Introduction
The idea of interface thermal resistance has been put forward early in 1936. Before that, people usually believe that contact thermal resistance is small, and does not consider. KEESOM et al. Proposed in 1936, the thermal resistance of the contact interface may be very large, but there is no careful study. In 1941, Kapitza published an experimental study on temperature drop on solid and liquid helium contact interface, and therefore, the interface thermal resistance is also named Kapitza thermal resistance.
principle
The main reason for the thermal resistance of interface is due to the different electron properties and vibration characteristics of the two substances in contact. When the ferrome (phonon or electronics, it is determined) attempting to pass through the contact interface, scattering occurs. The movement of the heat carrier after scattering depends entirely on the energy status available to the contact interface material.
Assume that passing through the thermal flow of the interface, the interface thermal resistance will cause temperature drop in contact interface, according to Fourier's law, there is the following expression:
For solid and liquid helium, and between metal and dielectric, between the dielectric (in close contact case) said thermal conduction therebetween mainly by phonon heat transfer through solid-liquid interface reaches the phonon helium, is reflected or refracted compliance sinα1 / sinαs = v1 / vs, since the speed of sound in the solid v < / b> S is much larger than the sound speed of V 1 in the liquid, so the critical angle αLC is very small, that is, only a small stereoscopic angle range may enter the solid, while solid and liquid The density of the helium is very different, and the sound speed is also very large.
Thus, only a part of the phonon of less than 10-5 can enter the solid, the energy transmitted is small, and the reduction of energy on the interface is reduced, and the karmyin thermal resistance occurs.
Formula
The membrane coagulation of the vapor and cooling vertical wall of the low Prave Special (PR) substance is calculated, and one of the required Additional conversion heat transfer resistance. Therefore, the thermal resistance is generated on the steam-liquid two-phase interface, so the name interface thermal resistance. Common Symbol "R P " means that the unit is "(m · ° C) / W". Its mathematical expression is: R p = (t s -t i ) / q = r a, t > -R λ, l . In
, t s is a saturation temperature (° C) under the respective pressure of steam; T i is a true temperature on the vapor-liquid interface ( ° C); q is a convection heat transfer heat transfer (W / m) at the time of film-shaped; R A, T is a total convection thermal thermal resistance of steam to the cooling wall [(M · ° C) / w]; R λ, L is a thermally conductive thermal resistance [(M · ° C) / W] composed of a condensed liquid film.
Experimental study shows that for low PR media, there is always an interface thermal resistance, and as its value increases, the "temperature jump" in the steam-liquid interface is also more significant. That is, the real temperature on the interface is much less than the saturation temperature.
Effects
The size of the kariography and the solid surface conditions are particularly sensitive to surface mechanical damage. Understanding the thermal resistance between materials, is especially important for electronic products, because there is a lot of contact interfaces in today's electronic devices, which affects the heat dissipation of the electronic device. The interface thermal resistance is more important at the nanometer scale, because in the nanometer scale, the contact interface is more complicated.