Slip ratio (gas-liquid flow)
Encyclopedia
Slip ratio in gas-liquid (two-phase) flow, is defined as the ratio of the velocity of the gas phase to the velocity of the liquid phase.
In the homogeneous model of two-phase flow, the slip ratio is by definition assumed to be unity (no slip). It is however experimentally observed that the velocity of the gas and liquid phases can be significantly different, depending on the flow pattern (e.g., plug flow, annular flow, bubble flow, stratified flow, slug flow, churn flow). The models that account for the existence of the slip are called "separated flow models".
The following identities can be written using the interrelated definitions:
where:
For homogeneous flow, S = 1.
The Chisholm correlation is:
The Chisholm correlation is based on application of the simple annular flow model and equates the frictional pressure drops in the liquid and the gas phase.
In the homogeneous model of two-phase flow, the slip ratio is by definition assumed to be unity (no slip). It is however experimentally observed that the velocity of the gas and liquid phases can be significantly different, depending on the flow pattern (e.g., plug flow, annular flow, bubble flow, stratified flow, slug flow, churn flow). The models that account for the existence of the slip are called "separated flow models".
The following identities can be written using the interrelated definitions:
where:
- S - slip ratio, dimensionless
- indices G and L refer to the gas and the liquid phase, respectively
- u - velocity, m/s
- U - superficial velocitySuperficial velocitySuperficial velocity , in engineering of multiphase flows and flows in porous media, is an hypothetical fluid velocity calculated as if the given phase or fluid were the only one flowing or present in a given cross sectional area. Other phases, particles, the skeleton of the porous medium, etc...
, m/s - ε - void fraction, dimensionless
- ρ - density of a phase, kg/m3
- x - steam quality, dimensionless.
Correlations for the slip ratio
There are a number of correlations for slip ratio.For homogeneous flow, S = 1.
The Chisholm correlation is:
The Chisholm correlation is based on application of the simple annular flow model and equates the frictional pressure drops in the liquid and the gas phase.