Re: Catalytic Converter Shapes and photo 29KB

["Lanny Henson" <lanny@roman.net>]

Kevin,
Thanks for the very excellent answer to my catalytic converter question.
You ask about my location. It is Rome, Georgia

Lanny

----- Original Message -----
From: Kevin Chisholm <kchishol@fox.nstn.ca>
To: Lanny Henson <lanny@roman.net>
Sent: Saturday, January 26, 2002 10:34 AM
Subject: Re: Catalytic Converter Shapes and photo 29KB


> Dear Lanny
> ----- Original Message -----
> From: "Lanny Henson" <lanny@roman.net>
> To: "Kevin Chisholm" <kchishol@fox.nstn.ca>
> Sent: Saturday, January 26, 2002 8:53 AM
> Subject: Re: Catalytic Converter Shapes and photo 29KB
>
>
> > Kevin
> > I have not tested the coil. This is my test piece to see if the
> construction
> > method will work. It is 3" OD and looks to be about 60% restrictive.
> > Before I go further I need to know how catalytic converters work? Do
they
> > simply provide a hot zone for the reaction?  And diffuse the gas into
> small
> > channels?  Maybe you could fill me in or point me in the right
direction.
>
> A "catalyst" is a material which enters into a reaction to promote its
> occurrance, but which is unchanged on completion of the reaction.
> Consider a reaction:
>     A + B = AB
>
> It may not occur at a tremperatue of say 400 C. However a catalyst could
> enable it to go at 400 C as follows:
>
> A + B + Catalyst = A + (B)(Catalyst)
> A + (B)(Catalyst) = AB + Catalyst
>
> Two major points to note are:
>
> 1:Catalysts only assist on reactions which are thermodynamically possible
> (You can't burn CO2)
> 2: You must have the necessary reactants.(To burn smoke, you must have
> adequate oxygen present)
>
> Contact of reagents is important. You can't burn smoke if the smoke is in
> location "A" and the air is in location "B". Intimate contact and mixing
is
> important, but that requires physical work, ie "pressure drop" Automobile
> catalysts use a ceramic substrate with small passages, in the order of 1
to
> 2 mm,  through which the gases must flow.... this creates a backpressure n
> the exhaust system.
>
> Many reactions have a significant "activation energy"; this is an energy
> condition that is required to get a "do-able reaction" "over the
> hump."Temperature can usually do this. In other words, if you needed a
> platinum-palladium catalyst to make a reaction occur at 400 C, you could
> probably have the reaction work quite well if you raised the temperature
to
> say 500C..
>
> As it applies to your application:
> 1: You can't us expensive catalysts, like those in the auto trade, bcause
of
> the prohibitive cost.
> 2: You can't use tiny passages to promote intimacy of reactant contact,
> because your stove system does not have surplus draft.
>
> Chemical reactions are dependant on temperature.... an increase in
> temperature will enable a reaction to "go." So in the first instance, you
> don't really need a catalyst.... as long as you can ensure that your
> reactants are at, or above, the necessary reaction temperature. The
mistake
> made most often in the design of smoky stoves is that there is "too much
> heat extraction from the wrong places."
>
> The first thing to do is to ensure that the reactants (in correct
> proportions) are at, or above, the temperature at which they will ignite
> without the need for a catalyst. Your ceramic insulation system has the
> potential to be very helpful in this regard.
>
> The next thing is "intimacy of contact of reagents." Your ceramic
insulation
> system also has the potential to be helpful here. A roll of ceramic felt
> with an annular passage will have roughness and asperities and "torturous
> passages" that will promote mixing and contact. Heres where the very
> practical problem comes up: the greater the "mixing", the greater the
> pressure drop. How much pressure drop will your stove system permit?????
> Thats the question that determines how much mixing effect you can design
> into your stove.
>
> For example, if your ceramic blanket faces are spaced 10 mm, there may be
> great mixing, but the extra pressure drop slows the rate of burn to the
> point where the basic system does not work. On the other hand, 50 mm
> passages may give a stove that works well with the available draft, but
with
> little mixing effect. This is a tremendous "optimization problem."
>
> Thus, I would suggest that if you pursue the "ceramic spiral concept", it
> should work by virtue of providing extra temperature to ignite marginally
> cool products of combustion, and that your "developmental challenge" will
be
> to find the optimal spacing for the blanket faces.
>
> Hope this is helpful.... keep me posted on your progress.
>
> Kevin Chisholm
>
> (BTW.... where are you?)
>
>


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