Fractal Prediction Model of Thermal Contact Conductance of Rough Surfaces

The thermal contact conductance problem is an important issue in studying the heat transfer of engineering surfaces, which has been widely studied since last few decades, and for predicting which many theoretical models have been established. However, the models which have been existed are lack of objectivity due to that they are mostly studied based on the statistical methodology characterization for rough surfaces and simple partition for the deformation formats of contact asperity. In this paper, a fractal prediction model is developed for the thermal contact conductance between two rough surfaces based on the rough surface being described by three-dimensional Weierstrass and Mandelbrot fractal function and assuming that there are three kinds of asperity deformation modes： elastic, elastoplastic and fully plastic. Influences of contact load and contact area as well as fractal parameters and material properties on the thermal contact conductance are investigated by using the presented model. The investigation results show that the thermal contact conductance increases with the increasing of the contact load and contact area. The larger the fractal dimension, or the smaller the fractal roughness, the larger the thermal contact conductance is. The thermal contact conductance increases with decreasing the ratio of Young＇s elastic modulus to the microhardness. The results obtained indicate that the proposed model can effectively predict the thermal contact conductance at the interface, which provide certain reference to the further study on the issue of heat transfer between contact surfaces.

Thermal contact conductance at continuous roll-casting interface

The effects of surface roughness, strain rate, friction coefficient and pressure on real contact area were analyzed based on the research of Stupkiewicz. The real contact area model taking account of the effect of friction and deformation of material was obtained. The model of contact conductance at the rolling interface was obtained by integrating the specific feature of heat transfer through the interface of continuous roll-casting. The results indicate that the real contact area increases obviously when the material is under yield, and the real contact area varies inversely with surface roughness, whereas it varies exponentially with friction coefficient, strain rate and pressure, and the power factor depends on strain rate.

Modeling of thermal conductivity for disordered carbon nanotube networks

Several theoretical models have been developed so far to predict the thermal conductivities of carbon nanotube(CNT)networks.However,these models overestimated the thermal conductivity significantly.In this paper,we claimed that a CNT network can be considered as a contact thermal resistance network.In the contact thermal resistance network,the temperature of an individual CNT is nonuniform and the intrinsic thermal resistance of CNTs can be ignored.Compared with the previous models,the model we proposed agrees well with the experimental results of single-walled CNT networks.

Investigation on Thermal Contact Conductance Based on Data Analysis Method of Reliability

The method of reliability is proposed for the investigation of thermal contact conductance （TCC） in this study. A new defini- tion is introduced, namely reliability thermal contact conductance （RTCC）, which is defined as the TCC value that meets the reliability design requirement of the structural materials under consideration. An experimental apparatus with the compensation heater to test the TCC is introduced here. A practical engineering example is utilized to demonstrate the applicability of the pro- posed approach. By using a statistical regression model along with experimental data obtained from the interfaces of the struc- tural materials GH4169 and K417 used in aero-engine, the estimate values and the confidence level of TCC and RTCC values are studied and compared. The results show that the testing values of TCC increase with interface pressure and the proposed RTCC model matches the test results better at high interface pressure.

Thermal contact conductance estimation and experimental validation in hot stamping process

The variation in temperature of the blank would make major contribution to the mechanical properties of final component in hot stamping of ultra high strength steel(UHSS).It is important to use accurate thermal contact conductance(TCC) to carry out finite element simulation of hot stamping for reliable caculation results.In this paper,a flat compression test was performanced on a servo press.A fast response temperature measurement and data acquisition system was designed to obtain the temperature history of blank and die under different pressures.The thermal contact conductance between blank and die was got using an optimization algorithm.The error between the temperature curves using calculated thermal contact conductance and the curves of measurement temperature was analyzed.Result shows that reliable simulation results of temperature can be got through accurate thermal contact conductance.

Influence of body contact of SOI MOSFETs on the thermal conductance of devices

The thermal conductance of devices with different body contacts is studied. A new analytical expression is proposed. This expression can be used in parameter extraction, which gives both good efficiency and high precision. The ratio of thermal conductance of the body contact region to that of the body region is nearly equal to the ratio of the area. The use of an H shape gate body contact is suggested to aid power dissipation in SOI MOSFETs.

Heat transfer analysis for the roller shell under the condition of periodic thermal shock

According to the actual working conditions of roller shell in the process ofcontinuous roll casting, the Fourier heat transfer law is used to conduct the simulating analysisfor the temperature distribution of the roller shell under the condition of periodic thermal shock.The temperature variation law inside the roller shell is studied during the process of continuousroll casting, and the steady temperature distributions of the roller shell at different castingvelocities have been obtained when the thermal contact conductance between the roller shell and thecasting strip is considered.

