DYNAMIC VOID FRACTION MEASUREMENTS IN HORIZONTAL DUCTS WITH SUDDEN AREA CONTRACTION

Void fraction distributions in horizontal pipes with sudden area contr action have been experimentally investigated. The experiments are aime d at analysing the effect of the singularity characteristics on void f raction profiles and phase distribution. The technique employed to obt ain the cross-sectional average void fraction along the test pipes is based on the instantaneous measurement of the electrical impedance of the air-water mixture. The instrumentation set up consists of ring ele ctrode pairs placed on the internal wall of the cylindrical test duct, flush to the pipe surface. Two different test sections, a 70/60 mm i. d. pipe and a 70/36 mm i.d. pipe have been employed. Plug and slug flo w regimes were investigated in order to obtain the mean void fraction along the channel in five different locations upstream and downstream the singularity. The analysis of the results, in terms of mean values and probability distributions, shows that the characteristics of the f low restriction deeply modify the how structure upstream and downstrea m the discontinuity. (C) 1998 Elsevier Science Ltd. All rights reserve d.