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The atomizer is a crucial component in spray columns used in mass transfer applications. Proper function of the atomizer can enhance mass transfer and reduce sorbent evaporation and droplet drift (physical loss). Commonly used atomizers for spray column application suffer from excessive droplet drift and high spray polydispersity. Flat fan sprays were beneficially used to reduce droplet drift in agricultural applications and in studies dealing with CO2 capture. Six 3D printed flat fan atomizers with different internal channel geometry (elliptical, cone-shaped) were tested at four inlet pressures in this study. The liquid sheet breakup length and spray cone angle derived from high-speed visualization are compared for each atomizer design. No systematic difference was found between the elliptical and cone-shaped channels. The spray cone angle and breakup length were corelated only with experimental regimes (Reynolds number and Weber number). Perforations were responsible for the breakup of the liquid sheet at lower injection pressures, whereas the combined effect of perforations and waves dominated the liquid sheet breakup at higher injection pressures.

With recent advance in print resolution of stereo lithography (SLA) 3D printers, a cheap and fast prototyping method of many industrial components is available. This paper examines the limits of the low- end SLA printer with a pixel resolution of 35 μm for the prototyping of pressure-swirl atomizers. Several differently sized atomizers with exit orifice diameter in range from 0.3 to 1.2 mm were produced with all dimensions evenly scaled. The circularity of the exit orifices was inspected by an optical microscope. Atomizers were operated under the same Reynolds numbers, which were selected to cover a pressure range between 4 and 10 bar for the smallest atomizer. The generated spray was observed with a high-speed camera. The discharge coefficient, spray cone angle (SCA) and circumferential liquid distribution were compared. Even the atomizer with 0.46 mm exit orifice produced a decent spray, almost comparable to the machined version. The discharge coefficient was slightly dependent on the size of the atomizer up to the exit orifice of 0.6 mm with the indices to print inaccuracies.

Nebulizers are medical devices for inhalation treatment that create an aerosol from liquid drug formulation. The efficacy of the treatment is dependent on the particle size distribution (PSD) of generated aerosol. PSD can be influenced by the inhalation flow rate as well. Within the here-presented study PSD of aerosol generated by nebulizer Pari LC Sprint Star was measured by Phase Doppler Anemometry for inhalation flowrate of 8; 12; 20 and 40 l/min. The nebulized solution consisted of a liposomal system (20 %) from dipalmitoylfosfatidylcholine (DPPC), phosphatidic acid (PA) and cholesterol (Chol), and MiliQ – ultrapure water (80 %). Slight dependence of PSD on inhalation flow rate was identified. With the increasing flow rate, the particle size of generated aerosol is decreasing. However, the change of Dv50 with the measured flow rates was smaller than 1 µm. According to the results, the change in particle size induced by flow rate will not have a significant impact on drug delivery.

A Monte Carlo simulation of Phase Doppler systems has been developed. It consists of three sections, the droplet flow description, generation of the photomultiplier signals and then their processing to determine droplet velocities and the time shift between the signals from the three scattered light detection apertures. With highly realistic Doppler bursts being simulated and processed, the question arises as to whether the signal processing software could be used to process ‘real-world’ experimental signals. In a preliminary assessment of its capabilities in such a situation, actual spray Doppler signals (from a Dantec fibre-based PDA system with a BSA signal processor) were recorded and used as input to the software signal processor. The signals from the three photomultipliers were input first into a Picoscope and then into the BSA processor. In this way droplet velocities and size estimates would be available from the BSA as control data. The signal outputs were taken as csv files, and input directly into the software signal processor. Initially the software determined the time location of the centre of each signal burst envelop. This approach was shown to measure signal delays from single cycle to multiple cycles. For this experiment, the software was modified by adding a zero-crossing approach to measure the single cycle delays. The introduction of this method should establish the accuracy of the complete software package in the real world as the results from the preliminary experiment show good agreement between the two techniques.

