Atomization Behavior of Single Droplet Impinged on a Surface Oscillating with Ultrasonic Frequency(2nd Report, Effect of Physical Properties on Liquid Atomization)

( Masataka Arai ),( Akira Ishii ),( Masahiro Saito ) 한국액체미립화학회 2005 한국액체미립화학회 학술강연회 논문집 Vol.2005 No.-

Atomization behavior of a single droplet impinged on surface oscillating with ultra-sonic frequency of 20 kHz was investigated as a new method of fine-spray formation. Distilled water, ethanol and 50-80wt% glycerin solution were used as the test liquids to find the effects of viscosity and surface tension on ultra-sonic atomization. The amplitude of oscillation A and the droplet volume Vd were changed between A =25-125μm, Vd = 4-20 mm3 respectively. As the result, it was found that a fine spray was formed after the droplet impingement when the amplitude was smaller than A =50μm, while ligament and large droplets were formed at larger amplitude than A =50μm. The SMD of the spray after impingement was about D32=70μm when the amplitude was small, but the SMD became large with increase of the amplitude. Also, at low amplitude of A =25μm, the surface energy of spray after impingement increased remarkably compared with that of droplet before impingement. On the contrary, at amplitude of A >50μm, the kinetic energy after impingement has exceeded the surface energy. Namely, the oscillation energy was acted for rebounding of droplet rather than the atomization of droplet. The atomization efficiency decreased exponentially with increasing the amplitude of oscillation independent of the physical properties of test liquids. Thus, the low amplitude of oscillation could allow fine atomization by the disintegration of liquid film after the droplet impingement.

Atomization Improvement of a Liquid Jet with Wall Impingement and its Application to a Jet Engine Atomizer

Shiga, Seiichi The Institute for Liquid Atomization and Spray Sys 2006 한국액체미립화학회지 Vol.11 No.3

In the present study, capability of improving the liquid atomization of a high-speed liquid jet by using wall impingement is explored, and its application to a jet engine atomize. is demonstrated. Water is injected from a thin nozzle. The liquid jet impinges on a wall positioned close to the nozzle exit, forming a liquid film. The liquid film velocity and the SMD were measured with PDA and LDSA, respectively. It was shown that the SMD of the droplets was determined by the liquid film velocity and impingement angle, regardless of the injection pressure or impingement wall diameter. When the liquid film velocity was smaller than 300m/s, a smaller SMD was obtained, compared with a simple free jet. This wall impingement technique was applied to a conventional air-blasting nozzle for jet engines. A real-size air-blasting burner was installed in a test rig in which three thin holes were made to accommodate liquid injection toward the intermediate ring, as an impingement wall. The air velocity was varied from 41 to 92m/s, and the liquid injection pressure was varied from 0.5 to 7.5 MPa. Combining wall impinging pressure atomization with gas-blasting produces remarkable improvement in atomization, which is contributed by the droplets produced in the pressure atomization mode. Comparison with the previous formulation for conventional gas-blasting atomization is also made, and the effectiveness of utilizing pressure atomization with wall impingement is shown.

ATOMIZATION AT ULTRA-LOW LIQUID FLOW RATE USING NOVEL INJECTOR

( Mohammed Asad ),( Hrishikesh Gadgil ),( Sudarshan Kumar ) 한국액체미립화학회 2017 한국액체미립화학회 학술강연회 논문집 Vol.2017 No.-

Efficient atomization and evaporation at ultra-low flow rates is an additional challenge for small-scale combustion application since the atomization efficiency deteriorates with decreasing liquid flow rate. Experimental study at ultra-low liquid flow rate (5 - 150 mlph) unveiled the three distinct atomization regimes while air flow rate increases from 0.5 to 5 slpm. For a given ultra-low liquid flow rate, significant shift in injector characteristic was observed with increase in air flow rate; from bubble bursting to weak spray and finally at high air to liquid ratio, recirculation of atomizing air into a liquid tube gives fully developed spray. Injector is designed such that it allows co-flow air to flow back into a liquid tube. Internal flow analysis on Plexiglas injector replica shows that atomization regimes exist due to distinct two phase flow interaction inside the injector. Current study shows that critical air to liquid ratio at which air back flow triggers, decreases as liquid flow rate increases from 5 to 150 mlph. In weak spray regime, atomization occurs through prompt mode of atomization. While two phase slug flow formation inside the liquid tube leads to fine atomization in fully developed spray regime. Shadowgraphy experimental results validate the larger droplet in weak spray regime and fine atomization in fully developed spray regime due to formation of two phase slug flow. A proposed theoretical correlation shows that droplet size (SMD) is only function Reynolds number, Weber number, air to liquid ratio and injector design.

