Serious Heat Extraction

[Rhodrons]

I originally posted this question on LEV Forum but I think perhaps HVAC may get more of you replying!

I have a 400kW heat source (H2/O2 flame) and I need to remove the heat from it. THe flame is about 5 metres below roof level. I estimate that if I have a flow of 1 cubic metre/second then I will need to extract the air at around 400degC. TO me there seem to be three ways of extracting the heat:
1) Install a chimney adequately sized to give an updraught of 1m3/s. Can anyone tell me how big this would need to be?
2) Install a "small" diameter trunking with a bifurcated fan and achieve a high extraction velocity
3) Install a "large" diameter trunking with a bif'd fan and achieve a low extraction velocity.

How would I choose between 2) & 3)? Is it a case of deciding which will be least noisy?

 

[SAK9]

What you need is a chimney.The design of the chimney would depend on the volume of gases produced (to be calculated from the rate at which H2 and O2 are fed) and the temperature at which combustion takes place.I beleive if you give the above information to a chimney supplier he should be able to help you.If the combustion temperature is high enough,a natural draught chimney may do the job.

I would not recommend using an extraction fan as such a fan will be rather expensive.Even a bifurcated fan motor also will get heated to a high temperature due to heat transmission through the drive shaft.

 

[Rhodrons]

Thanks SAK9.
A chimney has a certain elegance about it. Basically the "ball" of flame is burning at 3300degC and is fed by 120 m3/hr of H2 and 60 m3/hr of O2. Putting these two together gives a ball of 3300degC and a total volume of 50 litres per second of hot steam!

Does anyone know an appropriate method of sizing chimneys?!

 

[SAK9]

This might help you get started

http://energyconcepts.tripod.com/energyconcepts/chimneys.htm

 

[MintJulep]

Stack draft can be calculated by:

D = L * (Ra - Rg)/5.2

Where

D = draft, in inches of water column
L = height of the stack in feet.
Ra is density of ambient air in lb/ft^3
Rg is density of gas of interest in lb/ft^3
5.2 is a constant to make the units work out.

Once you obtain the available draft, you can use the ASHRAE duct charts in reverse to select the chimney size. Duct friction must be less than the draft.