3He-Superfluid-4He Mixtures: Convection, Anomalous Thermal Conductivity, and Boundary Resistance

技术摘要：本项目将研究两个科学问题：极稀超流氦混合物中的异常热流和超流氦混合物中的对流。异常热流研究的目的是了解当氦3浓度趋近于零时超流体混合物的有限热导率的实验观察。这些观察结果与理论相矛盾，理论预测，当氦3浓度趋于零时，热导率趋于无穷大。这项工作将使用交流电技术来分离流体和其他热流路径，提供有关边界电阻的信息。对流研究的目的是表征超流体混合物中的对流流动。实验技术将产生与普朗特数范围广泛相关的模式和热流数据。要研究的问题涉及瑞利-贝纳德对流模式和时空混沌、模式形成系统的不稳定性和混沌状态。非技术摘要：将研究氦3和超流氦4的混合物中的对流和热流。从技术角度来看，超流氦4是有趣的，因为它有效的无限导热性使它成为从冷却的电子设备中提取热量的杰出流体。它的目的是潜在地降低该系统中由自然存在的氦3引起的热流限制。还计划表征对流氦的非线性动力学和混沌。对流发生在环境（大气、海洋、技术过程）中，是研究更广泛的非线性动力学和模式形成的杰出系统。超流体混合物与液态金属和半导体具有相似的性质，更好地了解氦中的对流可能与净化这些材料有关。

Abstract Technical abstract: This project will address two scientific issues: anomalous heat flow in very dilute superfluid helium mixtures, and convection in superfluid helium mixtures. The objective of the anomalous heat flow study is to understand experimental observations of a finite thermal conductivity of superfluid mixtures as the helium 3 concentration goes to zero. These observations conflict with theory that predicts that the thermal conductivity approaches infinity as the helium three concentration goes to zero. The work will use alternating current techniques in order to separate fluid and other heat flow paths, providing information on the boundary resistance. The objective of the convection study is to characterize convective flows in superfluid mixtures. The experimental techniques will yield pattern and heat flow data which pertain to a broad range of Prandtl numbers. The issues to be investigated concern Rayleigh-Benard convection patterns and spatio-temporal chaos, instabilities of pattern forming systems, and chaotic states. Non-technical abstract: Convection and heat flow will be investigated in mixtures of helium 3 in superfluid helium 4. Superfluid helium 4 is interesting from a technical viewpoint, because its effectively infinite heat conductivity makes it an outstanding fluid for extracting heat from cooled electronic devices. It is aimed to potentially reduce limits to heat flow in this system caused by the naturally present helium 3. It is also planned to characterize nonlinear dynamics and chaos in convecting helium. Convection occurs in the environment (atmosphere, ocean, technical processes), and it is an outstanding system for studying the broader topic on nonlinear dynamics and pattern formation. Superfluid mixtures have similar properties to liquid metals and semiconductors, and a better understanding of the convection in helium is potentially relevant to purifying these materials.