[Stoves] Heat Exchanger in Pots

[Crispin Pemberton-Pigott]

Dear Friends

 

Here is a new example of a copper tube heat exchanger in a pot:

 



 

This was made at the YDD Lab in June.

 



 



 



The white cable ties were covered with epoxy to seal them.

 

This is a smaller pot that normal and holds 5 litres. Now we have two and
can test a two pot stove.

 

Here is a set of temperature profiles during a test.



The top Cyan line is the water temperature in the pot not rising higher than
60 degrees.

The second brown line is the temperature at the gas sample point.

The 3rd green line is the heat exchanger (water out)

And the 4th line, light blue, is the inlet side of the heat exchanger. The
difference can be read to 0.01 degrees and the noted drift between the two
RTD's was 0.004 max.

 

The two low lines, red and blue, are the chiller temps - the gas is chilled
using a vortex tube and compressed air to drop the water vapour before going
to the gas analyser. This approach is very simple, cheap, and can be used in
a high humidity environment for continuous testing even with very high water
vapour loads. By changing the compressed air pressure, the chiller can be
brought down to 2 C or even lower. The gas warms on the way to the analyser
and the relative humidity drops dramatically ensure the cells are not
contaminated. The system has no moving parts after the compressor.

 

The calculated heat gain by the pot is 

Water mass x 4.186 x Delta T in the pot, 

plus the flow rate though the heat exchanger x Delta T x 4.186.

 

The shorter 3-metre tube in the large pot is able to handle more than 3 kW
of heat gain. The second pot has about 6m of tubing.  The flow rate is
typically 34-35 cc/second. This is calibrated before and after each test
using a bucket and a scale and has proven to be very constant. The 10 second
resolution is a few tens to a few hundreds of Joules.

 

Any burn cycle can be conducted on the stove and the heat gained by the pot
determined for any selected interval. It can faithfully report the heat
transfer efficiency at any time when combined with a gas analyser that
detects water vapour, O2, CO2 and CO (at a minimum).

 

Regards

Crispin

 

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