Liquid Jet Diameter Research Articles

Visualization experiment and machine learning modeling for falling-film systems

The liquid film coverage over the tube wall is important in flow hydrodynamics, and flow hydrodynamics are important in heat transfer performance in falling-film systems as well. An experimental setup is used with the aid of a high-speed camera to visualize the flow behavior, which is challenging to see with the naked eye. The set of experiments are carried out by varying the important working parameters such as Reynolds number (250−458) and inter tube distance (20/30/40 mm). The Sobel image analysis method is developed to quantify flow parameters such as jet diameter and axial film thickness. The liquid jet diameter increases with increasing tube spacing for the same Reynolds number and decreases with increasing inter tube distance for the same Reynolds number. The formation of connected droplets causes disturbances near the liquid jet head. The connected droplet phenomenon causes the liquid jet diameter to increase and decrease in this region. Furthermore, there is a distinct pattern in the axial film coverage beneath and above the tube wall. Three data sets are generated for each parameter using an image analysis approach, which can then be used to train and develop machine learning models. The findings indicated that the Decision Tree, Random Forest, and Gradient Boosting models consistently better performed the other models on all features. Although a few models have lower error percentages below the datum line, consistency in each feature is still required. The results of the flow visualization experiments, as well as the machine learning models developed, can be used to quantify flow parameters and improve flow characteristics for better design.

Early Microjet Experimentation with Liquid Water in Vacuum.

ConspectusIn this brief look at the history of liquid microjets, I recollect some personal reminiscences on initial challenges for introduction of this method, as well as unexpected problems and exemplary results using this new tool for liquid evaporation and photoelectron spectroscopy studies.Many efficient and direct, atomic level diagnostic instruments in use at solid state surfaces and in gas-phase atom or cluster studies require high vacuum. They have therefore not been applied to investigations of aqueous solutions because liquid water both strongly evaporates and rapidly freezes in vacuum. Only fairly recently, over the past three decades, have liquid microjets been considered as practicable targets for research on liquid-water interfaces in vacuum. The working principle is analogous to the functioning of a free molecular beam source, where molecules enter through a small aperture into a vacuum without being disturbed by subsequent collisions in their original Maxwellian velocity distribution. Similarly, above a microjet surface in vacuum, water vapor molecules do not interact with each other, or with different probe particles, as long as the liquid jet diameter is small in relation to the mean free path of the liquids' vapor at equilibrium conditions. For pure liquid water, this constraint is Djet < λvap < 10 μm for 6.1 mbar vapor pressure at the triple point of water. A high streaming velocity of the liquid jet, >50 m/s, delays freezing and exposes a steadily renewed fresh vacuum surface for experiments.For experimental verification of the microjet free surface concept, H2O vapor velocities were measured in a molecular beam time-of-flight experiment. These studies showed Maxwellian velocity distributions with the expected local water-jet temperatures for 5 and 10 μm jets, whereas larger liquid jet diameters of 50 μm exhibit narrowed vapor velocity profiles. This narrowing is the known signature of incipient, collision dominated, supersonic hydrodynamic expansions in nozzle beam sources. As a completely unexpected new result in evaporation studies of carboxylic acid solutions, freely evaporating acetic acid dimers showed apparent non-equilibrium liquid surface source temperatures several hundred kelvin above the simultaneously measured monomer temperatures, a phenomenon shown to be correlated with surface tension.Continuing with improvements, the vacuum water microjets were implemented inside a photoelectron spectroscopy apparatus that was modified for handling large amounts of water vapor. After initial complications with liquid jet charging phenomena, the first partial liquid-water photoelectron spectra were recorded using 21 eV photons from a He I discharge lamp. In the next step, the equipment was taken to a synchrotron radiation beamline at BESSY II, resulting in substantial improvements of signal intensity and in photon tunability for narrow band monochromatic soft X-rays up to 1 keV. Two early examples of these continuing experiments are considered, briefly, for aqueous alkali halide salt solutions and for the pH-value dependent protonation of an NH2/NH3+ group in an amino acid directly in a photoelectron spectrum of a solution.In conclusion, liquid microjets have opened up a completely new approach to studies of arbitrary liquids with chemical and biological relevance.

