Hsin-Sen Chu

Effect of interface thermal resistance on heat transfer in a composite medium using the thermal wave model

Abstract This study analyzes how interface resistance affects heat transfer in a two-layered composite media under an incident pulse energy exerting on the exterior surface of one layer by using the hyperbolic heat conduction equation. The incident energy is absorbed and a pulse width temperature wave is generated within the skin depth of the first layer, which subsequently emanates to the second layer. Reflection and transmission occur when the initial pulse wave impacts the contact surface of the dissimilar material. In addition, the radiation-boundary-condition model based on Acoustic Mismatch Model or Diffuse Mismatch Model is used to predict the interface resistance. Analysis results indicate that the reflection–transmission combination phenomena strongly depend on the interface condition. Moreover, the thermal resistance restricts the energy transmission across the interface, creating a temperature difference at the interface and ultimately alerting the reflected wave feature. Our results further demonstrate that the critical thermal resistance magnitude to approach the perfect contact condition varies with the two-layered properties ratio and the absorption skin depth.

Radiative heat transfer in ultra-fine powder insulations

Abstract This paper reports the first systematic study of the spectral radiation heat transfer through the ultra-fine powder insulation Aerosil 380. Experimental results are obtained for the spectralextinction coefficient from infra-red transmission measurements and for the effective thermal conductivity using a guarded-hot-plate apparatus. These results are compared and assessed with relevant theoretical calculations. In comparison to total effective conductivity experiments in the temperature range of 320–400 K, radiation heat transfer accounted for approximately 10% of the total heat leakage through the insulation, with the remaining by gaseous conduction. At high temperatures, the radiation contribution is expected to increase sharply, reaching over 50% at about 1000 K.

Propagation and reflection of thermal waves in a rectangular plate

The wave nature of heat propagation in a two-dimensional rectangular plate with an instantaneous thermal disturbance released in an arbitrary position is investigated by solving the hyperbolic heat conduction equation. The exact analytical solutions are developed for the temperature field and heat flux using the Greens function technique to deal with two limiting boundary conditions, the constant wall temperature and the adiabatic condition, around the region. The disturbance gives rise to a severe thermal wave front, which differs completely from that obtained through one-dimensional analysis, traveling through the medium at a finite speed with a sharp peak at the leading edge. The significant findings in these results are that a negative trailer is generated and follows behind the wave front. In addition, the magnitude of the front is significantly attenuated from the side adjacent to the trailer because the increasing area available to it for diffusion, and decays exponentially along its path of trave...

Hyperbolic heat conduction in thin-film high Tc superconductors with interface thermal resistance

Abstract This article numerically analyzes the hyperbolic heat conduction problem in the film and substrate composites under an imposed surface heat flux on the exterior film surface. The radiation heat flux model is employed to take account of the interface thermal resistance. The reflection and transmission occur at the contact surface of the dissimilar material which depends on the substrate properties and interface conditions. The interface resistance restricts the energy transmission across the interface and alerts the reflected and transmitted waves strength. Neglecting the interface thermal resistance causes the temperature distribution in the film to be greatly underestimated. Moreover, the hyperbolic equation predicts significantly different results with those predicted by the parabolic equation at small time scales. The discrepancies between the solutions in an investigation of superconductor Y–Ba–Cu–O film depositions on several commonly used substrates are examined.

Propagation of thermal waves in a composite medium with interface thermal boundary resistance

This article numerically analyzes the hyperbolic heat conduction problem in a two-layer composite medium under an initial temperature pulse emanating from the exterior surface of one layer. Reflection and transmission occur when the initial pulse wave impacts the contact surface of the dissimilar material. An interfacial layer with low conductivity and narrow thickness exists at the interface, which is employed to model the thermal boundary resistance at the contact surface. Analysis results indicate that the interface resistance significantly influences the wave pattern and strength. The presentation of the wave nature in the interfacial layer deforms the initial wave feature and induces secondary wavelets behind the reflected and transmitted wave. In addition, the piecewise secondary wavelets become smooth when the interfacial width is very thin. Also examined herein is the effect of conductivity and thickness width of the interfacial layer coupled with variation of the two-layer properties ratio on the reflection-transmission-combination phenomena.

