Measurement and description of the flow of isobutane and of R142b through anodic alumina membranes with pore sizes from 25 nm to 80 nm

Abstract

Anodic alumina membranes have a very regular pore space of evenly distibuted, parallel, straight pores [Petukhov et al., Nanotechnology 23, 335601 (2012)]. Measurements of the permeance of the flow of vapors partially under conditions where condensation occurs through anodic alumina membranes with pore sizes between 25 nm and 80 nm are reported. The upstream state and the downstream pressure are prescribed, the downstream temperature and the mass flow rate is measured. For the pressure-driven flow through a porous body, a vapor close to saturation may condense (i) either due to capillary condensation or (ii) due to heat transfer in downstream direction from a vapor near saturation at the upstream side of the membrane caused by the Joule-Thomson effect.

The experimental data is compared with predictions from a one-dimensional description of the process that involves Darcy’s law, the energy balance, but assuming local thermodynamic equilibrium and applying Young-Laplace’s and Kelvin’s equations at interfaces [Loimer et al., Sep. Purif. Technol. 215, 548–556 (2019)]. There is good qualitative and, to a certain extent, quantitative agreement between experimental data and prediction. However, the solution is sensitive to the conditions at the downstream side of the membrane. A small heat flux from the membrane cell to the membrane surface might significantly alter the mass flow rate. Also, a hysteresis in the experimental data could not be explained from the current model. The description might be improved by either allowing a contanct angle hysteresis, or by including non-equilibrium effects at fronts of phase change.