Transient temperature characteristics of friction clutch disc considering thermal contact conductance under sliding conditions

High temperatures are generated due to the sliding contacts between the rubbing surfaces of the friction clutch system.In this work,by considering the effective thermal contact conductance under sliding conditions,a simulation model of a two-dimensional transient temperature field of the clutch disc was developed.A numerical solution to obtain the surface temperature at different radii was presented based on the finite difference method.Compared with the experimental data,the proposed model for estimating the surface temperature is more accurate than the conventional prediction method.The results showed that the errors of the calculated temperatures at radii of 114 and 106 mm have obviously reduced by 12.98%and 12.60%,respectively.In addition,the influences of pressure and relative speed on the surface temperature were investigated.The temperature increases with the increase of the relative speed and pressure during the sliding period,and there is an interaction effect between pressure and speed on the surface temperature rise.

航天器用界面导热填料应用状态接触传热系数分析

为解决航天器用RKTL-DRZ-2型导热脂及RKTL-DRNJ-1型导热凝胶2种新开发导热填料无实际应用状态下接触传热系数数据的问题,采用试验方法对其接触传热系数进行研究,得到在航天器上设备典型尺寸及不同固定螺钉分布情况下的接触传热系数。试验结果表明:在相同安装状态下,与目前常用的RKTL-DRZ-1型导热脂相比,RKTL-DRZ-2型导热脂对界面接触传热性能改善效果较好,RKTL-DRNJ-1型导热凝胶较差。此外,获取了保证导热填料填充效果的实施经验,并给出了导热填料的选用建议。试验分析结论可应用于选用导热填料时的航天器热设计及热控实施。

基于相似性原则的橡胶颗粒-砂混合物热导率理论模型

为准确定量评价人工隔热材料橡胶颗粒-砂混合物的导热性能,突破现有经验关系模型适用性较差的局限性,以Wiener土体热导率模型为框架,基于相似性原则,通过对混合物中各介质的导热性能进行分析,建立用于计算混合物热导率的理论模型,分析模型中计算参数的意义和确定方法,根据文献报道热导率测试数据,对比验证模型的有效性,并探讨模型进一步完善和拓展的研究方向。研究结果表明:橡胶颗粒和孔隙液的导热能力相似,可将两者归属为相似类传热介质应用于Wiener串、并联模型中;模型综合考虑了橡胶掺量、粒径比、饱和度和孔隙率等对橡胶颗粒-砂混合物结构和导热性能的影响,准确描述了混合物热导率和橡胶掺量、粒径比的相关关系,与实测数据的对比结果显示了较高的精确度。探明复杂应力状态和极端气候条件对刚-柔性颗粒混合物导热性能的作用规律,是进一步完善和拓展本文模型的重要研究内容。

碳填料/天然橡胶复合材料热导率及层间接触热阻对微波加热效果的影响

制备炭黑/天然橡胶(NR)、石墨烯/NR和碳纳米管/NR复合材料,采用试验与数值模拟相结合的方法研究复合材料热导率和层间接触热阻对微波加热的影响。结果表明:炭黑、石墨烯和碳纳米管自身热导率越大,复合材料的热导率越大,层间接触热阻越小;通过增大填料用量来增大复合材料的热导率和减小层间接触热阻具有一定的局限性,需考虑复合材料的配方设计适用性和经济性;复合材料的热导率对微波加热过程中高、低温区域分布规律和微波加热效率基本无影响,但影响复合材料的温度分布均匀性。为保证微波加热硫化均匀性,多层复合材料的层间接触热阻不可忽略。

考虑颗粒形貌的干砂热传导特性研究

为揭示颗粒形貌对干砂热导率的影响规律,通过砂颗粒形貌测量和室内热探针试验,研究不同天然河砂的二维颗粒形貌统计分布特征以及颗粒形貌特征参数与热导率的相关关系,同时从细观尺度探讨砂颗粒接触传热的内在机制。结果表明:天然河砂颗粒圆度和球度值的统计分布具有正态分布特征,期望值可作为定量表征颗粒形貌的参数;干砂热导率随孔隙率增加而减小,在半对数坐标中两者具有良好的线性关系,直线斜率与“平均形貌因子”Am呈线性减小关系;相同孔隙率下,浑圆颗粒的干砂热导率值较大,不同干砂间热导率值的差异随孔隙率的增加而逐渐减小;提出的热导率计算新模型综合考虑了颗粒形貌和矿物组分的影响,相比于传统Côté和Konrad模型,具有更好的适用性和先进性;颗粒形貌对干燥状态下无黏性土热传导特性的作用受多因素综合影响,与应力环境、颗粒刚度等密切相关。

固态均热板外壳的典型设计参量影响分析

文中识别了固态均热板模块外壳的典型设计参量,并以一个高热耗模块为背景,开展了各典型设计参量对模块整体导热性能影响的研究。研究结果表明,外壳的整体导热性能与高导热层的平面导热系数、Z向尺寸、固态均热板“三明治”结构的异种材料间水平接触热阻3个设计参量的关联较大,与高导热层垂直导热系数、X向尺寸、固态均热板“三明治”结构的异种材料间垂直接触热阻关联较小。此外,还对研究数据进行了敏感度分析。分析结果表明,高导热层的平面导热系数、Z向尺寸与外壳整体的传热性能呈线性相关,“三明治”结构异种材料间的水平接触热阻与外壳整体的传热性能呈非线性相关。该研究成果为后续固态均热板壳体在材料、结构尺寸和“三明治”构型加工工艺的设计选型提供了依据。

