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If we take a surface gas consumption (call it SAC or RMV which ever you prefer). We could measure it is litres per minute, or some other unit which is volume/time.

To calculate a RMV at depth we take the product of the surface gas consumption and a function of depth.

The function of depth is 1 + (depth)/10 - the units for this is atmospheres.

So we have an equation the results in volume per minute by multiplying volume per minute by atmospheres.

I'm happy with the concept, but why do the units not balance on either side of the equation?

Mike
 

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The worlds slowest sailor.
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If we take a surface gas consumption (call it SAC or RMV which ever you prefer). We could measure it is litres per minute, or some other unit which is volume/time.

To calculate a RMV at depth we take the product of the surface gas consumption and a function of depth.

The function of depth is 1 + (depth)/10 - the units for this is atmospheres.

So we have an equation the results in volume per minute by multiplying volume per minute by atmospheres.

I'm happy with the concept, but why do the units not balance on either side of the equation?

Mike
they do balance.
just need to multiply the surface rate by the pressure.
 

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Muppet
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350 Posts
I've wondered myself.

It would be 20l/(min atm), but since it's obvious we're talking about 1atm, we leave it out for practical purposes.


Just my thoughts

EDIT: apparantly, the standard for gas measurements is the normal cubic metre. Which supposes 1atm and 0 degrees Celsius.
The liter is defined as 1/1000th of that. I guess that's your answer
 

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Nigel Hewitt
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You are multiplying not by pressure in atmospheres but by p1/p2 a ratio of pressures where p2 is 1 atm.

The units cancel so the ratio is a pure number. Remember you are factoring volume using p1v1=p2v2.
 
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