[Stoves] Natural draft TLUD turn-down

[Crispin Pemberton-Pigott]

Howzit Lanny!

Yes, the idea is that if the internal chimney section of the stove (anything above the fuel bed in TLUD's) is hotter than the down-drafting section that is the secondary air preheater, it flows up and the secondary air flows down. The 'thickness' of the secondary air channel matters - mustn't be too broad or cold air will pass in and out again.

The trick is to have the secondary air get less preheating when the power is turned down so it doesn't halt the secondary air feed.

The reason this works is in part because air has quite a lot of oxygen and the ‎air pressure is what it is.

That means in the case of a side-fed stick burner, that there will always be too much air getting in if the draft is always upward - typically 6-800% excess air which is too much to burn cleanly.

At low power the EA will run to 200‎0 per cent easily in a side feed stove with an open architecture.

One simple way to ‎limit it is to lower the pot and use it as a flow controller but it is only 'right' at one power setting. The down-drafting approach can be right across the power range.

Regards
Crispin

BBM 2B567C3
From: Lanny Henson
Sent: Tuesday, May 20, 2014 08:48
To: Discussion of biomass cooking stoves
Reply To: Discussion of biomass cooking stoves
Subject: Re: [Stoves] Natural draft TLUD turn-down



Interesting, is this self regulating?

> On May 15, 2014, at 9:39 PM, Crispin Pemberton-Pigott <crispinpigott at outlook.com> wrote:
> I can suggest one additional effect to try which is to put a shell around the outside that is closed to the body at the bottom and open at the top. This is a down-drafting secondary air preheater. The height of the upper lip strongly affects the performance so you need to find where to put it. The effect of this is to create a negative draft on the secondary air supply that balances the heat inside in such a way that you get the exact airflow level you want at different power levels.
> Crispin
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