Annular Gas Jet Research Articles

Experimental investigation on submerged water jet wrapped in an annular gas jet

To reduce the energy dissipation of the submerged water jet, a series of experiments of the submerged water jet wrapped in an annular gas jet are performed under different gas ventilation rates, annular sizes, water jet nozzle diameters, and water jet velocities in a transparent water tank. In the experiments, a ventilated cavity is created by the annular gas jet that encloses the submerged water jet. The submerged water jet is separated from the surrounding water within a certain distance after leaving the nozzle exit by the ventilated cavity, which contributes to the effective working length of the submerged water jet significantly increasing, referring to the energy dissipation decrease. Furthermore, the geometry of the ventilated cavity changes periodically, i.e., the cavity length and diameter decrease after increasing to the peak values in each cycle. Moreover, the ventilated cavity development process can be mainly divided into formation, collapse, and intermission stages. The maximum cavity length of the ventilated cavity decrease with the per unit time momentum ratio between the water jet and the gas jet. Namely, the per unit time momentum ratio between the water jet and the gas jet is the dominating parameter of the cavity geometry.

Gasdynamic and Acoustic Characteristics of a Subsonic Jet-Edge Rod Generator of Acoustic Radiation

The design of a subsonic jet-edge rod generator of the Hartmann-type oscillator and a scheme of measuring its acoustic parameters are presented. In this generator, unlike the Hartmann oscillator, not a cylindrical gas jet but an annular gas jet, moving along the thin cylindrical rod positioned at the axis of the generator nozzle, is used. A parametric investigation of the gasdynamic and acoustic processes arising in the tubular cavity of such a generator as a result of the interaction of a subsonic gas jet with this cavity has been performed with consideration for the nonstationary structure of the gas flow in the generator cavity. Recommendations on the choice of the design of a jet-edge rod generator of acoustic radiation with regard for its practical application are given.

Investigation of the Pulsed Annular Gas Jet for Chemical Reactor Cleaning

The most economical technology for production of titanium dioxide pigment is plasma-chemical syntheses with the heating of the oxygen. The highlight of the given reaction is formation of a solid phase as a result of interactions between two gases, thus brings the formation of particle deposits on the reactor walls, and to disturbing the normal operation of the technological process. For the solving of the task of reactor internal walls cleaning the pulsed gaseous system was suggested and investigated, which throws circular oxygen jet along surfaces through regular intervals. Study of aerodynamic efficiency of the impulse system was carried by numerical modeling and experimentally with the help of a specially created experimental facility. The distribution of the pulsed flow velocity at the exit of cylindrical reactor was measured. The experimental results have shown that used impulse device creates a pulsed jet with high value of the specified flow rate. It allows to get high velocities that are sufficient for the particle deposits destruction and their removal away. Designed pulsed peelings system has shown high efficiency and reliability in functioning that allows us to recommend it for wide spreading in chemical industry.

Self-oscillatory regimes of cavitation interaction between counter-streaming fluid flows

The effects of unsteady cavitation interaction between a coaxial system of a continuous water jet and a surrounding annular gas jet and a counter-streaming water flow in a cylindrical tube is investigated both experimentally and numerically. The distinctive features of the mechanism of the formation of regular self-oscillatory interaction regimes and their salient features are studied. The dependence of the mean self-oscillation frequency on the ratio of the counter-streaming water flows is determined at different gas jet flow rates. The Froude number effect on the self-oscillation frequency is analyzed. The dependence of the maximum value of the longitudinal displacement of the nose of a developed oscillating cavity penetrating into the counter stream and of the displacement amplitude on the flow rate of the supplied gas is determined. The idea on the pressure distribution in the cavity in different stages of flow development is obtained. The nature of the dependence of the self-oscillation frequency on the degree of tube flow blockage by the cavity is established.

Reverse Flow Pressure Limiting Aperture.

The reverse flow pressure limiting aperture is a device that creates and sustains a substantial gas pressure difference between two chambers connected via an aperture. The aperture is surrounded by an annular orifice leading to a third chamber. The third chamber is maintained at a relatively high pressure that forces gas to flow through the annular aperture into the first of said two chambers. The ensuing gas flow develops into a supersonic annular gas jet, the core of which is coaxial with the central aperture. A pumping action is created at the core of the jet and any gas molecules leaking through the aperture from the second chamber are entrained and forced into the first chamber, thus creating a substantial pressure difference between the first and second chamber.

