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[Display omitted] • Single and twin-fluid atomizers in spray column conditions were investigated. • Link between spray properties, entrained fraction and pressure loss was established. • ΔP is controlled mainly by liquid velocity at the atomizer exit orifice. • Entrainment model was adjusted to twin-fluid atomizers and empirical correlation was provided. • ΔP model was developed considering both droplet size and droplet distribution shape. The interaction of spray with counter-flowing flue gas causes pressure loss (ΔP) and influences droplet entrainment and sorbent loss in gas–liquid scrubbers. As these phenomena were usually investigated separately and not linked with atomizer characteristics, it is difficult to obtain insight into the scrubber operation and select an atomization device proper to particular process. Atomizers typically used in a spray column, together with pressure-swirl and twin fluid effervescent types, were tested in column-like conditions. All the atomizers were tested at the same liquid flow rate of 140 kg/h, with inlet pressure (p in) from 0.025 to 0.2 MPa under the counter–flow velocity (u cf) ranging from 0 to 1 m/s. A small-scale low-speed wind tunnel was specially designed to simulate spray column flow conditions. The ΔP and droplet entrainment were correlated with atomizer operating regimes. Empirical and analytical models of ΔP were compared with experimental results for different atomizers. Limitations of both models are discussed. The ΔP is influenced by the spray velocity at the discharge orifice (u L) and correlates well with the liquid kinetic energy (E k) and Reynolds number at the discharge orifice. The atomizers working on higher p in , provide a larger interfacial area, but yield higher E k at the discharge orifice, causing larger ΔP and a greater risk of sorbent loss due to presence of smaller droplets. [ABSTRACT FROM AUTHOR]

Sprays are exposed to ambient flow in most of their applications, which alters the spray behaviour. The understanding of spray performance in realistic conditions allows for nozzle improvements, process intensification, or emission reductions. The present paper investigates the pressure-swirl atomizer operating at three Reynolds numbers in the inlet ports (Re p) 960, 1330 and 1880, subjected to low-turbulence cross-flow with aerodynamic Weber number (We) from 0 to 7.1. High-speed visualization and phase Doppler anemometry (PDA) captured the characteristic shape and trajectory of the spray, droplet dynamics, droplet collisions, and spatial droplet distributions. An empirical correlation for a mean spray trajectory prediction was developed for a wide range of flow parameters. An analytical model of the droplet trajectory was assembled and validated using PDA data. The model accurately predicts trajectories for droplets larger than 40 μ m. A mutual interaction of droplets was investigated. Elevated cross-flow velocity (v) increased the impact Weber number and the total droplet collision rate and enhanced the droplet mixing. A bag breakup regime was observed for the liquid to the air momentum ratio (q) lower than 300. The bag breakup modified the initial droplet velocity. The experiments imply the formation of a complicated vortex structure around the pressure swirl spray in cross-flow. [ABSTRACT FROM AUTHOR]

[Display omitted] • 25 tailor-made atomizers investigated at constant sorbent flow rate in spray column. • Absorption rates depend primarily on Sauter mean diameter. • Sorbent entrainment limits reduction of droplet sizes. • Initial spray velocity has limited effect on absorption rate. • Pressure-swirl and flat-fan atomizers are the most all-round atomizers. CO 2 is one of the most severe greenhouse gases released into the atmosphere and is responsible for increasing global temperatures. Post-combustion CO 2 capture can reduce the amount of CO 2 released. Spray columns, as simple gas cleaning reactors, can utilize different types of atomizers. The CO 2 capture process requires well-tailored spray characteristics, such as suitable mean drop size and drop size distribution, droplet density, spray cone angle, and droplet velocity. Small droplets are prone to be carried away by ambient flow causing significant sorbent losses, while large droplets have a small surface area, which limits the rate of CO 2 mass transfer. This paper compares pressure-swirl, flat-fan, twin-fluid, and showerhead atomizers operated at a constant solvent flow rate of 140 kg/h. Atomizer rescaling was used to change the liquid pressure. Droplet sizes were probed with a high-resolution shadowgraph sizer. Absorption tests were carried out on a laboratory-scale spray tower with a diameter of 0.2 m and a height of 2.5 m. The absorption liquid was a 30 wt% monoethanolamine (MEA) solution, and the modeled flue gas contained a 10% CO 2 mole fraction. The absorption efficiency systematically increased with a reduction in Sauter mean diameter (D 32), i.e. with atomizer input energy. Pressure loss in the spray column is directly proportional to absorption efficiency. Effervescent atomizers achieved the worst energy efficiency and the largest fraction of droplets carried away by the ambient flow, resulting in significant sorbent loss. Flat-fan and pressure-swirl types were found to be excellent all-round atomizers. [ABSTRACT FROM AUTHOR]

