[Stoves] Fwd: RE: Explaination of downdraft in TLUD updraftstoves ---was--Re: Mis-information

[Kirk H.]

Alex,

This is a natural draft stove in the drawing, and the stove is supposed to be able to operate by natural draft.  If only the forced air version had been put forward then I would not have expressed any concern.  I am trying to understand how this natural draft stove, with no chimney, could have a down-draft.

For this natural draft stove, without the annulus draft there would not be a Venturi at the bottom.  A natural draft stove powers any Venturi by draft.  Draft is what makes the air move to create Venturi low pressure.  The air/gas mixture which is burning is emanating from the annulus, so that is where the draft would be.  If it is truly down-draft in the fuel chamber, the annulus draft is necessary.  In fact a Venturi may not even be of consequence.  All natural draft stoves where down-draft exists have to have a larger up-draft someplace driving the gas movement, usually in a chimney.  In the case of this stove, the only driving up-draft possibility would be from the annulus flame.

You have included some interesting chemistry insights.

The tall flame is a diffusion flame which indeed has no oxygen in its center.  This type of flame indicates inadequate mixing within the stove.  With good mixing there would be no lack of oxygen in the center and the flame would burn quicker and not be so tall.  

Kirk H.

Sent from Mail for Windows 10

From: alex english
Sent: Sunday, April 1, 2018 10:22 AM
To: Discussion of biomass cooking stoves
Subject: Re: [Stoves] Fwd: RE: Explaination of downdraft in TLUD updraftstoves ---was--Re: Mis-information



Kirk,
A powerful  forced air venturi could absolutely pull down on the gasses as you have drawn.  He has quite a swirl in that Nova Video. That tall flame is starved for O2 in the center. If there is any mass separation of the gasses by gravity or centrifuge the C02 is heaviest then O2,  then N2 and CO. Could they be differentially heated??  I see glowing embers at the edges. The so called flame cap does not extend to the outer edges. It would be very O2 rich there and relatively cold. Some of that could easily end up reacting lower down.

Alex

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