Effects of the Geometry of an Injector on the Atomization and Combustion Characteristics Using a Jet Engine Fuel Injector with Wall Impingement

( Satoshi Yamamura ),( Nobuaki Motegi ),( Mikiya Araki ),( Hideshi Yamada ),( Hisao Nakamura ),( Seiichi Shiga ) 한국액체미립화학회 2010 한국액체미립화학회 학술강연회 논문집 Vol.2010 No.-

Effects of the geometry of a jet engine fuel injector with wall impingement on the atomization and combustion characteristics are investigated. The atomization characteristics were evaluated by mean droplet size (SMD) obtained by a light scattering technique (LDSA) under atmospheric condition. Combination of pressure atomization with air-blasting gives remarkable improvement of the atomization. The effect of droplet size and spray dispersion on the combustion characteristics are also investigated experimentally. Results showed that SMD decreased with the decrease in the nozzle diameter D. Spray dispersion became better with the decrease in the D. EI(NOx) decreased with the decrease in the D. Spray dispersion became worse with the decrease in N. EI(NOx) decreased with the increase in N. The relationship between the rate of decrease in SMD and the rate of decrease in EI(NOx) was defined and was verified to be useful. According to the result of the effect of nozzle number N on the atomization and combustion characteristics, it is shown that the dispersion is more important than the atomization.

GENERATION AND CHARACTERIZATION OF NANO SPRAY USING EHD NOZZLE

Koji TERASHIMA,Wamadeva BALACHANDRAN 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.10

The aim of this research is to generate and characterize nano-spray by conejet type ElectroHydro Dynamic atomization. Sprays produced by various nozzle types were observed under different operating conditions. Although it is relatively easy to produce very fine jet and drops with using insulating liquid such as Con oil, Ethanol etc., compared to conducting liquid like water, de-ionized-water is used as sample liquid in this research because it is too small to characterize insulating liquid spray. This is mainly because of the difference of conductivity and hence difference of charge relaxation tim e. It is possible to make steady con며et water spray, however, stable conejet atomization condition was very small. Compared to stable conejet atomization condition, quasi-stable conejet like atomization condition was large. In this case, the tip of the jet vibrates at very high speed causing the water jet breaks up, thus a mixture of very large as well as fine drops was produced during the short period of atomization. This problem could be minimized and even overcome by optimizing the size and the design of the nozzle. In quasi-steady condition, the jet diameter close to the breakup point was estimated to be less than 1㎛. In this condition, the drops generated are estimated to be in the submicron range.

Characteristics of Twin-Fluid Micro-Atomizer with Internal Mixing Mechanisms

( Muh Rong Wang ),( K. H. Yang ),( J. S. Chiu ),( Deng Sang Lai ),( T. S. Leu ),( Sheng Chih Shen ) 한국액체미립화학회 2005 한국액체미립화학회 학술강연회 논문집 Vol.2005 No.-

The twin-fluid atomizer has three micro channels fabricated via MEMS bulk micro-machining processes, one for the liquid supply and two for introducing the atomization gas. The effects of the length scale of the micro-channels on the atomization performance are investigated. The orifice hydraulic diameter (dH) of the micro atomizer is 45μm. Malvern Insitec RT-Sizer is used to measure the particle size. Results show that the twin-fluid micro-atomizer with internal mixing mechanisms can produce fine spray with Sauter Mean Diameter of 5μm under the gas pressure of 5kg/cm2 and liquid flow rate of 0.1ml/min, a performance better than the micro atomizers reported in the literature. Flow visualization through a microscope shows that the micro-spray is unstable when the two impinging gas flows are staggered inside the atomizer. The micro-spray began to twist by these two impinging gas flows when the gas pressure goes up to 2 kg/cm2. The twisting angle and the cone angle of the spray remain constant when the gas pressure is more than 3 kg/cm2. Significant decrease in the particle size takes place when the gas pressure is more than 4kg/cm2. The atomization efficiency of the twin-fluid micro-atomizer with internal mixing mechanism is several times higher than other type of twin-fluid atomizers.

Key Mechanisms of the Effect of Atomization on Lean Blow-Out Limits of Aero Engines

Xiwei Wang,Yong Huang 한국항공우주학회 2023 International Journal of Aeronautical and Space Sc Vol.24 No.2

The appearance of the lean blow-out (LBO) will seriously threaten the aircraft from safety. For an aero engine using liquid fuel, the atomization characteristics such as mean droplet size (SMD), spray pattern and initial droplet velocity will impact the combustion performance. In this paper, the influence of atomization characteristics on flame stability is studied by using two types of swirlers and nine atomizers. Data from relevant literature are also cited for analysis. The experimental results show that the structure of the swirler is the main factor that determines the spray spatial distribution. The flame pattern of the combustors with the same swirler is similar. The relationship between the LBO limit and the atomization characteristics is derived in this paper. Compared with the Lefebvre’s relation that only considers SMD, the correlation factor of the relation between the atomization characteristics and the LBO limit in this paper is increased from 0.2496 to 0.836. Further analysis shows that the influence of atomization characteristics on LBO performance can be divided into two aspects. On the one hand, the different atomization affects the performances of the spray flame. Among these performances, the minimum heat release required to maintain the flame corresponds to the ideal LBO limit. On the other hand, the SMD and initial droplet velocity affect the combustion efficiency, that is, the degree of the combustion close to the ideal LBO limit. Considering the influence of the above two aspects on LBO performance, the actual LBO limit can be obtained.

