[Stoves] air for gazification

[AJH]

On Mon, 11 Jun 2007 09:34:51 +0200, Crispin Pemberton-Pigott wrote:

>Dear Andrew
>
>>So the answer would be about 20 grammes of air or ~25
>>litres.
>
>Is that dry air?

Well it is in that I neglected the smaller constituents of air,
concentrating on ~80% nitrogen and 20% oxygen, anyway the figures were
ball park rather than precise.
>
>How would I go about calculating the volume and mass of air at 70% relative
>humidity?

First you must know the temperature of the air, from this you can use
the partial pressure of water vapour to calculate the volume of water
in the sample, from this volume you can calculate the mass of water as
you know the molar weights of all the components and that each mole of
gas occupies 22.4 litres at stp.

That's all too difficult, much easier to look at a chart. So at 30C
air is saturated with ~28grammes of water per m^3. 70% of this is
~20grammes. The air weighs about 1200grammes so its about 1/60 th of
the mass, fairly insignificant. It becomes more significant when
related to volume as H2O as vapour is lighter than the other major
constituents of air. 40 years out of school made me lazy on some of
these basic calculations and I remember Tom Reed running me through a
similar calculation, on this list, when I wondered if lighting a fire
(inside) in the rain could have an effect.
>
>And this is directly relevant to Frank's question
>
>>But once again I run into problems with the units. The flow rate for the
>>primary air is reported as [ Primary air flow(g/sec) ]???? Typical numbers 
>>are
>>0.4 to 0.9 g/sec.
>
>>Is there any way to convert g/sec to cm/sec? And what are the grams they 
>>are
>>referring to? 

Yes this is fairly trivial but it is temperature dependant again. As
this is a bit out of context for me I'm guessing this refers to air
mass. So working on 0.9 grammes of air per second at STP and air
having a density of 1200 grammes per m^3 at STP you can get the volume
at stp this looks like 0.75 litres. If the ambient temperature is 30C
then this expands to 0.83 litres/sec. Someone had better check my
notoriously poor maths!


AJH