Bubble-point with gas permeation(wet and dry flow method)
The bubble-point method gives only limited information and a another method was developed that combines the bubble-point concept with the measurement of the gas flow through the emptied pores. Here at first the gas flow is measures through a dry membrane as a function of the pressure and generally a straight line obtained(see figure-8). Then the membrane is wetted and again the gas flow is determined as a function of the applied pressure. At very low pressures the pores are still filled with the liquid and the gas flow,which is determined by diffusion through the liquid, is very low.
At a certain minimal pressure (the bubble-point) the largest pores will be empty and the gas flow will increase by convective flow through these pores. A further increment in pressure will open smaller pores according to the Laplace equation. At the highest pressure the gas flow of the dry membrane must be equal to the wet membrane. The dry and wet flow are both depicted in figure-9 and the pore size distribution can be determined. This method is suitable for characterization of macropores and can be applied for microfiltration membranes with pore sizes up to 50nm.
As said in the above, this method is similar to the Bubble-point method, while there is a little different. And for the membrane filter and syringe filter's testing, usually we use this method when the pore size is small, like 50nm, etc. For the pore size is 0.1um to 10um. We don't use this method.