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# Cavitation and liquid jet in a cylindrical nozzle (DN = 4 mm, Cu = 64, L/DN = 4) rational design of pressure atomizers. It should be noted that the spray angle θ (6) in the supercavitation regime is smaller in the case of smaller C u , i.e., the spray angle θ is 16 o for C u = 7.6 and 2.9, while θ = 9 o for C u = 1.5. The values of the conventional cavitation number σ defined by Eq. (3) are shown in Figs. 3 and 4 (6),(14) .

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The effects of nozzle geometry on cavitation in the nozzle of pressure atomizers and the liquid jet are examined using various two-dimensional (2D) nozzles with different geometries. Then, whether or not the conventional cavitation numbers can be used to predict the formation of supercavitation, in which liquid jet atomization is enhanced, is exami...

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... The change of flow path then results in totally different flow characteristics as well as its injected spray. The studies in a transparent symmetric scaled-up nozzle, both in cylindrical nozzle [27] and two-dimensional nozzle [14,28] have shown that the hydraulic flip occurs in both nozzles by increasing the flow rate so that the flow reattachment on the nozzle wall does not occur and results in a complete flow change without cavitation. The spray angle also becomes very narrow as a result of flow change from cavitation flow to hydraulic flip flow due to the extinction of cavitation cloud collapse in the hydraulic flip flow [14]. ...
... The spray angle also becomes very narrow as a result of flow change from cavitation flow to hydraulic flip flow due to the extinction of cavitation cloud collapse in the hydraulic flip flow [14]. Furthermore, an attempt to change the hydraulic flip thickness was done by changing the nozzle upstream width so that the incoming flow angle, which affecting the separated boundary layer, also changes proportionally [28]. However, the previous studies have not explained the complete mechanism and the whole phenomenon which left the hydraulic flip effect to remain unknown. ...
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Hydraulic flip is a common phenomenon that occurs in a short injector nozzle with a contraction flow which results in a separation flow without a wall reattachment. This phenomenon usually occurs in a gasoline direct injection (GDI) injector because the nozzle’s length-to-diameter ratio is low with high injection pressure. The efforts to investigate the hydraulic flip in a fuel injector nozzle have been paid in several studies. However, the investigation on the phenomenon in an actual GDI injector has not been well clarified yet since it is complicated to be quantitatively investigated due to its microscale and the flow location inside a solid non-transparent material. Besides, the hydraulic flip also affects the near-nozzle spray characteristics, but the previous studies are insufficient to explain the whole mechanism and characteristic despite their importance on the engine combustion quality. In this study, the hydraulic flip characteristic is investigated by varying the hydraulic flip thickness. The nozzle with a thinner hydraulic flip resulted from the application of hydro-grinding machining on the nozzle inlet so it forms a nozzle with a round inlet edge and less flow contraction. The characterization of internal flow and its correlation with the injected spray was done by investigating the effect of hydraulic flip thickness. The hydraulic flip phenomenon and the injected spray were captured by a high-speed visualization using a synchrotron X-ray to obtain a phase-contrast image. As a result, the hydraulic flip phenomenon was observed clearly in the tested actual GDI injector nozzles. The hydraulic flip thickness difference and how it affects the spray characteristics, i.e., velocity distribution, flow coefficients, turbulence intensity, spray dispersion, and SMD, were clarified. The results show that the thinner hydraulic flip leads to a higher discharge coefficient, lower turbulence intensity which results in slightly worse atomization, and a slightly narrower spray angle with more uniform spray velocity distribution.
... (ii) Mechanical vibrations, shock-waves, and cavitation in sprays ( Fig. 3): as liquid ows through a capillary, then, depending on the liquid thermophysical properties, ow rate, shearing gas-ow rate, dissolved gases, capillary geometry, etc., shock waves and cavitation events can take place. [41][42][43] Cavitation implosion of bubbles in water can lead to extremely high temperatures and pressures in localized "hot spots", leading to the production of OH radicals that could yield H 2 O 2 . 32 (iii) Dissolution of airborne ozone in water and its autodissociation ( Fig. 4-6): atmospheric/ambient ozone gas could dissolve in water and react to form H 2 O 2 . ...
