Running gas pipe

[Balenza]

sanj wrote

a reducer that goes from 22 to 28mm

A reducer can't go from 22 to 28mm unless you want to call it an "upducer".

 

[chrishutt]

A reducer can't go from 22 to 28mm

It can if you fit it the wrong way round.....

 

[Agile]

Lets call it a transition!

I havew been wondering how to make a test length of 22/28 which I can reverse to measure the actual pressure loss.

But I cannot think of how I could do it (yet).

Tony

 

[Gasguru]

It might be a useful project for one of the gas colleges - re-write the tables for the real world.

 

[sanj.varah]

equivalent to 0.25m at 22mm

 

[Agile]

equivalent to 0.25m at 22mm

Could you advise the question thats the answer to please?

If its the resistance for a 28-22 transition then whats the resistance of a 22-28 transition?

According to this information a 10 m length of 22 mm would have a greater resistance if it was upsized every metre to 300 mm of 28 mm.

If true that defies common expectation and the tables we use.

Does anyone know of a simple computer program for pipe sizing? Or can anyone write one for us?

Tony

 

[Garthzog]

Does anyone know of a simple computer program for pipe sizing? Or can anyone write one for us?

Tony

ChrisR said earlier he has the calculation for that, so perhaps someone could write a simple Excel spreadsheet with it?

G

 

[Balenza]

Sanj.varah, I've very grateful for your explanations. I think I follow most of it, but there's at least one matter that still puzzles me.

If a certain length (including allowance for fittings, etc.) of 22mm pipe has a pressure drop of say 0.5 mbar for a given gas flow and a much longer length of 28mm pipe has the same pressure drop of 0.5 mbar, then when the two pipes are joined end to end the total pressure drop for the given gas flow will be 1.0 mbar.

However you seem to be saying that it will make a difference if the 22mm pipe is upstream of the 28mm pipe rather than vice versa (due to "recovery"). I can't see this, since the resistance of each pipe is exactly the same. Is it due to greater turbulence arising at the junction between the two pipes where the smaller (higher velocity) pipe leads into the larger (lower velocity) pipe?

If the transition from higher velocity to lower velocity causes more resistance than vice versa, would it not depend very much on the smoothness of the transition and would it actually be significant for a typical in-line reducer? Also where the outlet from the gas meter is 22mm anyway would it then make any significant difference which pipe came first?

Yep spot on, the position of the reducer has a marked effect. Due to the nature of the copper fittings, its much better to have the reducer getting smaller than bigger.

Pressure drop is always greater when you are "expanding" the flow. You get flow separation which causes the pressure drop. Here's a picture, have a look at the top picture.

Pressure drop is always greater when you are "expanding" the flow.

Are you still around sanj ?.

Your explanation is not very clear.
The drawing above only shows 2 types of restriction centered between pipes of the same diameter.
How can expanding the flow create more pressure drop. ?? ( I take it you are talking about pressure drop which leads to a greater load on say a pump at the begining of a pipe run to give an example and yes this could be pumping gas also.)
And how can you be expanding the flow in your example if the pipe diameter stays the same ??.

 

[megawatt]

Balenza: Forget the end-to-end pressure here, the important aspect to the discussion we've been having is what happens to the pressure from that measured at the centre of the venturi to that at the right hand end ... It will decrease.

This is, as both I and Sanj have explained, due to Boyles law ... As the volume of the duct is increased the pressure decreases.

MW

 

[Balenza]

megawatt wrote

As the main thing we are trying to do is to minimise pressure drop end to end

Then he wrote

Forget the end-to-end pressure here

eh ?.

It will decrease

So why do the following tables show a sudden enlargement in a transition joint causing more restriction as opposed to a sudden contraction which shows less restriction in equivalent length of pipe.

As the volume of the duct is increased the pressure decreases.

Measuring pressure at the transition and the pressure drop through a pipeline are totally separate.
Are the tables above incorrect ?.

 

[clf-gas]

megawatt wrote

As the main thing we are trying to do is to minimise pressure drop end to end

Then he wrote

Forget the end-to-end pressure here

eh ?.

It will decrease

So why do the following tables show a sudden enlargement in a transition joint causing more restriction as opposed to a sudden contraction which shows less restriction in equivalent length of pipe.

 

[sanj.varah]

apologies i have been away.

the main reason for the pressure loss when "expanding" the flow is due to the streamlines getting all turbulent. Ideally you want to slow velocity down and get pressure but as no process is 100% efficient this doesn't happen.

When contracting the flow, gases tend to behave a lot more predictably and you get increased velocity quite readily.

hope this helps

sanj

 

[sanj.varah]

http://www.iklimnet.com/expert_hvac/piping_eq_length.html

here's anothet link

 

[megawatt]

Balenza: I was clearly referring to static pressures measured at both points.

And if you want to quote something I've written at least have the courtesy to quote it all so that the context of what I've said isn't totally lost.

Your previous post does you no justice at all and just makes you look like a t i t.

Sanj has answered well enough for me so no need to discuss further as far as I can see.

If you still don't get it there are courses at college if you can spare the time.

MW

 

[Balenza]

http://www.iklimnet.com/expert_hvac/piping_eq_length.html

here's anothet link

Thanks for the link.
Their is quite a variance between the two tables.
How can these estimates be given without having reference to flow velocities ?.
Surely with differing flow velocities the pressure drops these contractions and enlargements create will then vary.