based on the predicted droplet trajectory, a conceptual model for droplet flux is proposed for the scenario with the face shield.

Computational Modeling of Nasal Drug Delivery Using Different Intranasal Corticosteroid Sprays for the Treatment of Eustachian Tube Dysfunction.

Eustachian tube dysfunction (ETD) is a common otolaryngologic condition associated with decreased quality of life. The first-line treatment of ETD is intranasal corticosteroid sprays (INCS). Computational fluid dynamics (CFD) was used to study particle deposition on the Eustachian tube (ET) using two commercial INCS (Flonase and Sensimist). Simulations also considered the effects of nostril side, insertion depth, insertion angle, cone spray angle, inhaling rates, wall impingement treatment, and fluid film. Flonase and Sensimist produced different particle size distributions and sizes. Sensimist droplets are smaller, less sensitive to asymmetry in nostrils anatomy and variation in insertion angle, and therefore can reach the posterior nasopharynx more readily. Flonase produces larger particles with greater inertia. Its particles deposition is more sensitive to intrasubject variation in nasal anatomy and insertion angles. The particle deposition on the ET was sensitive to the wall impingement model. The deposition on the ET was insignificant with adherence only <0.15% but increased up to 1-4% when including additional outcomes rebound and splash effects when droplets impact with the wall. The dose redistribution with the fluid film is significant but plays a secondary effect on the ET deposition. Flonase aligned parallel with the hard palate produced 4% deposition efficiency on the ET, but this decreased <0.14% at the higher insertion angle. INCS with larger droplet sizes with a small insertion angle may be more effective at targeting droplet deposition on the ET opening.

Aerodynamics and motor control of ultrasonic vocalizations for social communication in mice and rats

BackgroundRodent ultrasonic vocalizations (USVs) are crucial to their social communication and a widely used translational tool for linking gene mutations to behavior. To maximize the causal interpretation of experimental treatments, we need to understand how neural control affects USV production. However, both the aerodynamics of USV production and its neural control remain poorly understood.ResultsHere, we test three intralaryngeal whistle mechanisms—the wall and alar edge impingement, and shallow cavity tone—by combining in vitro larynx physiology and individual-based 3D airway reconstructions with fluid dynamics simulations. Our results show that in the mouse and rat larynx, USVs are produced by a glottal jet impinging on the thyroid inner wall. Furthermore, we implemented an empirically based motor control model that predicts motor gesture trajectories of USV call types.ConclusionsOur results identify wall impingement as the aerodynamic mechanism of USV production in rats and mice. Furthermore, our empirically based motor control model shows that both neural and anatomical components contribute to USV production, which suggests that changes in strain specific USVs or USV changes in disease models can result from both altered motor programs and laryngeal geometry. Our work provides a quantitative neuromechanical framework to evaluate the contributions of brain and body in shaping USVs and a first step in linking descending motor control to USV production.

Analysis of Wall impingement Spray and Film Formation Process of Direct Injection SI Engines under Low Temperature Conditions

Analysis of Wall impingement Spray and Film Formation Process of Direct Injection SI Engines under Low Temperature Conditions

MODELING OF SPRAY WALL IMPINGEMENT AND FUEL FILM FORMATION UNDER THE GASOLINE DIRECT INJECTION CONDITION

Direct-injection spark-ignition (DISI) engines, which have a better fuel economy than conventional gasoline engines, have been widely introduced in the market. However, in these engines, the rich air−fuel mixtures associated with fuel films during cold starts, caused by spray impingement, produce particulate matter. To predict soot formation, it is important to predict the mixture field precisely; thus, accurate spray and film models are prerequisites for creating a soot model. Previous wall impingement models were well matched with low Weber number collision conditions, such as those of diesel engines, which have relatively high ambient pressures and small Sauter mean diameters. In this study, the outliers of the previous model were observed to decrease as the collision distance increased and when a strong droplet dissipation occurred owing to a high ambient pressure. However, the kinetic energy in DISI engines is considerably larger than the dissipation energy calculated using the Weber number and surface tension; thus, the amount of dissipation energy should be determined within a realistic range. To analyze the two-dimensional (2D) spray-wall impingement phenomenon more accurately, a 2D child droplet generation was considered. Finally, the film and spray behaviors were measured to validate the SNU model. The Mie scattering images of the gasoline spray near the wall were captured to measure the rebound spray radius. Then, a laser-induced fluorescence with a total internal reflection was used to determine the film shape and thickness. Compared with existing models, the SNU model exhibits better agreement with the Mie experimental results without requiring case-dependent changes to the model constant. However, the film simulation part needs improvement in future work.