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Recent reports on the formation of hydrogen peroxide (H$_2$O$_2$) in water microdroplets produced via pneumatic spraying or capillary condensation have garnered significant attention. How covalent bonds in water could break under such conditions challenges our textbook understanding of physical chemistry and the water substance. While there is no definitive answer, it has been speculated that ultrahigh electric fields at the air-water interface are responsible for this chemical transformation. Here, we resolve this mystery via a comprehensive experimental investigation of H$_2$O$_2$ formation in (i) water microdroplets sprayed over a range of liquid flow-rates, the (shearing) air flow rates, and the air composition (ii) water microdroplets condensed on hydrophobic substrates formed via hot water or humidifier under controlled air composition. Specifically, we assessed the contributions of the evaporative concentration and shock waves in sprays and the effects of trace O$_3$(g) on the H$_2$O$_2$ formation. Glovebox experiments revealed that the H$_2$O$_2$ formation in water microdroplets was most sensitive to the air-borne ozone (O$_3$) concentration. In the absence of O$_3$(g), we could not detect H$_2$O$_2$(aq) in sprays or condensates (detection limit: 250 nM. In contrast, microdroplets exposed to atmospherically relevant O$_3$(g) concentration (10-100 ppb) formed 2-30 $\mu$M H$_2$O$_2$(aq); increasing the gas-liquid surface area, mixing, and contact duration increased H$_2$O$_2$(aq) concentration. Thus, the mystery is resolved - the water surface facilitates the O$_3$(g) mass transfer, which is followed by the chemical transformation of O$_3$(aq) into H$_2$O$_2$(aq). These findings should also help us understand the implications of this chemistry in natural and applied contexts.
... These results may correspond to the study conducted by Satyanarayana et al. [19], showing that fluid properties significantly depend on the cross-section of the nozzle that further affects the flow within the nozzle. Experiments on two-dimensional nozzles were also performed by Mashida and Sou [20] and Sou et al. [21] for analyzing cavitation in liquid jets under different Reynolds number and cavitation condition. Another study in 1999 was conducted by Badock et al. [22], who focused on the impact of nozzle geometry and internal flow on the velocity of fuel droplets and spray characteristics. ...
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The study aims to determine the effect of nozzle groove on fluid flow through viscous 2D planar fluid. To fulfil the study’s aim, numerical method was adopted to introduce grooves of different dimensions from the nozzle exit. The study adopts SoldWork software was used to design nozzles and introduce groove shaped nozzles, each consisting of six different designs. The nozzle base model used in this study was similar to the one used in a previous study. The procedure was performed with different pressures (8, 10, and 12 bar) at the similar firefighting nozzle. The velocities contours were predicted based on the choice of nozzle section during the numerical stimulation. The results of present study demonstrated a new approach that can be used for increasing velocity at various types of modified nozzles through grooves at different pressures and locations. For grooves, dimensions 1×1 (mm) and location 15 mm at 8 bar, 10 bar and 12 bars showed no effect on velocity as it reduces velocity by increasing surface area. The velocity increases with increasing pressure in proportion relationship. This clearly explains that the groove has no effect on velocity as it increases due to increase in pressure. This is because the groove reduces the velocity by increasing surface area. The study concludes that use of groove increases velocity of water that further improves nozzles operation.
... Atomization of spray is enhanced at super cavitation (SP) and imperfect hydraulic flip (IHF) with long cavitation along the orifice wall. To quantitatively predict cavitation length in an orifice, we have confirmed that a dimensionless index, the modified cavitation number c based on the local pressure at vena contracta of the orifice, can be used to quantitatively predict cavitation length, cavitation inception and super cavitation formation, which is defined by [5][6]: ...