Both pulmonary airway geometry and breathing pattern evolve from birth to adulthood. These gradual changes significantly influence airflow dynamics and subsequently particle transport and deposition. Regarding the airway structure, the differences between infants and adults are most profound till 5 years of age. Since that age the child airway geometry can be downsized from adult lungs. The objective of the present work was to investigate airflow patterns in child airways. The digital model of male respiratory airways was downsized to dimensionally correspond to a 5–year old child. Airflow simulations with properly validated RANS k–ω turbulence model were performed under steady inhalation boundary conditions. The inspiratory flow rate was 12.5 L/min. The velocity profiles just upstream of the first bifurcation were validated by Laser–Doppler anemometry (LDA) experiments. A replica of the same geometry as the one used in the simulation was 3D printed and part of the trachea was replaced by a glass tube. LDA measurements in several points upstream of the first bifurcation were carried out. The validated flow patterns were compared to the ones obtained in adult lungs.

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.

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.

A rotating packed bed (RPB), as a device for mass transfer enhancement, can be divided into three main parts. An eye of a rotor, a packing, and an outer cavity. It has been reported that a contribution to the total mass transfer of the outer cavity can reach up to 30% of the whole device. Mass transfer is highly influenced by the droplet hydrodynamics and dimensions, hence the liquid dispersion from the outer surface of a metal foam packing was recorded with a high-speed camera. The recordings were analysed with an in-house MATLAB® code to determine the droplet dimensions, and with a PIVlab software to evaluate velocity fields. It has been found that the droplet dimensions and velocities were influenced primarily by a packing speed, as the higher packing speed resulted in a presence of the smaller droplets. Two peaks in histograms for the droplet diameters could be explained with a breakup theory of a liquid jet which breaks into large, mother, and small, satellite droplets. The droplet velocity corresponded to a peripheral velocity of the packing. A liquid flow rate influenced only the number of droplets dispersed from the packing.

Majority of power producing, and industrial processes generate a significant amount of carbon dioxide (CO2). To reduce their CO2 emissions, CCS (carbon capture and storage) can be used. One of the ways for CO2 capture is rotating packed bed (RPB), which operates on a similar principle as an absorption tower. However, in the RPB, mass transfer rate is driven by a centrifugal force, hence the RPB could be much smaller than the absorption tower, which relay on gravitational force. Also, the internal design of the RPB could affect efficiency of CO2 capture. There are several types of packing design, such as raised mesh, Zigzag, metal foam, or wire mesh. This study is focused on testing and construction of a transparent wire mesh packing, which could be used for analyse of fluid behaviour inside the packing e.g., a flow character, a liquid hold up and a liquid-gas interfacial. The operating packing speeds in the experimental part were 300 rpm, 600 rpm, 1200 rpm and 1800 rpm. The operating liquid (water) was supplied by six plain orifice nozzles with 1.44 mm diameter. Water was supplied to the system in a range of liquid flow rates from 44 to 176 kg/h. This corresponds to the jet velocity of 1.25 – 5.00 m/s. The observed area was the entry of the water jet into the wire mesh, where the atomization is the most intense. For the measurement, a high-speed camera was used. It is evident from results that with the higher jet velocity, the penetrating distance is larger, and the atomization is more intense.

Liquid dispersion on a wire mesh is a phenomenon that is utilized in many industrial applications, such as rotating packed beds. It is a very simple method of liquid atomization without a need for complex nozzles. This research focuses on an elementary case of a liquid dispersion on a crossing of two wires. Experiments were carried out in a wind tunnel to elucidate the influence of counterflow air velocity on a liquid sheet and droplets. High-speed camera was used to capture the impact of droplets on the crossing. Images were then processed using MATLAB® addon PIVlab. The effect of the input parameters, including a liquid flow rate in the range of 3.8 to 12 kg/h and air flow velocity varying from 0 to 9 m/s on the angle and velocity of dispersed droplets downstream of the crossing, was investigated. Finally, a qualitative description of the dispersion was evaluated. Results show that with an increasing liquid flow rate, the droplets dispersed in a wider angle. On the other hand, the influence of the air counterflow is significant only for low liquid flow rates. The atomization rate, determined by the number of small droplets, was better for higher liquid flow rates.

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.

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 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.