Comparison of membrane permeability of enthalpy exchangers
Permeability is one of the key characteristics of enthalpy exchangers. Ideally, the exchanger should only transfer water molecules.
We had membranes from two established manufacturers tested and compared their permeability with the RECUTECH membrane Metalpic.
How did the membranes perform in an independent test?
The membranes were tested in an independent laboratory at the University of Science and Technology in Prague. The test focused on measuring the permeability of CO2, CH4, N2 gases.
The measurements were performed at 2, 4, 6 and 8 bar on the side of the gas under test, the pressure on the opposite side corresponded to the standard atmospheric pressure. At least 3 samples were tested for each membrane type. The permeability was first measured with a bubble meter, which measures the gas concentration after permeation through the membrane.
Testing results
As can easily be seen from the measured values, the differences in the permeability of the individual membranes are enormous.
For sample 1 we were able to measure the gas concentration by simply measuring with a bubble meter, the other membranes had to be analysed with a chromatograph due to their lower permeability.
According to the permeability results, it can be concluded that membrane 1 is microporous, while the other two membrane samples are ion-exchangeable. As can be seen from the measured values, a relatively large amount of all the gases tested pass through membrane 1, which is definitely not desirable for the use of this membrane in air conditioning. It is preferable to use an ion-exchange membrane, which passes an order of magnitude less of the gases tested.
Compared to microporous membranes, ion-exchange membranes are significantly more advantageous in that they do not clog the pores over time, the membrane does not foul and the desired moisture transfer is not reduced.
As can be further seen from the measured data, the Recutech Metalpic membrane has a significantly lower permeability for all gases tested and thus emerges from the measurements as the best choice for the manufacture of enthalpy exchangers.
Metalpic
In Recutech enthalpy exchangers we use a unique material called Metalpic. This material has been developed by Recutech solely for this purpose. It is a sandwich material where each component has its clearly defined function.
The Metalpic consists of specially treated aluminium mesh with the largest possible open surface. The primary function of the mesh is to support the other component, a thin polymer membrane. Why aluminium? Because this material has excellent heat conductivity and it is easy to recycle.
The second component is the polymer membrane. Its primary function is humidity transfer while keeping the complete plate tight. The membrane is a ion-exchange semi-permeable type.