POLARIZED TRANSIENT HOT-WIRE THERMAL-CONDUCTIVITY MEASUREMENTS

Additional experimental uncertainty is introduced in thermal conductivity data obtained with the transient hot-wire technique when bare hot wires are used in polar liquids. The use of a dc polarization voltage applied between the hot wires and the cell wall greatly reduces this uncertainty for polar liquids. Differences between polarized and nonpolarized experiments are described for the alternative refrigerants 1,1,1,2-tetrafluoroethane (R134a) and 1-chloro-1,1-difluoroethane (R142b). Comparisons are made between data from the polarized transient hot-wire technique and other experimental techniques for R142b. The polarization technique enables existing transient hot-wire instruments with bare wires to study the thermal conductivity of moderately polar liquids with confidence.