Transient heat-transfer phenomenon of two-dimensional hyperbolic heat conduction problem

This article presents a numerical analysis of the two-dimensional hyperbolic heat conduction problem in an anisotropic medium under a point heat source with different boundary conditions. A simple model has been developed to solve the anisotropic problem. In this analysis, the second-order total variation diminishing (TVD) scheme is employed to solve this problem. The effects of boundary conditions and anisotropy on the thermal wave induced by different types of heat sources in the medium are examined in detail. The results show that the transient behavior of the propagation of the two-dimensional thermal wave is muck more complicated than that of the one-dimensional thermal wave due to a circular wave formed to propagate uniformly in alt directions, reflections by boundaries, interaction with each other, and serious discontinuity on the wavefront.

Bolometric Response of High-Tc Superconducting Detectors to Optical Pulses and Continuous Waves

This work presents a thermal analysis on predicting the temperature increase and the voltage response of high-T c superconducting bolometers. Two heat transfer models, that is, the surface heating model and the heat generation model considering the skin depth, are introduced and compared. The surface heating model is found to be valid only for situations where the skin depth is much smaller than the film thickness. To consider the thermal boundary resistance between film and substrate, a radiation-boundary-condition model based on acoustic mismatch model (AMM) and an interfacial-layer model (ILM) are employed. The thermal boundary resistance significantly influences the voltage response. Additionally, several common substrates are examined. SrTiO 3 (100) or LaAlO 3 (100) is a better substrate for high-T c superconducting bolometers. One interesting finding was that when compared with experimental data, all the theoretical values from the present study as well as the other previously theoretical treatment overestimate the voltage response near the transition temperature.

Study on the intrinsic thermal stability of anisotropic thin film superconductors with a line heat source

Abstract This paper presents an analytical method to investigate the intrinsic thermal stability of anisotropic thin film superconductors. A three-dimensional analysis is introduced to consider an instantaneous release of energy in the form of a finite length line source. Through the transformation of coordinates, an isotropic form of heat conduction equation is obtained. To solve this initial and boundary value problem, the method of separation of variables is employed, which gives an exact solution. The results of limiting cases of this study are compared with those of two previous investigations. Results from this study also show that the anisotropy of highly oriented films of superconductors has a great impact on the thermal stability. The stability parameter also depends on the location of the line source, the length of the line source, the magnitude of disturbance energy, the Biot number and the aspect ratio in the plane of thin film and normal to it.

Substrate effects on intrinsic thermal stability and quench recovery for thin-film superconductors

Two-dimensional conjugate film/substrate conduction equations considering an instantaneous release of energy in the form of a line source, anisotropic thermal conductivity of the film, and Joule heat are employed to investigate substrate effects on the intrinsic thermal stability and quenching recovery of thin-film superconductors. The results show that substrate effects exert significant influences on thermal stability of superconductors, because the higher thermal conductivity of substrates than those of films can cause heat feedback from the substrates. Both critical current densities related to intrinsic stability and recovery are calculated for different ratios of thermal conductivity and thickness of film to substrate, substrate materials, superconductors, Biot numbers, and operating temperatures.

Influence of thermal boundary resistance on bolometric response of high-Tc superconducting films

Abstract This work presents a thermal analysis on predicting the temperature increase and the voltage response of high- T c superconducting bolometers. To consider the thermal boundary resistance between film and substrate, an acoustic mismatch model (AMM), a diffusive mismatch model (DMM), and an interfacial layer model (ILM) are employed. The thermal boundary resistance significantly influences the voltage response. Additionally, several common substrates are examined. SrTiO 3 (100) or LaAlO 3 (100) is a better substrate for high- T c superconducting bolometers. Furthermore, we demonstrated that there are several factors to affect the voltage response, such as the pulse duration for a constant total incident energy or a fixed highest incident heat flux, the pulse distribution function in time, optical penetration depth, the thermal conductivities of the film and substrate, initial operating temperature, thickness ratio, and the amount of incident heat flux. One interesting finding was that when compared with experimental data, all the theoretical values from the present study as well as the other previously theoretical treatment overestimate the voltage response near the transition temperature.