Re: Air flow, Partial Pressures, CO-2 Absorbants

[SFreihof <SFreihof@aol.com>]

Hi Ken;

In a message dated 98-03-15 12:49:22 EST, you write:

<< Stan,
 
 I would be very interested in looking at the sources you mentioned you had or
 if you will as you have indicated. The reason I am interested in the
 polycarbonate is the visibility where I dive is an average of 20 feet. If my
 Sub is moving at 5 knots this does not give me much time to dodge rocks. The
 polycarbonate may survive but the acrylic won't. Since the cost and labor is
 high I don't want to be constantly buying ports or worse, making them. >>

I think you confused me with someone else.  I don't know of any sources for
bubble ports.  I did say I'd provide infor from the NOAA Dive Manual, so here
it is:

"Partial pressure of oxygen should be
maintained at between 0.19 to 0.5 atmospheres. 
Partial pressure of Carbon Dioxide should be
between 2 to 7 mm of mercury.  Carbon Monoxide,
as a trace contaminant, must not exceed a partial
pressure of 15 X 10(-3) mm of mercury."

Also, requirements for flow rates for cabin venting without scrubbers:
2 cubic feet per minute (cfm) for each person at rest, 4 cfm for persons not
at rest.

Scrubbers use barium hydroxide, soda lime, or lithium hydroxide.  Absorbancy
is affected by temperature and some scrubbers require external insulation and
heating both to improve performance and to avoid moisture condensation.  Soda
Lime is lowest cost, but rarely used because it forms a highly caustic
solution with water.  Lithium hydroxide is the lightest, but also forms a
caustic solution with water.  NOAA advises designing for 3 times the absorbent
capacity needed at 70 degrees Farenheit.  Absorbants are also affected by
relative humidity.  Barium hydroxide and soda lime work best at 70% relative
humidity or higher.

Stan