Mw. Wambsganss et al., DETERMINATION AND CHARACTERISTICS OF THE TRANSITION TO 2-PHASE SLUG FLOW IN SMALL HORIZONTAL CHANNELS, Journal of fluids engineering, 116(1), 1994, pp. 140-146
Two-phase pressure drop and fluctuating static pressuresf were measure
d in a small horizontal rectangular channel (hydraulic diameter = 5.44
mm). The two-phase fluid was an air/water mixture at atmospheric pres
sure tested over a mass flux range of 50 to 2000 kg/m2.s. Two-phase pa
tterns were identified and an objective method was found for determini
ng the flow pattern transition from bubble or plgu flow to slug flow.
The method is based on an RMS static pressure measurement. In particul
ar, it is shown that the transition is accompanied by a clear and abru
pt increase in the RMS pressure when plotted as a function of mass qua
lity. Use of the RMSf pressure as a two-phase flow pattern transition
indicator is shown to have advantages over pressure-versus-time trace
evaluations reported in the literature. The transition is substained b
y a clear local change in slope in in the literature. The transition i
s substained by a clear local change in slope in the curve of two-phas
e pressure drop plotted as a function of either Martinelli parameter o
r mass quality. For high mass fluxes, the change in slope in distingui
shed by a local peak. Some degree of substantiation was found in previ
ous work for both of the results (the RMS static pressure change and t
he local pressure drop change) at the transition to slug flow.