Twin-fluid atomization of viscous liquids: The effect of atomizer construction on breakup process, spray stability and droplet size

Twin-fluid atomization of viscous liquids: The effect of atomizer construction on breakup process, spray stability and droplet size MLKVIK, M.; STÄHLE, P.; SCHUCHMANN, H.; GAUKEL, V.; JEDELSKÝ, J.; JÍCHA, M. International Journal of Multiphase Flow 2015, vol. 77, December 2015, pp. 19-31 ISSN: 0301-9322 DOI: https://doi.org/10.1016/j.ijmultiphaseflow.2015.06.010 Accepted manuscript © 2012. This manuscript version is made available under the CC-BY-NC-ND 4.0 license (http://creativecommons.org/licenses/by-nc-nd/4.0/), doi: https://doi.org/10.1016/j.ijmultiphaseflow.2015.06.010 Final version available from https://www.sciencedirect.com/science/article/pii/S0301932215001494 dspace.vutbr.cz 1 Title: TWIN-FLUID ATOMIZATION OF VISCOUS LIQUIDS: THE EFFECT OF ATOMIZER CONSTRUCTION ON BREAKUP PROCESS, SPRAY STABILITY AND DROPLET SIZE Corresponding Author: Marek Mlkvik, [email protected], +421 907 304 850 Authors: M. Mlkvik, Brno University of Technology, Technicka 2896/2, 616 69 Brno, Czech Republic P. Stähle, Karlsruhe Institute of Technology, Institute of Process Engineering in Life Sciences, Section I: Food Process Engineering, Kaiserstraße 12, 76131 Karlsruhe, Germany, philipp staehle@kit edu H. P. Schuchmann, Karlsruhe Institute of Technology, Institute of Process Engineering in Life Sciences, Section I: Food Process Engineering, Kaiserstraße 12, 76131 Karlsruhe, Germany, heike schuchmann@kit edu V. Gaukel, Karlsruhe Institute of Technology, Institute of Process Engineering in Life Sciences, Section I: Food Process Engineering, Kaiserstraße 12, 76131 Karlsruhe, Germany, volker gaukel@kit edu J. Jedelsky, Brno University of Technology, Technicka 2896/2, 616 69 Brno, Czech Republic, [email protected] M. Jicha, Brno University of Technology, Technicka 2896/2, 616 69 Brno, Czech Republic, [email protected] Keywords: twin-fluid atomizer, two-phase flow, atomization, liquid breakup, spray imagining, spray stability, comparison of atomizers HIGHLIGHTS - We compare a Y-jet, effervescent and an in-house developed CFT atomizer for spraying viscous liquids. 2 - The comparison looked at spray stability, primary breakup visualization and droplet size. - The best stability was observed with the Y-jet atomizer and the “outside in liquid” atomizer. - The breakup for all liquids with the OIG, OIL and CFT atomizers was characterized by We = 1–10. This was considerably lower with the Y-jet atomizer (We = 0.1–3). - The smallest droplets were produced by the OIL atomizer. ABSTRACT This study focuses on the low-pressure spraying of viscous liquids (μ = 60, 147 and 308 mPa∙s) using four types of internal-mixing twin-fluid atomizers. We compare two well-known designs, namely the Y-jet and “outside in gas” (OIG) effervescent atomizers, with our new design (CFT) and an “outside in liquid” (OIL) configuration for the effervescent atomizer. The atomizers were operated by two gas inlet pressures (0.14 and 0.28 MPa) and various gas-to-liquid ratios (GLR = 2.5, 5, 10 and 20%). The comparison focused on internal liquid–gas flow, spray stability, primary breakup, and droplet size. The primary breakup was investigated using a high-speed camera. A near-nozzle spray pattern was related to the ratio of forces, which affects liquid deformation, by dimensionless numbers. The breakup was driven mainly by air resistance in the OIG, OIL, and CFT atomizers and by surface tension in the Y-jet atomizer. The OIL and Y-jet atomizers provided the most stable spray, regardless of the working regime or atomized liquid. The OIL atomizer produced the smallest droplets at low GLRs, while the droplet sizes for the Y-jet atomizer increased significantly at low GLRs. For the OIG atomizer, spray stability was influenced by the GLR, with the best stability being achieved at a GLR of 10% and 20%. The presence of large droplets at a low GLR caused an increase in droplet size. Switching the inlet ports of the effervescent atomizer (OIG - OIL) affected the internal flow, which differed under the same working regimes for these two configurations. The 3 internal flow pattern of the OIL atomizer was estimated to be annular for all regimes, while for the OIG atomizer, it changed from a plug to slug flow with