Interface Structure Influence on Thermal Resistance Across Double-Layered Nanofilms

This work investigated the interface influence on the thermal resistance across double-layered thin films by non-equilibrium molecular dynamics (NEMD) with Lennard-Jones potential. Layer A is a solid argon with a face-centered cubic structure and Layer B is obtained by changing atomic mass only. A flat interface is formed when each of the contacting atomic planes from the two layers has the same kind of atoms. A staggered interface is obtained by mixing atoms A and B around the interface region. The temperature profile, vibration amplitude, and structure factor are studied to observe the interface effects. It is found that the thickness of the staggered atomic layer has significant influences on the normal thermal conductivity. With a staggered interface thickness of two atomic planes, the normal thermal conductivity is sharply increased. Further increasing the staggered thickness will gradually decrease the normal conductivity. This result suggests a possibility to control the thermal conductivity of the double-layered structure by engineering its interface condition.     

Thermal resistance of crystal interface: Molecular dynamics simulation

Non‐equilibrium molecular dynamics computer simulation was carried out to investigate a thermal resistance phenomenon at interfaces of Lennard‐Jones particle crystals. Inside an FCC crystal, one‐dimensional steady thermal energy flow was realized using a pair of temperature‐controlled heat baths. Four types of sharp and flat interfaces between the following crystals were investigated: (i) crystals with different particle masses, (ii) crystals with different interaction energy parameters, (iii) crystals with various surface interaction parameters, and (iv) crystals with different size parameters. Except for case (iv), observed temperature profiles have a discontinuity at the interface, from which the temperature gap is evaluated. Due to the temperature discontinuity, the thermal energy flux is smaller than that through a single crystal without an interface. The observed reduction of the energy flux is larger than that predicted with a simple acoustic model. Interfaces with finite width, or composition gradient, were also examined. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(3): 135–146, 2005; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/htj.20058     

Thermal Stresses in Multilayer Gun Barrel with Interlayer Thermal Contact Resistance

A hybrid numerical method of the Laplace transformation and the finite difference is applied to solve the transient heat transfer problem of a gun barrel, in which the interlayer thermal contact resistance between the steel cylinder and the chrome coating is taken into account in the boundary conditions. The general solutions of the governing equations are first solved in the transform domain. Then the inversion to the real domain is completed by the method of Fourier series technique. The transient distributions of temperature and thermal stresses for the gun barrel in the real domain are calculated numerically.     

Molecular Dynamics Study on Thermal Conductivity of Carbon Nanotubes

The thermal conductivity of a (5, 5) carbon nanotube at room temperature is studied by non‐equilibrium molecular dynamics simulations. The thermal conductivity increases from 30 W/(m·K) to 1000 W/(m·K) as the tube length increases from 6 nm to 4 µm. It is proportional to the tube length when the tube length is less than 40 nm, which indicates that the heat conduction is in the ballistic transport regime. The thermal conductivity relates to the tube length by an exponential function as the tube length increases, and the length dependence exponent decreases and approaches zero, which indicates that the phonon transport changes from the ballistic regime to the diffusive regime. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; 39(7): 455–459, 2010; Published online in Wiley Online Library ( wileyOnlinelibrary.com ). DOI 10.1002/htj.20311     

柴油机缸内壁面边界层的数值模拟

利用二维边界层微分方程数值模拟了缸内壁面速度和热边界层,获得了不同工况下的速度和热边界层厚度,将二维边界层微分方程的数值计算结果和在TY1100柴油机上的测量结果进行了对比分析,结果表明,二者的变化趋势是一致的,建立的数值模拟模型可以较好地预测缸内壁面速度和热边界层的变化规律．     

层流脉动流中平行圆柱体的温度边界层

采用数值模拟方法研究了一个平行圆柱体在层流脉动流中的温度边界层特性。数值模拟结果与实验数据一致。研究发现脉动流中平行圆柱体形成了形状不规则但相对稳定的温度边界层,并在流动方向上周期性脉动。脉动流中平行圆柱体的温度边界层平均厚度小于稳定流动下的温度边界层平均厚度,并以脉动流的频率进行脉动。此外, 脉动流中平行圆柱体的壁面温度小于稳定流动下的壁面温度,表明脉动流下圆柱体的对流传热得到了强化。在一个脉动周期内,圆柱体在后半周期的温度边界层厚度和热阻均小于前半周期的温度边界层厚度和热阻。     

An Experimental Investigation of Thermal Performance of a Polymer‐Based Flat Heat Pipe

A polymer‐based flat heat pipe (PFHP) was fabricated. The heat transfer performance was measured and analyzed when deionized (DI) water and acetone were used as the working fluid, separately. Input power ranging from 2.8 W to 14.2 W was provided to the evaporator section while the device was at different filling ratios. Experimental results revealed that, when the polymer‐based flat heat pipe was laid in a horizontal position, the thermal resistance (1.02 K/W) was much smaller than that (4.6 K/W) of a copper plate with the same thickness at the thermal power of 10.3 W and the value decreased as the tilt angle changed from 0° to 90°.     

