一种双臂型低温导热带的性能研究

详细介绍了低温导热带的设计特点。从理论上分析了低温导热带的冷量传输性能和减振特性,得到通过利用高导热率材料可以有效地减小导热温差和降温时间。通过实验验证了低温导热带与制冷机和高温超导滤波器的耦合实验,耦合温差为2.5K。实验结果和理论值基本吻合,分析了造成温差的原因。根据实验结果,提出了新的改进和实施方案。

钼铜的低温导热研究

研究了熔渗法制备的Mo-Cu复合材料从350～20 K的导热率变化。结果表明,该材料在350 K的导热率为200 W/(m.K)。随着温度降低,导热率降低,降温至200 K后导热率升高,20 K时导热率达305 W/(m.K)。将样品用浓硝酸腐蚀去除铜组分后观察微观组织发现,Mo在熔渗制备过程中已烧结成骨架结构,这种结构的形成是低温材料导热率升高的原因。

离子束混合技术制备低温导热减震器材料的研究

采用离子束混合技术 ,将具有良好导热性能的金属 Ag沉积在具有良好减震性能的金属 Cu上 ,将 1 0 0 ke V的 Ar+ 注入 Ag-Cu基合金中 ,研究离子注入对 Ag-Cu基合金界面混合的影响。分析结果表明 :当 Ar+ 注入剂量达 1× 1 0 1 6 ion/ cm2 时 ,Ag与 Cu基合金界面出现明显的过渡层 ,界面实现原子级混合。利用该方法获得在低温时具有良好表面导热及减震性能的复合材料 ,并根据此原理 ,应用全方位离子注入增强沉积技术 。

高压熔渗金刚石/铜复合材料的低温导热特性

为研究高压熔渗金刚石/铜复合材料导热率在低温区的变化规律,采用高压熔渗(HRF)的方法分别制备了不同粒度(100μm,250μm,400μm)的金刚石/铜复合材料,利用扫描量热法分析评价了高压熔渗法制备的不同粒度金刚石/铜复合材料的低温导热特性,采用扫描电子显微镜(SEM)分析其显微组织。研究结果表明:由于高压熔渗制备的金刚石/铜复合材料中的部分金刚石发生聚晶反应,导致金刚石颗粒间晶界传热的热阻远小于界面传热热阻;高压熔渗条件下,金刚石颗粒内部变形破碎导致缺陷增多,且100~150K低温下以声子为主要热载子的传热对裂纹和间隙等缺陷敏感,导致在较低温区内金刚石/铜复合材料的导热率低于普通压力熔渗(PF)所制备的金刚石/铜复合材料的导热率。

多层绝热低温有效导热系数试验研究

叙述了多层绝热低温有效导热系数试验方法,对两种国产多层绝热材料有效导热系数测试结果进行了分析比对,在特定的绝热材料预处理过程下,得到了工程应用数据。

液氮罐内低温氮气的温度场研究

对装有少量液氮的液氮罐内的温度分布进行了系统研究,提出了相应的温度分布模型。研究表明,在10 L容积的液氮罐内注入少量液氮时,罐内温度可保持低于-130℃持续约25天,适用于多种场合的超低温保存。通过调节距离液氮面的高度,可选择保存样品的温度范围并控制样品的升降温速度。理论计算的温度分布与测量的结果符合较好,证实了所建立模型的合理性和有效性。

Oxidative heat release intensity in coal at low temperatures measured by the hot-wire method

Directly measuring the oxidative heat release intensity at low temperatures is difficult at present.We developed a new method based on heat conduction theory that directly measures heat release intensity of loose coal at low temperatures.Using this method, we calculated the oxidative heat release intensity of differently sized loose coals by comparing the temperature rise of the coal in nitrogen or an air environment.The results show that oxidation heat release intensity of Shenhua coal sized 0～15 mm is 0.001～0.03 W/m3 at 30～90 °C and increases with increasing temperature.The heat release intensity at a given temperature is larger for smaller sized coal.The temperature effect on heat release intensity is muted as the coal size increases.At lower temperature the change in heat release intensity as a function of size becomes smaller.These results show that the test system is usable for practical applications and is easy to operate and is capable of measuring mass samples.

Design and Analysis of a Thermally Insulating and Heating Scheme for Piezoelectric Stack Actuators Used in the Cryogenic Environment

In cryogenic wind tunnel tests,piezoelectric stacks are adopted to realize the vibration control of the cantilever sting.However,the free stroke and blocking force of the piezoelectric stack would decrease dramatically as the temperature decreases.This paper proposes a convenient and effective warming structure for the piezoelectric stack,which could keep it working at operating temperatures when the ambient temperature drops.The piezoelectric stack actuator is wrapped with the heating film,and this resulting assembly is then wrapped with the aerogel material for thermal insulation.Both ends of the piezoelectric stack actuator make direct contact with the payload structure.Both one-dimensional and two-dimensional theoretical analyses of the heating conduction problem of the piezoelectric stack actuator are conducted.These analyses results are compared with those of the finite element simulation analysis.The finite element method results show a good consistency with the two-dimensional theoretical results,and a slight deviation of only 0.91 K is observed,indicating its potential for protecting piezoelectric stacks at low temperatures.

Measurements of Static Heat Loss and Unloaded Q_0 on the BEPCⅡ SRF Cavities

The static heat loss and unloaded Q_0 are the most important values for both the cryogenic and the RF systems.The BEPCⅡ SRF cavity operates in a liquid helium bath contained in a vacuum insulated,liquid nitrogen cooled radiation shielded vessel.During the horizontal test at the test station,thermodynamic method is used to measure and calculate the static loss and Q_0 value of the SRF cavity.This paper has briefly introduced the method and process to measure the static loss and Q_0 value of the SRF cavity.The results under different experimental conditions are presented as important data for acceptance test of the SRF cavity.

Qualitative analysis on adiabatic and dynamic stability of LTS/HTS hybrid conductor with concentric configuration

The I-V characteristic of a superconductor is generally described by power-law,in which the superconductor with a high n transfers quickly from superconducting state to the normal conducting state.With a high transport current,in the low n value area,flux flow voltage becomes lower than in the high n value area,so that the transient characteristics strongly affect its stability.Based on those properties,we propose a new hybrid conductor which is made of low temperature superconductor(LTS) and high temperature superconductor(HTS) with concentric configuration in which the HTS coat is located outside of the LTS core.According to their power-law models,the modified adiabatic and dynamic stability criteria are qualitatively obtained by taking account into not only their critical currents but also n values.As a result,the new hybrid conductors have potential applications with higher engineering current density and improved stability.

Diffusive Thermal Conductivity of Superfluid Fermi Gas in p-Wave State at Low Temperatures

The diffusive thermal conductivity tensor of p-wave superfluid at low temperatures is calculated by using the Boltzmann equation approach. We use the Sykes and Brooker procedure and show that Kxx is equal to Kyy and these are related to T-1, also Kxx is proporated to T-3.