Characteristics of flowrate transients in slug flow

A study of the effect of flowrate transients within the slug flow regime was carried out in the WASP Facility at Imperial College. The test section consisted of a 36 m long, nominal 3-inch diameter stainless steel 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 of conductivity probes, pressure transducers and a gamma densitometer. When the gas flowrate was increased, the pressure was found to peak above the new steady state value before recovering. In addition, a temporary period of intense slugging was observed, particularly at higher liquid superficial velocity, as well as a decrease in holdup. When the gas flowrate was decreased, a rarefaction in the inlet pressure was observed together with a period of stratified flow, even though conditions were such as to cause slug flow in both the initial and final steady states. The period of stratified flow was observed to be longer for lower liquid flowrates. For an increase or a decrease in the gas flowrate, the amplitude of the pressure peak was observed to increase with the ratio of the higher to the lower gas flowrate. In contrast, changes in liquid flowrate were accommodated by smooth transitions between the corresponding steady states. (C) 1998 Elsevier Science Ltd. All rights reserved.