Formation Of Liquid Sheet Research Articles

Liquid sheet formation and spray characterization of N-heptane spray jet from a swirl atomizer: Numerical analysis and validation

This paper analyzes the liquid atomization mechanisms of an N-heptane spray jet emerging from a swirl simplex atomizer using numerical and experimental techniques. In particular, a direct seamless coupled Volume of Fluid and Lagrangian Particle Tracking approach together with adaptive mesh refinement within the Large Eddy Simulation framework offers a suitable way to accurately simulate the complex behavior of spray atomization, spray evolution, and droplet dispersion as a whole while using manageable computational cost. The achieved simulation results are first presented in terms of qualitative properties, characteristics of liquid sheet, air core generation, flow recirculation zones, and vortex patterns. For validation purposes, the numerical results are then compared with detailed experimental data obtained by a two-component Phase Doppler Anemometry technique. The assessment includes especially droplet statistics which strongly determine subsequent possible spray combustion process and related product and species emissions. The overall reported agreement demonstrates the capability of the adopted methodology in predicting and comprehensively investigating the complex phenomena associated with a pressure swirl fuel atomizer. In particular, it is found out that the normalized number-based probability density function of droplet size fits well with a lognormal distribution.

Experimental characterization of early, quasi-steady and post-injection evolution of single-hole direct injection sprays for spark-ignited engines

The atomization characteristics of the ethanol-gasoline (E85) blended fuel using a single-hole GDI atomizer were studied. The spray at early development, quasi-steady, and post-injection stages were studied in the near-nozzle region. A Galilean-type beam expander and an achromatic lens were used to achieve the desired magnification. In the early development stage, the jet velocity was measured to estimate the breakup regime based on the Ohnesorge (Oh) and Reynolds (Re) numbers. Spray during the initial stage at 2 MPa injection pressure shows second wind-induced breakup under 0.6 MPa chamber pressure (Pch). A transition between second-wind and atomization breakup for jets under 0.03 and 0.05 MPa Pch. The jet experiences atomization breakup under 0.1 MPa Pch. The effect of the injection pressure and chamber temperature were also studied. The post-injection liquid sheet formation near the nozzle exit was observed. Results show that the size of the liquid sheet depends on the liquid-to-gas density ratio (ρlg). The size of the sheet for E85 fuel at ρlg of 2363 was found to be 6 mm, which was reduced by 75 % with a reduction in ρlg by 95 %. The chamber temperature increased from 303 K to 363 K, ρlg increased from 702 to 842, and a reduction in the liquid sheet was observed from 2.5 mm to 1.8 mm, respectively. The necking phenomenon of the liquid sheet was observed at the nozzle tip before the sheet detached and disintegrated into droplets. The necking length for the E85 was compared with gasoline fuel.

Experimental and numerical study on the falling film flow characteristics outside circular tube applied in floating liquefied natural gas (FLNG) under offshore conditions

Spiral wound heat exchanger (SWHE) relying on falling film evaporation and boiling is often used for FLNG. The performance of SWHE can be impacted strongly by the motion of the FLNG caused by the wave and typhoon. The falling film characteristics of SWHE outside circular tube are studied experimentally and numerically by a visualization experimental device based on the high-speed camera and a numerical model based on the dynamic grid. The results show that the wave crest of the liquid film moves to the titled side under offshore conditions. The evolution process of falling film flow pattern outside circular tube with the tilt angle of 9° can be divided into four stages: droplet formation and migration, liquid column formation and migration, liquid column coalescence, liquid sheet formation. A correlation permitting the prediction of the falling film flow pattern outside circular tube and the other one permitting the prediction of the average film thickness of circular tube are developed respectively based on the experimental and numerical data.

