Twin-fluid Atomizer Research Articles

Air-Assisted Atomization at Constant Mass and Momentum Flow Rate: Investigation into the Ambient Pressure Influence With the Smoothed Particle Hydrodynamics Method

Abstract A twin-fluid atomizer configuration is simulated by means of the two-dimensional (2D) weakly compressible smoothed particle hydrodynamics (SPH) method and compared to experiments. The gas-to-liquid ratio (GLR), the momentum flux ratio, and the velocity ratio are set constant for different ambient pressures, which lead to different gaseous flow sections. The objectives of this study are (i) to investigate the effect of ambient pressure at constant global parameters and (ii) to verify the capability of 2D SPH to qualitatively predict the proper disintegration mechanism and to recover the correct evolution of the spray characteristics. The setup consists of an axial liquid jet of water fragmented by a coflowing high-speed air stream (Ug = 80 m/s) in a pressurized atmosphere up to 16 bar. The results are compared to the experiment and presented in terms of (i) mean velocity profiles, (ii) drop size distributions, and (iii) Sauter mean diameter (SMD) of the spray. It is found that there exists an optimal pressure to minimize the mean size of the spray droplets. Finally, two new quantities related to atomization are presented: (i) the breakup activity that quantifies the number of breakup events per time and volume unit and (ii) the fragmentation spectrum of the whole breakup chain, which characterize the cascade phenomenon in terms of probability. The breakup activity confirms the presence of the optimal pressure, and the fragmentation spectrum gives information on the type of breakup, depending on the ambient pressure.

Experimental investigation on the influence of system pressure on resulting spray quality and jet breakup applying pressure adapted twin-fluid nozzles

The present work aims for the isolated investigation of the influence of system pressure on spray quality of twin-fluid atomizers. An approach of pressure adapted nozzles was applied, allowing for constant mass flows, gas-to-liquid ratio as well as fluid velocities at the nozzle orifice independent of system pressure. Two Newtonian liquids featuring viscosities of 1 and 100 mPa · s were used, varying the system pressure from 1 to 16 bar for gas velocities of 60, 80 and 100 m·s−1. A phase doppler analyzer was applied for measurement of resulting drop size and velocity. Primary breakup morphology was detected by a high-speed camera. Two regions with different dependencies of spray quality on system pressure were identified. Applying pressure adapted nozzles while increasing system pressure, first results in a decrease of droplet size followed by an increase. A maximum of the dynamic pressure of the gas phase was determined at minimum droplet size, which is explained based on the theory of a free jet. The observations are underlined by images of the high-speed camera. Here, a change in breakup morphology from fiber type to a mixture of fiber type and non-axisymmetric Rayleigh type breakup at high system pressure was observed.

Effect of Crossflow on Atomizing Behaviors of Liquid Jet Injected from Twin-Fluid Atomizer

Effect of Crossflow on Atomizing Behaviors of Liquid Jet Injected from Twin-Fluid Atomizer

Observation of Internal Flows and Sprays of Twin-Fluid Atomizer

Observation of Internal Flows and Sprays of Twin-Fluid Atomizer

Examination on Fire Extinguishing Performance of Full Cone and Hollow Cone Twin-fluid Atomizers: Effects of Supply Gas and Water Mist

Examination on Fire Extinguishing Performance of Full Cone and Hollow Cone Twin-fluid Atomizers: Effects of Supply Gas and Water Mist

Spray-dried anti-Campylobacter bacteriophage CP30A powder suitable for global distribution without cold chain infrastructure.

