【作者】 张群；

【导师】 张振宇；

【作者基本信息】 大连理工大学 ， 机械工程（专业学位）， 2021， 硕士

【摘要】 热容是一种基本的热力学参数,是研究和理解材料晶格振动、结构转变、磁性和超导等现象的重要参数,也是节能、热管理、热设计模拟等目标实现的重要参数。目前测量热容的仪器主要有综合物性测量系统（PPMS）、差示扫描量热仪（DSC）、高温落入式量热仪和绝热量热仪,其中绝热量热仪测量凝聚态物质中温区热容的准确性高于上述其他仪器。传统绝热量热仪所需样品质量较大（约50-100 g）,并且仪器稳定性的研究缺乏。然而,部分新材料成本较高,制备困难,难以大量获取,严重限制了新材料热力学性质的探索,阻碍了新材料的发展与应用。针对上述问题,本文建立了中温区小样品量绝热量热仪并研究了仪器的准确性、精密性和稳定性。具体研究内容如下:基于传热理论和绝热量热仪结构特点对影响样品池绝热环境和仪器性能的因素进行了分析。对仪器主要部件进行结构设计:样品池主体材质为银,加热丝无感双绕在样品池表面,铂电阻温度计通过温度计套管与样品池中心位置的入口阱配合,E型热电偶安装在对称焊于样品池底部的1对热电偶套筒内,样品池采用银为垫片,蒙乃尔合金为刀口材料的软金属刀口密封;该仪器有2层绝热屏,3层防护屏,其下盖通过热屏固定组件固定;真空室采用法兰密封。为减小样品池辐射传热,利用Comsol Multiphysics仿真软件,通过对样品池在一个加热周期内的辐射热通量和温度进行研究,确定出较合理的防护屏空间位置。另外,仿真结果也表明:3层防护屏与0层防护屏相比,3层防护屏使样品池辐射热通量在一个加热周期内下降约77%;同时,样品池平衡期温度变率也有62%的改善。最终,经过加工、组装和调试建立起绝热量热仪。利用上述自主研制仪器通过铜和α-Al₂O₃（SRM 720）的热容测试结果对该仪器性能进行了研究。结合测量铜所得热容实验值与美国国家标准与技术研究院（NIST）推荐的铜热容数据,计算出空池在300-570 K下的热容。通过α-Al₂O₃在300-570 K下的热容实验值与NIST推荐值,得出仪器准确性在±0.5%以内,精密性在±0.3%以内,稳定性在±0.15%以内。更多还原

【Abstract】 Heat capacity is a basic thermodynamic parameter,which is an important parameter to study and understand lattice vibration,structural transformation,magnetism,superconductivity and other phenomena of materials.It is also an important parameter to achieve the goals of energy saving,thermal management and thermal design simulation.At present,the main instruments for measuring heat capacity are physical property measurement system（PPMS）,differential scanning calorimeter（DSC）,high-temperature drop calorimeter and adiabatic calorimeter.Among them,the adiabatic calorimenter has higer accuracy in measuring heat capacity in the medium temperature region of condensed matter than other instruments mentioned above.In addition,But,traditional adiabatic calorimeter needs a large sample mass which is about（50-100）g and there is a lack of research on the repeatability of adiabatic calorimeter.However,some new materials are expensive and difficult to prepare a large number of samples,which seriously limits the exploration of thermodynamic properties of new materials and hinders the development and application of new materials.In response to the above problems,this paper mainly established a small sample-size adiabatic calorimeter in the middle temperature region,and the accuracy,precision and repeatability of the instrument were studied.The main research work are as follows:Based on the theory of heat transfer and structural characteristics of the adiabatic calorimeter,the factors affecting the adiabatic environment of the sample cell and stability of the adiabatic calorimeter were analyzed.The structure of the main parts of the adiabatic calorimeter were designed.The main material of the sample cell was silver.The heating wire was non-inductively wound on the surface of the sample cell.The platinum resistance thermometer was matched with the inlet well in the center of the sample cell through the thermowell.The thermocouples of E type were installed in a pair of thermocouple sleeves symmetrically welded on the bottom of the sample cell.The sample cell was sealed with soft metal knife edge with silver gasket and Monel alloy as knife edge material.The instrument has two layers of adiabatic shields and three layers of radiation shields.The lower covers were fixed by the heat shields fixing component.The vacuum chamber was sealed by flange.In order to reduce the radiation heat transfer of the sample cell,Comsol Multiphysics simulation software was used to study the radiation heat flux and temperature of the sample cell in a heating cycle,so as to determine a more reasonable space position of the radiation shields.In addition,the simulation results also showed that:compared with the 0-layer shield,the 3-layer shield reduced the radiant heat flux of the sample cell by about 77%.Meanwhile,the temperature variability of the sample cell was improved by 62%in the equilibrium period.Finally,after processing,assembling and debugging,the adiabatic calorimeter for small sample-size in medium temperature zone was established.The performance of the self-developed instrument was studied based on the heat capacity measurement results of copper and-Al₂O₃（SRM 720）.The heat capacity of the sample cell was calculated by combining the experimental data of copper heat capacity and the copper heat capacity data recommended by NIST in the temperature range of 300 to 570 K.The results show that the accuracy,precision and repeatability of the instrument were within±0.5%,±0.3%and±0.15%,respectively,according to the experimental values of heat capacity of-Al₂O₃ and NIST recommended values in temperature range from 300 to 570 K.更多还原