Enhanced thermal conductance at a copper-liquid helium interface in the presence of acoustic streaming

In a conventional Kapitza resistance experiment involving heat transfer across a copper surface into liquid helium, an acoustic streaming velocity field (at 10 MHz) was directed transverse to the surface normal. Ultrasound had no observable effect on the heat transfer to the superfluid phase (He-II), but in the normal fluid phase (He-I) the thermal conductance increased linearly with acoustic velocity amplitude, reaching a value 2.5 times the zero sound conductance for a sound velocity amplitude of 0.8 cm s^?1.     

Kapitza conductance measurement of silver: Dislocation dependence and near acoustic mismatch

A report is presented of a study in which good agreement is obtained between theory and experiment for the Kapitza conductance of silver, with heat transfer coefficients as low as 2.5%. Also clear experimental evidence is presented of the dependence of the Kapitza conductance on the dislocation density near to the silver to helium interface.     

Kapitza conductance of Bi/sapphire interface studied by depth- and time-resolved X-ray diffraction

We present Kapitza conductance measurements of the bismuth/sapphire interface using depth- and time-resolved X-ray diffraction, for Bi film thicknesses ranging from 65 to 284 nm. Our measurements provide complementary information about heat transport in the films; we directly observe the thinnest film to be uniformly heated within 1 ns, whereas the thickest film sustains a large near-surface temperature gradient for several ns. The deduced Kapitza conductance is 1950 W/cm²/K. This value is close to the theoretical prediction using the radiation limit.     

Thermal conductance of hydrophilic and hydrophobic interfaces

Using time-domain thermoreflectance, we have measured the transport of thermally excited vibrational energy across planar interfaces between water and solids that have been chemically functionalized with a self-assembled monolayer (SAM). The Kapitza length--i.e., the thermal conductivity of water divided by the thermal conductance per unit area of the interface--is analogous to the "slip length" for water flowing tangentially past a solid surface. We find that the Kapitza length at hydrophobic interfaces (10-12 nm) is a factor of 2-3 larger than the Kapitza length at hydrophilic interfaces (3-6 nm). If a vapor layer is present at the hydrophobic interface, and this vapor layer has a thermal conductivity that is comparable to bulk water vapor, then our experimental results constrain the thickness of the vapor layer to be less than 0.25 nm.     

Unexpected large thermal rectification in asymmetric grain boundary of graphene

We have investigated the lattice thermal transport across the asymmetric tilt grain boundary between armchair and zigzag graphene by nonequilibrium molecular dynamics (NEMD). We have observed significant temperature drop and ultra-low temperature-dependent thermal boundary resistance. More importantly, we find an unexpected thermal rectification phenomenon. The thermal conductivity and Kapitza conductance is direction-dependent. The effect of thermal rectification could be amplified by increasing the difference of temperature imposed on two sides. Our results propose a promising kind of thermal rectifier and phonon diodes based on polycrystalline graphene without delicate manipulation of the atomic structure.     

The Kapitza conductance of Mica

The Kapitza conductance between cleaved mica and superfluid helium is measured by the second sound technique from 1.2 K to 2 K. The data are reproducible. The temperature exponents is 4.1.     

The effect of phonon lifetimes on the Kapitza resistance

The effect of attenuation of phonons in the solid on the Kapitza resistance at a solid-⁴He boundary is discussed using a transfer Hamiltonian formalism. It is explicitly shown why the attenuation of Rayleigh waves is a dominant mechanism for the thermal boundary conductance.     

Kapitza resistance in basic chain models with isolated defects

We explore numerically the boundary Kapitza resistance in one-dimensional chain models with isotopic and/or coupling defects for variety of the inter-particle potentials. In linear models, the Kapitza resistance is well-defined and size-independent (contrary to the bulk heat conduction coefficient), but depends on the parameters of thermostats used in the simulation. For β-FPU model one also encounters the dependence on the thermostats; in addition, the simulated boundary resistance strongly depends on the total system size. Finally, in the models characterized by convergent bulk heat conductivity (chain of rotators, Frenkel-Kontorova model) the boundary resistance is thermostat- and size-independent. In linear chains, the Kapitza resistance is temperature-independent; thus, its temperature dependence allows one to judge on significance of the nonlinear interactions in the phonon scattering processes at the interface.     

Weak thermal links for thermal cycling experiments

Two types of thermal links-wire coupling and Kapitza coupling-for thermal cycling (TC) experiments are studied. Quantitative models describing static and dynamic behaviour of the sample temperature are developed and experimentally tested. There is a wide range of applications for both couplings, the most severe limitations are imposed by nuclear heat capacities. Kapitza coupling is restricted to thin foil samples, but potentially offers the fastest response.     

The scattering of phonons of arbitrary wavelength at a solid-solid interface: Model calculation and applications

A one-dimensional lattice model of a solid-solid interface is presented within which it is possible to characterize the scattering of phonons at the interface as a function of wavelength. The probability for a phonon to be transmitted across the interface is found generally to decrease with decreasing wavelength, although phenomena such as total reflexion and resonant transmission may occur. Conditions for the existence of a localized interface mode are given. The thermal boundary resistance for heat flow across the interface is expressed in terms of an average temperature-dependent phonon transmission coefficient which generally increases with decreasing temperature and approaches the continuum value at very low temperature. Applications of these results to three-dimensional interfaces in general, and particularly to heat dissipation in catalysts, high-frequency phonon radiators, and Kapitza resistance, are discussed.     