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Cavitation along orifice walls, string cavitation in a sac and orifices, and turbulent flows in multi-hole mini-sac diesel fuel injectors play an essential role in the characteristics of the fuel sprays, which affect the thermal efficiency and exhaust gas emissions of diesel engines. Thus, numerous visualization experiments and numerical simulations on the turbulent cavitation flow in mini-sac nozzles with various geometries and sizes have been carried out, which reported different characteristics of wall cavitation, string cavitation, and sprays. However, we cannot predict quantitatively the turbulent cavitating flows and the sprays since their governing dimensionless indices have not been clarified yet. In this study, we carry out high-speed visualizations of cavitation and liquid jets, high-speed stereo PIV, high-speed PIV, and numerical simulations of turbulent cavitating flows in various transparent multi-hole mini-sac nozzles with different injector sizes, needle lifts, liquid flow rates, nozzle hole numbers, hole diameters, hole positions, needle tip geometries, and liquid fuel properties to clarify the cavitation and flow structure in them as well as spray characteristics. Then, we propose new dimensionless indices, by which we can quantitatively predict the circulation in the sac, string cavitation diameter, cavitation length in an orifice, and the resulting spray angle.
... 10 Several experimental studies have examined the effect of the injector nozzle geometry on the characteristics of internal flow and consequently the issuing spray. 11,12 Strong recirculation evolves due to the sudden contraction at the inlet flow passage to the nozzle. Ranz 13 found that the initial disturbance of the injected liquid is caused by the nozzle entrance shape. ...
... 19 Regarding the passage geometry, the cavitation process in a nozzle with a two-dimensional (2D) cross section is the same as a nozzle with a circle cross section. 12 The geometry of the nozzle passage regarding its shape of being constant, divergent, or convergent affects the flow velocity and its jet characteristic. It is defined by its degree of conicity (k c ), which is defined as follows 20 ) where D N,i and D N,o are the inlet and outlet diameters, respectively, measured in microns. ...
... Regarding the effects of flow passage and injected liquid properties, Figure 9 presents a comparison among the Reynolds number values corresponding to the inception of cavitation according to some previous studies (Sou et al., 12,30,31 Nurick, 16 Park et al., 29 and Suh et al. 32,33 ) together with the results from the developed model. These studies were selected as the nozzle geometries are characterized by a regular rectangular cross section with a sharp entrance edge. ...
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In the present paper, the formation and development of cavitation inside the nozzle of an atomizer with different geometrical characteristics have been studied numerically. Different shapes of inlet nozzles and different nozzle-length-to-diameter ratios have been investigated. The developed model has been built as a three-dimensional (3D) one, where the turbulence is modeled considering large eddy simulation. The obtained computational results showed good agreement with the reported experimental results. It has been found that the occurrence of cavitation depends on the amount of energy needed to overcome the viscosity and friction between the liquid layers. The mass flowing through the nozzle decreases with increasing cavitation. The intensity of cavitation depends on the nozzle entrance shape. Sharp edges cause cavitation to occur early in the nozzle, followed by an inclined shape, and then the curved entrance. The dissipative energy in the cavitation and bubble collapse result in an increase in the turbulent kinetic energy of the issuing liquid. This causes more liquid disintegration, leading to larger spray volume and smaller droplet size. The obtained results for spray droplet size distribution have been compared with experimental data developed by other researchers, and a good agreement has also been found.
... At high pressure gradients, the cavitation envelope stretches very quickly in the direction of flow, and in the order of tens of µ s reaches the level of the tube outlet 10 . After reaching the level of the tube outlet, the opened cavitation layer is filled with air and the hydraulic flip phenomenon occurs [9][10][11][12] . The hydraulic flip has been experimentally studied in several publications, namely Cui et al. 11 and Sou et al. 12 ...
... After reaching the level of the tube outlet, the opened cavitation layer is filled with air and the hydraulic flip phenomenon occurs [9][10][11][12] . The hydraulic flip has been experimentally studied in several publications, namely Cui et al. 11 and Sou et al. 12 ...
