Pressure loss on gas pipe (BS 6891 pipe sizing)

[Windy]

Hi,
I'm doing my ACS and have an issue with pressure loss calculations!!
sample question : "what would the pressure loss per meter be on copper tube of 15mm feeding a 12kw (gross) gas hotplate"
I can't for the life of me get the correct answer.....
I nett the hotplate 10.81kw divide that by 9.7 to get 1.11M3/h I then use the pipe length table which shows 15mm 1.3M3/h is maximum length of 12meters.
That means (i think) in 12meters of 15mm copper the loss is 1mb, so if i divide 1 by 12 it gives me 0.0833mb drop per meter ??
but the answer is 0.1042mb

I look forward to your help.....

 

[Harvest Fields]

Hold on. You say you have given the answer at the end??? I haven’t checked it though. So it could be wrong. You having us on here?

 

[ShaunCorbs]

12 kw gross

10.90 kw net

15mm at 10 m with 1 mbar drop 1.1 m3/h

1.1 divided by 10 = 0.11 mbar drop

 

[Windy]

Not having you on, Harvest...
got the question from an online site.....

 

[ShaunCorbs]

Hi,
I'm doing my ACS and have an issue with pressure loss calculations!!
sample question : "what would the pressure loss per meter be on copper tube of 15mm feeding a 12kw (gross) gas hotplate"
I can't for the life of me get the correct answer...
I nett the hotplate 10.81kw divide that by 9.7 to get 1.11M3/h I then use the pipe length table which shows 15mm 1.3M3/h is maximum length of 12meters.
That means (i think) in 12meters of 15mm copper the loss is 1mb, so if i divide 1 by 12 it gives me 0.0833mb drop per meter ??
but the answer is 0.1042mb

I look forward to your help...

you need to divide 1.3 by 12 not 1 = 0.1083 m bar

 

[Windy]

you need to divide 1.3 by 12 not 1 = 0.1083 m bar

where does the 1.3 come from?

 

[ShaunCorbs]

where does the 1.3 come from?

1.3 m3/h at a max length of 12m

So you have 12 m of copper and at the end of it you can pass / pull off 1.3m3/h with your 1 mbar pressure loss

Eg the capacity of the pipe at 12m

 

[Windy]

1.3 m3/h at a max length of 12m

So you have 12 m of copper and at the end of it you can pass / pull off 1.3m3/h with your 1 mbar pressure loss

Eg the capacity of the pipe at 12m

I thought the maximum lengths on the table were equivalent to 1mb drop?

 

[ShaunCorbs]

I thought the maximum lengths on the table were equivalent to 1mb drop?

this will confuse you now

To estimate pressure loss across a pipe leg

(mbar) = (328785 ÷ dia + 7558) x m3/h x m3/h ÷ dia ÷ dia ÷ dia ÷ dia ÷ dia x Length

so

328785 divided by the dia of the pipe (15mm) plus 7558 = 29477

29477 x 1.3 x 1.3 = 49816.13

49816.13 divided by the dia of the tube 5 times then times by the length

49816.13 ÷ dia ÷ dia ÷ dia ÷ dia ÷ dia x 1 = 0.065 mbar per m of 15mm

 

[ShaunCorbs]

this one might be better

 

[Harvest Fields]

this one might be better

Has the site changed shaun? Been having trouble opening attachments like this.

 

[ShaunCorbs]

Has the site changed shaun? Been having trouble opening attachments like this.

No computer normally opens them fine phones can be a bit hit and miss

 

[Windy]

i can't open those.....
but we have a lot of different answer....

 

[Windy]

if i do the question on my Anton app it comes out at 0.1042
exactly as the question states!! I'm glad its not just me but won't help me for the exam

 

[ShaunCorbs]

It’s all aprox especially when your working by the m

 

[Windy]

It’s all aprox especially when your working by the m

i get that BUT the answers are 0.1414 0.2296 0.1042 0.0719 so you could choose at least 2 of those answers and maybe even 3 and be aprox (as you say) and fail its annoying

 

[ShaunCorbs]

Go back to your tutor and ask them to do a lesson on it

 

[Harvest Fields]

Go back to your tutor and ask them to do a lesson on it

I posted that first then deleted it.

 

[Windy]

Go back to your tutor and ask them to do a lesson on it

yeah i will.... thanks all hope i haven't be a pain

 

[Riley]

Not at all

 

[Chuck]

i get that BUT the answers are 0.1414 0.2296 0.1042 0.0719 so you could choose at least 2 of those answers and maybe even 3 and be aprox (as you say) and fail its annoying

Hmm. I'd convert 12kW gross flow by dividing by 10.76, giving 1.12 m^3/hr, which everybody seems to be happy with. According to Table 1, here:

https://copperplumbing.org.uk/sites...achments/domestic-gas-planning-and-sizing.pdf

1.1 m^3 / hr gives a pressure drop of 1 mbar along 15m of 15mm/0.7mm tube, i.e. a drop of 0.067 mbar/m, which is very close to SaunCorbs's value in post #9.

However, if one uses the more sophisticated formula and calculator here:

Natural Gas - Pipe Sizing Calculator

with 13.6mm (id) for the pipe, 1.063 mmH2O (0.1042 mbar) for the pressure drop, and 1m for the pipe length, and 0.6 for the specific gravity of the gas you get a flow rate of 1.13 m^3 / hr, which is close enough to make me think that it is this formula that has been used to set the test and calculate the model answer.

 

[Old Account]

Hold on. You say you have given the answer at the end??? I haven’t checked it though. So it could be wrong. You having us on here?

Is he referring to pipe size calculation how big the gas pipe supposed to be?

 

[Harvest Fields]

Is he referring to pipe size calculation how big the gas pipe supposed to be?

Neither Ron.

 

[Old Account]

Neither Ron.

I was reading it once more and got to the same conclusion. Thank you harvest.

 

[Windy]

Just to update you (if interested). I hadn't been on my gas course since doing the preliminary exams over 2 years ago (due to personal reasons) as I have now got my head back into the books to get this done as soon as i can, it seems a few things have changed. There are now new pipe sizing tables in the updated NIC/EIC books, which I have just purchased....... So in simple terms the question answer is.....
12kw gross = 1.11M3h go to table 5.5 using flow rate 1.25M3h shows 0.1042mb/m drop........
seems i was over thinking it!
Thanks for everyone that helped.