Numerical Study on Fuel Atomization in a Coal-Fueled Engine

Choi, G. H. 啓明大學校 産業技術硏究所 1997 産業技術硏究所 論文報告集 Vol.19 No.2

A cycle simulation for a coal-fueled, internal combustion engine was modified and used to investigate the role of fuel atomization on the ignition and combustion processes. Four different atomization models were considered for this work. These included : (1) separate droplets and particles being formed ; (2) concentric single or agglomerate particles in each droplet ; (3) multiple particles in each droplet without agglomeration ; and (4) initial multiple particles in a droplet with subsequent secondary atomization. For this work the secondary atomization was assumed to occur at the point when 50 percent of the liquid by volume was vaporized. The engine parameters and operating conditions were chosen to be representative of a locomotive type engine operative at 1050rpm. The major conclusions of this work include : (1) the highest peak thermal efficiency for different atomization models was similar to each other; (2) the particle agglomeration worsened ignition qualities and lowered peak indicated thermal efficiencies; (3) concentric particles inside droplets led to long ignition delay times : and (4) secondary atomization allowed faster burnout yielding higher efficiency. Overall, atomization was identified as an important process which could significantly impact both the ignition and combustion processes.

Fundamental Study on Electrostatic Atomization of Biofuel/Water Emulsion

( Chien-hua Fu ),( Osamu Imamura ),( Kazuhiro Akihama ),( Hiroshi Yamasaki ) 한국액체미립화학회 2017 한국액체미립화학회 학술강연회 논문집 Vol.2017 No.-

This paper reports the experimental investigation of electrostatic atomization of BDF/water emulsion. Biofuel, such as Bio Diesel Fuel (BDF), is expected as the alternate fuel because of its carbon-neutral characteristics. In the process of making the biofuels, biofuels include water and the separation energy cost is relatively high. From this viewpoint, it is expected that the water in the biofuel is utilized in a positive manner. Biofuel and water mixture usually have large electric conductivity in comparison with hydrocarbons and it is possible to control of atomization using the electrostatic energy. In addition, if the droplets and spray are charged, the spray shape and flame pattern could be controlled to enhance the combustion and to reduce the heat loss to the wall. From this background, the paper mainly is focused on the electrostatic atomization of the BDF/water mixture. For the comparison, n-hexadecane is used as a reference fuel. The mixture fraction of water is the parameter of the fuel. To keep the stable mixture, surface active agent was added in the tested fuels. The viscosity of some tested fuel was high and the characteristics of non-Newtonian viscosity were researched prior to atomization experiments. The thin capillary to inject the fuel and wire netting over the capillary are used as electrodes and direct current voltages are applied to the electrodes. The fuel is pushed by the pressurized nitrogen and injected to the air through the capillary. As the results, fraction of water affects the onset of mode change, such as dripping, spindle, cone-jet etc. Droplets diameters and droplets velocity were measured from the video images and the electric charge distribution was discussed to understand the electrostatic atomization.

Characterization of shear and extensional rheology of fibre suspensions prior to breakup and atomization

( Siti N. M. Rozali ),( A. H. J. Paterson ),( J. P. Hindmarsh ),( Lee M. Huffman ) 한국액체미립화학회 2017 한국액체미립화학회 학술강연회 논문집 Vol.2017 No.-

Spray drying of fruit juices from liquid to powder is desirable as the powders are easier to handle, especially for storage and transportation. Previous studies have shown the potential use of pomace fibres as a drying aid during spray drying. The main attraction of this drying aid is that the pomace fibres are originally derived from the fruit itself. However, the addition of micro-sized fibres to fruit juices is expected to affect the rheology and subsequent atomization behaviour during the spray drying process. This study focuses on the determination and characterization of the behaviour of juice-fibre suspensions inside the nozzle, to ensure a high efficiency of powder production by enabling good atomization of the suspensions. Rheology or behaviour of the juice-fibre suspensions provides an insight into the limitations that will be faced during atomization, and this finding will assist in choosing the best nozzle design that can overcome the limitations introduced by the fibre particles thus resulting in successful atomization. Juice-fibre suspensions are expected to exhibit shear thinning behaviour with a significant extensional viscosity that might limit the atomization if simple pressure nozzles are to be used. Two types of flow fields present inside the nozzle or during the atomization are shear and extensional fields. A commercial capillary rheometer is used to characterize the shear behaviour while a portable extensional rheometer has been built to study the extensional behaviour. Methods and equipment will be presented along with the initial results.