Liquid flow and breakage behaviors of two liquid jets impacting on the wire mesh with different impinging angles

The flow and breakage behaviors of two liquid jets is of great importance for liquid–liquid mixing and reaction applications. However, the flow behaviors and breakage processes of two liquid jets impacting on the stainless steel wire mesh (SSM) is not clear. In this work, the high-speed photograph method was employed to study the behaviors of two liquid jets impacting on SSM. Effects of impinging angle (2θ), liquid initial velocity (u0), mesh number (M), and liquid jet diameter (D0) on liquid flow and breakage behaviors were investigated. Experimental results showed that the jets of water-water impacting on the SSM were broken into liquid jets and further broken into daughter droplets. The cone angle of dispersion increased with the increase of 2θ, u0, M, and D0, and reached the maximum value of 180°. The average diameter of daughter droplets at 2θ = 90° decreased maximally by 32%, compared with the condition of 2θ = 30°. For two liquid jets of water-n-hexane impacting on the SSM, a liquid sheet was formed. Under different operating conditions, the breakage mode of liquid sheet could be divided into marginal breakup and internal breakup. The breakage model at mesoscale is the result of surface tension and inertia force, both of which are relevant to the complex impact and flow behaviors. The liquid sheet length (Ls) decreased with the increase of u0 and M. A correlation to calculate Ls/D0 was proposed and the calculated results lied within ± 15% of the experimental values. This study provided a theoretical basis for the guidance of mass transfer enhancement and the reactor design with liquid–liquid system.

Characterization of column flow regimes on horizontal tubes for falling‐film systems: An experimental approach

AbstractThe intertube flow regimes and hydrodynamic behavior of the liquid profile have a significant impact on the functioning of falling‐film evaporators. Column flow is one of the fundamental flow modes, which is actively observed in many industrial evaporators. A high‐speed digital photographic device is utilized to visualize the complete progression of column flow phases for intertube distances of 10/20/30/40 mm and Reynolds number (Re) values ranging from 41 to 583. The Sobel edge detection algorithm is implemented to quantify the flow parameters for each frame of a sequence. The research results indicated that the column flow regime between the inline horizontal tubes can be broadly classified into the following phases: columnar droplet flow, periodic column flow, satellite drops column flow, drift column flow, and mixing liquid film column flow. The findings show that the liquid jet diameters between the tubes range from 1.6 to 8.46 mm, an increase in the liquid jet diameter with Re and a decrease with tube‐to‐tube distance. The axial coverage of the liquid film profile beneath the tube differed from 2.07 to 3.99 mm and over the tube surface ranged from 1.14 to 2.68 mm. The formation of dry spots and flooding is a major problem in the operation of falling‐film heat exchangers. The shape and size of the liquid jet have a direct impact on the interfacial area; understanding the entire progression of column flow regimes, as well as their characteristics, can help designers avoid the aforementioned problem.

Effect of gas jet angle on primary breakup and droplet size applying coaxial gas-assisted atomizers

This study investigates the influence of gas jet angle on primary jet breakup and the resulting droplet size distribution for coaxial gas-assisted atomizers. In industrial applications, the gas jet of these atomizers are typically angled towards the liquid jet, whereas in most spray investigations in literature, parallel flow configurations are used. To enable a detailed analysis of the influence of the gas jet angle, three atomizers with angles of 0°, 15° and 30° were examined. Other geometric parameters, such as liquid jet diameter, gas gap width and wall thickness were kept constant. For each atomizer, two gas velocities at constant liquid mass flow were investigated i.e., two gas-to-liquid ratios (GLRs). An additional set of experiments was performed at increased system pressure using three atomizers with identical gas jet angles, but with an adapted gas orifice area in order to keep gas velocity, GLR and momentum flow ratio constant for all pressure levels. Water and a glycerol/water-mixture were applied in order to investigate the influence of liquid viscosity. The primary breakup process was monitored by a high-speed camera, whereas the resulting droplet size was detected using a phase-Doppler anemometer. For all system pressures and liquid viscosities under investigation, a distinct influence of gas jet angle on primary breakup as well as on resulting droplet size distribution was observed for low gas velocity.

Design and experimental investigation of an internal mixing twin-fluid atomiser for the generation of test aerosol particles

ABSTRACT Internal mixing twin-fluid atomiser is known to be one of the prominent atomisers for the generation of spray or spray-like dispersion from bulk liquids. This paper designs and investigates the performance of a customised liquid siphon type internal mixing twin-fluid atomiser for the generation of test aerosol particles from oleic acid in an ethyl alcohol solution. Experimental results show the effect of airflow rate on suction height and liquid consumption rate of the atomiser with different design parameters. Variation of suction height and liquid consumption rate are investigated for six different design atomisers by varying the airflow rate between 18 and 230 lpm. It is seen that the atomiser with optimum design can have a suction height of up to 103 cm and a liquid consumption rate of up to 1545 ml/h. Atomiser 3 (with air inlet diameter = 18 mm and liquid jet diameter = 2 mm) produces better test aerosol participles with constant S/D = 0.66 and 10% solution concentration. While using this atomiser for the production of test aerosol, the lowest geometric standard deviation found in the experiment was 1.2.

