Hi there,
i am estimating sort of the shelf life or a product in da Polyethylene bag.
Bag Thickness is 200 microns, accessible area is 800 cm^2 or 0,08 m^2. Volume of the bag 100ml or 0,0001 m^3.
I found permeation coefficients of e.g. 12 Barrer (1). As Barrer is defined via CGS units (1 Barrer = 1e-10 (cm^3 cm)/(cm^2 s cmHg)), i converted it to SI units, then to molar flow. That is:
9,00072E-17 (m^3/s)*((m)/(m^2*Pa)) // SI
4,0152E-15 (mol/s)*((m)/(m^2*Pa)) // molar
The flux is usually calculated using this simple relationship:
J = (P/x)*(phigh-plow)*A
where J is the permeation flow, P is the permeation coefficient, x is the film thickness, plow and phigh the partial pressures inside and outside the bag and A the accessible surface for the permeation process.
For a 100 relative humidity at 25°C (3160 Pa) and zero inside the bag i calculate a flux of
5,07521E-09 mol/s
That is:
4,38E-04 moles per day and (molar weight of water is 18 g/mol)
7892 µg a day.
That sounds like a large value and it felt like that, but i double checked.
Of course, this is the steady-state case.
Can someone:
- reproduce this?
- give me an estimate of how long it takes to reach the steady state? or give me literature according to this?
Thanks in advance,
Max
Refs:
(1) Metz, S. J. (2003). Water vapor and gas transport through polymeric membrane.
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