• An air-assisted impinging jet atomizer is evaluated for CCS applications. • Developed a regime map for operation with different concentrations of MEA in water. • Identified critical non-dimensional parameters for change in the atomization regimes. • Proposed a correlation between spray characteristics and non-dimensional parameters. Spray scrubbing for carbon dioxide (CO 2) absorption has attracted research interest because it is a viable retrofitting option for existing power plants. For effective absorption, desired spray characteristics must be attained for a wide range of absorbent liquids with distinct physical properties. In this study, an air‑assisted impinging jet atomizer was evaluated to determine its suitability for CO 2 absorption using monoethanolamine (MEA). The study focused on understanding the influence of various physical parameters on the overall atomization process. Spray experiments were performed under quiescent atmospheric conditions at different liquid flow rates and air-to-liquid mass flow rate ratios (ALR). High-speed imaging and laser diffraction techniques were used for spray visualization and droplet size characterization, respectively. The study revealed that the primary atomization was either a hydrodynamic mode of breakup caused by hydrodynamic instabilities in a liquid sheet or an aerodynamic mode of breakup, where the breakup was dominated by gas-liquid interaction. A transition between these breakup processes occurred at an air-to-liquid momentum ratio of ∼0.6, and a gas Weber number of ∼30. Improved atomization was obtained in the aerodynamic mode of the breakup. A Sauter mean diameter (SMD) of the order of 60 µm, along with a narrow size distribution, was obtained at high liquid flow rates, even at an ALR of 4 %. Furthermore, empirical correlations were proposed for SMD and spray angle as functions of gas Weber number, liquid Weber number, and Ohnesorge number. The detailed spray characterization performed in this study provides valuable insights into the atomization process of an air-assisted impinging jet atomizer and is crucial for testing this atomizer configuration in a spray column for CO 2 capture. [Display omitted] [ABSTRACT FROM AUTHOR]

• Study examined impact of liquid sheet stability on breakup length and drop size. • Breakup length models were validated for cross-flow with modified term of relative velocity. • Breakup length is controlled mainly by relative velocity between liquid sheet and cross-flow. • Differences in breakup length of different atomizers decrease with aerodynamic forces. • SMD significantly depends on the breakup length and cross-flow velocity. A variety of industrial devices use liquid injection into the traverse stream of air. Ambient flow changes the spray characteristics, which can alter a system's function. Two different spill-return pressure-swirl atomizers (SRA) were investigated under cross-flow. One of the tested atomizers generates a conical liquid sheet with shorter breakup lengths due to reduced internal air-core stability. Phase Doppler anemometer (PDA) was used for 2D velocity and droplet size measurements, along with high-speed visualization to record instantaneous spray behaviour. A wide range of operating parameters was tested, e.g., inlet pressure (p l) ranging from 0.25 MPa to 1 MPa, spill-to-feed ratio (SFR) from 0 to 0.9, and cross-flow velocity from 0 to 32 m/s. As the cross-flow velocity increases, the spray starts to tilt and the breakup length (l b) shortens as a result of increased aerodynamic forces. This reduces the differences between atomizers. Moreover, the droplet diameter depends on the l b , yet no semi-empirical model was found to accurately predict the droplet sizes. A map of breakup modes was established, and a transition point from long- to short-wave mode was identified. The Linear Stability Analysis of the liquid sheet breakup was used and compared with a semi-empirical approach for the first time for the SRA and cross-flow conditions. The results imply that considering only quiescent ambient conditions during atomizer development might not lead to the optimal design. [Display omitted] [ABSTRACT FROM AUTHOR]

