[Stoves] Heat transfer and in-line water heater

[AJH]

On Tue, 4 Dec 2007 08:44:57 -0500, Crispin Pemberton-Pigott wrote:

>> I'm told that pulse combustors are actually able to disrupt this
>> boundary layer but in general the boundary layer is the limiting
>> factor in convection.
>
>It recall having a conversation about these a few years ago on this list and
>someone mentioned being accused of having a machine gun hidden in the woods.

I don't see pulse combustors being viable as stoves, I was trying to
draw some attention to the boundary layer and these are the only
things I know that manage to scour it away.

I've had a few exciting moments with combustion experiments but not
with wood, the most startling was with a series of small acetylene
explosions, my ears did ring!
>
>
>> Of course despite Crispin not considering radiant heating being
>> significant it is not limited by this boundary layer.
>
>Let's not over-react....
>
>Let's see some numbers attached to all  these claims.

I gave some in a reply to Paul, it looked like the maximum radiation
from a stoichiometric wood burn at 1600C in a combustion chamber 150mm
diameter was 13kW(t), use wet wood and increase excess air such that
the combustion chamber dropped to 800C and you reduce this tenfold.
>
>I think Dean wrote
>> > Higher velocity flue gases get more heat into the pot.
>
>We have to separate the very different concepts of thermal EFFICIENCY and
>the RATE of heat transfer.  They are very different and are confused with
>abandon in these conversations.

Not at all but rate of heating is important, especially when you
consider inevitable losses from the pot. As I said there is a cost in
increasing gas velocity at the pot and that is drag 
>
>Increasing the velocity will increase the heat transfer RATE in J/sq cm /
>second. 

Which is the same as saying the power into the pot increases, for
efficiency to remain the same the flue gases after the pot must be the
same as the previous case.

AJH