Campylobacter jejuni is a leading cause of foodborne illness globally. In this study, a spray drying and packaging process was developed to produce a thermally-stable dry powder containing bacteriophages that retains biological activity against C. jejuni after long distance shipping at ambient temperature. Spray drying using a twin-fluid atomizer resulted in significantly less (p < 0.05) titer reduction than spray drying using a vibrating mesh nebulizer. The use of centrifugation and dilution of filtered bacteriophage lysate in the formulation step resulted in a significantly greater (p < 0.05) proportion of bacteriophages remaining active relative to use of no centrifugation and dilution. The spray-dried bacteriophage powder generated using leucine and trehalose as excipients was flowable, non-cohesive, and exhibited a high manufacturing yield. The powder retained its titer with no significant differences (p > 0.05) in biological activity after storage in suitable packaging for at least 3 weeks at room temperature and after ambient temperature shipping a total distance of approximately 19,800 km, including with a 38 °C temperature excursion. The bacteriophage powder therefore appears suitable for global distribution without the need for cold chain infrastructure.

A twin-fluid injector for FCC feed injection

In Fluidized Bed Catalytic Cracking (FCC) process, hydrocarbon feed undergoes vapour phase cracking in presence of hot regenerated catalyst to produce valuable products like LPG, Gasoline and Diesel. FCC feed injection system is most critical hardware component of FCC unit in order to get desired product yield by minimizing the undesirable dry gas and coke yield. Typically, twin-fluid nozzles (hydrocarbon and stream) are used to atomize the feed. In the present study, a twin-fluid injector, with an internal impactor to minimize the droplet size and velocity, is designed, developed and characterized. The performance of the feeding injector was evaluated using water and air as operating fluids and the droplet size and velocity were measured 150 mm downstream of the injector tip using a PDPA system for different water and air flow rates. The average droplet size (D32) showed an increase while the droplet velocity remained almost constant with the increase in the liquid flow rate for a given flow rate of air, consistent with the increase in droplet size with decreasing air-liquid ratio for twin–fluid atomizers. But, for a given liquid flow rate, the droplet SMD decreased and the droplet velocity increased with increasing airflow rate, which can be attributed to the increase in overall kinetic energy due to the increase in air flow rate. The flow rate of liquid was seen to be independent of air flow rate unlike conventional twin-fluid atomizers. The droplet size was found to be a function of ALR and the local volume flux of the droplets was found to be a function of the liquid flow rate.

First step towards atomization at ultra-low flow rates using conventional twin-fluid atomizer

The formation of a fine spray at ultra-low liquid flow rates remains a long lasting challenge that limits the use of liquid fuels in various science and engineering applications. This work demonstrates the spray formation for liquid flow rate nearly 25 times lower than those reported in the literature for similar studies. The experiments are carried out at liquid flow rates of 2.78–41.7 mg/s (2.78–41.7 µL/s) with air flow rate varying from 0.01 to 0.1 g/s (8.33–83.3 mL/s). This study reveals that for ultra-low liquid flow rates, air entrainment and development of slug bubble inside the liquid tube helps in the formation of a high shear zone, resulting in the formation of a uniform spray. Three spray regimes: (i) bubble bursting, (ii) weak spray, (iii) fully developed spray are observed with a gradual increase in air flow rate due to a distinct liquid-gas interaction inside the injector. A fine spray formation with Sauter Mean Diameter (SMD) ~ 32–76 μm was observed in fully developed spray regime. Coarser droplets with SMD greater than 200 μm were observed to form in the weak spray regime. A new SMD correlation in terms of governing parameters is proposed for fully developed spray regime. The analysis of the experimental results show that an atomization efficiency of 0.1% can be achieved for ultra-low flow rate conditions through the application of a flow-blurring atomization concept.

Twin-Fluid Atomized Spray Combustion of Straight Vegetable Oil at Elevated Pressures

The effect of the chamber pressure on combustion of a twin-fluid-atomized spray of straight vegetable oil (VO) in a swirl stabilized combustion system is experimentally studied. A system with high pressure capabilities was developed, and flame and emissions characteristics of VO are investigated at elevated pressures up to about 5 bars, different heat release rates (HRRs), and atomizing air to liquid ratios (ALR) by mass. An image analysis technique was developed to infer flame and soot characteristics from visual images acquired by a digital camera. An increase in the ALR resulted in improved combustion of VO, characterized by blue flames, lower CO and NOx emissions, and minimal soot formation. For a given fuel flow rate, an increase in the chamber pressure resulted in smaller volume flames with lower CO levels but higher NOx emissions. Compared to diesel, as pressure increased, straight VO flames produced lower NOx and more voluminous flames characterized by distributed combustion with less soot formation. Overall, straight VO could be atomized and combusted at elevated pressures using the twin-fluid atomizer of the present study, and the resulting VO flames exhibited less sensitivity to chamber pressure variations.

