【作者】 石零；

【导师】 王惠龄；

【作者基本信息】 华中科技大学 ， 制冷及低温工程， 2006， 博士

【摘要】 低温固-固接触界面间热传输的优劣决定着器件的热可靠性和器件的使用寿命,同时,在航空航天、低温工程、超导器件冷却等领域,固-固界面间的热传输直接决定着系统的热控成败。用实验和理论的手段研究低温固-固接触界面间的热传输,一方面可以解决技术关键,另一方面可以解决学科的科学问题,所以揭示固-固接触界面间的传热机制已成为一个研究热点。本文的主要任务是从实验和理论上研究低温固-固接触界面间的热传输。高温超导材料和小型低温制冷机的出现,使制冷机直接冷却超导器件成为一种超导冷却方式。小型超导磁体的制冷机冷却,因超导体间、超导体与金属间的热接触传输存在接触界面而影响超导磁体以及系统各部件的温度分布均匀性,所以超导磁体的热稳定性和影响温度分布的关键是接触界面热阻(电阻)。本文建立了高温超导直接冷却实验系统,用静磁场准稳态的方法对35KJ模型SMES磁体进行了直接冷却实验研究,获得了磁体的温度分布和直接冷却特性。研究表明,减小低温界面热阻(电阻)是实现直接冷却超导器件和系统的技术关键。本文以高温超导直接冷却中的接触热传导研究作为切入点,在国家自然科学基金(51076013)、863国家高技术项目(2002AA306331-4)、教育部博士学科专项基金(20040487039)项目的资助下,展开了对接触界面热传导的研究。从微结构低温工程学角度看,两接触固体的界面处存在一层微米或纳米级厚度的低温界面层,该界面层的组织结构和特性不同于两接触物体,低温界面层的存在是引起接触热阻的一个主要原因,因此从微结构低温工程学角度研究低温界面层的特性、界面层热阻和界面层上的热输运过程具有重要的理论意义和实际应用价值。稳态法接触界面热阻研究中,用温度外推法获得的接触界面温差,忽略了接触界面层的微结构对温差的影响,因而对研究接触界面热阻存在不足。为弥补这种不足,本文利用了调制激光光热法原理,探索性的提出了调制激光光热研究方法,用低温制冷机作为冷源,建立了研究低温固-固接触界面的热传输研究光热实验平台。材料的热物性是研究接触热阻的基础参数,工程材料由于成分的细微差别会导致热物性出现较大差别。考虑材料的这种差别,保证接触热阻研究的可靠性,本文首先在所建立的光热实验平台上,进行了铜、不锈钢、铝的低温热扩散系数的实验研究。报导了采用全新的调制激光光热原理获得的,在20-300K低温度范围内的,低温工程材料铜、不锈钢和铝的热扩散系数。低温热扩散系数的调制光热法研究结果,与已获得热扩散系数数据基本一致。在低温热扩散系数的调制光热法研究的基础上,本文使用调制光热法重点研究了铜、不锈钢、铝间的接触界面层热阻,在1.2――4.28 MPa的接触压力范围内,在20――300K温度范围内,接触界面层热阻随温度和接触压力的增加而降低。低温热扩散系数和接触界面层的调制光热法研究使用了新方法、新理论,为低温接触热传导(热阻)的研究,开辟了的新途径。低温界面层的微观描述是揭示接触热传递的基础,本文较全面的阐述了“三维低温界面层”概念,明确地把界面层分成两个物理构成――界面和亚表面层。用热载子在界面层内的弹道传递和扩散传递,建立了扩散弹道界面层热阻模型(DBITR)。在亚表面层内采用类比声子波和电磁波的辐射衰减相似性,获得了声子扩散弹道传递系数。DBITR模型的热阻预测值与光热接触界面热阻实验值基本吻合。声子的界面层内传输用传递系数表示。传递系数与界面条件、声子态密度、温度、声子入射角度等因素有关。由于传递系数的复杂性,现在还没有全要素研究声子传递系数的报导。本文对AMM和DMM模型中的声子传递系数,结合界面条件,从声子散射的能量(温度)和动量角度,对声子的镜面弹性传递、非镜面传递的传递系数做了理论上的分析。以YBCO和MgO的膜基接触界面为例,指出了实验值和理论值存在差别的原因是模型忽略了亚表面层对声子传递的影响。在声子垂直入射条件下,从扩散弹道声子传递系数得出了AMM模型中传递系数。论文比较了AMM和DBITR两个接触热阻模型,从比较结果来看,膜基固-固接触间热阻的DBITR预测值和实验值间还存在较大的差异,而压力接触间的固-固接触热阻DBITR模型值与实验值符合的较好,而且DBITR模型的预测值要比AMM模型的预测值更接近实验值。DBITR模型的建立对研究复杂的低温固-固接触热传导的科学问题,即是从理论上做了有益的探索,也是对实验研究的补充。更多还原