Spray patterns of multi-element swirl coaxial injector of interacting spray under different injection conditions

Multi-element injectors have been used in liquid rocket engines to obtain high thrust, and the gas-centered swirl coaxial injector is a representative injection system because it provides high mixing performance. Investigations of the spray characteristics of injection systems have focused on the characteristics of single-element injectors, including the spray angle, breakup, and atomization mechanism of the liquid sheet formation. However, the spray characteristics of multi-element injectors need to be studied because of their usage in real rocket engine systems. In this paper, spray patterns and interacting spray under different injection conditions are analyzed using the backlight imaging technique, and the dominant flow fields are observed using the dynamic mode decomposition method. The spray angle in the case of the gaseous nitrogen with a high Reynolds number is calculated to be lower than the case with a low Reynolds number. From the averaged images, it is found that there are two dominant flow fields: one is located in the vicinity of the injector head and the other is in the interacting spray zone, which is related to a secondary breakup via an adjacent injector. As a result of the dynamic mode decomposition analysis, however, the spray zone near the injector is confirmed to be a more dominant flow field than the interacting spray zone.

The process of preparation of tellurium epitaxial films and layers with high structural perfection during vapor-deposition process in the pure hydrogen environment

The work is devoted to studying a new methodology for epitaxial films preparation on the mi-ca (muscovite) plates and based on carrying out the tellurium vapor-deposition process in the pure hydrogen environment. The formation of Н2Te molecules during reaction of H2 with sol-id Te in the hot zone, diffusion of Н2Te towards the cold surface with efficient thermalization due to high thermal conductivity of H2, Н2Te dissociative adsorption on the growth surface followed by H2 desorption and atomic Te accumulation are considered as key steps of crystal-line epitaxial films formation. Atomic Te assists the appearance and growth of directional liquid nucleuses at cold plate temperatures near Te melting point (about 450C). During coa-lescence of these liquid nucleuses the gradual formation of a liquid film is observed with a mosaic of voids of various size. After continuous liquid sheet formation, auto-epitaxial film growth begins also taking place according to vapor-liquid-crystal process described. The structural perfection of films formed is closed to three-dimensional monocrystalline samples. As a result, Te films with such characteristics may be put to use in various branches of micro-, opto-, acoustoelectronics.

Drop impact close to the edge of an inclined substrate: Liquid sheet formation and breakup

Experiments on the impact of a drop near the edge of an inclined substrate are reported. A liquid sheet forms beyond the edge, then fragments into droplets. This configuration is a minimal model of the crucial raindrop impacts on plant leaves that are responsible for the dispersal of crop diseases.

Analysis of viscous fluid flow in a pressure-swirl atomizer using large-eddy simulation

A computational fluid dynamics study is carried out on the inner nozzle flow and onset of liquid sheet instability in a large-scale pressure-swirl atomizer with asymmetric inflow configuration for high viscosity fluids. Large-eddy simulations (LES) of the two-phase flow indicate the unsteady flow character inside the nozzle and its influence on liquid sheet formation. A novel geometric volume-of-fluid (VOF) method by Roenby et al. (2016), termed isoAdvector, is applied for sharp interface capturing. We carry out a Reynolds number sweep (420 ≤ Re ≤ 5300) in order to investigate the link between the asymmetric inner nozzle flow and liquid sheet characteristics in laminar, transitional and fully turbulent conditions. Inside the nozzle, the numerical simulations reveal counter-rotating Dean vortices, flow impingement locations, and strong asymmetric flow features at all investigated Reynolds numbers. A helical, rotating gaseous core is observed when Re ≥ 1660. For laminar flow (Re=420), an S-shaped liquid film is observed, while the gas core presence at Re ≥ 1660 results in a hollow cone liquid sheet. For the intermediate value Re=830, the numerical simulations indicate a liquid sheet of mixed type. Consequences of the inflow asymmetry and Reynolds number to the uniformity of the injected liquid mass distribution and liquid sheet instability are pointed out.

Simulations of splashing high and low viscosity droplets

In this work, simulations are presented for low viscosity ethanol and high viscosity silicone oil droplets impacting on a dry solid surface at atmospheric and reduced ambient pressure. The simulations are able to capture both the effect of the ambient gas pressure and liquid viscosity on the droplet impact and breakup. The results suggest that at early times droplet impact and gas film behavior for both low and high viscosity liquids share the same physics. However, at later times, during liquid sheet formation and breakup, high and low viscosity liquids behave differently. These results explain why for both kinds of liquids the pressure effect can be observed, while at the same time different high and low viscosity splashing regimes have been identified experimentally.

