Flow in Gas Pipeline

[dingelde]

Hello,

I have a quick question that I cant seem to get an answer to. The velocity for gas in a pipe is calculated taking into account temperature and pressure:

v=14.7349(Q_b/d_s)(P_b/T_b)(ZT/P)

I understand this to be the velocity of a gas particle on a streamline travelling from point a to point b.

My question is, what is Flow/Area for gas in a pipeline? It is a velocity, but what is this velocity? Is it a gas particle on a streamline as well? For the same system, the two equations give two very different velocities. Thanks!

 

[zdas04]

It really depends on how you are planning to use the information. If I was trying to set a no-flow alarm, I'd use the slowest velocity calculated in the system. If I was trying to set an exclusion-zone alarm I'd use the fastest velocity calculated in the system. I can't imagine a use for this data that the best number to use would be an average of the average velocities in the two line sizes. Maybe there is one, but it isn't coming to me.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

 

[dingelde]

Latexman, a "squeezer" is what we call our mechanical vice that literally squeezes the Poly Ethylene Pipe shut. It can then be released slowly and the pipe bounces back to full diameter. It would be used in the same way a stopper is on a steel line.

zdas04/ione thanks for your thoughts. I wouldnt have been too concerned with it if it wasnt for the fact that the two velocities (and therefore time) are so different. Using the standard flow rate gives a velocity about 6X faster than the calculated "actual" velocity for pipe 1 in the example I gave above. I may consider using the slower velocity to ensure displacement is occuring. The time estimate is not as big of a deal, I will run some field tests and see what I get. Thanks!

 

[zdas04]

A VELOCITY "CALCULATED" DIRECTLY FROM A STANDARD FLOW RATE WITHOUT CONVERTING TO ACTUAL FLOW RATE HAS ZERO PHYSICAL MEANING. None. It doesn't mean a single thing. It cannot be used for anything. Ever. Don't compare it to anything. Don't use it for anything. It is meaningless.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

 

[ione]

Using flow rate at standard conditions to calculate actual velocity is the same as that completely neglecting the effects of compressibility and treat a clearly compressible flow as it were incompressible.

 

[zdas04]

It is really a lot worse than that. It is more like thinking you are writing a check when you are actually drawing a cartoon.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat