improved biomass cooking stove for household use - (PDF, 101 mb ...

Results and Discussion
The effect of the grate-to-pot distance on the stove performance is
shown in Table 5.27 and Fig. 5.15. As the distance increases from 9 cm to
about 11.0 cm, the average efficiency increases from 24.7 to 27.7%. However,
as the distance increases further, tile stove efficiency drops. This
behavior is also observed with the charcoal stove.
At the small grate-to-pot distance, it is likely that the glowing wood
is too near to the gap, causing high convective heat loss through the gap.
Moreover, with too small a distance, fUrewood pieces would tend to jam up
the combustion chamber causing limited flame to come into contact with the
pot bottom and insufficient temperature of the chamber itself to initiate
off-gas combustion with the incoming secondary air. When the distance
increases, this loss reduces; the performance, hence, improves. However,
at great distances the radiative heat which is intercepted by the pot drops
more quickly than the decrease in heat loss through the gap, resulting in
the poor performance of the stove.
External Variables
Only two external variables are studied: wind effect, and fuel feed
rate.
Wind effect
Table 5.29 Test result of the effect of wind ol wood sto.'e performance.
Stove No. No. of tests Wind velocity Time to boil HU
(km/hr) (min) (%)
2/2S 3 normal 13.0 17.65
2/2B 3 6.3 13.7 16.21
2/21N 3 normal 16.0 21.63
2/21W 3 6.0 14.7 17.03
2/25C 8 normal 11.9 21.64
2/25D 3 5.0 14.0 14.58
Results and Discussion
From Table 5.28, wind is found to have a strong effect on the efficiency
of the wood stove, in one experiment, the HU values dropped from 21.63% to
17.03%, when the wind is induced through the use of an electric fan. In
another experiment, the IIUvalues decreased from 21.64 to 14.58%. All of
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