Dual-mode nonlinear instability analysis of a confined planar liquid sheet sandwiched between two gas streams of unequal velocities and prediction of droplet size and velocity distribution using maximum entropy formulation

Twin fluid atomizers utilize the kinetic energy of high speed gases to disintegrate a liquid sheet into fine uniform droplets. Quite often, the gas streams are injected at unequal velocities to enhance the aerodynamic interaction between the liquid sheet and surrounding atmosphere. In order to improve the mixing characteristics, practical atomizers confine the gas flows within ducts. Though the liquid sheet coming out of an injector is usually annular in shape, it can be considered to be planar as the mean radius of curvature is much larger than the sheet thickness. There are numerous studies on breakup of the planar liquid sheet, but none of them considered the simultaneous effects of confinement and unequal gas velocities on the spray characteristics. The present study performs a nonlinear temporal analysis of instabilities in the planar liquid sheet, produced by two co-flowing gas streams moving with unequal velocities within two solid walls. The results show that the para-sinuous mode dominates the breakup process at all flow conditions over the para-varicose mode of breakup. The sheet pattern is strongly influenced by gas velocities, particularly for the para-varicose mode. Spray characteristics are influenced by both gas velocity and proximity to the confining wall, but the former has a much more pronounced effect on droplet size. An increase in the difference between gas velocities at two interfaces drastically shifts the droplet size distribution toward finer droplets. Moreover, asymmetry in gas phase velocities affects the droplet velocity distribution more, only at low liquid Weber numbers for the input conditions chosen in the present study.

Smoothed Particle Hydrodynamics Simulation of an Air-Assisted Atomizer Operating at High Pressure: Influence of Non-Newtonian Effects

A twin-fluid atomizer configuration is predicted by means of the two-dimensional (2D) weakly compressible smooth particle hydrodynamics (SPH) method and compared to experiments. The setup consists of an axial liquid jet surrounded by a high-speed air stream (Ug ≈ 60 m/s) in a pressurized reactor, which is operated at up to 11 bar. Two types of liquid are investigated: a viscous Newtonian liquid (μl = 200 mPa·s) consisting of glycerol/water mixture and a viscous non-Newtonian liquid (μ1,apparent. ≈ 150 mPa·s), which is a carboxymethyl cellulose solution. Three-dimensional (3D) effects are taken into account in the 2D code by introducing: (i) a surface tension term, (ii) a cylindrical viscosity operator, and (iii) a modified velocity accounting for the divergence of the volume in the radial direction. The numerical results at high pressure show a good qualitative agreement with experiment, i.e., a correct transition of the different atomization regimes with regard to pressure, and similar dynamics and length scales of the generated ligaments. The propagation velocity of the Kelvin–Helmholtz (KH) instability is well predicted, but its frequency needs a correction factor to be globally well recovered for the Newtonian liquid. The Sauter mean diameter (SMD), calculated from the spray size distribution, shows similar trends of the reactor pressure dependency. The simulation of the non-Newtonian liquid at high pressure shows the same breakup regime with finer droplets compared to Newtonian liquids, and the simulation at atmospheric pressure shows an apparent viscosity similar to the experiment.

