[Stoves] Too much turbulence can be bad??? Re: Airflow For Biomass Fired Appliances- Natural Draft Stoves

Tue Apr 16 08:10:34 CDT 2013

Fellow Stovers,

Turbulence is a goldilocks problem.  It must be carefully balanced with well controlled primary air amounts and distribution.  Generally, I observe too little consideration of the primary air system which can only lead to sub-optimal results.

A simple test to evaluate the presence of unburned CO is to put a metal pot of cold water over, or in,  the exit point of the stack gases.  If soot, created  when hot CO hits cold metal, is deposited on the pot, then the combustion of CO is incomplete. Black soot on pot bottoms is a warning that the combustion process is sub-optimal. Brother Hugh explained all this to me.

I find that central spires of flame are generally more likely to be "dirty" and much more likely to eject particulate matter and soot at far greater rates than when I use my vortex generators with three deflectors. As a result, I work hard to avoid central spires of flame. 

For example, I keep the inner ring of primary air holes out from the center to keep the air flow  more focused on the outer portions of the feed stock in the pyrolysis zone.  I never use a primary hole in the center - altho that was where I started. 

Just observations from trying many different secondary air and primary air approaches.

Regards,

Jock

Extract CO2 from the atmosphere!

On Apr 15, 2013, at 10:56 PM, Paul Anderson <psanders at ilstu.edu> wrote:

> 
> On 4/15/2013 6:53 PM, Alex English wrote:
>> Paul,
>> Too much air can be 'bad' even if it creates more turbulence. Too much turbulence could be 'bad' if it comes at too high a price for the extra power or hardware. Commercial burner designers might quibble on the finer point about where the turbulence occurs inside the flame. Otherwise its hard to argue against more turbulence.
>> Alex
> Paul Anderson replies:
> The 3 T's are Time, Temperature and Turbulence.    Well, having lots of turbulence could have a negative impact on the other two.   
> 
> Time of the gases in the turbulent area might be shortened.    It is certainly shorter than in a longer taller flame.
> 
> And if the increased turbulence is hiding excessive secondary air, the excess air will be cooling the flame and combustion emissions.
> 
> And as Alex and Crispin and others have pointed out, when there are no visible emissions, there could still be improvement of the emissions.   (and CO is not visible anyway).
> 
> I think there is serious quantitative work to do concerning the TLUD and other micro-gasifiers and the high-turbulence "fan-jet" or vortex stoves.   This will NOT be best studied with WBT that take so long and have so many confounding variables.   We need to be watching real-time results while we make changes in the air flows, etc.
> 
> Paul
> 
>> Paul S. Anderson, PhD  aka "Dr TLUD"
>> Email:  psanders at ilstu.edu   Skype: paultlud  Phone: +1-309-452-7072
>> Website:  www.drtlud.com
>> 
>> On 14/04/2013 10:49 PM, Paul Anderson wrote:
>>> Dear Alex, Lanny, Dean and all,
>>> 
>>> We are learning things about short flames and flame color that should have been learn years ago!!!   Thank you both (and others) for getting this information to us.    
>>> 
>>> And Crispin has been telling us all along (and showing up with his device at ETHOS etc) that a combustion analyzer is useful.   We (the generic we) need to get more serious.   
>>> 
>>> And Dean wrote:
>>>> 
>>>> >The very hot yellow/white flames easily make black carbon.
>>>> >The less hot deeper yellow/red flames make less/no black carbon.
>>> Notes:
>>> 1.  Why isn't a combustion analyzer (as used for furnace work) part of the standard equipment for stove testing, either for formal protocol testing or for more simple testing at our workshops and factories?
>>> 
>>> 2.  Is this "turbulance" and "forced air" (flame height and color) information telling us something about the "fan-jet" or "vortex" stoves like Philips-FA and the Biolite and the RTI FA stove tested in Kenya and others with STRONG forced air.   The Kenya study (presented by Mike Sage at GACC Forum) found that the emissions were not as low as were hope for stoves with fans.   Is it possible that the extra turbulence of those stoves is actually working against their lowering of emissions?    
>>> 
>>> To me, this is BIG and I hope that CSU and Tami and Aprovecho and testing centers can check on this with modeling and testing.    (or is this basic knowledge in some specialist fields?  )
>>> 
>>> Be sure to read Alex's message below if you have not already done so.
>>> 
>>> Paul     
> 
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