Permeation sources

The tracers in building infiltration studies are released using permeation sources.  These sources are small vials containing liquid PFT that are sealed with permeable membranes.  Vials are filled with approximately 5cc (8.5g) of tracer.  The membranes allow PFT vapor to diffuse into the environment at rates of micrograms per minute.  The lower molecular weight, more volatile PFTs have the fastest permeation rates.  These sources are passive.  They require no power.  They have been used in indoor building transport and infiltration studies and atmospheric dispersion experiments on meter to kilometer scales.  The rate at which the PFT permeates the membrane is dependent on area and thickness of the membrane, and vapor pressure of the PFT which makes the release rate temperature dependent.  The temperature dependence is given by:

where:

S = permeation rate at Temperature T

S_o = permeation rate at the reference Temperature T_o

D H_eff = effective enthalpy of permeation

R = Molar gas constant

H_eff/R is an effective enthalpy of permeation and is determined empirically by measuring the release rate as a function of temperature.  Release rate is determined gravimetrically using a precision balance to weigh a sample of sources stored for a specified time period at a series of controlled temperatures.

Last Modified: November 12, 2009
Please forward all questions about this site to: Linda Satalino