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In this work we present experimental results of cross-sectional speed of water flow in narrow cylindrical metal tubes at high pressure gradients up to 1.1 GPa·\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\cdot$$\end{document}m⁻¹. The measurement draws attention to the paradoxical behaviour of flowing water in internal diameters less than 250 μ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\upmu$$\end{document}m. At constant pressure gradient, its cross-section speed decreases with decreasing diameter in accordance with the classical hydrodynamic prediction for turbulent flow in rough cylindrical tube. However for very low diameters below 250 μ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\upmu$$\end{document}m, the cross-section speed rises again and reaches almost the maximum theoretical value of the outflow speed for the appropriate pressure without energy loss caused by contraction or hydraulic friction. Our contribution describes mainly experimental character of the new phenomenon and its motivation is to promptly provide the material for further study to the professional public.
... Lin and Reitz (1998) draw attention to the need for considering the internal flow behavior. Other authors studied the effect of flow regime and injector geometry and were able to classify different types of cavitation (PAYRI et al., 2011;SOU et al., 2008;TO-MIYAMA, 2009;De Giorgi;FICARELLA;TARAN-TINO, 2013;BADOCK et al., 1999). The change of phase in a pipe due to heat transfer (named: chill-down) again is initiated prior to the injector (SHAEFFER; HU; CHUNG, 2013; RAMÉ; HARTWIG; MCQUILLEN, 2014), Generally, in particular for cryogenic fluids, the flow across the injector, in some extent may be twophasic and thus it interfere with a classical atomization process. ...
... Prior to the establishment of fully liquid flow regime, inside the injector a two-phase flow will be present (Fig. 8). For injector pressures higher than 15 bar the two-phase flow appear in the channel of injector and looks like the hydraulic flip described by Sou et al. (2008). Banuti e Hannemann (2010) suggest that this phenomenon could originate from heat transferred into the fluid from tube wall instead of cavitation. ...
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As part of an effort to understand the conditions for the ignition of cryogenic propellants in the low pressure environment, we conducted a research of internal flow of cryogenic jet. In this paper, the experimental investigation was exerted focusing on the qualitative morphology study of the cryogenic flow inside the jet injectors. The test facilities were carefully designed and allow for visualization and characterization of the flow. The results show a strong dependence of mass flow rate on the fluid temperature. The two-phase flow was observed even for a long time chilling down of the injector. The Jacob number is proved to be a good indicator for the flow regimes, and the bubbles are present in the flow every time. The injector geometry has an influence on the flow rate, with the tapered injector demonstrating a higher flow rate than the sharp one.
... (1) The lack of fundamental insights into the mechanism of spray-related multiphase flow. Although there have been plenty of optical studies working on explaining the physics of cavitation and flash boiling [10,16,151], in our opinion, dimensionless parameters such as Cavitation number and Superheat number cannot completely reflect what really happens inside the nozzle. It has been demonstrated both in this review and many other research works that various factors such as injector geometry, fuel property, flow fluctuation, nozzle surface roughness can substantially change the outcomes of the internal flow, while we have very limited knowledge on such process. ...
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Two-phase in-nozzle flows, such as cavitation and flash boiling, have been well studied as effective means to enhance spray breakup and atomization via phase change both within the nozzle and outside the nozzle. However, the challenges in observing the transient and complex phase change phenomena for such sprays have prevented further insights into the physics behind. The analysis and investigation on multiphase flow inside an atomizing nozzle are significant to elucidate the physics of liquid breakup mechanism and spray evaporation phenomenon. As such, optical accessible injectors and corresponding non-intrusive measurement techniques have been utilized in recent years to thoroughly investigate the multiphase flow characteristics within the nozzle. This work presents a comprehensive review of recent experimental efforts on using optical diagnostics and/or transparent nozzles. Aspects such as typical experimental apparatus, multiphase flow characteristics, measurement capacities and limitations, etc. are presented and discussed. The advantages/drawbacks of each technique are also incorporated. Finally, this review article comments on future opportunities and challenges of non-intrusive investigations for two-phase in-nozzle flows in obtaining better spray atomization performance.
... In this way, the states from no cavitation till hydraulic flip (flipping flow) were reproduced. All of them can be classified by the Reynolds and the Cavitation numbers computed from Eq.1, highlighting here that Re and  numbers are not closely related, Sou et al., 2008, being both necessary for this flow classification. In the Fig.2 caption, both the flow structure and the notation/meaning of the variables from the ...