an increase in the GLR. 1. INTRODUCTION Internal-mixing twin-fluid atomizers have been used in countless commercial applications over the recent decades, such as in gas turbine engines (Lefebvre 1988), internal combustion engines (Wade 1999), scramjet engines (Gadgil 2011), spray drying (Mujumdar 2010), spray coating (Esfarjani 2009, Qian 2011), process industries (Loebker 1997) and fire suppression (Huang 2011, Lal 2010). Y-jet nozzles in particular have been widely used in oil boilers, industrial furnaces, agricultural sprays, spray dryers and paint sprays (Zhou, 2010). Atomizers with internal mixing are favored for their good atomization quality at low pressure (Sovani 2001) and their low sensitivity to a liquid’s rheological properties when compared with high-pressure atomizers. Twin-fluid atomizers provide easy and independent control of the individual spray parameters (Karnawat 2006). The consumption of atomizing gas is lower than with their externally mixed counterparts. The capability to process highly viscous liquids is advantageous in several areas, especially in the combustion of heavy fuels, liquid wastes (Buckner 1990, Ferreira 2009, Jedelsky 2009, Kermes 2008, Loebker 1998), coal–water (Chawla 1985, Daviault 2012, Jagannathan 2011), and coke sludge slurries. It also helps in the spray drying of food (with suspensions of water and gelatinized native corn starch or native waxy corn starch, Schröder et al., 2011 ) and pharmaceutical and consumer products (PEO solutions (Broniarz-Press 2010) such as water–oil emulsions (Broniarz-Press 2009 Schröder et al., 2012), black liquor (Risberg 2009), and liquids for fluid catalytic cracking (Jolodar 2005). Published designs for internal-mixing twin-fluid atomizers appear in a variety of internal configurations, as indicated above and in several reviews (Jedelsky 2009, Sovani 2001). The internal design of an atomizer certainly affects its performance and predetermines its possible uses. In some applications—such as combustion, surface coating, and powder generation—a temporally unsteady spray has a negative effect. For example, it leads to increased combustion noise and it puts extra load on the combustion chamber. On the other hand, some engineering applications can profit from such an unsteady spray. For example, it can enhance the air 4 entrainment rate in consumer products (Liu 2011, Panao 2005). The generation of a fine spray, or the ability to control spray size, is a traditionally common requirement for most applications. The internal flow is a process that greatly influences the work of twin-fluid atomizers (Bukner, 1991, Lorcher 2003, Stähle et al. 2014). This can be estimated using theoretical flow regime maps (Barnea 1987) or experimental ones (Baker 1954, Hewit and Roberts 1969, Golan and Stenning 1969). Theoretical maps have the advantage of not being limited by experimental parameters. Experimental maps, meanwhile, can only be applied with the specific range of experimental parameters (e.g. pipe size, working fluids, GLR) specified by the researcher. This disadvantage was partially solved by Schicht (1969) and Weisman and Kang (1981) when they attempted to find generalized dimensionless parameters to cover a wide range of working parameters. Another approach to identify the internal flow, which is especially useful for Y-jet atomizers, was introduced by Song (1996). He used the liquid-to-gas momentum ratio Φ = ml2∙dl2∙ρg∙sinΘ / (mg2∙dg2∙ρl) and related it to the observed internal flow regime. Here, the mass flux per surface unit is denoted as “m”, density as “ρ”, port diameter as “d” and the intersecting angle as “Θ”. The indexes “l ” and “ g “ denote the liquid or gas. A number of studies deal with twin-fluid atomizers (Ochowiak 2013), Xiuyuan 2013, Pougatch 2014, Barroso 2014, Hong 2014), but these are very rarely compared. Chung (2000), Linchetta (2002), Ferreira (2009) or Gottlieb (2004) compare their designs with commercial atomizers, but this does not extend over several types of these devices. In this paper, we therefore decided to provide a systematic comparison of four selected twin-fluid atomizers (Figure 3) that differ widely in their mixing principles under the same working conditions. According to the available literature, each type was evaluated in several variations of its internal