[Stoves] Pressure calculations

Frank Shields frank at compostlab.com
Mon Jun 27 12:30:58 CDT 2011


I found the problem of the unexpected pressure build-up (not a negative
pressure) in the reaction vessel was due to an old copper tube that had been
previous used in a composting experiment and had a plug of compost blocking
it in the center near a bend. Once cleaned out it worked as expected. As the
water in (A) wants to go down it would pull in air (or try) from the tube
going to the reaction vessel creating a partial vacuum. 


But, since asking the question I have been receiving great ideas from off
the list responses. This is a great group and I am glad to be part of it. 

Thanks


Frank Shields
Control Laboratories, Inc.
42 Hangar Way
Watsonville, CA  95076
(831) 724-5422 tel
(831) 724-3188 fax
frank at compostlab.com
www.compostlab.com
 
> no pressure as the 1/4” tubing is open going into A. Is there a back
> pressure from the water in A on the gas coming out of C? Does the
> height of C relative to A (top or bottom) have any bearings on the set
> up?

C is a sealed container so I don't think so. The pressure in C is dictated 
by the pressure in A because they are connected by the tube, The pressure 
in A is set by the difference in height of the water column between A and 
the surface of B. The surface of B is atmospheric and the top of the 
water column in A is atmospheric minus the height of water up the side of 
A. If A could be totally immersed in B then the inside and outside 
pressure  of A would be equalised when the water level in A is the same 
height as B's. Bear in mind that atmospheric pressure is about 9m (30ft) 
of water so your 0.46m column container only changes in pressure by -5% 
of an atmosphere when full to atmospheric when empty.

Last time I did calcs like this was 53 years ago at school so they bear 
some checking.

AJH

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