roakey:
Nevermind, the answer has been in front of me all along!
For CCR and O2 rebreathers at fixed depth there is no change in volume
Roak
I will have to say that Roakey, you were right the first time with your proposal. Here is why:
OK, everyone, the oxidation and Krebs cycle equations are an interesting diversion, but the buoyancy equation we use here uses only two factors. Remember Archimedes principle.
More on the equation here:
http://www.physics.smu.edu/~scalise/mechmanual/archimedes/lab.html
An object is buoyed up by a force equal to the weight of liquid the object displaces.
The two factors to consider are:
1. TOTAL WEIGHT (or MASS, since distance to the center of the Earth remains static)
2. TOTAL VOLUME
Roakey is CORRECT in saying that it is a closed system, and no mass (weight) is being added. So that part of the equation does not change. If we ask the question proposed by Roakey that no more oxygen is added to the system, we see the following:
If you use up the oxygen (gas) in the collapsible counterlung(s), you decrease the volume of the system..
THE TOTAL VOLUME OF THE SYSTEM DECREASES, THUS THE REBREATHER DIVER WILL EXPERIENCE A MEASURABLE LOSS OF BUOYANCY.
If, however, the electronics (or diver flying manual) adds the correct amount of gas to the system as the diver uses it at a constant depth, there will be no net effect on buoyancy.
Because, assuming an ideal rebreather that does not leak, etc, we see that
NO CHANGE IN MASS (WEIGHT) ON THE CLOSED SYSTEM
NO CHANGE IN VOLUME ON THE CLOSED SYSTEM
THUS NO CHANGE IN BUOYANT FORCE