[Stoves] Thermal efficiency

[Crispin Pemberton-Pigott]

Dear Friends

 

As we are, at the CAU stoves conference, talking about thermal efficiency
tomorrow, here is something to think about.

 

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Efficiency is a ratio, but of what to what? Let us follow the heat and
decide which 'efficiency' we want to report. 

 

1.	Heat available in the raw fuel if it was to be burned completely
2.	Heat available in the dry portion of the raw fuel
3.	Heat available from the fire considering incomplete combustion
4.	Heat available to the pot, at the pot in the hot gas stream passing
by

 

5.	Heat transferred to the pot - all of it
6.	Heat transferred to the pot and subsequently lost from the pot into
the surrounding environment
7.	Heat absorbed the pot material changing its temperature
8.	Heat absorbed by the water - all of it
9.	Heat absorbed by the water changing its temperature 
10.	Heat absorbed by the water and evaporating water (whether the water
is hot or not)
11.	Heat absorbed by the water and lost from the water (by radiation,
not by evaporation)
12.	Heat absorbed into the food and being absorbed chemically
(transforming it into cooked food)

 

System efficiency [Overall thermal efficiency] is (7+9+10+12)/1.   [When
boiling water only #12=0]

 

Heat transfer efficiency is .. ?  Which one is the one you were thinking of
when asked about 'thermal efficiency'?

 

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Regards

Crispin

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