[Stoves] kgharris stove test

kgharris kgharris at sonic.net
Tue Jun 7 13:22:37 MDT 2016


Crispin,

The stove is a test stove intended to test verious ideas, not to be put on 
the market.  You can put what ever pot stand, pot, skirt, or other cooking 
arrangment on it that you want to.  The power level is 1.6 kw to 6kw with 
cushion on each end.  What ever cooking arrangment design you use is up to 
you and heat flux will change accordingly.  If the people in Java can use a 
stove with 1.6 to 6 kw, and can use that heat effectively, then the power 
level is adiquate for Java or anywhere else.  The same combustor principles 
can be used on larger or smaller stoves if this range is not adiquate.

(raising the skirt)"This will reduce the draft and reduce the burn rate and 
reduce the heat transfer efficiency (aka thermal efficiency)."
I don't necessarily agree.  Some of the draft may be lost, but the flow 
resistance will be reduced which will counter the draft loss.  I am 
intending to do some testing on the effect of raising the pot stand, so I 
intend to find out.  Also I want to do some tests on the effects of ambient 
conditions on the stove.  The skirt needed raising only when the ambient 
temperature was higher.  Most cooks will not even use a skirt so the 
question may be less important than we think.  Without a skirt there would 
be no problem with ambient temperature on turn-down.

Don't forget the low emissions.  Don't get fixated on narrow issues.

Kirk H.
----- Original Message ----- 
From: "Crispin Pemberton-Pigott" <crispinpigott at outlook.com>
To: "'Discussion of biomass cooking stoves'" 
<stoves at lists.bioenergylists.org>
Sent: Saturday, June 04, 2016 1:11 PM
Subject: Re: [Stoves] kgharris stove test


> Dear Kirk
>
> From your original post:
>
>>The high power used in the tests was around 3.25 kw.
>
> What was the cooking power during the hot start test? That means, from 
> ambient to boiling, the heat gained divided by time to gives Watts 
> (J/sec), and further, what was the heated area of the pot? I want to 
> calculate the heat flux to see if the cooking power is acceptable to, for 
> example, people in Central Java.
>
>>At 24C room temperature there was no problem keeping the water in the 93C 
>>to 97C test simmering range.  At 30C room temperature the simmering water 
>>temperature could not be held below 97C.  The pot skirt had to be raised 
>>to release some heat to maintain the test temperature.
>
> You do not 'fail' by not having the water between those temperatures. Yes, 
> as a result it will increase the evaporation of water from the simmering 
> pot.
>
>>Raising the skirt....
>
> This will reduce the draft and reduce the burn rate and reduce the heat 
> transfer efficiency (aka thermal efficiency).
>
> The effect of this on your calculated result is important. If you 
> evaporate more water, you get a smaller number of litres at the end. This 
> is divided into the mass of fuel you burned (well, not the mass of fuel, 
> but the dry fuel equivalent of the energy that was released from the mass 
> of fuel that went missing).
>
> The result is that for any given dry mass of fuel equivalent, you get a 
> higher SFC number. Because the number of litres has not effect on the fire 
> (at all) we do not really know what the fuel consumption is, only what the 
> dry fuel equivalent divided by the number of litres remaining is.
>
> It would be helpful for us if you reported the dry fuel equivalent, or 
> better yet, the actual mass of fuel needed to complete the whole test (hot 
> start and simmer). The reasons is that we can consider what effect the 
> various conditions such as skirt elevated or not, have on the performance.
>
> For example I would be very interested in the power (burn rate) with the 
> skirt in the two positions, and the Heat Flux as well. That is very useful 
> information, particularly if the skirt increases the firepower and set the 
> minimum power level.  It is quite legitimate to make a stove with a skirt 
> and the instructions for turning it down include - 'raise the skirt', or - 
> 'remove the skirt'.
>
> The Chinese heating and cooking stoves almost all have a mechanical insert 
> that is placed in the top of the stove when turning the power down to a 
> long 10 hr burn. Without that device they can't possibly burn 8 or 10 kg 
> of fuel for 10 hrs and have enough left to raise the flame back to life 
> (which is part of the national test).
>
> You get the idea?  There is no problem with having 'mechanical controls' 
> on the stove to bring the power down to 0.5 kW.
>
> Regards
> Crispin
>
>
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