Critical heat flux

Prediction of the slug-to-churn flow transition in vertical two-phase flow

Flooding and churn flow in vertical pipes

The linear stability of the two‐layer flow of immiscible, incompressible fluids in an inclined channel is considered. In the long‐wave limit, mechanisms for linear instability, and the consequences of competition between mechanisms, are identified. For arbitrary wave numbers, air–water and olive oil–water systems are considered, in order to determine the influence of the channel thickness and the mean interfacial height on the stability of the flow. This paper characterizes those physical situations in which the primary instability is to long‐wave interfacial disturbances. The odd Orr–Sommerfeld shear mode within the water layer, which is necessarily stable in plane Poiseuille flow, is found to grow and even be the dominant mode of instability for the olive oil–water system. The consequences beyond linear stability are discussed.

Linear stability theory of two-layer fluid flow in an inclined channel

A comparison between flooding correlations and experimental flooding data for gas-liquid flow in vertical circular tubes

Countercurrent flow of a gas and a liquid in direct contact with each other is, of necessity, gravity dominated. That is, in the absence of electromagnetic force fields, thermocapillary effects, or concentration-capillary effects, countercurrent flow can be sustained only as a result of the difference in the gravitational force per unit volume on the gas and on the liquid. If the gas and liquid are simultaneously introduced into a porous medium or into a vertical or inclined pipe, the gas tends to rise relative to the liquid. If conditions allow complete separation, it is possible to maintain steady countercurrent flow in which the liquid discharges at the bottom while the gas flows out from the top. The countercurrent flow is opposed by interfacial friction between the phases, which always seems to increase monotonically as the relative countercurrent mean velocity of the phases increases. Hence, for a given geometry and liquid-gas pair, there is a maximum relative velocity that can be sustained in countercurrent flow. This point is known as the onset of flooding. Further increases in gas or liquid input ratas result in only partial delivery of the liquid out of the bottom. Eventually, if the gas velocity becomes sufficiently high, none of the liquid is delivered at the bottom, and fully cocurrent upward flow is established. If the liquid is being introduced from an upper plenum, none will penetrate into the pipe or porous medium when this second critical gas velocity is reached.

Sang Chun Lee

Papers

A critical review of the flooding literature