EÚ-odbor termomechaniky a techniky prostředí

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Air–liquid interactions in a pressure-swirl spray
(Elsevier, 2018-01-02) Jedelský, Jan; Malý, Milan; Del Corral, Noé Pinto; Wigley, Graham; Janáčková, Lada; Jícha, Miroslav
The energy transfer between a liquid hollow cone spray and the surrounding air has been studied using both imaging and phase-Doppler techniques. The spray was produced by a pressure-swirl atomizer discharging Jet A-1 fuel at inlet over pressures of dp = 0.5, 1.0 and 1.5 MPa into quiescent ambient air. The liquid exits the nozzle as a conical film which thins as it spreads and develops long- and short-wave sinusoidal instabilities with breakup occurring, at the length smaller than that predicted by the inviscid model, to form film fragments and ultimately droplets downstream the spray. The single shot imaging characterised the spray regions of near-nozzle flow, the breakup processes and the developed spray. The phase-Doppler system resolved the three components of velocity and size for the droplet flow as measured on radial profiles for four axial distances from the nozzle exit. A Stokes number, Stk, analysis of the droplets’ response times to the airflow time-scales showed that droplets < 5 µm followed the airflow faithfully and so were used to estimate the local airflow velocity. This allowed a comparison of both the droplet and airflow fields in terms of their mean and fluctuating velocity components to be made. The formation of the hollow cone spray and the interaction of the fragments and droplets with the air, through viscous drag, induce complex entrained airflows. The airflow was found to be highly anisotropic, fluctuating preferentially in the downstream direction, and spatially varying within three distinct spray regions. The air drag establishes a positive size–velocity correlation of droplets; their Stk reduces with axial distance and increases with droplet size and dp; so that Stk 1 for 20–40 µm droplets and the largest droplets (80–160 µm, Stk > 10) move ballistically. The spatially resolved mean and turbulent kinetic energies of the air and spectra of the droplet velocity fluctuations are detailed in the paper. These findings are relevant to scientists and engineers modelling the complex two-phase flows.
Effect of liquid preheating on high-velocity airblast atomization: From water to crude rapeseed oil
(Elsevier, 2019-04-01) Urbán, András; Malý, Milan; Józsa, Viktor; Jedelský, Jan
Airblast atomization is a suitable model platform to understand atomization physics since the atomizer geometry has an insignificant influence on the spray formation. Besides its theoretical relevance, this configuration is used in several practical applications ranging from healthcare to combustion. Presently, a plain-jet airblast atomizer has been investigated experimentally under atmospheric conditions at various atomizing pressures and liquid preheating temperatures. To cover a wide range of liquids by viscosity and surface tension, water, diesel oil, light heating oil, and crude rapeseed oil were atomized to evaluate the droplet size-velocity correlations when the spray is fully developed. Increasing the temperature of high-viscosity liquids prior to atomization improves the spray characteristics until their kinematic viscosity decreases to a certain value that is newly introduced as a limiting viscosity. Further preheating has a marginal effect on droplet size-velocity plots, and the spray becomes more homogeneous. Several SMD-estimating formulae were analyzed and improved to consider the effect of liquid preheating and to extend their range of validity. When the kinematic viscosity exceeded the limiting viscosity, the part containing the Weber number was corrected linearly by the preheating temperature. The coefficient of the Ohnesorge number was corrected by the inverse of the kinematic viscosity, without considering the limiting viscosity. The above results help to correct the SMD of atmospheric measurements to elevated liquid temperatures and to contribute to advanced atomization models for numerical software.
Spraying of viscous liquids: influence of the fluids mixing mechanism on the performance of the internal-mixing twin fluid atomizers
(MDPI, 2020-07-30) Mlkvik, Marek; Jedelský, Jan; Karbstein, Heike P.; Gaukel, Volker
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 (mu=60and143mPa center dot 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 mu m), 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.
Internal flow characteristics in scaled pressure-swirl atomizer
(Technical University Liberec, 2018-06-04) Malý, Milan; Sapík, Marcel; Jedelský, Jan; Janáčková, Lada; Jícha, Miroslav; Sláma, Jaroslav; Wigley, Graham
Pressure-swirl atomizers are used in a wide range of industrial applications, e.g.: combustion, cooling, painting, food processing etc. Their spray characteristics are closely linked to the internal flow which predetermines the parameters of the liquid sheet formed at the discharge orifice. To achieve a better understanding of the spray formation process, the internal flow was characterised using Laser Doppler Anemometry (LDA) and high-speed imaging in a transparent model made of cast PMMA (Poly(methyl methacrylate)). The design of the transparent atomizer was derived from a pressure-swirl atomizer as used in a small gas turbine. Due to the small dimensions, it was manufactured in a scale of 10:1. It has modular concept and consists of three parts which were ground, polished and bolted together. The original kerosene-type jet A-1 fuel had to be replaced due to the necessity of a refractive index match. The new working liquid should also be colourless, non-aggressive to the PMMA and have the appropriate viscosity to achieve the same Reynolds number as in the original atomizer. Several liquids were chosen and tested to satisfy these requirements. P-Cymene was chosen as the suitable working liquid. The internal flow characteristics were consequently examined by LDA and high-speed camera using p-Cymene and Kerosene-type jet A-1 in comparative manner.
Characterization of aerosol nebulized by Aerogen Solo mesh nebulizer
(EDP Sciences, 2020-11-18) Mišík, Ondrej; Malý, Milan; Cejpek, Ondřej; Lízal, František
Nebulizers are commonly used devices for inhalation treatment of various disorders. There are three main categories of medical nebulization technology: jet nebulizers, ultrasound nebulizer, and mesh nebulizer. The mesh nebulizers seem to be very promising since this technology should be able to produce aerosol with precisely determined particle size and is easy to use as well [1]. Aerosol generated from the mesh nebulizer Aerogen Solo was measured in this work. Particle size distribution with a mass median of aerodynamic diameter (MMAD) was determined by two different methods.

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