Heat transfer through stack wall 1

[rd78]

I'm a little out of my league on this, but I'm looking into the amount of heat lost through the wall of a chimney liner as the hot gas moves upward. It sounds like a textbook kind of question, but beyond me at this point. Can someone point me in the right direction? Thanks.

 

[rmw]

You have got a basic one tube heat exchanger problem here, and, yes, it would make a good textbook question if most of the parameters involved were defined for a specific point in time. I hope it isn't that. however.

Inside the liner you have a known gas, flowing at a known flow rate, (velocity) with many other determinable properties all of which affect heat transfer, such as temperature, specific heat, thermal conductivity, dynamic viscosity, etc. etc to mention only a few.

All of these heat transfer specific properties could be changing over time due to a variety of factors back at the boiler or furnace.

Outside the liner, you have a big unknown. Is the space between the liner and the chimney wall essentially enclosed, or is it open at the top, semi-open at the top, or what. Where is the heat that transfers through the liner going. If it is a dead or essentially dead space, then you are going to arrive at a terminal temperature outside the liner, and quit transferring heat through the liner.

What is going on outside the liner is critical to heat transfer, and I suspect that whatever it is, it is essentially a laminar flow regime, (low reynolds numbers) and therefore not considered to be of much effect regarding heat transfer.

Then, you have to consider the chimney material, and its thermal conductivity to its outer skin of whatever material that is, concrete, brick, or steel, and then the convection off of the outer surface to the atmosphere, which will vary day by day, minute by minute with ambient conditions.

Is that enough variables for you to have to deal with??

For a rigerous discussion of a lot of the parameters involved, if you can find a copy of a book by Babcock and Wilcox, a major boiler manufacturer, named "Steam, its generation and use", chapter 23 in the 40th edition, (my most recent copy,) has a great deal of information on this topic, mostly related to stack losses, and draft effect, which I suspect is what you are looking for anyway.

Hope this points you in the right direction.

rmw

 

[JoeTank]

ASME STS-1 addresses this issue

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com