Flow in Eccentric Annuli

[Atholl]

Hi all,

Does anyone know of any correlations to estimate the velocity in the narrow gap area of an eccentric annulus? I know the velocity is lower in this area and heard that there are simple empirical relations to estimate how much lower the velocity is (probably as a function of inner pipe eccentricity) in relation to concentric annulus values. I know there are many full analytical solutions for eccentric velocity profiles, but I'm looking for the quick rule of thumb correlation.

Thanks in advance,


Atholl

 

[tlee123]

OK, I'll give it a try. Since flow rate is a function of the cube of the gap and the flow area is a linear function of the gap (for small changes in gap), then I would say that the velocity is a function of the square of the gap (average velocity=flowrate/area).

So if the gap were to be cut in half, I would expect the average velocity to be only 1/4 of the original in that area.

For my answer to work, two assumtions are made:

1) You say the gap is narrow. With a very narrow gap, the flow can be analyzed as flow between parallel plates. Figure that the ratio of ID to OD should be at least 0.95.

2) The flow must be laminar. Look for Reynold's number to be less than 1000 to be safe.

Tom