dimensions, with the best being chosen for this study. Our aim was to investigate differences in the breakup process, spray stability and droplet size while spraying liquids of different viscosity. We judged their performance and evaluated their potential for various applications. The Y-jet and OIG atomizers are well-known atomizing devices that are widely used in many industrial applications (Mullinger 1974, Lefebvre 1988, Chung 2000, Sovani 2001). The OIL atomizer is a variant of the effervescent atomizer, where the liquid and gas ports are switched, thus influencing the mixing mechanism of the flow components. The CFT atomizer is a new design that was recently developed at the Brno University of Technology. It was inspired by atomizers 5 invented by Chin (1995), Ferreira (2001), and Tamaki (2004), and its name represents the initials of these authors. 2. EXPERIMENT The near-nozzle spray was observed using a high-speed camera (OLYMPUS i-speed2) with a framerate of 10 000 fps and an exposition time of 5 μs. The measuring volume was illuminated by a continual LED light with a light diffuser being used to provide a uniform image background (Figure 1). The focusing optics comprised a PENTAX TV lens (50 mm, f1:1.4) with extension rings for a total length of 25 mm in order to achieve image magnification. Droplet sizes were measured 100 mm downstream of the discharge orifice using a Malvern Spraytec laser diffraction system. Figure 1. Arrangement of the measurement and visualization systems The atomizers were operated under a wide range of working parameters defined by the inlet air pressure (Δp = 0.14 and 0.28 MPa) and gas-to-liquid ratio of the mass (GLR = 2.5, 5, 10 and 20%). Three liquids of different viscosity were sprayed (Table 1). The temperature of the air and liquid was kept within 18–20oC. 6 Table 1. Physical properties of the water–maltodextrin solutions at room temperature (Stähle 2013) Maltodextrin concentration [%] designation μ [mPa∙s] σ [mN/m] ρ [kg/m3] 50 MD50 308 ± 24 75.736 ± 1.035 1242 ± 2 45 MD45 143 ± 16 74.258 ± 0.778 1121 ± 2 40 MD40 60 ± 4 74.454 ± 0.386 1185± 1 * μ – viscosity, σ – surface tension, ρ – density The air inlet pressure was kept constant for varying GLRs. The liquid injection pressure was changed as GLR changed to compensate for the pressure loss between the liquid inlet port and the mixing chamber of the atomizer. This value was measured for safety reasons, namely for the load on the hydraulic system, but it was not recorded. 2.1. EXPERIMENTAL RIG A simplified schematic of the test rig is shown in Figure 2. An eccentric screw pump (2NL 20A, Erich Netzsch GmbH & CO. Holding KG, Selb, Germany) was used at a constant rotation speed to pump the solutions. The flow was controlled by a bypass valve. The volume flow rate towards the atomizer was adjusted using a needle valve and measured with a flow meter (VSE GmbH, Neuenrande, Germany). Compressed air from a house supply was used and adjusted by a pressure-reducing valve to provide the atomizer with atomization gas. The gas pressure was measured using a pressure gauge just a short distance upstream of the atomizer. A thermal gas mass flow controller (a High-Tech EL-Flow from Bronkhorst Mättig GmbH, Kamen, Germany) indicated the gas mass flow. After ejection, the spray was collected in a vessel that was connected to an exhaust fan. 7 Figure 2. Simplified schematic of the experimental rig 2.2. ATOMIZERS The atomizers investigated are outlined in Figure 3, and their important characteristics are given in Table 2. The Y-jet atomizer (Figure 3a) is a well-known atomizing device with a simple design (Mullinger 1974) that uses a well-described internal two-phase flow (Song 1996). The internal flow is created by injecting liquid into the high-velocity axial gas stream. The OIG atomizer (Figure 3b) is frequently reported as well (Lefebvre 1988, Sovani 2001). A two-phase flow is created by introducing gas into the liquid upstream of the discharge orifice through a perforated aerator. The internal two-phase flow pattern for this type of atomizer is mainly affected by the Δp and the flow rates of the liquid and gas (Brennen 2005). The OIL atomizer (Figure 3c) uses a similar design to the OIG atomizer, but the inlet ports are switched. In this case, the air is introduced into the mixing chamber from the top, while the liquid is injected through the perforated wall of the mixing chamber (the aerator in the OIG atomizer). The main difference between these configurations is the mixing mechanism of the flow components, which in this case is more similar to the Y-jet atomizer. 