Spraying of Viscous Liquids: Influence of Fluid-Mixing Mechanism on the Performance of Internal-Mixing Twin-Fluid Atomizers

The thermal usage of liquid fuels implies their combustion, which is a process strongly influenced by the performance of the atomizer, which disrupts the fuel into drops of the required sizes. The spray quality of the twin-fluid atomizers with internal mixing (IM-TFA) is primarily influenced by the two-phase flow pattern inside the mixing chamber. We studied the performance of the four types of the IM-TFA nozzles by the optical diffraction system (Malvern Spraytec) to answer the question of how the mixing chamber design influences the spray quality at low atomizing gas consumption. We tested the effervescent atomizer in outside-in-liquid (OIL) and outside-in-gas (OIG) configurations, the Y-jet nozzle and new nozzle design, and the CFT atomizer when spraying model liquids with the viscosities comparable to the common fuels (μ=60and143 mPa· s). We found that the effervescent atomizer performance was strongly influenced by the configuration of the inlet ports. Although the OIL configuration provided the best spray quality (D32 = 72 μm), with the highest efficiency (0.16%), the OIG nozzle was characterized by unstable work and poor spray quality. Both the devices were sensitive to liquid viscosity. The Y-jet nozzle provided a stable performance over the liquid viscosity spectrum, but the spray quality and efficiency were lower than for the OIL nozzle. Our findings can be used to improve the performance of the common IM-TFA types or to design new atomizers. The results also provide an overview of the tested atomizers’ performances over the wide range of working conditions and, thus, help to define the application potential of the tested nozzle designs.

Experimental Characterization of a Liquid Jet Emanating From An Effervescent Atomizer

The study focuses on experimental characterization of the primary atomization associated with an effervescent atomizer. Unlike the existing designs available in the literature that inject air perpendicular to the liquid flow direction, the present atomizer design utilizes coflowing air configuration. In doing so, the aerodynamic shear at the liquid–gas interface create instability and enhance the subsequent jet breakup. Both integrated and intrinsic properties of the liquid jet were extracted by utilizing high-speed flow visualization techniques. The integrated property consists of breakup length, while the intrinsic property involves primary and intermediate breakup frequencies. The primary instability is characterized by low-frequency sinusoidal mode, whereas the intermediate instability consists of high-frequency dilatational mode. Dimensionless plots of these parameters with Weber number ratio leads to a better collapse of data, thereby generating appropriate universal functions. The combined diagram of frequencies converge with increasing relative velocity. This may be due to the dominance of energy consuming sinusoidal wave as the aerodynamic shear increases.

Unsteady Behaviour of the Effervescent Atomizer

The effervescent atomizer is a well-established type of the twin-fluid nozzle with internal mixing of fluids. It is popular for the ability to process highly viscous liquids, such as liquid fuels, into a fine spray with low gas consumption. This study aims to investigate the performance of the effervescent nozzle when spraying the liquids with a viscosity up to 308 mPa·s. The working parameters of the nozzle were defined by the mass flows ratio of the gas to the liquid (GLR =2.5 to 20 %) and the gas pressure at the nozzle inlet (Δp = 0.14 MPa). The spray quality was investigated by the laser diffraction system, measuring the spray drop sizes. The investigated nozzle was able to atomize all of the model liquids. However, the liquid viscosity increase led to the need to operate the nozzle with the larger gas consumption. The minimum GLR for the spraying of the liquid with the viscosity 308 mPa·s was 10 %, while the less viscous liquid (60 mPa·s) was processed with the GLR = 2.5 %. It was observed that the spray quality was, at the low GLRs, lowered by unstable nozzle work, caused by the presence of the plug flow in the mixing chamber of the atomizer.

Effect of the two-phase hybrid mode of effervescent atomizer on the atomization characteristics

In this paper, the atomization characteristics of an effervescent atomizer were investigated. The velocity, Sauter Mean Diameter (SMD) and atomization cone angle of the droplets were measured using the Phase Doppler Analyzer (PDA) to discuss the effect of different design parameters. The results showed that the atomization was unstable at a small Gas-Liquid Rate (GLR) while the atomization proved gradually by increasing the GLR. The optimal atomization region was at a GLR=0.1. In the atomization process, there existed a typical velocity distribution for the swirl atomizer. The design parameters of atomizer provided a great influence on the Sauter Mean Diameter (SMD) and atomization cone angle. The experiment results showed that some droplets had negative velocities.