6 replies to this topic

[August]

A 3 inch branch on a 8 inch steam line. Medium is superheated steam at 5 barg, 350 C. flow =7.5 kg/s in the 8 inch line.
I want to know the flow in the 3 inch branch line.

I tried Bernouli's Equations. But I could not get a reasonable result.

Can anybody give me a clue....

Thanks in advance.

[Art Montemayor]

First, you have to give us a LOT of clues - like a detailed sketch. We don't know where you are adding (or is subtracting?) the branch flow.

We need basic data - like pressures. There is no flow in either line without a corresponding driving force. What is the driving force?

[August]

Here is the sketch. very limit knowns.
steam from a steam tank with pressure 5.7 barg at the outlet. Pressure drops to 5 barg at the tie-in(the 3"inch) point.

Attached Files

•  flow cal.png   5.1KB   9 downloads

Edited by August, 10 December 2012 - 04:45 PM.

[kkala]

Let the steam pressure at end of 8" line be P1, and P2 at end of 3" line. P1 and P2 are given. Evidently P1+ΔP1=P2+ΔP2=5 barg (1), ΔP = pressure drop in the line.
Let q1=flow in 8" line and q2=flow in 3" line; q1+q2=7.5 kg/s (2).
Steam flow (as in many other gas flows) is usually restricted by valves, located downstream of the tie-in.
For an assumed q1, estimate opening of valve on 8" line to result in total pressure drop = 5 barg - P1. Then for q2=7.5 kg/s - q1, estimate opening of valve on 3" line to result in total pressure drop = 6 5 barg - P2.
Repeat above calculation for several pairs of q1, q2; explore and check where valves can control the flow (probably for Cvs between 10% and 85% of max Cv concerning globe valves).
Use of piping software would make things easier (even so, better to do some calculations manually).
Actual situation may be more complex, but hopefully above provides a tip.

Editing note 13-12-2012: typo corrected

Edited by kkala, 13 December 2012 - 03:02 AM.

[S.AHMAD]

As mentioned by kkala, we need to know the final pressure, length of pipe and fittings for each respective branch.

[August]

As mentioned by kkala, we need to know the final pressure, length of pipe and fittings for each respective branch.

I don't have them. If I have, I think I am managed to do the calculation. I am wondering, is that possible, to calculate the flow in the branch line without downstream data. Like to calculate the liquid flow in the branch.

[wojtar]

The calculation is very simple but cannot be done with almost no data. How do you know that the flow in main pipe is 7.5 kg/s?
Where is it measured -> before or after the branch?

All you need is:
1) Detailed drawings of existing pipelines (with all valves, flow meters other sources of pressure drop).
2) Pressure at the begining of main pipeline.
3) Pressures at the end of main pipe and branch.

Without such information you are not able to do the calculation.

Edited by wojtar, 14 December 2012 - 11:09 AM.