Dipole moments of seven partially halogenated ethane refrigerants

Abstract

Dielectric constant measurements have been performed on seven partially halogenated ethanes, currently being considered as alternative refrigerants, in the gaseous state over the range 305-415 K in order to determine their dipole moments. Argon was also studied to test the apparatus. Five of the refrigerants have temperature-independent moments: R125 (CF{sub 3}CHF{sub 2}), {mu} = 1.563 {plus minus} 0.005 D; R134a (CF{sub 3}CH{sub 2}F), {mu} = 2.058 {plus minus} 0.010 D; R143a (CF{sub 3}CH{sub 3}), {mu} = 2.340 {plus minus} 0.010 D; R152a (CHF{sub 2}CH{sub 3}), {mu} = 2.262 {plus minus} 0.008 D; and R124 (CF{sub 3}CHClF), {mu} = 1.469 {plus minus} 0.012 D. Two refrigerants have conformer-dependent moments, making their time-averaged moments temperature dependent: R134 (CHF{sub 2}CHF{sub 2}), with a moment ranging from 0.991 {plus minus} 0.004 D at 309 K to 1.250 {plus minus} 0.004 D at 413 K; and R143 (CHF{sub 2}CH{sub 2}F), where the moment ranges from 1.680 {plus minus} 0.001 D at 309 K to 1.745 {plus minus} 0.001 D at 410 K. Accurate estimation of a molecule's temperature-dependent dipole moment requires an independent determination of its polarizability; this determination has been made from index of refraction measurements. Where possible, the present results are compared withmore » earlier determinations of dipole moments. In all but one instance, the agreement is good.« less