The effect of electrode shape and arrangement on breakup of dielectric liquid jet in electric field

In this study, the behavior of dielectric liquid jet in the presence of electric field was analyzed and the effects of electrode geometry and electric field direction on surface wave frequency, jet breakup, and produced droplet characteristics were investigated. When a dielectric liquid jet flows through an electric field, three types of electric forces can be imposed on the flow field: electrophoretic, dielectrophoretic, and electrostriction forces. Flow of liquid jet in gaseous surrounding is affected by electrophoretic and dielectrophoretic forces. Considering the direction of electrophoretic force, applying the electric field in the direction of jet flow thickens the jet by decelerating the flow; nevertheless, inverse field increases the diameter of jet by accumulation of liquid in the downstream region of electrodes. Dielectrophoretic force does not depend on field direction and always increases the diameter of liquid jet. Results showed that breakup length is shortened by electric field and applying a 6 kV electric potential difference can reduce the upper limit of breakup length by 27% in comparison with non-electrified case. Furthermore, the electric field increases the production of round droplets and decreases the number of irregular and sharp-edged droplets. Increase in electric field strength usually leads to reduction in droplet size. Besides, parallel–triangular electrodes in direct field and star–triangular electrodes in inverse field are more effective in the production of round droplets. Although smallest droplets are produced using star–triangular arrangement, parallel–triangular electrodes can produce droplets with more homogeneity in size distribution.

Flapping instability of a liquid jet

We measure experimentally the frequency of the large-scale instability developing on a liquid jet incompletely atomized by a parallel fast gas stream. We demonstrate that this flapping instability can be triggered by different mechanisms: in a first regime it is synchronized with the shear instability developing upstream, provided the wavelength of this shear instability is larger than the liquid jet diameter HL. When the shear instability exhibits wavelengths shorter than HL, a second regime is observed where the flapping instability becomes independent of the gas stream velocity. This second regime is characterized by a constant Strouhal number, provided the Froude number of the jet is correctly taken into account.

Comparison of Electrospinning and Gas Jet Fiber Processes for Fabrication of Bi‐Component Polymer Nanofibers from Single Solutions

SummaryIn this study, the rates of nanofiber production are compared between single needle electrospinning and single nozzle gas jet fiber (GJF) processes by considering bi‐component nanofibers of two immiscible polymers. The spinning solutions consist of two immiscible polymers and two mutually miscible solvents. The solvent pairs with different vapor pressure are used to obtain three morphological forms − interpenetrating network (IPN), bi‐lobal, and core‐shell. As baseline for comparison, electrospinning conditions are chosen to produce the same equivalent liquid jet diameter as in the case of GJF process. It is observed that nanofibers of IPN, bi‐lobal, and core‐shell morphologies are easily produced in the GJF process at high rates while nanofibers of only the IPN and bi‐lobal morphologies are produced via electrospinning, although at much lower rates. The core‐shell nanofibers cannot be produced via electrospinning process for the combinations of polymers and the solvents chosen in this work.

Global stability of stretched jets: conditions for the generation of monodisperse micro-emulsions using coflows

AbstractIn this paper we reveal the physics underlying the conditions needed for the generation of emulsions composed of uniformly sized drops of micrometric or submicrometric diameters when two immiscible streams flow in parallel under the so-called tip streaming regime after Suryo and Basaran (Phys. Fluids, vol. 18, 2006, 082102). Indeed, when inertial effects in both liquid streams are negligible, the inner to outer flow-rate and viscosity ratios are small enough and the capillary number is above an experimentally determined threshold which is predicted by our theoretical results with small relative errors, a steady micrometre-sized jet is issued from the apex of a conical drop. Under these conditions, the jet disintegrates into drops with a very well-defined mean diameter, giving rise to a monodisperse microemulsion. Here, we demonstrate that the regime in which uniformly sized drops are produced corresponds to values of the capillary number for which the cone-jet system is globally stable. Interestingly enough, our general stability theory reveals that liquid jets with a cone-jet structure are much more stable than their cylindrical counterparts thanks, mostly, to a capillary stabilization mechanism described here for the first time. Our findings also limit the validity of the type of stability analysis based on the common parallel flow assumption to only those situations in which the liquid jet diameter is almost constant.