包含倾斜晶界的双晶ZnO的热输运行为

用嵌入位错线法和重合位置点阵法构建含有小角度和大角度倾斜角的双晶氧化锌纳米结构.用非平衡分子动力学方法模拟双晶氧化锌在不同倾斜角度下的晶界能、卡皮查热阻,并研究了样本长度和温度对卡皮查热阻和热导率的影响.模拟结果表明,晶界能在小角度区域随倾斜角线性增加,而在大角度区域达到稳定,与卡皮查热阻的变化趋势一致.热导率随样本长度的增加而增加,卡皮查热阻表现出相反的趋势.然而随着温度的增加,热导率和卡皮查热阻都减小.通过比较含5.45°和38.94°晶界样本的声子态密度,发现声子光学支对热传导的影响不大,主要由声子声学支贡献,大角度晶界对声子散射作用更强,声学支波峰向低频率移动.     

Thermal rectification in nonmetallic solid junctions: Effect of Kapitza resistance

Based on Fourier's law for heat conduction, we investigate the asymmetric heat flow in two segment rods of nonmetallic materials. Specifically, we study the effect of the Kapitza resistance at the boundary of the segments on the thermal rectification. To understand basic features of the rectification, we first develop analytical calculation for the heat currents in an ideal rod of a macroscopic length. Explicitly, this is made by assuming that the thermal conductivity of each constituent has a power-law dependence on temperature and also assuming the continuity of temperature at the boundary. Then, we introduce the temperature jump at the boundary due to the Kapitza resistance and show that this effect on the thermal rectification becomes significant as the length of the rod decreases typically to submillimeters. In particular, we find that the temperature jump yields a finite rectification even when no asymmetry is predicted in the heat currents from the continuity of temperature at the junction. The obtained results have an important implication for the analysis of the thermal rectification of a rod consisting of semiconductors Ge and Si.     

New results and a simple model for the anomalous power dependence of the Kapitza resistance of copper

We report a new anomalous Kapitza Resistance, much stronger than the effect previously described by Cheeke and coworkers.¹ The effect can be described using a localised heat transfer model based on the resonant heat transfer theory.^5,6     

Integral relations for the heat and mass transfer resistivities of the liquid–vapor interface

We derived integral relations for the heat and mass transfer resistivities of the liquid–vapor interface in a one-component system. These relations were obtained assuming the validity of the standard expression for the local entropy production rate as the product of the measurable heat flux times the gradient of the inverse temperature through the surface. The integral relations will be useful to interpret results from nonequilibrium molecular dynamics simulations. We verified in this paper that earlier results obtained using the nonequilibrium van der Waals square gradient model are reproduced. For this case, we calculated the Kapitza length along the coexistence curve.     

Overheating or overcooling of electrons in a metal because of the effect of an interface with an insulator

It has been shown that the temperatures of electrons and phonons are different at a heat flow through a metal-insulator interface. This effect leads to an additional contribution to the Kapitza thermal resistance because electrons transferring heat in the metal do not transfer it through the interface, but are rather involved in heat transfer only at a certain distance from it. Consequently, heat transfer near the interface is less efficient. The effect is independent of the insulator adjacent to the metal. An exact solution has been obtained in a linear approximation. The results explain the qualitative difference of predictions of previously accepted models from experimental data in the case of large transmission coefficients of phonons through the interface.     

低温下粗糙表面接触间隙气体热导的研究

对低温非真空环境下粗糙接触界面间隙中介质气体的传热进行了理论分析．依据克努森数的大小,建立了不同传热区域的间隙气体热导理论模型．并对影响接触界面间隙热导的克努森数、普朗特数、热导率、适应系数、压力等参数进行了分析,为实际情况下接触界面的传热提供了理论基础．而且通过实验证明了在界面接触压力较小的情况下,即使对于硬度较小导热性能好的接触固体,间隙气体的导热量仍大于通过实际接触点的导热量．     

Kapitza resistance at the liquid—solid interface

Using equilibrium and non-equilibrium molecular dynamics simulations, we determine the Kapitza resistance (or thermal contact resistance) at a model liquid-solid interface. The Kapitza resistance (or the associated Kapitza length) can reach appreciable values when the liquid does not wet the solid. The analogy with the hydrodynamic slip length is discussed.     

Extension of Planck’s law to steady heat flux across nanoscale gaps

Recent experiments report that the radiative heat conductance through a narrow vacuum gap between two flat surfaces increases as the inverse square of the width of the gap. Such a significant increase of thermal conductivity has attracted much interest because of numerous promising applications in nanoscale heat transfer and because of the lack of its theoretical explanation. It is shown here that the radiative heat transport across narrow layers can be described in terms of conventional theory adjusted to non-equilibrium structures with a steady heat flux.     

Electron and phonon cooling in a superconductor-normal-metal-superconductor tunnel junction

We present evidence for the cooling of normal-metal phonons, in addition to the well-known electron cooling, by electron tunneling in a superconductor-normal-metal-superconductor tunnel junction. The normal-metal electron temperature is extracted by comparing the device current-voltage characteristics to the theoretical prediction. We use a quantitative model for the heat transfer that includes the electron-phonon coupling in the normal metal and the Kapitza resistance between the substrate and the metal. It gives a very good fit to the data and enables us to extract an effective phonon temperature in the normal metal.     

The Kapitza Effect in Charge-Ordered Layered Crystals

It is shown that the Kapitza effect in charge-ordered layered crystals can be explained for the case of a parallelism of magnetic field and measuring current when the Landau quantization and its effect on the charge-carrier scattering are considered. There is a linear correlation between the magnetic field and longitudinal resistance under the assumption that the scattering of charge carriers by acoustic phonons is dominant, and the band-to-band transitions are suppressed. The relations for the Kapitza coefficient are derived for different degrees of electron gas degeneracy and different values of interaction resulting in layered charge ordering.