[Stoves] Powering a TLUD Fan

[ajheggie at gmail.com]

On Fri, 31 Aug 2012 04:54:18 +0700, Paul Olivier wrote:

>The second is the pressure resistance of the fan (40x40x28mm).
>For a gasifier of a 150 mm diameter, the pressure resistance has to be at
>least 0.87 InAq.

InAq being inches of water gauge above atmospheric? If so this is
about 250 Pascal, so 1 kg of dry biomass burned per hour at
stoichiometric air for complete gasification should be around 1m3 of
air, the 5m3 of air needed for secondary combustion would not need to
pass through the bed and as Crispin has said the offgas can entrain
the secondary air, though this is work it probably isn't much compared
with the resistance of the fuel bed. Rice husks have a high ash
content so I'm guessing its the ash that is serving to increase
resistance by blocking pores between the husks.

Does the same happen with other fuels previously mentioned?

1m3 of cold air per hour is about 1/3 of a litre per second. As power
is force time distance and pressure and volume have terms for distance
that cancel out then power is pressure time volume per second in SI
units.

250 Pascal times 0.0003 seems to be 0.075W so there seems to be a fair
loss of conversion efficiency in the system somewhere, fans should be
about 70% efficient but as things get small they tend to get more
lossy. Or are my calculations wrong? 

Axial fans are particularly good at thrashing air into heat with no
useful work as they stall, they are good at moving large volumes with
little drop in pressure across them, laptop fans seem to be better as
they tend to be centrifugal ones that push air along narrow ducts.

AJH