Spray froth transition

Froth-spray. Froth-spray transition has been investigated for sieve trays using a variety of techniques (12,24,88-92,103,108-110). The gradual nature of this transition bred a large number of criteria for defining it, and made its correlation difficult. Excellent overviews of the state of art were given by Lockett (12) and Prado and Fair (103). 

An early study (91) reports that a correlation derived by Barber and Wijn for sieve tray froth-to-spray transition is also applicable to valve trays. A more recent study by Dhulesia (112) disagrees, and reports that valve trays have a stronger tendency to operate in the froth regime than sieve trays. Dhulesia proposed an alternative froth-spray transition correlation for valve trays, but this correlation is based on air-water data from a single type of valve tray, and its extension to other situations has not been tested. 

The recommended range of application of the correlation is given in Table 14-10. The clear liquid height at the froth-to-spray transition ha is calculated using the corrected Jeronimo and Sawistowski [Trans. Inst. Chem. Engnrs. 51,265 (1973)] correlation as per Eqs. (14-82) to (14-84). 

Flow regime. Since the trays are unlikely to operate in the spray regime (Sec. 6.4.2), it is best to first examine the froth-emulsion transition. This check requires using the Hofhuis correlation for clear liquid height (Sec. 6.3.5). 

Clear liquid height at the froth-to-spray transition, corrected for the effect of weir height on entrainment, given by Eq. (6.29), in of liquid. 

Lockett, M. J., "The Froth to Spray Transition on Sieve Trays, Trans. Inst. Chem. Engs. (London), 59, 1981, p. 26. 

Porter and Jenkins (24) presented a simple correlation for the froth to spray transition.. .. 

LOO 73] Loon R.E., Pinczewski W.V., Fell C.J.D., Dependence of the froth to spray transition on sieve tray design parameters , Trans. Inst. Chem. Engrs, vol. 51, p. 374, 1973. 

York, 1992). Figure 14-29 demonstrates the effect of liquid rate and fractional hole area on CSB. As liquid load increases, CSB first increases, then peaks, and finally declines. Some interpret the peak as the transition from the froth to spray regime [Porter and Jenkins, I. Chem. E. Symp. Ser. 56, Summary Paper, London (1979)]. CSB increases slightly with fractional hole area at lower liquid rates, but there is little effect of fractional hole area on CSB at high liquid rates. CSB,slightly increases as hole diameter is reduced. 

Strictly, the Jeronimo and Sawistowski correlation predicts clear liquid heights at the froth to spray regime transition. However, it has been shown (27,92) that clear liquid height in the spray regime is much the same as clear liquid height at that transition. 

---