【Abstract】 At low temperature, the heat transfer between two contact bulks determinates the reliability and life of apparatus, at same time, in aerospace, cryogenics, cooling superconductor fields, the heat trasfer between two contact bulks determinates whether the thermal manager of system. The heat transfer between two contact bulks is investigated using experimental and thoerical method, which can resolve the technique key and problem of discipline. So it is a hot to disclosure the mechanism of heat transfer between two contact bulks. The main task of this paper is investigated the heat transfe between two contact bulks using experimental and thoerical method at low temperatue.With the development of the high temperature superconducting material and mini-cooler, the cooler cooling is a cooling for the cooling superconductor. The cooler cooling of superconductor, since the contact heat transfer exists between the superconductor, between superconductor and metal, it affects the temperature distribution of superconducting maganet and system, so the key factors which affects themal stability and temperature of the superconducting maganet is the contact interface resistance. The cryocooler conduction cooling system of the superconducting magnet is set up, the test is conducted in this system using static maganet and quasi-steady state, and the feature of cooling on the 35KJ model superconducting magnet is obtained. The study shown that decreasing and controlling the thermal contact resistance is the technology key. The thermal contact conduction on the cryocooler conduction cooling is the start of this study, and the investigation is conducted under supporting the National nature science Foundation(51076013), the National 863 Foundation Research(2002AA306331-4), and the Specialized Research Fund of the Doctoral Program of Higher Education(20040487039).From the Micro-Nano cryogenic view, there is a micrometer (nanometer) interface layer between two bulks contact interface, the microstructure of the interface layer is different from that of bulk material. The cryogenic interface layer may result in the thermal contact resistance, so it has an important significance and application value for studying the character of interface layer, interface layer thermal contact resistance and the heat transport of the interface layer. A temperature extrapolation is usually used at steady state method for studying the thermal contact resistance. Since the influence of microstructure of the interface layer on the thermal contact resistance is neglected using the temperature extrapolation, so it may be shortage for studying the contact interface resistance. The modulation laser photothermal is exploitively used for studying the thermal contact resistance. Using cooler as cold source, the photothemal experimental platform has been set up.The thermal physic property is basic for studying the contact resistance, since the difference of component results in the large difference of the thermal physic property. To consider the difference, ensure the reliabilty of the investigation on thermal contact resistance, first, the thermal diffusivity on the copper, stainless steel and aluminium is studied at photothermal experimental platform. The results are resported on the photothemal at a temperature range from 20 to 300K. It is consistence with the result obtained using the steady state. Based on the thermal diffusivity, the contact interface resistance is intimately investigated, at a contact pressure range from 1.2MPa to 4.28 MPa, at a temperature range from 20K to 300K, the contact interface resistance decreases with rising of the contact pressure and temperature. The new technique and theory is applied in this study, it exploit a new path to invetigation of the contact interface resistance at low temperature.The microstructure explain on cryo-interface layer is basic to resolve the contact heat transfer, the conception of three dimension cryo-interface layer is fully explain, the interface layer is clearly divided into two parts—the interface and the sub-surface. The DBITR model is set up using the ballistic and diffusive transport of the phonon. The phonon transfer coefficient is obtained using the attenuation similar between the phonon wave and electron maganet wave. The prediction of the DBITR and experiment is basiclly identical.The transfer coefficient of the phonon is affected by the interface conditon, state density of phonon, temperature. Since the transfer coefficient is complex, the full investigation on the transfer coefficient is seldom reported. The transfer coefficient of the AMM and DMM model is concluded under considering the interface condition, from the view of energy and momentum of the heat carrier, under the elastic specular scattering and diffusivity scattering. The application example about the transport coefficient between YBCO and MgO is given, the difference between the prediction and experiment is that the influence of the microstrcuture of the sub-surface layer on the phonon transport. The transfer coefficient in the AMM is obtained from the DBITR under phonon normal incidence.The comparison is conducted between the AMM and DBITR model, the result shown that the prediction of the DBITR is consistent with the experiment under the pressure contact interface, however, the difference is exist on film on matrix contact interface. It is value that the DBITR model is set up for studying the problem of the contact heat conduction.更多还原