What Does a Permeameter Do?

PMI liquid permeameter

PMI liquid permeameter

When characterising the porous nature of a material we measure many aspects of pore size, but often we are also interested in the material’s permeability. This is, quite simply, a measurement of its ability to allow fluid to flow through it. We can determine permeability using a permeameter, of which many different varieties exist, and this is the topic I would like to dwell upon today.

Essentially, a permeameter measures the pressure drop across a sample as fluid passes through it, along with the flow rate. The sample’s thickness and area, and the fluid’s viscosity, are also entered into an equation from which permeability can be calculated.

Results are expressed either as the material’s permeability, which is often referred to as ‘k’, or in terms of the observed flow rate per unit pressure gradient per unit area. There are also various commercial units of measurement, with names such as Frazier, Gurley and Rayl.

As you can see by visiting the PMI website www.pmiapp.com, there are numerous different permeameter types available. Each been developed specifically to tackle a particular aspect of permeametry, and the quality of data and performance produced by PMI’s instruments is very impressive.

Examples include the gas permeameters and liquid permeameters, which as their names suggest measure permeability of materials to gases and liquids. For determination of very small permeabilities of materials to gas or vapour, we can use microflow and diffusion permeameters. Vapour transmission analysers, which form a related category of instruments, can measure rates of vapour transmission caused by humidity gradients.

Within the range of PMI permeameters you will also find that extra features and functions have been designed to deal with specific needs. They include multiple sample chambers, and chambers which accommodate unusual sizes and shapes of sample.

Some permeameters are adapted to allow testing of samples without removing them from the product or other structure. Others deal with permeability of materials to strong chemicals or permit study of permeability under high temperatures or pressures. There are also adaptations which allow permeability to be measured in-plane.

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