Differential Gas Diffusion Porometer
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Applications
Pore structure characterization membranes containing very small pores. Delicate membranes sensitive to pressure can also be tested. Pore diameter as well as flow rates are measurable.
Principle
The flow rate of a gas is measured as a function of applied differential pressure across the sample. The gas flows through all the pores larger than the pore diameter of the gas molecule. The test is repeated using gases having different molecular diameters.
The flow rates are very small. Sample is loaded, the system is evacuated and the inlet chamber maintained at constant pressure. Time rate of pressure increase in outlet chamber measured.
Flow rate is computed using the following relation.
Where F is flow rate in volume at STP, p is gas pressure on the outlet chamber, t is time,
Vo is volume of the outlet chamber, Ts is standard temperature, T is test temperature and ps is standard pressure. Flow rate as low as 10-4 cm3/s measurable.
Change of outlet gas pressure with time for a sample
Measurable Characteristics
- Pore throat diameter
- Bubble point & Mean flow pore diameter
- Flow distribution
Distribution function: f
f = - dF/dD
where F is cumulative flow function, [F(M)1/2 / Dp] and D is pore diameter
Special Features
- Throat diameters of through pores measurable
- Very small pore diameters measurable
- Flow rates through the small pores measurable
- Flow distribution measurable
- Usable over wide pressure and temperature intervals employing a wide variety of gases.
- No damage to product
- Fully automated, very little operator involvement and robust