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 [email protected] 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/