Article
Cavitation in pressure injectors/atomizers strongly affects the liquid/spray jet behavior at its outlet. The type of atomization induced by cavitation allows developing more efficient devices if this cavitation state is controlled. Cavitating flow is related to turbulent and multiphase flows with mass transfer between the liquid and its gaseous phase. It is affected by several factors such as local pressure, local state of the turbulence, non-condensable dissolved gas concentration, nozzle geometry and others. Due to the high speed flow and small spatial and time scales involved, the study of cavitating flows by physical experiments is very expensive. On the other hand, several codes for numerical modeling of cavitating flows have been developed, but turbulent multiphase flow modeling is still a big challenge. Previous works showed that it is possible to capture several of the incipient cavitating flow characteristics performing a careful calibration of the Eddy Viscosity Models in nozzles with symmetrical inlet geometry and with round or square outlet sections. This work extends the study to nozzles with asymmetrical inlet geometry and square outlet section. It was demonstrated in previous works that a careful calibration task should be necessary, because there is a close relation between the cavitation inception/developing condition and the turbulence level in the flow leading to a 'non-standard turbulence state'. The spatial distribution and the slow decay of the turbulence level produced by cavitation could be related to some preferred turbulence scales in the process, so cavitating flows should not be modeled as typical turbulence. It is showed that based on the special characteristics of the incipient/slightly developed cavitating flows, a suitable calibration of the turbulence models allows obtaining improved results. These results become competitive when they are compared against ones computed by Large Eddy Simulations which need a lot of computational resources and an appropriate initial solution for running. It was also demonstrated that suppressing by calibration the level of the eddy viscosity in certain zones the vapor fraction predicted rises, provoking the incipient cavitation state in the flow. The obtained conclusions could be useful to improve injectors design using numerical modeling, because the detection of the incipient cavitation flow condition, useful to improve the atomization, could be captured accurately.
... In this way, the states from no cavitation till hydraulic flip (flipping flow) were reproduced. All of them can be classified by the Reynolds and the Cavitation numbers computed from Eq.1, highlighting here that Re and  numbers are not closely related, Sou et al., 2008, being both necessary for this flow classification. In the Fig.2 caption, both the flow structure and the notation/meaning of the variables from the ...
Conference Paper
Full-text available
Cavitation in pressure injectors/atomizers strongly affects the liquid/spray jet behavior at its outlet. The type of atomization induced by cavitation allows developing more efficient devices if this cavitation state is controlled. Cavitating flow is related to turbulent and multiphase flows with mass transfer between the liquid and its gaseous phase. It is affected by several factors such as local pressure, local state of the turbulence, non-condensable dissolved gas concentration, nozzle geometry and others. Due to the high speed flow and small spatial and time scales involved, the study of cavitating flows by physical experiments is very expensive. On the other hand, several codes for numerical modeling of cavitating flows have been developed, but turbulent multiphase flow modeling is still a big challenge. Previous works showed that it is possible to capture several of the incipient cavitating flow characteristics performing a careful calibration of the Eddy Viscosity Models in nozzles with symmetrical inlet geometry and with round or square outlet sections. This work extends the study to nozzles with asymmetrical inlet geometry and square outlet section. It was demonstrated in previous works that a careful calibration task should be necessary, because there is a close relation between the cavitation inception/developing condition and the turbulence level in the flow leading to a 'non-standard turbulence state'. The spatial distribution and the slow decay of the turbulence level produced by cavitation could be related to some preferred turbulence scales in the process, so cavitating flows should not be modeled as typical turbulence. It is showed that based on the special characteristics of the incipient/slightly developed cavitating flows, a suitable calibration of the turbulence models allows obtaining improved results. These results become competitive when they are compared against ones computed by Large Eddy Simulations which need a lot of computational resources and an appropriate initial solution for running. It was also demonstrated that suppressing by calibration the level of the eddy viscosity in certain zones the vapor fraction predicted rises, provoking the incipient cavitation state in the flow. The obtained conclusions could be useful to improve injectors design using numerical modeling, because the detection of the incipient cavitation flow condition, useful to improve the atomization, could be captured accurately.