Understanding the behavior of commercially available hydrophobic polymer membranes is important for applications where separating a gas (or vapor) from a two-phase mixture with liquid is beneficial. For example, in-situ vapor extraction can be used in microscale heat sinks to improve heat transfer and flow stability. In this paper, two working fluids (air and water, the latter in both superheated vapor and saturated liquid-vapor states) were experimentally studied flowing through membranes having an interconnected web of polytetra-fluoroethylene (PTFE) nanofibers. These membranes have a manufacturer specified average pore diameter of 0.45 μm and are supplied with an integrated mesh backing. Flow rate was acquired as a function of driving pressure differentials across the membrane. A linear variation in mass transport as a function of the applied pressure difference across a porous membrane is expected for Darcy flow conditions. However, for superheated vapor and air at the flow conditions studied here, mass transport does not vary linearly with pressure differential. Rather, transport of both air and superheated vapor is influenced by structural changes to the membrane. The structural changes are known as compaction and result from the applied pressure differential. Two models are considered to account for reduced transport resulting from membrane compaction. For saturated liquid-vapor studies, the departure from a linear relation between vapor extraction and applied pressure difference is more drastic than that compared to the single-phase studies, suggesting influences in addition to compaction. These influences are believed to be two-phase hydrodynamics as well as possible condensation within the membrane.

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