Numerical investigation of heavy fuel droplet-particle collisions in the injection zone of a Fluid Catalytic Cracking reactor, part II: 3D simulations

This study investigates the collisions between heavy gasoil droplets and solid catalytic particles taking place at conditions realized in Fluid Catalytic Cracking reactors (FCC). The computational model utilizes the Navier-Stokes equations along with the energy conservation and transport of species equations. The VOF methodology is used in order to track the liquid-gas interface, coupled with a dynamic local grid refinement technique in order to minimize the computational cost. Phase-change phenomena, as well as catalytic cracking surface reactions (2-lump scheme) are taken into account. In this paper, the numerical model is extended to investigate the droplet-particle collision process in three dimensions. In order to save computational resources, only half of the droplet is investigated, by imposing symmetry conditions. Firstly, single droplet-catalyst collisions are simulated and compared against the corresponding ones provided by 2D axisymmetric simulations and afterwards, the model is applied for the characterization of the collision dynamics between a single droplet and a particle cluster, i.e. a realistic 3D particle configuration. As the droplet flows through the space between the catalytic particles, important phenomena are observed, such as a) drop levitation due to the formed vapour layer and b) a thin liquid sheet formation, both of which affect the rate of gasoline production, as well as predictions for liquid pore blocking mechanism; a phenomenon frequently observed industrially. Results indicate that gasoline production decreases when the collision target is a particle cluster, instead of same number (as many as in the cluster) single catalysts, as the corresponding contact area decreases.

Formation of liquid sheets by deposition of droplets on a surface

Experiments were done to observe the coalescence of highly viscous liquid droplets (87wt% glycerin-in-water solutions) deposited onto a flat, solid steel plate. Droplets were deposited sequentially in straight lines or square droplet arrays. Droplet center-to-center distance was varied and the final dimensions of lines and sheets measured from photographs. When overlapping droplets were deposited surface tension forces pulled impacting droplets towards those already on the surface, a phenomena known as drawback. A dimensionless drawback index, quantifying the extent of droplet displacement, was calculated from experimental measurements for different values of droplet overlap. At large overlaps droplets deposited in a line or square array coalesced to form a circular film. When the droplet center-to-center distance increased, leading to less interaction, long, thin lines and square sheets were formed. As overlap was further decreased lines and sheets became discontinuous. A simple model was developed to predict the conditions under which rupture occurred. The lowest droplet overlap ratio (defined as droplet overlap distance divided by droplet spread diameter) at which a continuous liquid film could be formed was λ=0.293. At large overlap ratios (λ>0.6) droplets deposited in a square array formed a circular film. The minimum thickness of a continuous film formed by coalescence of droplets was shown to vary from 5% to 70% of the initial droplet diameter while increasing impact Weber and Reynolds number reduced the film thickness.

Special phenomena of droplet impact on an inclined wetted surface with experimental observation

The phenomena of droplet impact on an inclined solid surface covered with a pre-existing liquid film are observed using high speed camera at 10000 frames per second. The processes of droplet spreading, liquid sheet formation, splashing and droplet oscillation are observed and analyzed. From the results the relationship between spreading velocity and time is discussed quantitatively. Besides, the effects of impact velocity and impact angle on front and back spreading factors and initiatory spreading velocity are also revealed. At the impact angles ranging from 28.0° to 74.7°, it is found that with the decrease of impact angle, the deformation degree of the droplet oscillation on the film surface increases. The results also indicate that the front spreading factor can increases by increasing impact velocity or by reducing the impact angle, whereas the back spreading factor increases with impact angle increasing. The impact velocity almost has no influence on it. The initial spreading velocity can increase by increasing the impact velocity and the impact angle.