[Stoves] air for gazification

[Boll, Martin Dr.]

Dear Frank,

 

>Martin, Jeff and all,
> 
>We may have a chance of measuring the superficial velocity in the TLUD 
>but its much more complex to measure in the other configurations where 
>the primary pyrolysis occurs before the gases go through the fuel. If we 
>could come up with a Surrogate Standard that could be introduced in the 
>inflow air and is unaffected by heat and combustion these (and many 
>other) measurements would be much easier.
Would that not be grams of air?
> 
>I am not so sure we need to know the actual air speed around the 
>particles. We need to know that the speed around them changes with 
>changing small fuel characteristics and, from actual testing, know what 
>characteristic are best.   If we start with one inch blocks of wood we 
>find we cannot start the combustion in a TLUD. Cut each block in half 
>(increase the surface area, smaller void space, denser carbon as the 
>fuel packs into a smaller space etc- all things we can measure) then see 
>if it works.  If not cut each of them into half again and again etc 
>....  Finally we find the conditions that work with this fuel and stove 
>design (computer air fan, natural draft, size of fuel container etc).  
>As we cut each block in half the superficial velocity increases in the 
>fuel if the inflow remains the same. So I am thinking we are really
 
No! It is the same superficial velocity! You want to express another thing;
see below in my posting. 
 
>adjusting the fuel characteristics to achieve the optimum SV -without 
>really caring what that exact value is.
 
We could do another way: First choose the SV (not the pressure!!), and keep
it constant, while using different-big wood-pieces. So we have by all
different fuel the same SV.
It is not preferable first to give a certain pressure, and look how it works
with different-big wood-pieces. By that, the SV is different and difficult
to compare.
It could make sense first find out, what type of fuel in the same stack-type
would create what resistance. 
 
>We just need to know the 
>'classification' of the fuel that will give us the optimum SV value so 
>we can find other fuels, test them and determine if the stove design 
>will work with them also.  Or if slight changes need to be made to the 
>design.
 
Couldn't we better sort the fuel-type to (definite) different SVs, or
SV-ranges?
> 
>Am I getting way to detailed!??
No, so your ideas are clearly to understand!
> 
>Frank

 

 

The superficial velocity (SV) is so very close to filtering-actions, and
naturally to your soil-topics, as transport of substances or water from
surface  into deep.

Naturally, that depends extremely on the soil-structure, so does in
fuel-stacks of stoves.

 

But what -_YOU_ are interesting in is different! You _DO NOT_ want to know
the superficial velocity, because the definition of the SV does not count
with the wood-stick-cross-section within the cross section of the stack.

You want (possibly) to know, what speed the air/gasses have in the spaces
between the wood/fuel, -and so to know the speed nearby the surface of the
wood-pieces-.

 

The word "superficial velocity" leads us in a false way! Let us think better
of: filter-speed, as I wrote, and of the migration-speed e.g. of water in
the soil.

 

I would call the average-speed between the wood-peaces:
"interstitial-filter-speed" (IFS)  (derived from the medical expression:
Interstitium).

The simplest way to get a __LITTLE__ bit closer to that IFS, we can measure
the volume between the wood, by filling this space with water, and weight
the out-leaking water. So we can calculate the remaining cross-section of
the stack, through which the air flows.

 

I don't know this would help a lot. The only advantage I see is, that we can
compare the real measured pressure-loss of a definite flow through the
stack;

Compare with a model: The pressure-loss, which occurs in a tube with the
measure of the calculated cross section of the interstitial volume, (with
the same length of the fuel-stack). That could lead to interesting
experimental-curves: x-axis = particle size, y-axis= resistance  (= 1/ flow
per second).

This can be made first without fire, to get some basic impression, at least
what minimum pressure is needed to work.

 

Possibly by that curves, made with the same type of fuel-matter (wood) , we
can compare with same sized fuel of another type (other wood, grass-balls,
etc.)

 

But these are academic questions, which are not related, in what I want to
know. I don't want to dive so deeply into burning-theories of the
specialists.

 

Regards

 

Martin