考虑接触热导的电动扭矩扳子校准装置热特性分析

为了提升动态扭矩参数的测量准确度,基于分形理论,引入接触热导参数,建立结合面接触热导模型,并进行数值仿真。同时针对典型的电动扭矩扳子校准装置,利用接触热导模型对其轴承结合部进行温度仿真并与试验结果进行对比分析。结果表明:接触热导参数分别与接触载荷和材料特性参数呈现正相关增长趋势,而与尺度参数呈现负相关增加趋势;当2.1≤D≤2.7时,接触热导参数随分形维数D的增大而增大;当2.7≤D≤2.9时,接触热导参数反而随着分形维数D的增大而减小。考虑接触热导的上、下轴承结合部最高温度均比不考虑时高出4~6℃,且与试验结果接近,相对误差分别为2.7%和3.3%。

铝合金与5CrMnMo模具钢界面接触换热系数实验研究

利用自制的接触换热系数测量装置对铸造铝合金和挤压铝合金分别与5CrMnMo模具钢的接触换热系数进行了实验研究.分析了铝合金与5CrMnMo模具钢间的接触换热系数随接触表面温度和载荷的变化,发现接触换热系数与温度并不存在简单的正比关系,而与载荷的指数近似成正比关系,并且在相同的接触条件和测量条件下铸造铝合金与5CrMnMo的接触换热系数普遍要比挤压铝合金的小.

界面接触热阻的研究进展

界面接触热阻(TCR)是电子器件冷却、低温超导薄膜等领域研究中的一个热点。综合评述了对接触热阻传热机理的研究方法、测量方法以及减小接触热阻的主要措施,介绍了近年来国内外对接触热阻的最新研究成果和进展,现有的研究表明:对于界面接触热阻这一特殊物理问题,其理论研究既要从宏观上定量分析又要在微观上综合考虑声子、电子的散射、辐射等机理;在实验方面,目前的测量精度不够高,实验测量工作有待进一步完善;在减小接触热阻方面,除了常用的方法外,可以通过在接触表面生长新型的高性能导热材料(碳纳米管等)来实现。对已报道的研究工作进行了总结,指出了今后的研究方向。

基于电接触元件暂态热路建模的接触电阻测量研究

目前,接触电阻的检测主要是电压电流法或电桥法,其不足是仅适于离线应用。提出了一种在线式的接触电阻间接测量新方法。首先在建立电接触元件的理论物理模型和径向暂态热路分析模型的基础上,推导出热路响应方程;然后再在建立元件轴向热传导数值分析模型的基础上,最终推导出计及温度和电流的接触电阻曲线关系,提出通过曲线的时间常数计算电接触元件的接触电阻。大量的理论分析、计算与有限元分析ANSYS仿真表明,所研究的测量方法可以准确求取接触电阻的值,为电气设备的在线监测和热缺陷分析提供了理论依据。

热界面材料热导率和接触热阻的测试

热界面材料通常用于降低电子器件中固体界面的热阻。热界面材料的性质,如热导率、界面材料与固体表面间的接触热阻,对于电子器件的散热分析非常重要。然而,这些参数通常难以获得。依据ASTM D-5470测试标准,搭建了一个热界面测试系统。通过该系统测试了硅油和导热硅脂的热导率,以及它们与固体基板间的接触热阻。经分析,测试热导率和接触热阻的相对误差分别小于11.3%和41.3%。

吸附器中导热胶热传导系数的研究

本文在研究吸附式热泵吸附器传热性能的特性基础上,发现导热胶能有效降低吸附剂与吸附换热器表面间的接触热阻,随后研制并测试了导热胶对颗粒吸附剂与吸附换热器表面之间以及成型吸附剂与吸附换热器表面之间接触热阻的影响。实验结果表明,导热胶是降低吸附剂与金属表面之间接触热阻的一种有效方法,可以提高吸附剂与金属表面之间的传热性能,而对吸附剂的吸附性能影响不大, 为强化两种不同介质之间的传热提供了新的技术途径。

新型铜颗粒填充的液态金属热界面材料导热性能实验研究

为强化界面传热,研制了一种以铜颗粒为填充材料、Ga62.5In21.5Sn16液态金属为基体的新型复合热界面材料,并对其导热性能进行了测试。首先将所制备的热界面材料放置在两片铜片之间,制备3层结构试样,然后利用激光导热仪测量所制备试样的导热性能,并计算相应试样的接触热阻。实验结果表明:铜颗粒填充型液态金属可以大大提高氧化后液态金属作为热界面材料的性能,利用铜粉质量分数分别为5%和10%的液态金属所制备的试样,导热系数和接触热阻分别为(200.33±15.66)、(233.08±18.07)W/(m·K)和(7.955±0.627)、(5.621±0.437)mm2·K/W,较利用氧化后液态金属所制备试样的导热系数分别约提高了68%和96%,接触热阻分别约降低了57%和70%,并可以有效降低液态金属的流动性,从而减少液态金属在使用过程中溢出现象的发生。