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Prediction of the fate of inhaled fibres in human airways represents a significant challenge in comparison with spherical particles. There are several ways of computation ranging from a simplified approach assuming equivalent spheres with empirical corrections to sophisticated numerical solutions of momentum and rotations in three-dimensional flow. Each of these mathematical approaches has its area of application. However, their precision is still insufficient namely because of the lack of experimental data for validation. Especially data on the behaviour of fibres under transient flow in bifurcating channels is missing. This paper presents a description of the experimental setup for such measurement and statistically evaluated characteristics of the rotation and flips of micrometre-sized glass fibres. The results proved that there are significant differences in the rotations of fibres when compared to previously measured stationary flows.

Rotary atomization is used in a wide variety of fields, exploiting the external control option of the spray while no high-pressure fluid is needed. Most papers on rotary atomization deal with liquid jet breakup, while external spray characteristics are rarely evaluated; this is performed currently. The water spray was measured by a two-component phase Doppler anemometer. The optical setup requires a special measurement chamber to avoid spray deposition on the optical components. Therefore, the first goal was to find a proper filter that enables the removal of biased droplets by secondary flows. Since most droplets have a similar radial-to-tangential velocity ratio at each measurement point, i.e., scattering around a line, this was the first component of the best filter. The second component was the need for a positive radial velocity component. This filter efficiently removed droplets originating from alternative processes, increasing the R2 of the line fit. The physical soundness of this filter was checked by evaluating the effect of filtering on the angle of the velocity components of each droplet at a given measurement point. The proposed filter efficiently detected recirculation, a secondary effect of the measurement setup with less regular dataset shapes. Finally, the slope and intercept values of the fitted lines were evaluated and presented. The mean of the former followed the same trend irrespective of the rotational speed and the mass flow rate; it was principally dependent on the radial distance from the atomizer. The intercept showed a regular but less universal behavior. [ABSTRACT FROM AUTHOR]

A low-speed small-scale wind tunnel was designed for spray investigation under cross and co-flow conditions. Precisely defined profiles of mean velocity and turbulent intensity in the wind tunnel test section are crucial parameters for any rigorous flow study. Different velocity measurement techniques were used to evaluate the velocity and turbulent intensity profiles in the test section. Two non-intrusive techniques, Phase-Doppler Anemometry and Laser-Doppler Anemometry (PDA, LDA), and two intrusive techniques, Constant Temperature Anemometry (CTA) and pitot static tubes of S and L-type were applied. The velocity was measured in 19 equidistantly spaced positions in a centrally placed horizontal plane. The data were obtained for four different mean velocities in the test section (7, 14, 21, 28 m/s). Results of different measurement techniques were mutually compared, and repeatabilities and uncertainties of PDA and CTA measurements were assessed. Turbulent velocity spectra measured by the CTA were analysed. The effect of declination of the pitot static tubes (L-type and S-type) was briefly discussed and compared with an industrial velocity probe QuadraTherm® 640i In-Line Mass Flow Meter with a measuring range of 5–300 m/s. Velocity and declination of pitot static tubes were analysed only in the central point of the test section. The results show that a fully turbulent and uniform flow is developed 15 mm upstream the test section area. Mean velocity and turbulent intensity profiles obtained by different techniques are in a good agreement. Uncertainties of type B of PDA and CTA measurement method are below 5%. Turbulent intensity in the main stream is under 5%. Advantages and drawbacks of the presented measurement techniques were discussed. The PDA was found to be the most suitable measurement technique due to its precision and non–intrusive flow probing.

