[Stoves] diy TLUD flame / Laminar Flow

Thu Feb 27 15:34:25 CST 2014

That is a good experiment. I think you might do well to create some smoky source and let the some draft into the secondary air slot so as to be able to watch it for a while – see where the secondary air travels.

If the smoke is from rubber it will probably not burn out so remaining visible long enough to track it.

Bringing in the air using a ring can bring the flames away from the wall (a major achievement) and then stirring the centre will provide turbulence. What you never want is a flame to be running against one wall of the chamber, flickering (heating and cooling rapidly). That is guaranteed to destroy the surface even if it is a reasonably good ceramic. 

I just reviewed the paper again by Ibrahim that will come out in late March on the CFD modelling. The unit has 50mm diameter ‘upper’ combustion chamber which is far smaller than is usually seen. There is a vortex deliberately created inside it to keep the flames away from the walls.

Regards

Crispin

++++

Crispin,

I find I have no problem with my tin can "wall materials" with my deflectors set above a secondary air gap.  This appears to prevent laminar flows in the exhaust gases and to keep the flame more contained for longer periods [residence time in your parlance].  This may be because I use a secondary air slot rather than holes.  The use of the slot may tend to force the hot gases away from the wall materials?

The best way to see this is to simply make one of my units as described and illustrated in the Pyro-Grilling PDF on Greater Democracy.

I will try the experiment below when I get back from vacation [Anguilla].

Fill a TLUD with water and watch what happens when you invert it and allow the water to flow out thru a concentrator hole [bathtub drain]

Next, fill a draft can with deflector washers at one end with water, invert it, and watch the water flow out thru the deflectors.

What differences does this reveal? I will be most curious to see what I can see.

Cheers,

Jock

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