排气阀热边界条件分析及温度场有限元计算

排气阀在高温环境下工作,对内燃机的应用可靠性及使用寿命有着重要的影响。针对轻12V180型柴油机,分析排气阀的工作环境,计算了柴油机排气阀等效的热边界载荷,结合有限元分析软件ANSYS,建立热模型进行排气阀温度场分析,为排气阀工作负荷状况的改善与优化设计提供了理论依据。     

Experimental Study on the Permeability and Thermal Resistance of the Cement Clinker Accumulation

A device was designed for measuring the permeability of cement clinker accumulation in three dimensions. In addition, the equivalent permeability and equivalent thermal resistance coefficient were introduced to evaluate the penetration ability in high temperature. First, the equivalent permeability of the accumulation in three dimensions was measured at a room temperature of 298 K and the order of magnitude was decided to be 10^?6. The difference degree of equivalent permeability was less than 15% in each direction; Then the rule of equivalent permeability in three‐dimensional changed with temperature was obtained by the air‐cooled experiments of the cement clinker accumulation at an initial temperature – 773 K; Finally, the law of equivalent thermal resistance coefficient was obtained through comparing the change of the permeability from high temperature to room temperature. The results showed that the equivalent thermal resistance coefficient change with temperature was nonlinear and the equivalent thermal resistance coefficient changed from 1.0 to 1.3 when the temperature was in the range of 298 K to 773 K.     

固体表面之间接触热阻的辨识研究

介绍了接触热阻的测量原理和传统的实验装置。从接触界面热耦合的角度，结合传热方程的数值解法和参数辨识方法，对实验数据进行整理。通过与文献中数据的对比，说明本方法的可行性。此方法对热物性变化较明显的实验，更能体现出优越性。     

An Investigation of the Thermal Stresses Induced in a Thin-Film Thermoelectric Cooler

This work aims at investigating the thermal stresses induced within a four-layered thin-film thermoelectric cooler. The one-dimensional (1D) temperature and thermal-stress distributions are firstly analyzed under the consideration of Joule heating, the conduction heat transfer as well as Thomson heating. Followed are two-dimensional (2D) calculations of the thermal stresses with the commercial software ANSYS. The validity of the 1D analytical model is then examined by a comparison of its predicted thermal stresses with the numerical ones obtained from the 2D model. In the 2D model, the thermoelectric element becomes curved due to the shrinkage and the fixed boundary conditions. The latter also causes huge values and rapid changes of thermal stresses near the ends. In the middle portion of the thermoelectric element where the thermal effect dominates, the thermal stresses predicted by the 1D model are not much different from those computed from the 2D model. Quantitative differences arise from the fact that the 1D model does not count the stresses induced by the non-zero Poisson's ratios. In addition, the normal-stress distributions are pretty uniform across the layer thickness (the variation is less than 1MPa within each layer in the worst case). These results verify the possibility of using the 1D model for a preliminary estimate of the thermal stresses induced within the layered thin-film thermoelectric element. The 1D model nonetheless fails to capture the behaviors near the ends of the thermoelectric element.     

具有辐射边界的三维非规则域内稳态温度场分析

研究了具有辐射边界的空间非规则域内稳态导热问题,求解方法为在球极坐标系内分离变量,获得级数形式的解后,采用边界离散法确定级数项的待定系数,算例表明,边界离形方法不仅可以解决非正交边界问题,而且也可以处理诸如辐射边界的非线性边值问题。     

煤粉浓缩器阻力特性的试验研究

采用近似模化法研究了两种不装导流板的煤粉浓缩器－丘体和百叶窗的阻力随结构参数变化的特性。试验结果表明,随着丘体斜面长度的增加,阻力系数增大。对于百叶窗,阻力系数随着叶片倾角或叶片宽度的增加而增加,叶片间距比的变化对流体流动影响比较大,它在２．５～３．０之间变化时,流动阻力较小。     

Impact of the Relationship between Phase Change Temperature and Boundary Temperature on the Thermal Performance of a PCM Wall and the Presentation of PCM Thermal Performance Indexes

In the composite phase change material (PCM) building envelope, the matching relationship between the phase change temperature of the PCM and the wall's boundary temperature significantly affects the energy storage performance of the PCM building envelope. In this paper, a type of concrete hollow block with a typical structure and a common PCM were adopted to produce multiform composite PCM hollow blocks, and the temperature changing hot chamber method was performed to test the thermal performance of the hollow block walls under different temperature conditions. New indexes were proposed for the thermal performance evaluation of the PCM wall. Meanwhile, combined with experimental data, the effective heat capacity model and the enthalpy model were used to analyze the effect of correlations concerning how the relationship between phase change temperature and wall's boundary temperature influenced the thermal performance of PCM wall. Three main impact factors related to temperature were obtained through the analysis. In addition, approaches for improving the thermal performance of a composite PCM wall were put forward. This paper provides the theoretical basis, data reference and practical instruction for the proper use of a PCM wall and ways for improving the thermal performance of a composite PCM wall.     

