Numerical study of the effect of gas-to-liquid ratio on the internal and external flows of effervescent atomizers

In an effort to capture the complex evolving interface of internal and external flow in an effervescent atomizer, a compressible Eulerian method, along with the volume-of-fluid method coupled with the large eddy simulation model, are employed in a two-phase flow system. Water is injected into the atomizer with a constant mass flow rate of 0.0133 kg/s (i.e., 800 mL/min). The mass flow rate of air is adjusted to vary the gas-to-liquid ratio (GLR) from 0.55% to 2.6%. It is observed that the increase in the GLR is accompanied by an evolution of the internal flow from a complex bubbly flow to an annular flow, which consequently reduces the liquid film thickness at the discharge orifice. Further studies on the internal pressure illustrate the critical condition, which leads to choked flow and pressure oscillations at the discharge orifice. Increasing the GLR was found to affect the internal flow, resulting in changes to primary atomization parameters such as a shortening of the breakup length and a widening of the spray cone angle. The numerical predictions are in good agreement with the experimental results under the same operating conditions.

Numerical study of the effect of heat transfer on solid phase formation during decompression of CO2 in pipelines

CO2 solid phase formation accompanying rapid decompression of high-pressure CO2 pipelines may lead to blockage of the flow and safety valves, presenting significant hazard for safe operation of the high-pressure CO2 storage and transportation facilities. In this study, a homogeneous equilibrium flow model, accounting for conjugate heat transfer between the flow and the pipe wall, is applied to study the CO2 solid formation in a 50 mm internal diameter and 37 m long pipe for various initial thermodynamic states of CO2 fluid and wide range of discharge orifice diameters. The results show that the rate of CO2 solid formation in the pipe is limited by heat transfer at the pipe wall. The predicted amounts of solid CO2 are discussed in the context of venting of CO2 pipelines.

Fundamental analysis of liquid breakup mechanism in a rotary atomizer with square discharge orifice

An experimental investigation of breakup mechanism in a rotary atomizer with square shape discharge orifice atambient condition has been performed. The effects of a high aspect ratio noncircular discharge channels, particularly a square shape discharge channel, are considered. The motivation of this study is the use of this type of orifice in some small gas turbine engines as well as non-existing observation in literature concerning about high aspect ratio of discharge channel. Visualization experiments are conducted by high speed shadowgraph imaging technique with pulsed light illumination for the first time. The effects of rotational speed and volume flow rate are studied on the breakup structure. The visualizations indicates that the liquid film formed along the channel is pushed to one side of it due to Coriolis force which is dominant in this type of atomizer. Accordingly a crescent shaped liquid film is formed at the square channel exit covering two corners of the square, resulting the combination of Coriolis induced stream mode and surface tension induced stream mode breakup. Observations of the breakup process for different volume flow rates and rotational speeds indicate that the breakup of liquid film stream is dependent on injection conditions and the corresponding cross flow velocity created by atomizer rotation. The breakup regime map is provided as a function of weber number and momentum flux ratio. Four distinct regimes are identified: Rayleigh breakup, bag breakup, multimode breakup, and shear breakup. The present results leads to understandingatomization performance and creating some idea to improved spray quality in this type of atomizer.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.5640

EFFECT OF GEOMETRICAL PARAMETERS INTERACTION ON SWIRL EFFERVESCENT ATOMIZER SPRAY ANGLE

A wider spray angle produced by an atomizer is often required in providing a better spray dispersion. The formation and wideness of the spray angle were reported to be affected by the changes in geometrical parameters. In the present study, the effect of the interaction between two geometrical parameters (swirl-generating vane angle and discharge orifice diameter) on the swirl effervescent atomizer spray angle was studied. A newly-designed swirl effervescent atomizer was developed with 30°, 45° and 60° swirl-generating vane angle and 1.5, 2.0 and 2.5mm discharge orifice diameter. The atomizer performance tests were carried out using water as the working fluid and nitrogen gas as the atomizing agent. High-speed shadowgraph technique was deployed to record the resultant sprays produced. Video recordings, acquired using a high-speed video camera, were converted to a sequence of images for further analysis using image processing software. It was found that geometrical parameters of the newly designed atomizer have a great impact on the formation and characteristics of the spray angle. The combined effect of both swirl-generating vane angle and discharge orifice diameter has produced an increase in the spray angle. The largest spray angle was observed at the largest dimension of both geometries.

