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| Stoves Archive for May 2002 |
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| 102 messages, last added Tue Nov 26 17:31:37 2002 |
[Date Index][Thread Index]
Re: Temperature dilution
On Fri, 24 May 2002 19:22:10 -0500, "Paul S. Anderson"
<psanders@ilstu.edu> wrote:
>
>In reply, At 10:30 PM 5/24/02 +0100, AJH wrote:
>>Too simplistic, you must build in a factor for the "utility" of the
>>energy, a sort of heat opportunity cost. Electric energy for fans has
>>a far higher opportunity cost than heat for cooking.
>>
>>AJH
>
>Paul replies: I think I understand that and agree in the general
>case. But the electric energy to operate a very small (perhaps 12 volt DC)
>fan is SO SMALL, and in comparison, the heat energy from the burning of the
>biomass is SO GREAT.
I am not criticising the use of motive power to enable better
combustion, the pellet stove in my home has 3 electric motors which
have an average electric consumption of ~50W. Some of this is
compromised over what is needed because the combustion fan runs on
warmer than ambient air as part of the overall safety. In using this
electricity it releases up to 10kW of heat from a well prepared wood
fuel.
>
>My original statement or implied question (above) is related to the GREAT
>difference between the tiny bit of energy needed to do the blowing and the
>(we hope) increase in energy from better burning of the biomass.
The "Natural Draughters" would say they can burn well enough for a
"GREAT" difference not to occur.
>
>An extreme case would be to have a US$ 2 small fan with many months or
>years of useful life and a 12-volt battery that is occasionally recharged,
>which together make it possible to burn (in a gasifier or in some other
>stove) some form of biomass that is otherwise literally waste product to be
>thrown away. The heat is from the biomass. We are just trying to make it
>possible to burn the biomass by providing a small fan.
Paul, I am entirely in agreement with you on this, however the USD2
fan may not be readily available, the battery has a finite number of
charge cycles and the recharging system is not trivial. In fact the
*cost* of battery provisioned electricity can be phenomenal. So how
would you measure the utility of this motive power and the full cost
of getting it? Would a third world cookstove client be prepared to pay
a dollar sum for the powered air supply? Would the client be happier
forgoing the portion of fuel to raise 70g of steam per hour to do the
same job?
>
>Please note that my initial comment (at start of this message) was about
>getting HOT air to be available via fans. But now the discussion by Andrew
>and by me seems to be more "generic" about fans and their "opportunity
>costs." I am interested in BOTH:
>
>1. fans per se, and
>2, the value of getting hot air into the combustion chamber.
I am not a fan of using hot air however my little stove does use it by
default.
I find it interesting that both Dean and Rogerio are now tending
toward flued cookers. To my mind this makes the combustion easier to
control and accommodate. Also the mild induced draught available from
a chimney makes the devices inherently safer in keeping combustion
products out of the room. Were Tami's chinese coal fired cookers to
move toward the stoves Dean is now promulgating then I am sure we can
clean up cooking with coal. Similarly it would allow a modification of
the rocket geometry to mitigate the need for fuel metering by pushing
the sticks forward, reducing the need to constantly tend the fire.
AJH
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