Date of Award

Fall 1998

Document Type


Degree Name

Doctor of Engineering (DEng)


Chemical Engineering

First Advisor

Charles Sheppard


The two-phase flow system is a multifaceted engineering task with many industrial applications. The accurate prediction of the behavior of such systems is of special importance.

This study is directed toward improving and integrating what is known about the gas-viscous liquid flow behavior during vessel depressurization, specifically, visually characterizing the top venting of saturated-viscous fluids. The experimental results are needed to improve the design methodologies for pressure-relief systems.

Lab-scale vessel depressurization experiments with initially saturated fluids were performed. In particular, a problem arose when sodium tetraborate decahydrate solution (model fluid) saturated with carbon dioxide gas is vented from a 5.3-liter vessel.

The test facility has been constructed to permit the visual observation of various influential parameters' effect on depressurization. Parameters examined included the flow behavior response to a change in the fluid properties, the initial liquid fill, the initial pressure, and the vent line diameter. The fluids used were water, foamy fluids, and high viscosity fluids. The resulting level swell, vented mass, and pressure-time profile were recorded and analyzed for each case.

Photographic analysis has been used to examine bubble characteristics and to estimate the bubble size and bubble rise velocity. A high-speed, high-resolution digital camera has been used to capture the depressurization events.

The study presented a useful description for the venting process. The test results are of direct theoretical and practical importance for the design of pressure-relief devices. The study demonstrated that the two-phase flow during the vessel depressurization was strongly influenced by the initial conditions of vessel pressure and liquid level as well as the fluid properties like viscosity and foaming tendency. Further, the study examined the bubble characteristics like bubble size and bubble rise velocity. It was concluded that bubble behavior during depressurization is affected by the system pressure and the fluids physical properties.