The simultaneous flow of liquid and vapor/gas in a pipe has been a subject of interest for many years. Whereas single component flows can be shown to follow simple models, two phase flows have been shown to follow much more complex models. With the introduction of a second component of flow there is an increased pressure drop. This increase in pressure drop is due to the fact that the boundary of either phase is no longer the smooth wall of a pipe but a rough, wavy, and sometimes turbulent interface. Many investigators have studied this problem and have devised models with varying degrees of precision for predicting the characteristics of two phase flow and its associated increase in pressure drop.

There are typically 7 major flow patterns to consider when one speaks of two phase flow. This investigation will only be concerned with 4 of these flow patterns. These 4 flow patterns are illustrated in Fig. 1. Approximately in order of occurrence, as the ratio of gas to liquid flow increases, the 4 specific flow, patterns which are of interest are:

1. Bubble Flow - Flow in which bubbles of gas move along the upper part of the pipe at approximately the same velocity as the liquid.

2. Plug Flow - Flow in which alternate plugs of liquid and gas move along the upper part of the pipe.

3. Stratified Flow - Flow in which the liquid flows along the bottom of the pipe and the gas flows above, over a smooth liquid-gas interface.

4. Slug Flow - Flow in which a wave is picked up periodically by the more rapidly moving gas to form a frothy slug which passes through the pipe at a much greater velocity than the average liquid velocity.

This investigation encompasses all four of these flow regimes, with the main emphasis on stratified flow, plug flow, and slug flow.