Analysis of fuel film formation process at low temperature by wall impingement direct injection gasoline spray

Analysis of fuel film formation process at low temperature by wall impingement direct injection gasoline spray

Experimental investigations of the phase change impacts on flash boiling spray propagations and impingements

Flash boiling atomization technique has been considered a potential method for spray breakup performance enhancement utilizing the micro-explosion of superheated liquid. But the strong evaporative features of flash boiling atomization are not thoroughly investigated and understood. For instance, the impact of flash boiling atomization on the liquid mass fraction inside the spray plume and the influence on the formation of spray impingement wall film are not clear. Therefore, this work focuses on the phase change impacts of flash boiling atomization and measures the volume flux of the liquid component during flash boiling atomization using phase Doppler interferometry. This work further investigates the consequence of flash boiling spray collapse in the aspect of spray impingement, with the two-dimensional thickness and temperature distribution measured by laser-induced exciplex fluorescence technique. Both free sprays and impinging sprays with the same settings (and different temperatures) are examined for compassion. This investigation verifies that due to the phase change of flash boiling atomization, the liquid component inside the plume drops significantly so that the wall impingement performance cannot be evaluated with spray penetration length only. Such observations also hold even spray collapse takes place using a multi-hole fuel injector.

Mixing Performance of a Passive Micro-Mixer with Mixing Units Stacked in Cross Flow Direction.

A new passive micro-mixer with mixing units stacked in the cross flow direction was proposed, and its performance was evaluated numerically. The present micro-mixer consisted of eight mixing units. Each mixing unit had four baffles, and they were arranged alternatively in the cross flow and transverse direction. The mixing units were stacked in four different ways: one step, two step, four step, and eight step stacking. A numerical study was carried out for the Reynolds numbers from 0.5 to 50. The corresponding volume flow rate ranged from 6.33 μL/min to 633 μL/min. The mixing performance was analyzed in terms of the degree of mixing (DOM) and relative mixing energy cost (MEC). The numerical results showed a noticeable enhancement of the mixing performance compared with other micromixers. The mixing enhancement was achieved by two flow characteristics: baffle wall impingement by a stream of high concentration and swirl motion within the mixing unit. The baffle wall impingement by a stream of high concentration was observed throughout all Reynolds numbers. The swirl motion inside the mixing unit was observed in the cross flow direction, and became significant as the Reynolds number increased to larger than about five. The eight step stacking showed the best performance for Reynolds numbers larger than about two, while the two step stacking was better for Reynolds numbers less than about two.

Evaporating characteristics of diesel sprays under split-injection condition with a negative dwell time

This paper investigates the effects of the split-injection strategy with a negative dwell time using a multi-hole diesel injector under evaporating conditions. To compare with negative dwell conditions, the single-injection and positive and zero dwell conditions were adopted. The Laser Absorption Scattering (LAS) technique was employed to measure the temporal and spatial evolution of fuel evaporation and mixture concentration in the experiments. The split injection of 7:3 was selected according to the results of the previous study that proposed a homogeneous mixture after the end of injection. The dwell times of −50 us, 0 us, and 120 us were selected based on the measurement of the injection rate. The blended fuel consisting of 97.5% of n-tridecane and 2.5% of 1-methylnaphthalene in volume was used. The results show that a shorter spray tip penetration was present in the split injection with a negative dwell time. This phenomenon is expected to reduce the possibility of wall impingement and result in fewer nitrogen oxides (NOx) and unburned hydrocarbons (UHCs) under the injection conditions with a negative dwell time, especially for the conditions of a large injection amount and small-bore engines. Moreover, different spray shapes and behavior occurred in the case of different injection strategies. The spray of split-injection strategy with a negative dwell time has large radial dispersion, and it can improve the air utilization inside a cylinder.

