Gas entrainment rate and flow pattern of vertical plunging liquid jets

Abstract

For a vertical plunging liquid jet system using various liquids, the effects of the operating conditions including the nozzle length-to-diameter ratio on the gas entrainment rate Q, were evaluated experimentally. The differences in Q, were related to the changes in the jet shape before plunging and the velocity of the plunging liquid jet at the point where the gas sheath breaks up. Empirical relationships were also presented to predict the maximum depth Z of bubbles entrained by the diffusing jet. The changes of Z were further discussed in terms of the downward liquid velocity distribution in the submerged two-phase region, which depends mainly on the size of entrained bubbles.On a evalue de faqon experimentale pour un systkme a jet liquide plongeant utilisant des liquides varies, les effets des conditions d'opkration, notamment le rapport entre la longueur et le diamktre de l'orifice sur la vitesse d'entraineinent du gaz Q,. Les differences dans Q, ont Ct6 relikes aux changements dans la forme du jet avant l'immersion et B la vitesse du jet liquide plongeant au point ou I'enveloppe du gaz se brise. On a Cgalement present& des relations empiriques pour prCdire la profondeur maximum Z des bulles entrainees par le jet diffusant. Les changements dans Z ont ensuite CtC examines par rapport a la distribution de la vitesse liquide descendante dans la region biphasique immergee, qui depend principalement de la taille des bulles entrainkes.

Gas entrainment behavior of vertical plunging liquid jets in terms of changes in jet surface length

“…For the shape of the discharging jet, regardless of Fr and L,lD, or the liquids, roughly two types of jets were observed, as was the case in the previous works (Ohkawa et al, 1987;Kusabiraki et al, 1990); one is of a surface disturbance type at the dimensionless nozzle height H,, /D, below 20, and the other is a type of sinuous undulation at H,,/D,, above 20. At the present experimental conditions, no break-up of liquid jets occurred.…”

“…Some methods (Henderson et al, 1970;Burgess et al, 1972;Van de Sande and Smith, 1973;Ervine et a]., 1980;McKeogh and Ervine, 1981) to evaluate the change of jet shape are also available. The main objective of the present study is to investigate quantitatively the surface length change of the jet under various operating conditions and to find the relation between their changes and those in the gas entrainment rate observed in the previous work (Kusabiraki et al, 1990). The main objective of the present study is to investigate quantitatively the surface length change of the jet under various operating conditions and to find the relation between their changes and those in the gas entrainment rate observed in the previous work (Kusabiraki et al, 1990).…”

“…At the present experimental conditions, no break-up of liquid jets occurred. The results (Kusabiraki et al, 1990) of the dimensionless gas entrainment rate Q, /QL measured at the same operating conditions of D,, , L,, /D,, and H,, ID,, are shown in Figure 3b. The relationship between ( P , -H,,)/H,, and the Froude number, Fr, is shown in Figure 3a.…”

“…A conical nozzle with inside diameter D, between 0.007 and 0.0178 m having a contraction angle of 45" was used. Photographs of the jet from the nozzle exit to the designated position, i.e., that corresponding to the nozzle height H, in the previous work (Kusabiraki et al, 1990) which dealt with the gas entrainment rate Qg, were first taken. The range of the nozzle length-to-diameter ratio L, / Q 1 (aspect ratio) was between 5 and 70.…”

The detection and dimension of bubble entrainment and comminution

“…[7][8][9][10] Several studies have examined entrainment by liquid jets. [11][12][13][14][15][16] Acoustic emissions and ''signatures'' have been identified with other forms of liquid drop impact, including rainfall, [17][18][19][20] and wave breaking. 21,22 Such studies have in turn led to studies of the underlying fluid dynamics 23,24 and investigations of the possibility of using the acoustic signals for monitoring purposes.…”