Venting Velocity

Please tell us: were you sleeping during the lecture, or have you repurposed the money that was intended for textbooks? One (or both) should be true.

Will one of your classmates not share their notes?

Lecture notes won't help here. Despite the granular details of the information posted, there is no way of predicting what will happen from the incomplete details provided. We know nothing about the volumes of the pipe or "big buffer vessel" (that's a nebulous description) or where in this kilometer run this buffer resides or even where this ball valve resides. There's no description of any geometry or elevation change in the kilometer run. Most importantly the initial (t₀) conditions of pressure levels prior to opening this mystery valve are not given.

If we fully open the ball valve what will be the velocity at the pipe outlet end? Really fast.

What will be the pressure in pipe just before the venting end? Really high.

You don't provide any useful information here, except the excessively high velocity which will render any calculations meaningless.

Apply Colebrook Equation.

It appears that this equation can be applied for cases in hydraulics.

If designed correctly, the initial velocity will be around 40m/s.

The pressure at the venting end of the pipe will be somewhere between 40barg and the ambient pressure of the space into which the pipe is venting, and will decay roughly exponentially towards the latter value.

Without knowing something about the dimensions of the equipment involved and some temperatures it is difficult to say much more.

Thanks a lot for comments. Ball valve is installed at buffer vessel outlet. Temperature is 35 degC. I presumed that buffer vessel/pipe size may not be of that much importance for calculating rough velocity if we consider that buffer vessel is replenished to maintain 40 barg pressure. Anyway buffer vessel volume is 100 cu.m, and pipe is 10".

How you calculated that the initial velocity will be around 40m/s? What will be the later velocity? One of my colleague says that if we open the ball valve full venting velocity will be supersonic. can it happen?

Are you asking us if 40 meters/second is supersonic?

Of course it is possible to have initially a supersonic velocity when venting. Your colleague can see the whole structure and fill in all of the critical missing details we do not know. It took us this long to find out that your buffer vessel is twice as large a volume as your 1 kilometer long 10 inch inner diameter pipe. (Weird mixing of measurement units.) We still do not know if it is valid to assume that opening this ball valve does the venting or where this valve resides in this venting problem. Nowhere in this thread is there any information of a venting orifice size or at what physical point the dangerously high 40 bar(g) pressure gets maintained.

It is equally possible your colleague was reminiscing of their scholastic engineering project to make a supersonic wind tunnel. This venting process brought up fond memories for them. You simply misunderstood what they were talking about and this configuration will never reach supersonic velocities.

I hate twenty question challenges.

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GA. Pl ref #6 "Ball valve is installed at buffer vessel outlet"

It's not a challenge question any way. an approximate guidance is enough to answer my curiosity.

"Calculated"?

40m/s was in the spec in the original posting!

_{Yet another "20 Questions" approach....}

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