8 Inside the CFT atomizer (Figure 3d), gas is introduced from the top of the mixing chamber through four gas ports. The gas ports are tangential to the axis of the atomizer, creating a vortex flow inside the mixing chamber. Liquid is introduced through four ports perpendicular to the main axis of the atomizer. The atomizers were designed to work with similar gas and liquid flowrates (Table 3). To achieve this, the Y-jet atomizer needed a different diameter for its discharge orifice (Table 2). Figure 3. Schematics of the investigated atomizers: a) Y‒jet, b) OIG, c) OIL, d) CFT Table 2. The important geometrical parameters of the atomizers d l [mm] d m [mm] d g [mm] Θ N d d [mm] Y-jet 0.4 1 0.7 52 1 1 OIG 9 9 1 90 1 0.7 OIL 1 9 9 90 20 0.7 CFT 1 9 1 90 4 0.7 * dl – liquid port diameter, dm – mixing chamber diameter, dg – gas port diameter, Θ – liquid injection angle, N – number of liquid injectors, dd – discharge orifice diameter `Table 3. Measured liquid mass flow rates in [kg/hod] for all atomizers and working regimes 15 Figure 6. Liquid breakup regimes (The breakup regimes’ transitions curves were adapted from Faeth (1995)) 16 Figure 7. Near-nozzle spray pattern for μ = 308 mPa·s, Δp [MPa], GLR [%]. NAT denotes regimes where liquid was not atomized. 17 Figure 8. Near-nozzle spray pattern for μ = 143 mPa·s, Δp [MPa], GLR [%]. NAT denotes regimes where liquid was not atomized. 18 Figure 9. Near nozzle spray pattern for μ = 60 mPa·s, Δp [MPa], GLR [%]. NAT denotes regimes where liquid was not atomized. 19 3.2. SPRAY STABILITY AND INTERNAL FLOW This evaluation was based on qualitative observations of spray stability during the experiments. The spray stability assessment is summarized in Table 5, according to the criteria in Table 3. Table 5. Spray cone stability Y-jet OIG OIL CFT μ [mPa·s] μ [mPa·s] μ [mPa·s] μ [mPa·s] 60 147 308 60 147 308 60 147 308 60 147 308 0.14 MPa GLR [%] 2.5 2 2 N1 4 N1 N1 2 2 N1 2 N1 N2 5 2 2 N1 3 4 N1 1 2 N1 2 4 N2 10 1 1 2 1 2 2 1 2 2 1 2 N2 20 1 1 N3 1 1 1 1 1 1 1 2 N2 0.28 MPa GLR [%] 2.5 2 N1 N1 N1 N1 N1 2 2 N1 3 4 N2 5 1 2 N1 N1 N1 N1 1 2 N1 2 2 N2 10 1 1 1 3 3 3 1 1 1 1 3 N2 20 1 1 1 1 1 1 1 1 1 1 2 N2 The Y-jet atomizer produced stable sprays for the low-viscosity liquids (MD45, MD40) at GLRs of 10% and 20% (for both inlet pressures). For GLRs of 2.5% and 5%, occasional spray cone pulsations were observed. The spray was stable at Δp = 0.28 MPa and a GLR of 10% or 20% with the MD50 liquid. For low GLR values with MD50, a liquid jet was observed instead of a developed spray cone. Atomization at Δp = 0.14 MPa was only observed for a GLR of 10%. This atomizer was not able to achieve a working regime with Δp = 0.14 MPa and a GLR of 20% when using the MD50 liquid. The OIG atomizer produced a stable spray at a GLR of 20% only, although this worked for both pressures and all liquids. At a GLR of 10%, occasional (Δp = 0.14 MPa) or regular (Δp = 0.28 MPa) pulsations were observed. The atomizer failed to atomize any of the liquids at a GLR of 2.5% or 5% and when Δp = 0.28 MPa. 20 The OIL atomizer worked well with the MD45 and MD40 liquids, but it did not work with the MD50 liquid and a GLR of 2.5% or 5% for both inlet pressures. The spray produced with GLRs of 10% and 20% was stable for both pressures and all liquids. The CFT atomizer was unable to work with the maltodextrin solution with μ = 308 mPa∙s (MD50). After a very short working time (seconds), maltodextrin crystals blocked the discharge orifice. Any further attempt to atomize this liquid with the CFT atomizer was unsuccessful. MD45 spraying, meanwhile, could be described as unstable for all of the working regimes. The atomizer produced stable sprays at GLRs of 10% and 20% for both pressures when the low-viscosity liquid was used (MD40). It is well-known that the internal two-phase flow pattern influences the external flow (Buckner 1991, Santangelo 1995, Song 1996) and therefore the spray stability. As we could not examine the flow in the mixing chamber experimentally, we determined the internal flow using the available