Breakup Of Liquid Column Research Articles

Direct microscopic image and measurement of the atomization process of a port fuel injector

The main objective of this study is to observe and investigate the phenomena of atomization, i.e. the fuel break-up process very close to the nozzle exit of a practical port fuel injector (PFI). In order to achieve this objective, direct microscopic images of the atomization process were obtained using an ultra-high-speed video camera that could record 102 frames at rates of up to 1 Mfps, coupled with a long-distance microscope and Barlow lens. The experiments were carried out using a PFI in a closed chamber at atmospheric pressure. Time-series images of the spray behaviour were obtained with a high temporal resolution using backlighting. The direct microscopic images of a liquid column break-up were compared with experimental results from laser-induced exciplex fluorescence (LIEF), and the wavelength obtained from the experimental results compared with that predicated from the Kelvin–Helmholtz break-up model. The droplet size diameters from a ligament break-up were compared with results predicated from Weber's analysis. Furthermore, experimental results of the mean droplet diameter from a direct microscopic image were compared with the results obtained from phase Doppler anemometry (PDA) experimental results. Three conclusions were obtained from this study. The atomization processes and detailed characterizations of the break-up of a liquid column were identified; the direct microscopic image results were in good agreement with the results obtained from LIEF, experimental results of the wavelength were in good agreement with those from the Kelvin–Helmholtz break-up model. The break-up process of liquid ligaments into droplets was investigated, and Weber's analysis of the predicated droplet diameter from ligament break-up was found to be applicable only at larger wavelengths. Finally, the direct microscopic image method and PDA method give qualitatively similar trends for droplet size distribution and quantitatively similar values of Sauter mean diameter.

EFFECTS OF CANTED INJECTION ANGLES ON THE SPRAY CHARACTERISTICS OF LIQUID JETS IN SUBSONIC CROSSFLOWS

The effects of variably angled injection characteristics such as liquid column trajectory and liquid column breakup length have been experimentally studied in liquid jets injected into subsonic crossflow. The fuel injection velocity and injection angle were varied to provide jet operation conditions. The pulsed shadowgraph photography with high resolution and planar liquid laser induced fluorescence measurements were used to determine the liquid column trajectory and liquid column breakup length of angles of spray in a subsonic crossflow of the airstream. The main objectives of this research are to obtain the empirical formula of the liquid column trajectory and breakup length when the injection angle is <90 deg, and these results are compared to previous results. Also in this study, the empirical formula of the trajectory in the liquid column region by the reverse injection angle of subsonic airflow was derived. As a result, this research has shown that liquid column trajectories and liquid column breakup lengths were spatially dependent on airstream velocities, fuel-injection velocities, various injection angles, and normalized injector exit diameters. Furthermore, the empirical formulas of liquid column trajectories and breakup length have different drag coefficient results between forward injection and reverse angle injection in subsonic crossflow.

아음속 수직분사제트에서 분사각도 영향에 대한 분무특성 연구

본 연구에서는 횡단류 아음속유동장에서 연료가 여러 분사각도를 가지고 수직 분무시 나타나는 액주영역의 궤적과 분열지점에 관한 연구를 수행하였다. 직접 사진촬영 방법과 평면레이저유도형광(PLLIF) 기법으로 정방향 분사각도의 분무에서 액주영역의 궤적식과 분열지점까지의 거리에 대한 경험식을 도출하여 기존 연구결과와 비교 분석하고 대향분사의 액주 궤적식과 분열지점까지의 거리에 대한 경험식을 도출하였다. 실험을 통하여 액주영역의 궤적과 분열지점까지의 거리는 분사차압, 공기의 유속, 인젝터 지름 크기, 분사각도에 의하여 결정됨을 확인하였다. The liquid column trajectory and column breakup length characteristics have been experimentally studied in angled jets injected into subsonic crossflow. Pulsed shadowgraph photography and Planar Liquid Laser Induced Fluorescence measurements were used to determine the angled effects. And the main objectives of this research are to get a empirical formula of liquid column trajectory and breakup length with below the <TEX>$90^{\circ}$</TEX> degree injection angle conditions, and were compared with previous results. It was also found that the empirical formula, which reversed injection conditions of air stream. As the result, This has been shown that liquid column trajectories and column breakup length were spatially dependent on various injection angle, normalized injector exit diameter, air-stream and fuel injection velocity. Furthermore, the empirical formula of liquid column trajectories and breakup length has been some different of drag coefficient results between normal angled injection and reversed injection in subsonic crossflow.

Effects of Pulse Voltage on the Droplet Formation of Alcohol and Ethylene Glycol in a Piezoelectric Inkjet Printing Process with Bipolar Pulse

The dynamics of droplet formation of liquid in a piezoelectric inkjet printing process with bipolar pulse and drop-on-demand (DOD) mode is investigated in this study. Two liquids with different viscosities and surface tension coefficients; alcohol and ethylene glycol, are studied. The effects of pulse voltage on the droplet formation are also examined. A piezoelectric actuated inkjet printhead with a nozzle orifice of 30 mm in diameter is employed to conduct the investigations at room temperature (25 � C). The complex morphologies of the droplets during their formation, which include ejection and stretching of liquid, contraction of liquid column, pinch-off of liquid column from nozzle exit, breakup of liquid column into primary droplet and possible satellites, and combination of primary drop and satellites, are demonstrated. The droplet size is in the range of 23–37 mm. The investigations also show a workable pulse voltage range; between 28 and 40 volts, exists for the droplets to be smoothly generated and ejected for alcohol where viscosity and surface tension coefficient are smaller. The range is between 30 and 50 volts for ethylene glycol. Within this workable voltage range, one single droplet for each pulse can be achieved with lower voltage. For the intermediate voltage, two droplets are generated initially and collide into one during the flying stage. For the higher voltage, multiple droplets are formed without recombination. It is also found that the velocities of the main droplet and satellite droplet in the different voltage ranges are responsible for whether the multiple initial droplets can be recombined. [doi:10.2320/matertrans.MRA2007217]

