KapitsaS Temperature Jump

a phenomenon in superfluid liquid helium, discovered by P. L. Kapitsa in 1941, that consists in the fact that upon transfer of heat from a solid to liquid helium a temperature difference arises at the interface. Kapitsa’s temperature jump was subsequently found to be a common physical phenomenon at low temperatures: it arises at the interface of any mediums when there is a thermal flux from one medium to the other.

The temperature jump is

where Q is the thermal flux density and T is the temperature, and the factor A depends on the elasticity of the substances in contact.

Experiments have established that at the interface between lead and superfluid helium at temperature T = 1.3°K and stationary thermal flux density Q = 10 watts per sq m (W/m²), the temperature jump is ΔT = 0. 01°K. Thus R = 1.1 X 10-³m² · deg⁴/W, and the coefficient A = 2. 4 X 10 ³m2 · deg4/W. For other metals, under the same conditions and when the surface is treated in an identical manner, the coefficient R has values close to this.

In the scientific literature the quantity R, as well as the phenomenon discovered by Kapitsa, is often called the thermal resistance of the interface or the interface thermal resistance.

It has been demonstrated theoretically (by I. M. Khalatnikov in 1952) that at low temperatures the heat exchange between a fluid and solid is due to the emission and absorption of sound quanta (phonons) at the interface of the mediums. Because of the great difference in the acoustic resistances of solids and liquids (a factor of several thousand), the coefficient of transmission of sound from one medium to the other is negligibly small: the phonons of the hotter solid are reflected almost totally from the interface. As a result, a finite temperature difference—Kapitsa’s temperature jump—arises between the solid and the liquid. The jump is the main obstacle to the cooling of bodies to extremely low temperatures.