Pressure drop on UHPLC system

[thohry]

Hi all,

We start to use UHPLC more and more. Sometimes the pressure drop on the system only (not included column) is rather high. Anyone know the formula to calculate the pressure drop across a capillary providing that we know capillary diameter, length, mobile flow-rate and viscosity ?

[tom jupille]

http://en.wikipedia.org/wiki/Hagen%E2%8 ... e_equation

[thohry]

http://en.wikipedia.org/wiki/Hagen%E2%80%93Poiseuille_equation

Thank you very much.
By the way, in Darcy equation, the pressure drop through a column is inversely proportional to square particles id. But in this case the pressure drop is inversely proportional to the tubing id to the fourth.

[lmh]

At first glance, that sounds right. If you halve the size of the particles, you halve the size of the pores, so the pressure per pore goes up by 0.5^4, but meanwhile the number of pores per cross-section goes up by 2^2. Pressure-per-pore is divided by pores-per-column; x^4 divided by x^2. Not sure??? Is this right???

[Hollow]

some years ago I bothered myself with the pressure drop equations for columns.

Then was it when I found these references about the Kozeny-Carman equation:

Jack Dvorkin (JD), Kozeny-Carman equation revisited
http://pangea.stanford.edu/~jack/KC_2009_JD.pdf

freestudy.co.uk - Fluid Mechanics - Tutorial #4 - Flow through porous passages
http://www.freestudy.co.uk/fluid%20mechanics/t4203.pdf

actually I don't have all this mathematical stuff present in mind, but my conclusion then was that these equations work quite well