[Stoves] Powering a TLUD Fan

[Crispin Pemberton-Pigott]

Dear Andrew

Do you think a typical low noise (spiral bladed) CPU cooling fan is a
crossflow turbine, of sorts?

They have a fairly high blade density and the secret to getting pressure
from a fan mill at a low speed is related to that.

See http://www.rcgroups.com/forums/showthread.php?t=1245696&page=2 comment 1

The efficiency can be high and it is not really related to speed, just
appropriate design. I learned this from Dr Peter South at Canada's National
Research Centre when he was developing the 4 MW vertical mills they are a
bit famous for. Fan design is pretty well understood and the software is
dime-a-dozen. They are amazingly efficient these days.

The first thing to do is define the problem, not pick up some fan and try to
apply it. There are lots of different computer fans and they have quite
different performance intentions. 

As you have shown, the power needed is really low so a fan that is a
reasonably match should not have to be more than 1/2 or maybe 1 watt max.
The mis-fit between what is commonly used and the current stoves is not a
place to start from. 

What is the range of pressure needed, and how does a candidate fan respond
to the increasing flow resistance? Peter demonstrated how it is really hard
to know in advance what a  best choice will look. For example the most
efficiency low cost, wooden Darrius Rotor has only one blade in order to
maximise the chord thickness!

This discussion is far from over. A good place to start is
http://en.wikipedia.org/wiki/Computer_fan to see several different
applications just inside computers.

Regards
Crispin