Gas-liquid flow in tubes occurs in a wide variety of chemical, power generation and process industries. Depending on the flow configuration, it can take different forms, for example, flow in horizontal tubes, vertical tubes (upward or downward flow), inclined tubes or coiled tubes and can be either co-current or countercurrent flow. Also, the two phases may flow in separated layers as in stratified flow or in dispersed flow as in bubbly flow and gas-droplet flow or in a combination of both as in annular flow. All these flows are encountered in practical situations.
The nature of gas-liquid flow in tubes is quite complex due to the presence of a mobile and pliable interface between the two phases across which exchanges of mass, momentum and heat take place. Normally, the shape and structure of the interface determines the transport coefficients. Due to this, gas-liquid flow is classified in terms of flow patterns based on the configuration of the interface. Four major flow patterns are recognized for horizontal flow: stratified flow, bubbly flow, slug (or plug) flow and annular flow. In vertical flow, stratified flow does not exist but an additional flow pattern, namely, churn flow is often distinguished. (See entry Two-Phase Flows for details.)
Much research has been done over the past few decades on determining the characteristics of gas-liquid flow in tubes. Several methods have been developed to calculate important design parameters such as the flow patterns, pressure drop and liquid holdup (or void fraction) in two-phase flow. These have been summarized in standard textbooks [Wallis (1969); Hewitt and Hall-Taylor (1970); Govier and Aziz (1972); Hetsroni (1982)] as well as in the present book. A comprehensive treatment of heat transfer in gas-liquid systems is given in Hewitt et al. (1994).
Govier, G. W. and Aziz, K. (1972) The Flow of Complex Mixtures in Pipes, Van Nostrand Reinhold, New York.
Hetsroni, G. (1982) Handbook of Multiphase Systems, Hemisphere, New York.
Hewitt, G. F. and Hall-Taylor, N. S. (1970) Annular Two-Phase Flow, Pergamon Press.
Hewitt, G. F., Shires, G. L., and Bott T. R. (1994) Process Heat Transfer, CRC Press.
Wallis, G. B. (1969) One-Dimensional Two-Phase Flow, McGraw-Hill, New York.