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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) . 

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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... (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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... 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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... 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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... 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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... 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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... 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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... (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 ...
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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 ...
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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.