Showing papers on "Heat current published in 1970"

On the linear theory of heat conduction

Abstract: : A general linear theory of heat conduction is developed. General representation theorems are derived for the relations between energy, heat flow and temperature, temperature gradient. They contain aftereffect functions of a well defined class, the so-called positive definite functions. The results are given for isotropic as well as anisotropic materials. For a particular class of materials, noted as of the relaxation type, it is possible to give a non-equilibrium entropy in terms of a certain functional which satisfies a Clausius-Duhem inequality. Also a model for linear heat conduction in this class of materials is given which consists of a thermodynamic formalism with internal variables. (Author)

Measurements of the Kapitza conductance between metals and liquid helium II by the transmission of second sound

Abstract: Measurements have been made in the temperature range 1.0-2.0K of the alternating heat current transmitted through tin metal foils separating two second sound resonators. The experimental arrangement and analysis are described in some detail. The values of the Kapitza conductance obtained in this way of copper, and of indium, lead and tin, are comparable to those obtained using the usual steady state method, although the temperature dependence is always significantly higher: about T4. In general, the total foil conductance in the superconducting state is larger than in the normal state and it is believed that this is due to size effects arising from the long phonon mean free paths. An interpretation of these results suggests that the effective phonon transmission coefficient from lead to helium is greater than or approximately equal to 0.67.

Heat transfer and second sound in dielectrics with large drift velocities of a phonon gas

Abstract: : Nonlinear hydrodynamic equations are derived which describe the motion of a phonon gas in a dielectric at low temperatures. (Author)

On temperature variations produced by heat currents in liquid He II

Abstract: From linearized two fluid hydrodynamics it is shown that there is a spatially constant temperature rise if a heat current is switched on in a channel of infinite length. This leads to a maximum possible heat current vanishing atT gl. In a spherical geometry there is a similar temperature rise, but it decays exponentially with time.