• Novel so-called impinging effervescent atomizer was developed. • The spray results from impingement of effervescent streams. • The colliding liquid jets enhance spray properties in mass transfer applications. • The atomizer allows for adjustable spray cone and larger spray coverage area. • It also improves the spray monodispersity, and droplet spatial homogeneity. The concept design, testing of spray characteristics, and performance comparison of an original type of atomizer, the impinging effervescent atomizer (IEA), are introduced in this study. The liquid impinging is beneficially deployed in plain-orifice and external mixing twin fluid atomizers. IEA uses a collision of two or more effervescent liquid streams to improve the atomization and alter the spray characteristics. The Phase Doppler Anemometry (PDA) measurement technique and high-speed visualization of the liquid discharge and spray structure were used. The discharge coefficient (C d), atomization efficiency (η a) , spray characteristics as a spray cone angle (SCA), integral Sauter mean diameter (ISMD), integral relative span factor (IRSF), and droplet size and velocity distribution inside the spray were investigated. The correlations for C d , SCA , ISMD and IRSF are provided for a fast and reliable atomizer design to fit any application and operating conditions. The IEA provides a controllable SCA governed mainly by the exit orifice geometry. The ISMD is primarily controlled by the gas to liquid ratio (GLR) and the inlet pressure (p in). The impinging angle (β) has little effect on ISMD. A narrower droplet size distribution, mass redistribution within the spray, and a more uniform droplet size spatial distribution were observed for the IEA in comparison to other tested atomizers. The IEA spray covers 116% more area than single-orifice effervescent sprays, and the area coverage can be controlled by β. This coverage increases by 177% if β changes from 15 to 45°. Spray eccentricity (e) decreases with the increase of the number of the exit orifices (N o) resulting in a more uniform droplet spatial distribution. The β , GLR and p in have no effect on e. The η a of the IEA is equivalent to other internally mixing twin-fluid atomizers; the atomization air contains more than 90% of the delivered energy. The favourable IEA spray characteristics, such as IRSF , ISMD , spray coverage, SCA and η a, enable the potential use of IEA in mass-transfer related processes and especially in CO 2 capture columns. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hydrodynamic study of a unique transparent RPB simulating realistic processes. • The Rankine vortex can simulate gas flow but struggles with higher gas flow rates. • Upon impact, liquid partially rebounds as small droplets that circulate with gas. • Analytical hydrodynamic model was developed and validated for the droplet motion. • Impact velocity, residence time and trajectory length were derived from the model. Droplet motion in outer cavity zone of rotating packed bed is a complex phenomenon that requires analysis of liquid and gas flow to clarify influences of factors such as rotation speed, liquid flow rate, or gas flow rate. In this study, hydrodynamics is described using laser Doppler velocimetry and high-resolution visualization for droplet motion characterization. The results reveal that droplet motion initially depends on the peripheral velocity of the packing, while further from the packing, it loses kinetic energy mainly due to the drag force caused by the surrounding gas. Two-way coupling is investigated as both phases interact with each other. Rankine vortex theory is applied to simulate gas flow in the outer cavity zone. A model, based on Newton's second law, is developed to predict droplet dynamics, including impingement velocity, trajectory length, and total residence time. Validation of the model shows that it can predict the liquid velocity in the outer cavity zone accurately. Upon impingement of droplets on the casing, part of the liquid rebounds as secondary droplets into the cavity, where they circulate with the gas flow. Overall, this study provides insights into droplet dynamics in the rotating packed bed and offers a basis for optimizing process efficiency and design in various applications, including chemical processing and environmental engineering. [ABSTRACT FROM AUTHOR]

• The internal flows in transparent spill-return atomizers were investigated experimentally. • The modified inviscid analysis was applied for discharge coefficient and air-core size prediction. • Turn-down ratio decreases with increasing radius on which the spill-line orifices are located. • Three modes of liquid sheet dynamics were identified under identical operating conditions. • The air-core fluctuations determine the liquid sheet stability. The sprays produced by spill-return pressure-swirl atomizers are strongly dependent on the nature of the internal fluid dynamics. Several spill-return atomizers were compared in terms of the spatial and temporal behaviour of the internal air-core, liquid sheet thickness and its perturbations. The only difference amongst the test configurations was the geometrical arrangement of the spill-line (SL) orifice through which the liquid was spilled away. The flow field inside the swirl chamber was examined using high-speed imaging with image post processing using an in-house Matlab code and three orthogonal velocity components acquired using Laser Doppler Anemometry. The dimensions of the production atomizers did not allow direct visualization of their internal flow, so a scaled, modular, transparent plexiglass model was used. Its flow characteristics were equivalent to the original atomizer. The refractive index of the atomizer body was matched to the test liquid using a solution of 1-Bromonaphthalene and kerosene fuel type JET A-1. The test conditions were derived from the original atomizer and were limited to inlet port Reynolds numbers, from 700 to 2000 and spill-to-feed ratios, SFR , from 0 to 0.75. An inviscid analysis, originally derived for Simplex atomizers, was modified and applied to the spill-return version. This approach allows a theoretical prediction of the discharge coefficient and air-core diameter dependent solely on SFR. An axially located SL orifice inhibits any internal air-core forming in the swirl chamber. Off-axial SL orifices generate and stabilize the air-core, which leads to the regular formation of a liquid sheet and a high-quality spray. Nevertheless, some configurations changed the breakup nature of the liquid sheet and consequently the spray quality. Moreover, the turn-down ratio of the liquid supply rate and spray stability depend on the distance of the SL orifices from the swirl chamber centreline. The flow energy losses increase with SFR. The outcomes from this analysis allow the optimization of the SL configuration for specific application and extend the classical inviscid analysis. [ABSTRACT FROM AUTHOR]