Numerical Analyses of Fluid Dynamics of an Atomization Configuration

Computational fluid dynamic techniques were used to analyze the gas flow behavior of a typical atomization configuration. The calculated results are summarized as follows. The atomization gas flow at the atomizer's exit may be either subsonic at ambient pressure or sonic at an underexpanded condition, depending on the magnitude of the inlet gas pressure. When the atomization gas separates to become a free annular gas jet, a closed recirculating vortex region is formed between the liquid delivery tube and the annular jet's inner boundary. Upon entering the atomization chamber, an underexpanded sonic gas flow is further accelerated to supersonic velocity during expansion. This pressure adjustment establishes itself in repetitive expansion and compression waves. A certain protrusion of the liquid delivery tube is crucial to obtain a stable subatmospheric pressure region at its exit. The vortex flow under the liquid delivery tube tends to transport liquid metal to the high kinetic energy gas located outside the liquid delivery tube, thereby leading to an efficient atomization.

Liquid Jet Instability and Atomization in a Coaxial Gas Stream

▪ Abstract An overview of the near and far-field breakup and atomization of a liquid jet by a high speed annular gas jet is presented. The various regimes of liquid jet breakup are discussed in the parameter space of the liquid Reynolds number, the aerodynamic Weber number, and the ratio of the momentum fluxes between the gas and the liquid streams. Recent measurements of the gas-liquid interfacial instabilities are reviewed and used to analyze the underlying physical mechanisms involved in the primary breakup of the liquid jet. This process is shown to consist of the periodic stripping of liquid sheets, or ligaments, which subsequently break up into smaller lumps or drops. Models to predict the liquid shedding frequency, as well as the global parameters of the spray such as the liquid core length and spray spreading angle are discussed and compared with the experiments. The role of the secondary liquid breakup on the far-field atomization of the liquid jet is also considered, and an attempt is made to apply the classical turbulent breakup concepts to explain qualitatively the measurement of the far-field droplet size distribution and its dependence on the liquid to gas mass and momentum flux ratios. Models for the droplet breakup frequency in the far-field region of the jet, and for the daughter-size probability density function, which account for the effect of the liquid loading on the local turbulent dissipation rate in the gas, are discussed in the context of the statistical description of the spray in the far field. The striking effect of the addition of swirl in the gas stream is also examined.

Reverse Flow Pressure Limiting Aperture

The reverse flow pressure limiting aperture is a device that creates and sustains a substantial gas pressure difference between two chambers connected via an aperture. The aperture is surrounded by an annular orifice leading to a third chamber. The third chamber is maintained at a relatively high pressure that forces gas to flow through the annular aperture into the first of said two chambers. The ensuing gas flow develops into a supersonic annular gas jet, the core of which is coaxial with the central aperture. A pumping action is created at the core of the jet and any gas molecules leaking through the aperture from the second chamber are entrained and forced into the first chamber, thus creating a substantial pressure difference between the first and second chamber.

Magnetohydrodynamic instability of an annular gas jet or double perturbed interfaces

The magnetohydrodynamic (MHD) instability of an annular gas jet of double perturbed interfaces is analyzed. The MHD basic equations are linearized and solved. A general stability criterion is derived and discussed analytically and the results are confirmed numerically. Several stability criteria are recovered from the present relation. The capillary force is, acting along the gas-liquid interface, destabilizing only for small axisymmetric wavelengths and stable for all the rest. The electromagnetic forces in the gas and liquid regions are strongly stabilizing for all wavelengths in all modes of disturbance, and this is interpreted physically. Above a certain value of the applicable magnetic field, the electromagnetic force influences suppress the capillary instability and stability sets in. The thicker the radius of the liquid cylinder relative to that of the gas cylinder, the greater the destabilizing influence and the larger the MHD unstable domains for the same value of the fundamental basic magnetic field. Physically, the suppression of the capillary instability is due to the fact that the Lorentz force leads to twisting and bending of the lines of force and, moreover, it gives a measure of rigidity to the conducting fluid.

FRACTAL GEOMETRY OF LIQUID JETS UNDER BREAKUP

Fractal dimension of gas-liquid interfaces was measured in the breakup region of disintegrating liquid jets. The liquid jet is surrounded by an annular gas jet, and both are injected through an airblast coaxial atomizer. The gas-liquid interface is categorized by a fractal set with dimensions and cutoffs that were found to be related to the physical processes of atomization. The fractal dimension was measured as a function of axial location and a range of air and liquid velocities. It was found that the peak fractal dimension and the breakup point are approximately at the same axial location and a good correlation exists between the peak value of the fractal dimension and the average drop size measured in the core of the spray.

An experimental gas-dynamic cryogenerator

Results are shown of the trials of an experimental gas-dynamic cryogenerator. In contrast to the classical resonance tube, an annular gas jet is used. It is shown that periodic alternation of the resonance zones resulting from the cellular structure of the jet takes place when the tube moves relative to the nozzle. A schematic is provided of the gas-dynamic cryogenerator. One of the most important characteristics of a gas-dynamic cryogenerator is the temperature level at which the heat is diverted to the terminal heat exchanger. The trials of the experimental gas-dynamic cryogenerator showed that it is more efficient than the expanding throttling devices and is a promising apparatus for application in refrigerating and cryogenic engineering.