Yearbook 2013/2014 - ehedg

68 Flow behaviour of liquid jets impinging on vertical walls
Application to cleaning
Since R, and hence W, can now be estimated from Equation
(1), we can obtain a reasonable estimate of the wall area
contacted by the liquid in the jet and the stability of the falling
film generated. The influence of surfactants or the effect of
cleaning the surface, which will change the contact angle,
can also be assessed. Ongoing work in our group includes
investigations of inclined jets and non-vertical surfaces,
detailed analysis of the shape of the falling films, and
cleaning.
Acknowledgment
This work is not funded by a company or research council.
A PhD scholarship for Tao Wang and input from project
students is gratefully acknowledged.
References
Figure 4. Plot indicating stability of falling films generated by
horizontal jets impinging on a vertical glass wall. The lines show the
Hartley and Murgatroyd criterion, Equation (2), for water (in blue)
and an aqueous 0.1 mM Tween 20 solution (in red). Data points:
open symbols indicate that rivulet flow was observed, solid symbols
indicate gravity flow. Rivulet flow is expected for points lying on or
above the line. Test conditions: 1 mm nozzle, 20ºC.
The two lines on Figure 4 show the conditions under which
Equation (2) predicts a change in flow behaviour for water
and for a surfactant solution. The theory says that points lying
on or above the line should exhibit rivulet flow behaviour. For
the flow rates tested here, water exhibits rivulet flow, which
is consistent with Equation (2).
1. Morison, K.R., and R.J. Thorpe. (2002). Liquid distribution from
cleaning-in-place sprayballs. Food Bioproducts Proc., 80, 270-275.
2. Wilson, D.I., B.L. Le, H.D.A. Dao, K.Y. Lai, K.R. Morison, and
J.F. Davidson. (2011). Surface flow and drainage films created by
horizontal impinging liquid jets. Chem. Eng. Sci., 68, 449–460.
3. Wang, T., Davidson, J.F. and Wilson, D.I. (2013) 'Effect of
surfactant on flow patterns and draining films created by a horizontal
liquid jet impinging on a vertical surface', Chem. Eng. Sci., 88, 79-94.
4. Hartley, D.E. and W. Murgatroyd. (1964). Criteria for the breakup
of thin liquid layers flowing isothermally over solid surfaces. Intl
J. Heat Mass Transfer, 7, 1003-1015.
The presence of surfactant reduces the surface tension and
gives a smaller contact angle, which causes the transition
locus to move to larger Eötvös numbers. For similar flow
rates to the water tests, the surfactant solutions give wide
falling films, which is again consistent with Equation (2).