Dielectric properties of 1,1,1,3,3-pentafluoropropane (HFC-245fa)

The relative permittivity of 1,1,1,3,3-pentafluoropropane (HFC-245fa), a li quid hydrofluorocarbon developed as a blowing agent for plastic foams, is r eported. This fluid is being evaluated as a potential replacement for HCFC- 141b (1,1-dichloro-1-fluoroethane). The relative permittivity of HFC-245fa in the liquid phase was measured using the direct capacitance method at tem peratures from (217 to 303) K and at pressures up to 16 MPa, for a frequenc y of 10 kHz. The uncertainty of,the dielectric constant measurements is est imated to be +/-0.88 x 10(-2). A complete set of values of the relative per mittivity as a function of temperature, pressure, and density is presented that covers the needs for most engineering., applications. The results were ,correlated by polynomial equations as a function of density and temperatur e and also as a function of pressure and, temperature. To study the depende nce of relative permittivity on density and temperature on a molecular basi s, the theory developed by Vedam et al. and adapted by Diguet was applied t o analyze the data. The Kirkwood modification of the Onsager equation was u sed to obtain the value of its dipole moment in the liquid phase. The appar ent dipole moment obtained was mu* = 2.688 D.