Particle Matter Index and Fuel Wall-wetting Relations on Stochastic Pre-ignition

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;This work explores the effect of the particle matter index (PMI) and aromatic content on fuel wall impingement associated with stochastic pre-ignition (SPI). Statically significant measurements of SPI rates are directly coupled with laser induced florescence (LIF) measurements of fuel dilution from spray-linear impingement. Literature suggests that PMI is could be correlated with the number of SPI events, but the root cause(s) of PMI and SPI are directly causational or are a predicator of SPI. Three fuels have been used in this study with 3 different PMI and two different aromatic contents. The fuels are direct injected at two different injection timings, an earlier injection timing which initially targets the piston crown, 310°CA bTDC, and a later injection timing that the liner, 220°CA bTDC start of injection timings (SOI) respectively. The earlier 310 SOI injection increases soot, whereas the later 220°CA SOI targets the liner and increases wall-wetting. The findings of this work highlight that the SPI activity has a weak correlation with the soot promoted by the combustion process and increased PMI. However, SPI activity shows a strong dependency with high levels of oil dilution and aromatic content, suggesting that PMI might be an indicator of fuel chemistry conducive to SPI and the soot from increased PMI fuels is not a strong source of SPI relative to fuel wall wetting.&lt;span class="xref"&gt;&lt;sup&gt;1&lt;/sup&gt;&lt;/span&gt;&lt;/div&gt;&lt;/div&gt;

Numerical and experimental study of droplet-film-interaction for low pressure steam turbine erosion protection applications

One common approach for anti-erosion measures in low pressure steam turbines is to equip a hollow stator vane with slots on the airfoil surface in order to remove the water film by suction and consequently reduce the amount of secondary droplets. The purpose of this paper is to build an understanding of the predominant effects in fluid-film interaction and to examine the suitability of modern numerical methods for the design process of such slots. The performance of a suction slot in terms of collection rate and air leakage is investigated numerically in a flatplate setup with upstream injection of water. In order to model the relevant phenomena (film transport, edge stripping of droplets, transport of droplets in the surrounding fluid, wall impingement of droplets) an unsteady Eulerian-Lagrangian simulation setup is applied. The accuracy of the numerical approach is assessed by comparison with experimental measurements. The comparison of four cases with the measured data demonstrates that the chosen simulation approach is able to predict the main features of film flow and interaction with the surrounding fluid. The collection rate as well as fluid film properties show the same qualitative dependency from water mass flow rate and air velocity.

DEM investigation on conveying of non-spherical particles in a screw conveyor

Screw conveyors are extensively used in modern industry such as metallurgy, architecture and pharmaceutical due to their high-efficiency in the transportation of granular materials. And substantial efforts have been devoted to the study of the screw conveyors. Numerical method is an effective way to study screw conveyor. However, previous studies have mainly focused in the regime of spherical particles while the in-depth investigations for non-spherical particles that should be the most encountered in practical applications are still limited. In view of the above situations, discrete element method (DEM), which has been widely accepted in simulating the discrete systems, is utilized to investigate the conveying process of non-spherical particles in a horizontal screw conveyor, with particles being modeled by super-ellipsoids. In addition, a wear model called SIEM (Shear Impact Energy Model) is incorporated into DEM to predict the wear of screw conveyor. The DEM simulation results demonstrate that the particle shape is influential for the flow behaviors of particles and the wear of conveyor. The conveying performance evaluated quantitatively of both mass flow rate and power consumption is subsequently obtained to investigate the effect of sphericity of particle with different operation parameters. Moreover, particle collision frequency and collision energy consumption are acquired to investigate the possible particle breakage between particles and screw blade. The comparisons between particle–particle collision and particle–wall collision reveal that particles with large shape index have more possibility to be damaged in particle–wall impingement.

