by
Hollow » Tue Dec 20, 2011 3:47 pm
nice question raised:
from my thoughts, I would agree with the second statement about the similar volumes after the column (if one neglect temperature increase effects by frictional heat within the tubing/column...).
I guess the (simplest) compensation is done in that way as to give the set flow rate at the columns head under the given pressure.
Therefore the stroke frequency will be increased slightly, and with this a higher volume will be delivered, independent of the fluid (stroke volume*frequence)
So I would expect to get the same volumes in my cylinder.
But I'm not that sure about the real flow rate within the column (or at the column head). Probably usually reduced but under some circumstances maybe even an increased flow rate could be possible.
As the compressibility is a function of pressure, and this backpressure depends on the viscosity of the fluid, maybe the actuall compression of the fluid under the particular conditions will be less than that of water and so the pump will deliver a higher flow rate according to the increased pump frequency.
But that's only my theory.
Example (disregarding temperature effect):
Liquid 1: max compressibility is 2%, at 400 bar backpressure (viscosity 1),
therefore the pump delivers 102%, e.g 1020 µL/min as to give 1000 µL/min at column head.
Liquid 2: max compressibilty would be 3% at 400 bar, but its viscosity is only 0.5
With the compressibility settings for liquid1, the pump still delivers 1020 µL/min, but the backpressure would only be about 200bar.
Assuming the actual compression at 200bar is only 1%, then the real flow rate would be 1010 µL/min vs. 1000 µL with liquid 1.
After the column, both liquids will expand to 1020 µL/min.