Experimental Study of Cavitation and Hydraulic Flip Effects on Liquid Jet Characteristics into Crossflows

In this work, the effects of orifice internal flow, such as cavitation and hydraulic flip, on the breakup processes of the liquid jet injected perpendicularly into subsonic crossflows were studied experimentally. To provide several conditions for orifice internal flow, different orifice diameters, injection pressure differentials, and shapes (sharp and round) of the orifice entrance were used. Photographs of liquid flow inside the orifice confirmed the internal flow condition. A stroboscopic light was used to measure the liquid column breakup lengths and the liquid column trajectories. The results showed that the liquid column trajectories in noncavitation flows and cavitation flows had a similar trend, but the liquid column trajectories in hydraulic flip flows had different results because the surface of the liquid in the hydraulic flip flows was detached from the inner wall of the orifice hole. As cavitation bubbles developed inside the sharp-edged orifice, the liquid jet became more turbulent and unsteady. Therefore, the liquid column breakup lengths in the cavitation flows were shorter than those in noncavitation flows. In the hydraulic flip, the breakup lengths had smaller values because the liquid jet diameter was smaller than the orifice diameter, and the acceleration waves occurring on the liquid column spread upstream of the orifice exit, then the breakup process on the liquid jet started from the orifice entrance.

An investigation on effect of geometrical parameters on spray cone angle and droplet size distribution of a two-fluid atomizer

A visual study is conducted to determine the effect of geometrical parameters of a two-fluid atomizer on its spray cone angle. The liquid (water) jets exit from six peripheral inclined orifices and are introduced to a high speed gas (air) stream in the gravitational direction. Using a high speed imaging system, the spray cone angle has been determined in constant operational conditions, i.e., Reynolds and Weber numbers for different nozzle geometries. Also, the droplet sizes (Sauter mean diameter) and their distributions have been determined using Malvern Master Sizer x. The investigated geometrical parameters are the liquid jet diameter, liquid port angle and the length of the gas-liquid mixing chamber. The results show that among these parameters, the liquid jet diameter has a significant effect on spray cone angle. In addition, an empirical correlation has been obtained to predict the spray cone angle of the present two-fluid atomizer in terms of nozzle geometries.

Modeling atomization of a round water jet by a high-speed annular air jet based on the self-similarity of droplet breakup

Based on the self-similarity of droplet breakup in the secondary atomization region, the atomization process of coaxial air-blast atomizer has been investigated. The relationship of Sauter mean diameter (SMD) with the effects of gas jet velocity, liquid jet velocity and diameter and liquid/gas mass flux ratio was obtained according to the breakup time and motion characteristic of droplet in air stream. The four parameters in the relationship of SMD were estimated according to the experimental results of nine coaxial two-fluid air-blast atomizers with air and water. The results showed that the obtained relationship of SMD can be used to predict the SMD of coaxial air-blast atomizer when m>13.99dl−0.1285dg−0.9415.

The theoretical simulation of the effect of solid–liquid contact angle on the critical heat flux of saturated water jet boiling on stagnation zone

A theoretical simulation was carried out for predicting the critical heat flux (CHF) of convective boiling for a round saturated water jet impingement on the stagnation zone of a hot surface. The study was focused on the effect of the solid–liquid contact angle on the CHF. A theoretical model based on the Long wave instability was applied to calculate the maximum liquid sub-film thickness under boiling bubbles and finally a semi-empirical and semi-theoretical correlation was proposed by combining the simulated calculation and the experimental data from the common metal heating surface. The correlation revealed the comprehensive effects of solid–liquid contact angles, jet velocity and jet diameter on the CHF and agreed well with the experimental data proposed by authors in the previous study.

EFFECTS OF ORIFICE INTERNAL FLOW ON TRANSVERSE INJECTION INTO SUBSONIC CROSSFLOWS: CAVITATION AND HYDRAULIC FLIP

The effects of orifice internal flow, such as cavitation and hydraulic flip, on the breakup processes of the liquid jet injected perpendicularly into subsonic crossflows were studied experimentally. Orifice diameters, injection pressure differentials, and the shapes (sharp and round) of the orifice entrance were varied to provide several conditions for orifice internal flow. Photographs of liquid flow inside the orifice confirmed the internal flow condition. The liquid column breakup lengths, and the liquid column trajectories, which were believed to be important for designing injector/combustor and flame location, were measured using a stroboscopic light. According to previous research, the data were correlated by liquid/air momentum flux ratios and orifice diameters. The results showed that the liquid column trajectories in noncavitation flows and cavitation flows had a similar trend, but the liquid column trajectories in hydraulic flip flows had different results because the surface of the liquid in the hydraulic flip flows was detached from the inner wall of the orifice hole. As cavitation bubbles developed inside the sharp-edged orifice, the liquid jet became more turbulent and unsteady. Therefore, the liquid column breakup lengths in the cavitation flows were shorter than those in noncavitation flows. In the hydraulic flip, the breakup lengths had smaller values because the liquid jet diameter was smaller than the orifice diameter, and the acceleration waves occurring on the liquid column spread upstream of the orifice exit, then the breakup process on the liquid jet started from the orifice entrance.