experimental results from other researchers. In the work of Song (1996), the internal flow of the Y-jet atomizer was evaluated in terms of the liquid-to-gas momentum ratio (Figures 10 and 11, section 1). When the gas momentum was dominant (Φ < 1), the liquid would create a film on the mixing chamber wall just after leaving the liquid port. When the liquid momentum was comparable to the gas momentum (1 < Φ < 3), mixing took place in the central part of the mixing chamber, and the liquid was dispersed into the gas stream. When the liquid momentum overcame the gas momentum (Φ > 3), the liquid stream reached the wall opposite the liquid port and created a liquid film, similar to in the first case. The results comparison (Figure 10 and Table 4) shows that for Φ > 1 (i.e. GLRs of 2.5% and 5%), the spray either became less stable (with MD40/MD45) or no spray was produced (with MD50). These working regimes were characterized by intense liquid–gas interaction (i.e. deflection of the gas stream by the liquid). This interaction can produce gas pulsations in the mixing chamber, which influences spray stability. A stable spray was produced for Φ < 1, because the liquid stream formed the film on the wall just after reaching the mixing chamber, so it did not cause air stream deflections. This flow pattern was stable with low temporal fluctuations in the GLR, which led to stable spray generation. 21 Figure 10. Comparison of the gas-to-liquid momentum ratio for the OIL and Y-jet atomizers Figure 11. Estimated internal flow of the Y-jet atomizer (according to Song (1996)) There is no work investigating the influence of Φ on the OIG atomizer’s internal flow, so an online calculator (http://www.energetickeforum.cz/ext/2pf/maps/) with the modified baker’s map was used to determine the flow regime of this atomizing device (Table 5). Although this map was designed for fully developed multiphase flows that are not actually achieved in the mixing chamber, we used it because of its simplicity. The internal flow at GLRs of 2.5% and 5% was estimated as a plug flow (Figure 12). The plug flow indicates local fluctuations in the GLR inside the discharge orifice, which leads to an unstable spray (Lorcher 2003). For the regimes 22 Δp = 0.14 MPa, GLR = 2.5% (MD40) and GLR = 2.5 and 5% (MD40, MD45), it was observed that the OIG atomizer did not atomize the examined liquids at GLRs under 5%. The atomizer’s work for these regimes was characterized by long periods of only liquid being ejected from the discharge orifice, followed by short ejections of gas (with no liquid). This was the result of the inhomogeneous internal flow. The flow regimes at a GLR of 10% were identified as plug or slug flows. Slug flows contain large bubbles comparable in size to the diameter of the mixing chamber, separated by thin liquid layers. The passage of the liquid layers through the discharge orifice caused local fluctuations in the GLR, which led to an unstable spray. For increased Δp, the air in the mixing chamber was more compressed, so its void fraction decreased. The larger fraction of the liquid caused a thicker liquid film, separating the plugs and the slugs, so the GLR fluctuations and consequent pulsations were more intense when Δp = 0.28 MPa. Only slug flow was predicted for the working regimes with a GLR of 20%. When the void fraction increased, the slugs were divided into progressively thinner liquid films, so local fluctuations in the GLR in the discharge orifice became less intense. Table 6. Internal flow patterns of the OIG and OIL atomizers, estimated using the baker’s map Δp = 0.14 MPa Δp = 0.28 MPa μ [mPa·s] μ [mPa·s] 308 147 60 308 147 60 GLR [%] 2.5 Plug Plug Plug Plug Plug Plug 5 Plug Plug Plug Plug Plug Plug 10 Plug Slug Slug Plug Slug Plug 20 Slug Slug Slug Slug Slug Slug Increase of GLR 23 Figure 12. Two-phase flow patterns Our experimental results indicate that changing the effervescent atomizer from an OIG to an OIL configuration improves spray stability. The OIL atomizer’s spray was stable for almost all of the measured working parameters and atomized liquids, with the exception being the regimes with GLRs of 2.5% or 5% with the MD50 liquid. For both of the effervescent atomizer configurations (Table 3), the same internal flow patterns were estimated. This indicates that the mixing mechanism influences