LPG pipe sizing 1

[poseilus]

I am trying to calculate friction losses in a pipe in order to find out what size of pump I will need.

LPG in a liquid state is transfered through this pipe. For this case am I supposed to assume the LPG liquid as an incompressible fluid and use the moody diagram?

At the end consumers where the LPG is at the gas state do I need to assume it as a compressible gas? With what equation do I need to find out the friction losses and the density of the LPG gas state at various pressures?

Merry Christmas to all and happy new year.

 

[Montemayor]

poseilus:

On a practical basis, liquids are taken to be incompressible and normally evaluated for pressure drops by the Darcy-Weisbach relationship(s) outlined and demonstrated via examples in Crane's "Flow of Fluids Through Valves, Fittings, and Pipe" (a.k.a., Technical Paper No. 410). I highly recommend you obtain, digest, and work the examples given throughout the edition.

One of the commonly accepted bases for applying the Darcy-Weisbach relationships is that they can also be used to calculate compressible (gas, vapor) fluids' pressure drops - as long as the calculated pressure drop does not exceed 10% of the initial pressure. Under average, normal conditions of flow this is usually the case and the Darcy-Weisbach is used for this application.

I hope this response answers your basic questions and concerns. ¡Feliz Navidad y Prospero Año Nuevo!


Art Montemayor
Spring, TX

 

[poseilus]

Thank you Montemayor.

While calculating the friction losses what should I consider as a max speed of LPG in a pipe. Specifically are there any limitations on the speed of LPG at liquid and at gas state?

How can I find the Technical Paper No. 410 free?

Thank you for your precious time

Happy new year.

 

[Montemayor]

poseilus:

Normally, the velocity (not "speed") is that velocity that is acceptable to you while resulting in an acceptable pressure drop for the LPG you are transporting (whether as a liquid or as a vapor). I cite this generality because it is often the acceptable pressure drop that is the main criteria for the engineer. There are, of course, other effects in fluid flow that could set the velocity as an important criteria for design: pipe parent metal errosion, velocity noise, pipe vibration, etc. However, the assignment of a maximum velocity is normally set from empirical or prior knowledge about these effects and their relationship to the fluid in question. Engineering literature and books serve as a starting point in this respect and this background is normally reinforced in the engineer as he/she gain field experience and know-how.

There is a physical limitation with regards to gas/vapor flow in a pipe and it involves the velocity of sound. You will find all this explained in Tech Paper #410 in case you failed to obtain any teaching or engineering training on this subject.

You can find Crane Technical Paper No. 410 at:

http://www.cranevalve.com/tech.htm

It will cost you $36.00. Forget about finding it "Free" -- unless, of course, if get one for Christmas or you have no scrupples about stealing one. Like most valuable engineering knowledge, you have to pay a price. Another excellent fluid flow information source is "Cameron Hydraulic Data". There are several threads on this forum regarding how to find and order it on the internet.

I hope this information helps.


Art Montemayor
Spring, TX

 

[LREY]

Your you can use software the COSMOS FLOWORKS that comes associate to the SOLIDWORKS