[Stoves] Heat loss in gases

[Paul S. Anderson]

Dear Philip and all other Stovers,

I found very interesting what Dr. Philip Lloyd wrote
Quoting IPC <ipcipc at mweb.co.za>:

> Yes, there is some heat loss in the hot gases, but it is very small, because
> the heat content of gases is very small.  I cannot stress that enough - it
> is very counterintuitive, and I got caught by it as a young scientist.  I
> needed to heat a fluidised bed.  A long pipe carrying the gas had an
> electric element down its centre and was insulated on the outside.  The
> heater was set so that the exit temperature of the gas was 420deg C. The gas
> then passed through 5cm of un-insulated pipe before entering the fluidised
> bed. The bed never got even faintly warm - all the heat in the gas was lost
> over that uninsulated 5cm, even when the gas velocity was set high enough to
> blow the fluidised bed out of the pipe!
>
> The heat lost in the combustion stream at 100 deg or 150 deg C is measured
> in terms of a few joules, not kilojoules, and can be neglected.

I neither dispute nor confirm this, but please help me comprehend this 
so I can
apply it to TWO-pot cooking.

The volume (or mass?) of the hot gases would seem to be important.  If 
the long
pipe is only 1 cm in diameter or is 10 cm diameter would be a factor.  And the
speed of the exiting gases is higher if the same amount of gases goes through
the smaller or larger diameter, thereby influencing also the blowing of the
fluidized bed out of the pipe.

When trying to heat two pots in sequence (either laterally or horizontally
arranged, but not with both sharing the same flame simultaneously), is there
much chance of getting serious heat to the second pot only by the 
gases.  (This
question implies basically not relying on conduction of heat in a plancha top
and not having the flames extend past the first pot to reach the second pot.)

I am trying to understand the implications of what Philip wrote.

Paul


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