Thermal Transfer Ratio (in laymans terms) 1

[a31ford]

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Greetings All.

I'm not that good at this so please bear with me...

I'm looking for a basic simple conversion rate or factor that I can use to get "close" for finding the following.

(Close being "relitively near a reasonable answer")

I have a flame that I would like to put a horazontal firetube heat exchanger at the "Far End" of the flame. (After actual flame area, and simply in the flue gas path).

Here are the things I can work with, for the "simple" calculation.

A) Temperature of flame (F or C) (Really temp. of flue gases)

B) Thickness of steel used in firetubes (decimal or fractonal inches), With a surface area of one square inch.

C) The above A & B would give sum "C"

Eg: 1300f flue gases, with 1/8" steel would equal "N" where N is a devisor or dividand that I could use to figure out how many square inches of firetube surface area I would need to transfer heat from the flue gases to water, on the "outside" of the firetubes.

I relize that in actuality this is a much more complex calculation to take all factors into consideration (like reducing temperature of flue gases due to contact of said gasies with the fire tubes) etc. etc.

I'm simply too stupid to be able to do all those calcuations and keep track of it all...

There must be a simple method that will give a 'close" result (say +/- 200 degrees F, or something like that)

The end result is to capture the heat of the flue gases to water, without condensing the flue gases in the firetubes or chimney, assuming this unit is "always on, and runing".

Thank you in advance, if anyone can come up with a "Simpletons use" version of this calculation.

Regards,
Greg Manning

 

[dcasto]

Water path firetubes are usually designed or assumed to transimit 10,000 BTU/HR/FT of surface area. Lets say you have 10 feet of 8" fire tube. 8" * 3.14 / 12 = 2ft Area = 10 ft * 2 Ft = 20 Ft^2, 20 * 10,000 = 200,000 BTU/hr of heat transfer.

Flame temperature doesn't mean a whole lot because most of the heat transfer is Radiant heat. Radiant is the heat from the sun. Even on a blistering cold -10F day, you can still feel you face get hot. Now, some of the heat is transfered from the 1300 F hot air, but a small amount compared to the radiant heat energy.

 

[a31ford]

dcasto, first off thank you for the quick post, and information. But, if I can, one more question.

I'm looking to use only the heat of the flue gases, and NOT have the tubes anywhere near the actual flame, so "true" radiant energy is not available, surely heat only energy (like that of hot air on furnace ductwork) will still apply ??

The "Crazy Farmer"

Greg Manning

 

[IRstuff]

Radiant heat has the logest and quickest reach. In the Univeral Studios "Backdraft" attraction, the radiant heat from flamss 30 ft away can be felt.

TTFN

 

[mbeychok]

a31ford:

I don't want to be a wet blanket, but what you are trying to design is not for beginners and certainly not for laymen. If it is meant for the use in the US (and many other countries as well), the finished item will have to meet various design codes and safety codes. If it burns fuel, it may also have to comply with emission regulations by your local environmental protection agency. If you want to get liability insurance for it, it will need to meet the code requirments of the insurance company. The design may very well require the signature of a registered professional engineer.

If you try to circumvent the above requirements and design it yourself, you are letting yourself in for a world of litigation ... especially if any one is ever injured by the item. I might add that so are the well-meaning individuals who offer their help to you on this forum.

The best advice I can offer you is to let an experienced vendor design and construct it for you or to retain a consulting engineer experienced in that field.

Regards,


Milton Beychok
(Visit me at www.air-dispersion.com)
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