The concept design and study of twin-fluid effervescent atomizer with air stone aerator

The work presents effervescent atomizer with air stone aerator. The aerator used air stone AS30 by Tetratec. porous stone with fine pores gives small resistance and allow to use the full power of the aerator. Measurements of the pressure drop and droplets sizes and spray angle produced by an effervescent twin-fluid atomizer with air stone aerator were carried out using the microphotography method. The tests were conducted from 0.05 to 0.3(m3/h) and for liquid of 10 to 50 (l/h). The results showed that the drop of pressure increases with the rise of the gas flow rate and liquid flow rate. The discharge coefficient depends on the relation of the mass gas flow rate and the mass liquid flow rate. The spray angle increased with an increase in gas Reynolds number and with a decrease in liquid Reynolds number. Dimensionless equations were proposed that described the discharge coefficient and the spray angle. The obtained data is very important for atomizers designing, especially including some of twin-fluid atomizers.

Numerical Analysis of the Effects of Using Effervescent Atomization on Solution Precursor Thermal Spraying Process

The solution precursor thermal spraying (SPTS) process is used to obtain nano-sized dense coating layers. During the SPTS process, the in situ formation of nanoparticles is mainly dependent on combustion gas-temperature, gas-pressure, gas-velocity, torch design, fuel type, and Oxygen-Fuel (O/F) mixture ratios, precursor injection feeding ratio and flow rates, properties of fuel and precursor and its concentration, and the precursor droplets fragmentation. The focus of the present work is the numerical study of atomization of pure solvent droplets streams into fine droplets spray using an effervescent twin-fluid atomizer. For better droplet disintegration appropriate atomization techniques can be used for injecting the precursor in the CH-2000 high-velocity oxygen fuel (HVOF) torch. The CFD computations of the SPTS process are essentially required because the internal flow physics of HVOF process cannot be examined experimentally. In this research for the first time, an effervescent twin-fluid injection no...

Flameless Oxidation of liquid fuel oil in a reverse-flow cooled combustion chamber

This paper presents the experimental results on flameless oxidation of light fuel oil in a reverse-flow cooled combustion chamber. NOX and CO emissions as well as temperatures in the combustion chamber are used to determine combustion performance of the cold air flameless oxidation (FLOX®) burner. Five different twin fluid atomizers with varying spray angles between 0° and 80° and different bore diameters have been used and the influence of atomizing air pressure between 4 and 6 bar on the combustion performance was investigated. In the tests air stoichiometry ratios ranged from 1.1 to 1.9 and thermal inputs were varied between 50 and 150 kW.Results show that good combustion performance in flameless mode was achieved. Low NOX emissions combined with low CO emissions which meet strictest CO (according to DIN EN 267 class 3 burners, 60 mg/kWhth) and NOX regulations (according to 1. BImSchV, 110 mg/kWhth) were obtained at an air ratio of 1.1.

5-3 予蒸発を伴う灯油の二流体微粒化に関する基礎的研究((1)微粒子と微粒化,Session 5 燃焼・熱利用)

5-3 予蒸発を伴う灯油の二流体微粒化に関する基礎的研究((1)微粒子と微粒化,Session 5 燃焼・熱利用)

Low-pressure twin-fluid atomization: Effect of mixing process on spray formation

The present work comparably examines four different twin-fluid atomizers operated under the same operating conditions. Spray formation was examined by several approaches. The internal flow pattern was estimated using a simplified analytical approach, and the results were supported by the observation of the liquid discharge in the near-nozzle region. A high-speed back illumination was used for visualisation of the primary breakup. In the region of fully developed spray, the dynamics of droplets was studied using a phase-Doppler analyser (PDA). The information obtained from all methods was then correlated. Results show that the spray formation process depends mainly on the internal design of twin-fluid atomizer at low gas to liquid ratios (GLR). The amount of gas influences the character of the internal two-phase flow, a mechanism of the liquid breakup, droplet dynamics and a resulting drop size distribution. Differences among the atomizers are reduced with the increase in GLR. Moreover, it was shown that a certain mixing process can inherently create the annular internal flow which generates a stable spray characterized by relatively low mean droplet size.

