Parameters measured

In a typical CFP test a flow of pressurized gas is applied to the porous sample impregnated with the wetting liquid and the flow of gas through the sample, as the liquid is displaced out of the porous network, is measured. The “wet curve” represents the measured gas flow against the applied pressure.

Following the wet curve, the gas flow against the applied pressure on the dry sample (“dry curve”) is also measured. From data from the wet curve, the dry curve and the “half-dry curve” (dividing the flow values of the dry curve by 2) information about the porous network can be obtained.

Measuring curves and resulting parameters in CFP

(w = wet curve, d = dry curve, d/2 = half-dry curve, FBP = largest pore, MFP = mean flow pore, SP = smallest pore)

 

A full porometry test can provide information on:

  • Bubble point
    Maximum pore diameter
  • Smallest pore size
    Calculated at the pressure at which the dry curve meets the wet curve
  • Mean flow pore diameter
    Pore size at which 50 % of the total gas flow can be accounted (half the flow is through pores larger than this diameter)
  • Gas permeability
    In the same measurement it is possible to obtain the gas flow rate. If the material area and thickness are known, the gas permeability can also be accounted.
  • Cumulative filter flow [SUM]
    It shows which percentage of the flow (at the Y-axis) has passed through pores with a size larger than the value at the corresponding point at the X-axis. It is also known as filter efficiency.
  • Differential filter flow [DIF]
    It shows the percentage of flow (at the Y-axis), which has passed the pores with a corresponding size at the X-axis and the following size value at the same axis. According to ASTM this graph shows the so called “pore size frequency”.
  • Pore size flow distribution [CDIF]
    It shows the flow distribution normalized per unit of change in size (flow changes are divided by size changes). Sometimes it is also referred to as pore size distribution.