Thermal Conductivities of He, Ne, Ar, and of their Mixtures

Abstract

LON G I T U DIN A LOP TIC ALP H 0 NON -P LAS M 0 NCO U P LIN GIN CdS S1 where the distance between carrier electrons, dee, divided by the effective Bohr radius, ao', is not less than 1 at concentrations of 1018/cc. For cases where r. is less than 1, the self-consistent field theoryl8 is applicable and the polarizabilities of the electrons and 18 J. Lindhard, Kg!. Danske Videnskab, Selskab, Mat.-Fys.Medd., 28, 8 (1954). ions may be taken as additive. Varga's results are then derived for r. < 1 from the equations of motion of Born and Huang 19 and the Poisson equation.The second reflectivity minimum is one of the main points needing examination.The use of a line-source transient-heat-transfer technique to determine the thermal conductivities of He, Ne, Ar, and of their mixtures is reported along with results. The method employs existing rigorous analytical theory for a finite line source possessing heat capacity. The experimental and analytical techniques minimize the effects of instrument size, radiation, free convection, and thermal separation of the mixtures. The linesource diameter was 0.00763 cm with a central 0.OO203-cm nickel temperature sensing coil to provide temperature data. Experimental times of 270 msec or less and total temperature rises of less than lOoC were used to minimize radiation, free convection, and thermal separation effects. The data show excellent agreement with existing data and an internal consistency and accuracy believed to demonstrate elimination of undesirable effects upon over-all thermal-conductivity determinations.

Historical Evolution of the Transient Hot-Wire Technique

“…On the other side, in the parallel or the cross-array mode of the transient hot-wire instrument, instead of the wire acting both as sensor and a thermometer, a thermocouple is placed usually 1.5 cm from the heating platinum wire to register the temperature [37,58]. However, the errors that exist in the resistive mode of the hot wire, also appear in this one.…”

“…Four years later, in 1968, Burge and Robinson [37] proposed another four-terminal transient hot-wire instrument for gases employing lower times. The line source consisted of a 0.7 mm diameter, 20.6 cm length wire.…”

“…-the American 1999 ASTM C1113-99 Resistive Transient Hot-Wire test method [57], -the European 1998 EN 993-14 Cross-Array Transient Hot-Wire test method [37], and -the European 1998 EN 993-15 Parallel Transient Hot-Wire test method [58].…”

Measurement of the thermal conductivity of composite solid materials

“…In 1964, Mittenbühler [Mittenbühler, 1964] used a heating wire of one metal, with a thermocouple welded to the heating wire in the form of a cross, in order to measure the thermal conductivity of solids. [Burge & Robinson, 1968] proposed an instrument for gases employing lower times (Figure B.14), while Hayashi et al [Hayashi et al, 1971] propose an instrument for solids up to 1,473 K. [Burge & Robinson, 1968].…”

“…Figure B.14 Schematic of linesource thermal conductivity cell proposed by Burge and Robinson[Burge & Robinson, 1968]. …”