The experimental studies on atomization for conical twin-fluid atomizers with the swirl motion phenomenon

Measurements of the pressure drop and droplets sizes and mean droplet size produced by conical twin-fluid atomizers with the swirl motion phenomenon were carried out using the microphotography method. Atomizing gas flow rates of up to 5.6.10−4[m3/s] and liquid flow rate up to 1.11.10−4[m3/s] were used. The effect of atomizer dimensions on spray parameters was studied using several geometries of conical atomizers. It has been shown that the pressure drop depends on gas and liquid flow rates and dimensions of atomizer. Additionally, the swirl motion inside of atomizer affects the spray quality. The empirical correlation for Euler number and Sauter mean diameter were proposed. The obtained data is very important for atomizers designing, especially including some of twin-fluid atomizers.

Empirical Correlation of the Primary Stability Variable of Liquid Jet and Liquid Sheet Under Acoustic Field

The investigation focuses on optimizing the length of wind-pipe that transmits acoustic energy from the compression driver to the cavity of twin-fluid atomizers. To accomplish this objective, the primary variable of stability, that is, the breakup length of liquid jet and sheet under acoustic perturbations has been experimentally characterized for a range of wind-pipe length and liquid velocity. The analysis considers liquid phase Weber number in the range of 0.7–8, and the results are compared with primary breakup data without acoustic perturbations. The range of Weber number tested belongs to Rayleigh breakup zone, so that inertia force is negligible compared to surface tension force. It shows the existence of unique stability functions based on dimensionless products up to an optimum wind-pipe length, which extends greater for liquid sheet configuration. The present results may find relevance in atomizer design that utilizes acoustic source to enhance liquid column breakup processes.

Influence of Working Parameters and Primary Breakup Conditions on the Quality of Twin-Fluid Atomizers Spray Quality

In this study we investigated four twin-fluid atomizers with different internal mixing mechanisms: Y-jet, outside in gas (OIG), outside in liquid (OIL) and CFT atomizers. The main goal was to relate the measured droplet sizes, characterized by the Sauter mean diameter (ID32), to the corresponding working regimes of atomizers and primary breakup conditions characterized by the criterion Dmax, estimated from critical Weber number of the primary breakup. For the OIL, OIG and CFT atomizers, the common relation of the primary breakup characteristics and normalized droplet sizes (ID32/Dmax) was found. As the Y-jet atomizer showed a different trend, which was related to the considerably lower Weber numbers of the near-nozzle flow, a change in the normalization criterion was necessary to obtain similar results as for other tested atomizers. The main benefit of presented results is the potential to predict spray droplet sizes entirely from primary breakup characteristics regardless of the atomizer’s design or the atomized liquid.

Comparison of Y-jet and OIL effervescent atomizers based on internal and external two-phase flow characteristics

Presented paper focuses on spraying of two viscous liquids (μ = 60 and 143 mPa·s) by two types of twinfluid atomizers with internal mixing. We compared the well-known Y-jet atomizer with the less known, “outside in liquid” (OIL), configuration of the effervescent atomizer. The required liquid viscosity was achieved by using the water-maltodextrin solutions of different concentrations. Both the liquids were sprayed at two gas inlet pressures (Δp = 0.14 and 0.28 MPa) and various gas-to-liquid ratios (GLR = 2.5%, 5%, 10% and 20%). The comparison was focused on four characteristics: liquid flow-rate (for the same working regimes, defined by Δp and GLR), internal flow regimes, Weber numbers of a liquid breakup (We) and droplet sizes. A high-speed camera and Malvern Spraytec laser diffraction system were used to obtain necessary experimental data. Comparing the results of our experiments, we can state that for both the liquids the OIL atomizer reached higher liquid flow-rates at corresponding working regimes, it was typical by annular internal flow and higher We in the near-nozzle region at all the working regimes. As a result, it produced considerably smaller droplets than the second tested atomizing device, especially for GLR < 10%.