Energy loss of swift protons in liquid water and ethanol

Energy loss measurement has been performed for the first time for MeV energy hydrogen ions passing through a liquid jet target produced by our newly developed liquid-in-vacuum apparatus. Liquid jet targets of water and ethanol were ejected into vacuum through an aperture of 20μm in diameter. Preliminary experimental results of energy loss spectra are reported. It was found that the energy loss of swift protons in liquids are slightly different from the conventional stopping power data obtained from the SRIM code. However, this discrepancy is possibly attributable to our incorrect estimation of the liquid jet diameter.

Effect of liquid jet diameter on performance of coaxial two-fluid airblast atomizers

In this paper, the effect of liquid jet diameter on performance of coaxial two-fluid airblast atomizer has been investigated with water–air system in a wide region of liquid/gas mass flux ratio (0.137 < m < 15.6). The Sauter mean diameters (SMD) were measured using Malvern Laser Particle Sizer. The experimental results showed that the liquid jet diameter has striking effect on SMD for large m, but has no effect for small m. For a fixed large m, a decrease of SMD with liquid jet diameter was observed first, followed by an increase. A similar non-monotonic trend was also observed between SMD and liquid jet velocity, We, Re, and M (gas/liquid momentum flux ratio) at the same m, respectively. The minimum SMD is obtained when the velocity of liquid jet flow is about 1.5–4.0 m/s. The following correlation for SMD is developed from the measured data: SMD = 685.8 ( u g − 3.297 u l ) − 0.4813 m 0.3665 + 0.1824 d l m .

Improved liquid jet laser-plasma source for X-ray microscopy

We increase the x-ray flux from a liquid-jet laser-plasma x-ray source by optimizing the target geometry. A new nozzle fabrication method allows us to produce stable microscopic liquid jets with a wide range of diameters. The improved x-ray flux is demonstrated by optimizing the diameter of an ethanol liquid-jet for our 3 ns, □ =532 nm Nd:YAG laser and measuring the flux at the □=3.37 nm C VI emission line. Preliminary data suggest that the x-ray flux can be increased by more than a factor of 4 compared to previous experiments. The goal is to significantly reduce the exposure time of our laser-plasma-based compact x-ray microscope by improving the source.

Effects of confinement on the temporal instability of gas jets injected in viscous liquids

A temporal linear stability analysis of an inviscid incompressible gas jet injected into a coflowing viscous liquid confined within a tube was conducted to study the growth of small disturbances that lead to the breakup of the gas jet. For low-viscosity liquids, the confinement of the liquid jet did not affect the growth rates of the gas-jet disturbances. However, for high viscosity liquids, confining the liquid jet results in a significant increase in the disturbance growth rate and the range of unstable wave numbers. Also, for small ratios of the liquid jet diameter to gas jet diameter, the change in disturbance growth rate with Weber number is small. The effect of Weber number becomes significant only at large values of the diameter ratio.

Gas property effects on dropsize of simulated fuel sprays

Two-phase flow in pneumatic two-fluid fuel nozzles was experimentally investigated to determine the effect of gas properties on liquid-jet breakup in sonic-velocity gas flow. Dropsize data were obtained for the following atomizing gases: nitrogen, argon, carbon dioxide, and helium. The ratio of liquid-jet diameter to Sauter mean diameter (SMD) D0/Dyi was correlated with aerodynamic and liquid-surface forces based on the product of the Weber and Reynolds number WeRe and gas-to-liquid density ratio pg/pi. To correlate characteristic dropsize with breakup forces produced by using different atomizing gases, a molecular-scale dimensionless group was derived, piV3/gng. As a result, a semiempirical correlating expression was obtained that can be used in the design of fuel injectors for gas turbine and rocket combustors. This expression for liquid-jet breakup in two-fluid atomizer shows that Z>32 ~ (p^c)1'33, where pgVc is gas mass-flux at sonic velocity, and this agrees well with atomization theory for liquid-jet breakup in high velocity gas flow. Also, it was found that at the same gas mass-flux pgVc, helium was considerably more effective than nitrogen in producing small droplet sprays with SMDs in the order of 5 /un. This was attributed to the high acoustic velocity of helium.