A study of the effect of flowrate transients within the slug flow regi
me was carried out in the WASP Facility at Imperial College. The test
section consisted of a 36 m long, nominal 3-inch diameter stainless st
eel pipe. Air and water were used as the test fluids and the response
to a change for flowrate of either phase was measured using a series o
f conductivity probes, pressure transducers and a gamma densitometer.
When the gas flowrate was increased, the pressure was found to peak ab
ove the new steady state value before recovering. In addition, a tempo
rary period of intense slugging was observed, particularly at higher l
iquid superficial velocity, as well as a decrease in holdup. When the
gas flowrate was decreased, a rarefaction in the inlet pressure was ob
served together with a period of stratified flow, even though conditio
ns were such as to cause slug flow in both the initial and final stead
y states. The period of stratified flow was observed to be longer for
lower liquid flowrates. For an increase or a decrease in the gas flowr
ate, the amplitude of the pressure peak was observed to increase with
the ratio of the higher to the lower gas flowrate. In contrast, change
s in liquid flowrate were accommodated by smooth transitions between t
he corresponding steady states. (C) 1998 Elsevier Science Ltd. All rig
hts reserved.