[Stoves] big TLUD

[Frank Shields]

Dear Crispin, and Stovers,

Interesting topic. And there must be an optimum and way to measure and determine what this is.
 
I’m thinking its air channeling (sections of high air movement) that gives the problem resulting in un-even air front. 

In addition to size of particles.  Particles must be of a size able to ignite from radiant heat from neighboring particles. At stove camp they stated a value - something like no more than three times the size of the match(?). And that should apply here I would think. We can start with small particles on top to light and gradually go to larger particles as the flame front moves down? OR does that mean larger particles can be no more than three times the smaller particles so all neighbor particles will light. A test of particle distribution and uniformity coefficient might be a good test. 

How can we test for channeling? 
Perhaps: Have air flowing through the system then add pure CO2 and measure the CO2 increase at the other end. With even flow there should be a sharp increase but with channeling it would be a gradual increase?

Regards


Frank



Frank Shields
franke at cruzio.com


> On May 20, 2015, at 12:30 PM, Crispin Pemberton-Pigott <crispinpigott at outlook.com> wrote:
> 
> Dear Rolf
> 
> I have a general rule (which results from empirical testing) which is that
> the fuel particle has to be smaller than 1/6th of the diameter of the
> chamber. At 6 it is iffy - problems abound with the fire going out and
> difficulty igniting, high excess air, poor potential for secondary air
> management etc.
> 
> There is an upper limit too but I am not sure where it is. It is less than
> 25 and I suspect above 20 is a cause for concern. 
> 
> Packing density is an issue but it is an indicator, but 'the issue'.  "The
> issue" is the superficial and actual velocity of air moving through the
> system.
> 
> The numbers are influenced by the temperature of the surrounds so it is not
> as simple as saying 'here are the hard numbers'.  When you get to mixing
> different sizes together you will have to work with the actual air flow
> rate.
> 
> Regards
> Crispin
> .
> 
> Hallo "big TLUDers",
> 
> as I see from the various experiences and comments, the cross section of a
> big TLUD is to some extent limited.
> That means that in order to build a bigger unit, it has to grow by lenght,
> which in turn must enhance the resistance to the primary air flow. From
> Imberts we know that the relation between fuel size and hearth or throat is
> crucial.
> There must be enough space left between the particles to allow for a
> adequate air/gas flow.
> 
> My question: Does anyone have a clue on the matter of fuel size in TLUDs ?
> 
> Is it possible that larger diameters ask for larger chunks which in turn
> provide more space between them and ideally spread the upflowing air more
> uniformly?
> 
> Rolf
> 
> _______________________________________________
> Stoves mailing list
> 
> to Send a Message to the list, use the email address
> stoves at lists.bioenergylists.org
> 
> to UNSUBSCRIBE or Change your List Settings use the web page
> http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org
> 
> for more Biomass Cooking Stoves,  News and Information see our web site:
> http://stoves.bioenergylists.org/
>