the internal flow of this atomizer, so its evaluation using only the baker’s map is not suitable. To involve the mixing mechanism, we used Φ, which was formerly applied to the Y-jet atomizer. For Φ < 1, (i.e. all investigated working regimes of the OIL atomizer), the liquid was unable to penetrate to the central portion of the mixing chamber. It formed a film on the wall, while the gas formed a core in the central portion (Figure 13). This flow pattern was stable with small temporal fluctuations in the GLR and led to a stable spray. Figure 13. The estimated two-phase flow for the OIL atomizer The flow pattern in the mixing chamber of the CFT atomizer was difficult to determine without experimental observation. The interaction between the two liquid streams probably produced random liquid structures, which were then deformed by the gas’s drag force. The presence of maltodextrin crystals when using the MD50 liquid indicates that the liquid spent sufficient time in the mixing chamber to become dry and form crystals. 3.3 DROPLET SIZING 24 The liquid was atomized into fragments whose size reduced as the relative velocity of the liquid and gas increased. The droplet size for all atomizers therefore significantly decreased with an increase in the GLR, as shown in Fig. 14 and a number of other publications (Whitlow 1993, Sher 2000, Sovani 2001). A similar trend in SMD reduction, although not as strong and systematic, was found for increasing pressure. The OIL atomizer produced a spray with the smallest SMD at low GLRs and a fine spray for all other cases with MD40 and MD45. It also sprayed well with MD50 at GLRs of 10% and 20%, but it failed to atomize this liquid at lower GLRs. The spray stability, in terms of the STD of droplet size (Tab. 7), was the best among the tested atomizers for all cases and with each liquid. This agrees well with the visual observations. Among the set of tested atomizers, the spray with the best average drop size and stability was generally acquired with the Y-jet atomizer. It produced stable sprays for the less viscous liquids (MD40, MD45), with even a slightly lower SMD at high GLRs than with the OIL atomizer. The SMD and stability data for the OIG atomizer were below (MD40) or around (MD45) the average of the set. It performed similarly to the OIL and Y-jet atomizers for the MD50 liquid, which none of the atomizers were able to atomize for the full GLR range. 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"Effervescent Atomizer Operation and Spray Characteristics", Atomization and Sprays, Vol. 3, pp. 137–155 Xiuyuan M., Yufeng D., Meng L. (2013). “Atomization of petroleum-coke sludge slurry using effervescent atomizer”, Experimental Thermal and Fluid Science, Vol.46, pp 131-138, ISSN 0894-1777 Zhou Y., Zhang M., Yu J., Zhu X., Peng J. (2010). “Experimental investigation and model improvement on the atomization performance of single-hole Y-jet nozzle with high liquid flow rate”, Powder Technology Vol. 199, pp. 248–255 35 LIST OF FIGURES Figure 1. Arrangement of the measurement and visualization systems Figure 2. Simplified schematic of the experimental rig Figure 3. Schematics of the investigated atomizers: a) Y‒jet, b) OIG, c) OIL, d) CFT Figure 4. Image pre-processing Figure 5. Particle (ligament) tracking Figure 6. Liquid breakup regimes Figure 7. Near-nozzle spray pattern for μ = 308 mPa·s Figure 8. Near-nozzle spray pattern for μ = 143 mPa·s Figure 9. Near-nozzle spray pattern for μ = 60 mPa·s Figure 10. Comparison of the gas-to-liquid momentum ratio for the OIL and Y-jet atomizers Figure 11. Estimated internal flow of the Y-jet atomizer Figure 12. Two-phase flow patterns Figure 13. The estimated two-phase flow for the OIL atomizer Figure 14. Measured Sauter mean diameter at 100 mm downstream of the discharge orifice, measured only for regimes with well-developed sprays 36 LIST OF TABLES Table 1. Physical properties of the water–maltodextrin solutions at room temperature Table 2. The important geometrical parameters of the atomizers Table 3. Measured liquid mass flow rates in [kg/hod] for all atomizers and working regimes Table 4. Assessment of spray cone stability Table 5. Spray cone stability Table 6. Internal flow patterns of the OIG and OIL atomizers, estimated using the baker’s map Table 7. Calculated standard deviations of SMD [μm]