The need to reduce the energy demand of processes also creates pressure to make atomizers more efficient. A promising development path could be counterflow atomizers (CFA). An atomizer, or synonymously a nozzle, is a device that turns a liquid into a spray. The CFA is a twin-fluid type of atomizer because both the liquid and the atomizing gas are fed into it. Initial results suggest that CFA is capable of the same quality of atomization but using half the air mass flow rate compared to conventional twin-fluids atomizers when operated at identical inlet pressure. This means half the energy requirements with the same efficiency. This atomizer also shows a great promise in the atomization of highly viscous substances such as waste-based fuels and biomass oils. In CFA, the air expands twice; first, at the discharge from the air inlet canal into the mixing tube, and second, at the discharge from the atomizer to the surrounding atmosphere. Therefore, one of the main control parameters is the area ratio of the exit orifice and the air inlet canal. This study experimentally investigates the effect of this ratio on the spray quality for two different CFA atomizers using Phase Doppler Anemometry (PDA), which provides the velocity and size of individual droplet in the spray. The atomizers were operated at the air inlet pressure of 100 and 200 kPa and gas-to-liquid mass (GLR) ratios of 5, 10 and 20%. The effect of the double expansion can be well observed in the pressure differences between the air inlet and the pressure inside the mixing tube. The length of the air counterflow insert had a significant effect on the atomizer performance. For the shorter counterflow channel, a minimal effect on flow was observed; this atomizer behaved like a conventional twin-fluid atomizer and all expansions occurred downstream of the exit orifice. The longer counterflow canal changed the internal expansion ratios, larger droplets, wider spray and higher discharge coefficients (Cd) were obtained.

The spray behaviour and droplet trajectories in realistic conditions are of crucial importance in many industrial, agricultural and chemical applications. Droplet characteristics and spray trajectory in chemical applications (e. g. flue gas scrubbing, CO2 capture in spray column) determine the amount of mass involved in the gas scrubbing process, mass trapped by the flow or attached to the walls. Knowledge of the droplet behaviour can improve a nozzle design and scaling, increase the process efficiency, minimize the process liquid and blow away the fraction. In this study, experiments with pressure swirl nozzle in cross–flow of air were performed at one nozzle injection pressure (0.5 MPa) and several cross–flow velocities (8, 16, 32 m/s). The results on droplet trajectories are compared with numerical results obtained by ANSYS Fluent. Two Lagrange approaches for spray modelling were used. Injection of droplet groups and Linearized Instability Sheet Atomization (LISA) model incorporated within ANSYS Fluent were used to represent the spray. The CFD results of spray penetration and droplet trajectories are compared with experimental data. A simple analytical model is able to well predict trajectories of large droplets, but fails to predict trajectories of small droplets. The LISA model yields a better accuracy for spray in cross-flow prediction.

The replication of atomizers by 3D printing technology is a new approach of producing the pressure swirl atomizers. The surface roughness of 3D printed products and manufacturing accuracy of the 3D printing process influence the atomization of the liquid. The high-speed visualization of a spray, produced by scaled 3D printed atomizer, was performed. The spray stability, cone angle and breakup length were determined. Scaled 3D printed atomizers were tested at equivalent pressures of 0.25, 0.5 and 1 bar. Non-dimensionless parameter, Reynolds number, was preserved for the scaled atomizer. The effect of the surface roughness of the tangential ports, swirl chamber and discharge orifice on atomization was assessed at non-scaled pressure swirl atomizer. The roughness of a swirl chamber was created by corundum and ballotin blasting. The inlet pressures of 2.5, 5 and 10 bar were tested.

A scaled transparent modular model of pressure-swirl (PS) atomizer was prepared from cast PMMA (Poly(methyl methacrylate), Perspex™, Plexiglas™) with the aim to achieve a better understanding of internal flow and subsequent spray formation. Because of use of high-speed imaging and Laser Doppler Anemometry (LDA) the working liquid had to be selected with respect of a refractive index matching (RIM) with the atomizer material. The liquid should be colourless and chemically non-aggressive to the model material with suitable viscosity to achieve the Reynolds number of the internal flow of the original atomizer. Froude number should be high enough to neglect the influence of gravity on the flow. An extensive search for transparent liquids and materials of enlarged models was made with a focus on RIM in performed experiments. Several liquids were chosen, and their chemical effect on PMMA was tested. Despite the successful tests that proved the liquid suit the case, the model material was damaged and the tests proved to be insufficient. For this reason, the tests were modified to better involve the stress of the bolted model. It turned out that a force effect (bolt in the thread, pre-stressed bolt connection) on the material has a significant influence on the acceleration of the chemical effect. The internal flow was examined using a high-speed camera with several liquids.