Calculation of tube heating area

[Geoff StevensonParticipant @geoffstevenson56049]

[Geoff StevensonParticipant @geoffstevenson56049]

Would anyone have the formula, or better still, know how much heating area would be provided by a fire tube 8 inches long by 1/2 inch bore diameter.?

Many thanks.. Geoff.

[GoCreateParticipant @gocreate]

Hi Goeff

circumference x length = PI x bore x length

3.142 x 0.5 x 8 = 12.568 sq ins

Nigel

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Geoff ,

On earlier question of engine HP – look in pm’s .

Regards ,

MikeW

[jason udallParticipant @jasonudall57142]

Nigel …
Don’t disagree with maths
But shouldn’t that be the OD of pipe…

And should that be derated some ( ahh just by how much)
Beacause of shadowing from adjacent pipes…or itself..depending on heat source…

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Jason ,

Nigel’s calc is correct and uses the id as per conventional practice .

You raise an interesting point though . The spacing of tubes has an important influence on effective heating area .

Too far apart and you waste potential heating area in that you could have more tubes in the same space .

Too close and water can’t circulate properly between tubes and both effective heating area is reduced and there is danger of burnout .

Some full size boiler designs use a simple rule based on 1/2 or 2/3 tube diameter water spaces between tubes .

Some of ‘LBSC”s boilers are awful as regards tube spacing – he always had as many as possible regardless of whether there was adequate spacing and on a few at least regardless of whether they would even fit in the boiler !

Regards ,

MikeW

[Geoff StevensonParticipant @geoffstevenson56049]

Thank you gentlemen. I had very roughly worked this out by regarding the tube as being flat and multiplying the circumference (width) by height.. the width (circumference) of 1/2 inch bore is about 1 1/2 inches. 1.5 x 8 = 12. Seemed too simple to be true so I am grateful for the confirmation. The tips on spacing will be helpful too. I was going to allow a tube width spacing but I may amend that. Thank you and best wishes.. Geoff.

[julian atkinsParticipant @julianatkins58923]

hi geoff,

i dont know what you are building but on a miniature loco there are lots of other factors to be considered such as the free gas flow area as a percentage of the grate area, the keiller proportions, and the late jim ewin's findings that only say the first 1/3rd length of the tubes provide any heat transfer.

cheers,

julian

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