[Stoves] air for gazification

[Crispin Pemberton-Pigott]

Dear Kevin

That book ref. was very useful.

I once talked to Dr Peter South (NRC Ottawa, Darius rotor expert) about fan 
design and he said that one cannot estimate much in advance about the shape 
of a really good fan suited to a job.  I asked why and he replied that 
sometimes you input the problem and the formula pitches back a fan that is 
almost entirely hub, sometimes mostly blade, sometimes lots of blades and so 
on. You can guesstimate blade density ('coverage' %) based on 
circumferential tip speed relative to air velocity, within a blade type, but 
not much else apparently.

I also wanted to mention that I have an Averatec laptop somewhere with a 
radial fan, rather like a squirrel cage open on one side with curved blades. 
It runs at quite a high pressure and is attached to the CPU chip.  It is the 
only one of its type I have seen - all the others were axial and probably 
delivered more volume at a lower pressure.  Interesting little things.  I 
see from Martin's list ref. the lowest power one is 20 milliwatts and 
measures 16 x 6 x 4mm!  I'm glad I don't have to machine the bearings...

Regards
Crispin