[Stoves] Powering a TLUD Fan

[rongretlarson at comcast.net]

Andrew and list: 

This is to ask for your thoughts on a different approach to air control than a fan (with or without a battery). That is to use a (pre-pumped) air storage "bladder" . 
My rationale for this query includes: 
1. energy storage via air (CAES) has quite a few proponents. Large vehicles have operated on air storage (where electricity was a hazard) and there are companies building cars based on air storage.. 
2. compressed air supply is common in many places - as air-motors are lighter weight and cheaper than electric. 
3. What is needed in TLUDs is controllable primary air - not electricity. In Josh Kearn's bicycle-flywheel-fan proposal, one can compress air perhaps as easily as putting energy into a flywheel (using inner tubes or similar) and then conversion to a fan/blower. That is - one is storing exactly what you want to supply - no energy conversions needed. 
4. I think there are controllable constant volume-flow valves - that would also allow controlling power levels (turn down ratios). 
5. Your use below of the term 1 cubic meter per 1 kg biomass sounds potentially doable with moderate size "bladders". I have no idea how many atmospheres of pressure is reasonable, nor what material (if any) might be appropriate with simple TLUDs. The issue only is whether air storage might be cheaper than other approaches. As Crispin pointed out, the low pressure above the fuel supply reduces the needed pressure (but not the amount of needed air). 
6. The fact that the air will be heated going into the "bladder" and cooled coming out might not be a problem is the air is preheated by flowing downward through an outer air-tight "jacket" surrounding the fuel chamber. 
7. My gut feeling is that this will only work economically if a second use can be found for the "bladder". Solar plus rechargeable batteries can be pretty cheap when you are also getting lighting, radio, cell-phone-recharging, etc. 

Ron 

----- Original Message -----
From: ajheggie at gmail.com 
To: "Discussion of biomass cooking stoves" <stoves at lists.bioenergylists.org> 
Sent: Saturday, September 1, 2012 6:28:24 AM 
Subject: Re: [Stoves] Powering a TLUD Fan 

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 


_______________________________________________ 
Stoves mailing list 

to Send a Message to the list, use the email address 
stoves at lists.bioenergylists.org 

to UNSUBSCRIBE or Change your List Settings use the web page 
http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org 

for more Biomass Cooking Stoves, News and Information see our web site: 
http://www.bioenergylists.org/ 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.bioenergylists.org/pipermail/stoves_lists.bioenergylists.org/attachments/20120901/f090889d/attachment.html>