Primary Breakup of Turbulent Round Liquid Jets in Uniform Crossflows

An experimental investigation of the deformation and breakup properties of turbulent round liquid jets in uniform gaseous crossflows is described. Pulsed shadowgraph and holograph observations were obtained for turbulent round liquid jets injected normal to air crossflow in a shock tube. Crossflow velocities of the air behind the shock wave relative to the liquid jet were subsonic (36-90 m/s) and the air in this region was at normal temperature and pressure. Liquid injection was done by a pressure feed system through round tubes having inside diameters of 1 and 2 mm and length-to-diameter ratios greater than 100 to provide fully developed turbulent pipe flow at the jet exit. Test conditions were as follows: water and ethyl alcohol as test liquids, crossflow Weber numbers based on gas properties of 0-282, streamwise Weber numbers based on liquid properties of 1400-32,200, liquid/gas density ratios of 683 and 845, and jet exit Reynolds numbers based on liquid properties of 7100-48,200, all at conditions in which direct effects of liquid viscosity were small (Ohnesorge numbers were less than 0.12). Measurements were carried out to determine conditions required for the onset of breakup, ligament and drop sizes along the liquid surface, drop velocities after breakup, liquid column breakup as whole, rates of turbulent primary breakup, and liquid column trajectories. Phenomenological theories proved to be quite successful in interpreting and correlating the measurements.

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.

325 液体微粒化メカニズムに関する一体型シミュレーションと可視化(J11-2 流体情報学と可視化(2),J11 流体情報学と可視化,2005年度年次大会)

The 2-D and 3-D structure of liquid atomization behavior is numerically investigated and vizualized by the new type of integrated simulation technique. The present CFD analysis is focusing on the consecutive breakup of liquid column, formation of liquid film and droplets at the exit section of nozzle outlet. The governing equations for high-speed spray nozzle flow based on the LES-VOF model are presented, and then an integrateed parallel simulation are performed to clarify the detailed atomization process and to clarify the atomized droplets-gas two-phase flow characteristics.

Liquid breakup at the surface of turbulent round liquid jets in still gases

An experimental study of liquid column breakup lengths and turbulent primary breakup properties at the surface of turbulent round liquid jets in still air at standard temperature and pressure is described. Jet exit conditions were limited to non-cavitating water and ethanol flows, long length/diameter ratio (greater than 40:1) constant-diameter round injector passages, jet exit Reynolds numbers of 5000–200,000, jet exit Weber numbers of 235–270,000 and liquid/gas density ratios of 690 and 860, at conditions where direct effects of viscosity were small (e.g., liquid jet Ohnesorge numbers were smaller than 0.0053). Three liquid column breakup modes were observed, as follows: a weakly turbulent Rayleigh-like breakup mode observed at small jet exit Weber and Reynolds numbers, a turbulent breakup mode observed at moderate jet exit Weber numbers, and an aerodynamic bag/shear breakup mode observed at large jet Weber numbers. The turbulent primary liquid column breakup mode was associated with conditions where drop diameters resulting from turbulent primary breakup along the liquid surface were comparable to the diameter of the liquid column itself. The bag/shear liquid column breakup mode was observed when liquid turbulence caused large deformations of the liquid column so that portions of it were in a gaseous cross flow; this resulted in bag or shear liquid column breakup, very similar to the breakup of non-turbulent liquid jets in gaseous cross flow. Mean streamwise drop velocities after breakup were comparable to mean streamwise velocities within the jet whereas mean cross stream drop velocities after breakup were comparable to cross stream velocity fluctuations within the liquid. Rates of primary breakup at the liquid surface are reported as surface efficiency factors (the fraction of the maximum possible cross stream drop liquid flux at the surface based on the mean relative cross stream velocity of the drops at the surface and the liquid density). The resulting surface efficiency factors varied from small values near the onset of liquid surface breakup to values of the order of unity as conditions near breakup of the liquid column as a whole were approached.

Relaxation and breakup of a cylindrical liquid column

Instability of capillary wave and breakup of a square cylindrical liquid column during its relaxation have been investigated numerically by simulating three-dimensional Navier-Stokes equations. For this investigation a computer code based on volume-of-fluid (VOF) method has been developed and validated with published experimental results. The result shows that the agreement of numerical simulation is quite well with the experimental data. The code is then used to study the capillary wave and breakup phenomena of the liquid column. The investigation shows the underlying physics during relaxation of the square cylindrical liquid column, illustrates the formation and propagation of capillary wave, and breakup processes. The breakup behavior for the present configuration of the liquid column shows some significant differences from those predicted by conventional jet atomization theories. The formation of capillary wave is initiated by the surface tension on the sharp edge of the square end of the cylinder and the propagation of the wave occurs due to the effect of surface tension force on the motion of the fluid. The propagation of capillary wave to the end of liquid column causes a disturbance in the system and makes the waves unstable which initiates the breakup of the liquid column. The characteristics of the capillary wave show that the amplitude of the swell grows faster than the neck of the wave and that of the tip wave grows much faster than the other waves. The velocity of the liquid particle is dominated by the pressure in the liquid column. Keywords: Instability; Continuum surface force; Liquid disintegration; Capillary wave; Surface tension; VOF method doi:10.3329/jme.v39i2.1847 Journal of Mechanical Engineering, Vol. ME39, No. 2, Dec. 2008 57-64