TABLE OF CONTENTS Some of the most complex fluid flow problems arise in the depressurization or venting of vessels, particularly reactors and storage vessels. In order to specify the venting arrangements for a vessel, it is necessary to determine the flow, the phase condition of fluid and the vent area required for this flow. The venting of vessels is complicated by the fact that in many situations the flow is likely to be two-phase. It is necessary therefore, to be able both to estimate the vapour mass fraction, or quality, of the fluid entering the vent and the flow through the vent.
The need to determine the quality of the fluid vented has been highlighted during the work of the DIERS project. The quality of the fluid entering the vent is determined by liquid swell and vapour disengagement. There are two principal regimes that are recognized as occurring when a vessel is depressurized. If the liquid is non-foaming the regime tends to be churn turbulent, where as if it is foaming the regime is bubbly.
For a non-foaming liquid, methods have been developed to predict the onset of two-phase flow. In the depressurization of a vessel containing such a liquid there will, ingeneral, be a region in which the flow is all vapour and another region in which it is two-phase. A large initial vapour space, or freeboard, will favour all vapour flow. For a foaming liquid it is necessary to assume two-phase flow. Broadly, a pure...