Hydrogen retention and affecting factors in rolled tungsten: Thermal desorption spectra and molecular dynamics simulations

Hydrogen isotope retention of tungsten in nuclear fusion reactors is one of the hot research issues all along. In this paper, tungsten samples in different rolled surfaces were polished by mechanical processing, subsequently subjected to D₂⁺ irradiation and thermal desorption. To better understand the experimental observations, this study also performed molecular dynamics (MD) simulation and investigated the effects of temperature, grain number, grain boundary density, and crystal orientation on hydrogen retention. It is found that the grain number and grain boundary density of rolled tungsten increase successively in RD/TD, RD/ND, and TD/ND surfaces. The RD/ND surface exhibits the best hydrogen radiation resistance, whereas the TD/ND surface is unsatisfactory. MD simulations further indicate that hydrogen retention is more obvious with the increase of grain density in tungsten, and hydrogen atoms are more easily enriched at the grain boundaries. With the increase in temperature, the retention of hydrogen atoms in monocrystalline/polycrystalline tungsten decreases significantly. The average implantation depth of H atoms is deepest along the <111> and <112> crystalline directions, which reveals that hydrogen retention is dependent on the crystal orientations. The good agreement between the experimental data and simulation results reveals that grain boundaries play an important role in hydrogen retention.     

热箱-热流计法现场检测围护结构热阻

探讨了采用热箱-热流计法检测建筑物围护结构的热阻以实现非采暖季进行检测。由于检测面大量广,因此检测方法必须相对地简便易行。根据这一原则提出对热箱法中由于侧向热流引起的误差采用把在两侧测得的热流值加权平均的方法加以修正,以实现现场测试基本的精度。根据建筑围护结构检测的特定情况,用数值模拟的方法归纳总结出适用于不同保温形式的围护结构的加权平均系数,即修正系数。通过对多种常见的围护结构的形式的修正系数及其相应误差值的分析,表明这种修正方法可以满足对于建筑围护结构热工性能现场检测的要求。     

石墨烯泡沫热物性与界面热导温度相关性研究

石墨烯泡沫是将石墨烯立体化形成的复合材料,在锂离子电池等领域有较好的应用前景,而其导热性质成为限制工业应用的重要因素。基于瞬态电热技术,研究了石墨烯泡沫的导热性质及其随温度的变化。结果表明,不同于Umklapp声子散射机理,石墨烯泡沫的热导率随温度呈正相关性:由室温至373 K时,热导率由0.71升高至1.10 W/(m·K)。分析发现,泡沫内部的大量界面是其低导热性质的主要因素。利用分子动力学模拟验证了石墨烯与基体材料间的界面传热随温度成正相关,与宏观材料测量结果相符。     

上海市住宅建筑夏季室内热湿环境实态调查与分析

为切实掌握目前上海市住宅建筑夏季室内热湿环境实态，于2003年8月在上海地区随机对100户5年内新建住宅进行了相关问卷调查和实测，并对其中典型的10户住宅进行了室内温湿度实测。问卷调查包括建筑概况、空调设备、生活方式、能源消费及舒适性等内容。调查结果发现：上海地区的空调普及率为98％，以分体壁挂式为主；空调使用高峰期为7、8月份，夜间使用率明显高于白天；室内舒适性较差，约90％的室内空气状态点不在ASHRAE舒适区内。     

Thermal Stresses in a Hollow Cylinder with Convective Boundary Conditions on the Inside and Outside Surfaces

Analytical solutions for thermal stresses (radial, tangential, and axial) in a hollow cylinder with uniform internal heat generation for the thermal boundary condition of convective heating on the inside surface and convective cooling on the outside surface are derived. The analysis assumes the ends of the cylinder to be clamped, the axial strain to be negligible, and the radial stresses on the inside and the outside surfaces to be zero. Results are presented to illustrate the effects of internal heat generation parameter Q, convective environment temperatures ratio θ*, Biot number for convection on the inside surface Bi ₁, Biot number for convection on the outside surface Bi ₂, and the radii ratio ρ on thermal stresses distribution in the cylinder. The analytical solutions should serve as benchmarks for validating the numerical codes for dealing with more complicated cases.     

Thermal Green's Functions for a Heat Source in a Piezoelectric Solid with a Parabolic Boundary

Using the Stroh formalism combined with the analytical continuation principle of Muskhelishvili, the Green's functions for a line heat source in a piezoelectric solid with a parabolic boundary are obtained in closed form. The obtained Green's functions not only satisfy all the given boundary conditions, but also ensure the displacement and electric potential to be single-valued. As special cases, the solutions for a piezoelectric half-plane are also presented, and they are shown to be consistent with previous works.