Experimental and numerical study of the impinging aerosols method for the micro-encapsulation of phosphate solubilising microorganisms (PSMs)

This study demonstrates the application of the impinging aerosols method in encapsulating phosphate solubilising microorganisms (PSMs), replacing the microbial inoculant method. The method encapsulates PSMs in microbeads by impinging the bacteria-alginate droplets and CaCl2 sprays. Efficient coalescences between the bacteria-alginate and CaCl2 droplets warrant the birth of microbead-encapsulating microorganisms. The proposed method is modelled using a Eulerian–Lagrangian approach. The primary and secondary breakups and wall impingement are modelled using the Huh atomisation, Reitz–Diwakar models, and Bai–Gosman model, respectively. The resulting model is validated against the sizes and spray angles of experimental droplets with different flow rates. The simulation demonstrates that the flow rate, spray angle, droplet size, spray pattern, and alginate and CaCl2 concentrations must be considered to produce robust alginate microbeads and minimise the material loss caused by the formation of a fluid film on the wall. A lower alginate flow rate and concentration of CaCl2 should be used to promote the formation of the alginate microbeads.

Experimental investigation of wall heat transfer due to spray combustion in a high-pressure/high-temperature vessel

Combustion chamber wall heat transfer is a major contributor to efficiency losses in diesel engines. In this context, thermal swing materials (adapting to the surrounding gas temperature) have been pinpointed as a promising mitigative solution. In this study, experiments are carried out in a high-pressure/high-temperature vessel to (a) characterise the wall heat transfer process ensuing from wall impingement of a combusting fuel spray, and (b) evaluate insulative improvements provided by a coating that promotes thermal swing. The baseline experimental condition resembles that of Spray A from the Engine Combustion Network, while additional variations are generated by modifying the ambient temperature as well as the injection pressure and duration. Wall heat transfer and wall temperature measurements are time-resolved and accompanied by concurrent high-speed imaging of natural luminosity. An investigation with an uncoated wall is carried out with several sensor locations around the stagnation point, elucidating sensor-to-sensor variability and setup symmetry. Surface heat flux follows three phases: (i) an initial peak, (ii) a slightly lower plateau dependent on the injection duration, and (iii) a slow decline. In addition to the uncoated reference case, the investigation involves a coating made of porous zirconia, an established thermal swing material. With a coated setup, the projection of surface quantities (heat flux and temperature) from the immersed measurement location requires additional numerical analysis of conjugate heat transfer. Starting from the traces measured beneath the coating, the surface quantities are obtained by solving a one-dimensional inverse heat transfer problem. The present measurements are complemented by CFD simulations supplemented with recent rough-wall models. The surface roughness of the coated specimen is indicated to have a significant impact on the wall heat flux, offsetting the expected benefit from the thermal swing material.

A clinical study of functional outcome of unstable intertrochanteric fractures treated with proximal femur nail anti rotation system II

Introduction: Unstable, Comminuted intertrochanteric fractures continue to pose a challenge to the orthopaedic surgeon because of severe osteoporosis and medical disorders that increase the risks associated with surgery and anaesthesia. To overcome problems like lateral wall impingement and prominence of the proximal end of the nail, the PFNA-II was introduced in 2008. The PFNA II design modifications include the flat lateral shape of the proximal portion and a decrease in the mediolateral bending angle from 60 to 50. The purpose of the study is to confirm that the PFNA II eliminates the problem of lateral wall impingement experienced with previous intramedullary nailing systems and provides stable fracture fixation with positive functional outcome.Materials and methods: This study was conducted on 52 patient of which 32 were available till follow up of 6 months. All patients we were diagnosed with unstable intertrochanteric fracture of femur and underwent closed reduction internal fixation with proximal femoral nail anti-rotation system II. Functional outcome was assessed with Modified Haris Hip Score and radiological outcome was assessed with TAD score and implant related complications. Results: Fracture union was appreciated on an average 4 months of postoperative period. 4 patient had superficial infection while 1 patient had deep infection. Only 1 patient had cut off of helical blade. According to modified Harris hip score, excellent to good outcome was noted in more than 80% of patient. Conclusion: From our study, we conclude that PFNA II can be a reliable and implant of choice for the management of unstable intertrochanteric fracture with high rates of union, restoring the anatomical alignment with less chances of implant failure and reduced chance of implant failure.

Study on Wall Impingement Behavior of Fuel Spray in DI Gasoline Engines

Study on Wall Impingement Behavior of Fuel Spray in DI Gasoline Engines