Design and test of annular discharge orifice of shock transmission unit

The annular discharge orifice is a key parameter for the design of a shock transmission unit (STU). The proper dimension of the annular discharge orifice can make the stiffness difference of STU maximum in different conditions. Making use of three laws of fluid mechanics, the mathematical model for designing annular discharge orifice was developed. The STUs were subjected to the slow movement test, the fast movement test and the simulated dynamic test. During the slow movement test, the resistance force does not exceed 10% of the nominal rated force; during the simulated dynamic test, the deflection between the point of zero load and the point of maximum load does not exceed 12 mm, and the deflection during the sustained load portion of the test does not exceed 12 mm; during the fast movement test, the force can maintain the nominal rated force. The validity of the mathematical model is verified by these testing, and the mathematical model can instruct the design of annular discharge orifice of STU.

Spray Characteristics of Swirl Effervescent Injector in Rocket Application: A Review

Injector is one of the vital devices in liquid rocket engine (LRE) as small changes in its configurations and design can result in significantly different LRE performance. Characteristics of spray such as spray cone angle, breakup length and Sauter mean diameter (SMD) are examples of crucial parameters that play the important role in the performance of liquid propellant rocket engine. Wider spray cone angle is beneficial for widespread of fuel in the combustion chamber for fast quiet ignition and a shorter breakup length provides shorter combustion chamber to be utilized and small SMD will result in fast and clean combustion. There are several mechanisms of liquid atomization such as swirling, e.g. jet swirl atomization or introducing bubbles into the liquid and effervescent atomization. Introducing a swirl component in the flow can enhance the propellant atomization and mixing whereas introducing bubbling gas directly into the liquid stream inside the injector leads to finer sprays even at lower injection pressures. This paper reviews the influence of both operating conditions and injector internal geometries towards the spray characteristics of swirl effervescent injectors. Operating conditions reviewed are injection pressure and gas-to-liquid ratio (GLR), while the injector internal geometries reviewed are limited to swirler geometry, mixing chamber diameter (dc), mixing chamber length (lc), aeration hole diameter (da), discharge orifice diameter (do) and discharge orifice length (lo).

An Experimental Investigation on the Effect of Various Swirl Atomizer Orifice Geometries on the Air Core Diameter

Liquid atomization is a process of changing the liquid into small droplets. There are many applications which are related to liquid atomization including fuel injection in combustion systems and also in agricultural sprays. In pressure swirl atomizer, the liquid is injected into the atomizer through tangential port and a swirling motion is formed inside the swirl chamber. In high strength of swirling motion, an air core will be visible inside the atomizer. The liquid is then discharged from the orifice to form a spray which breaks up the liquid into small droplets. The objective of this research is to investigate the effect of various orifice geometries on the air core diameter. The injection pressure was varied in the range of 2 to 8 bar and water was used as the working fluid. Experiment data shows that the air core diameter increases as the injection pressure increased, regardless the discharge orifice diameter and discharge orifice length. It also found that the air core diameter increases as the discharge orifice length decreases and the discharge orifice diameter increases.

The possibilities of droplet spectrum regulation at application of plant protection products

Verification of the possibilities of a droplet spectrum regulation due to the change of working pressure, as well as the change of the size of the discharge orifice of a nozzle, was undertaken in laboratory conditions by measurement of the size of a droplet spectrum of the applied liquid. Selected types of low drift nozzles &ndash; Albuz AVI 025, Lechler ID 120, Lechler IDK 120-05, Lechler IDN 120-025, TurboDrop 03, Hardi INJET 02, Hardi B JET 02, Hardi LD 02<br />and a flat fan nozzle Hardi ISO F 02-110 &ndash; underwent the measurement. The measurement of droplet spectrum was carried out at the nozzle&rsquo;s working height of 500 mm, and at working pressures of 0.1, 0.2, 0.3, 0.5 and 0.7 MPa. A laser measure equipment was used to measure the droplet spectrum of liquid.