GOALI: Experimental Tests of Nonequilibrium Thermodynamics Beyond the Onsager Relation: Nonlinear and Far-From-Equilibrium Thermoelectrics

管理热流以控制温度在各种现代过程的正常运行中起着关键作用，从运行计算机芯片到加热/冷却房屋到加密货币采矿。有趣的是，热流的物理学只有在所谓的“近平衡”情况下才能得到很好的理解，在这种情况下，热区域和冷区域之间的温差和热传递都很小。然而，许多大规模的过程，如发电或运行现代数据中心，涉及温度差异很大的物体之间的相当大的热流。目前还不清楚是否可以使用现有的理解接近平衡的过程，以准确地模拟这种“远离平衡”的条件。该项目的主要目标是对违反近平衡理论主要假设的热流进行实验，并测试其结论在远离平衡的情况下是否继续成立或需要修改。研究结果将为建立先进的模型提供基础，以管理几乎所有商品和服务的工业生产中产生的远离平衡的热流。该项目是NSF GOALI在工业界和学术界之间的合作项目，将使学生接触到工业的视角和研究方法，这对学生和社会都是非常有价值的培训，当他们进入劳动力市场时。技术摘要：非平衡态热力学关注的是当能量、质量和电荷流由各种驱动力产生时，热量和熵的演化。一个中心问题是当微观粒子动力学是时间可逆和无耗散的时候，宏观的能量耗散和熵产生是如何发展的。昂萨格互反关系（Onsager Reciprocal Relationship，ORR）原理被认为是当前非平衡态热力学的基石，但它是在假设最简单的条件下推导出来的：微观时间反演对称性、线性力流动力学和接近平衡态的宏观系统。对更复杂的情况进行了理论上的研究，但对于是否可以应用ORR没有达成一致意见。没有可靠的经验指导来指导理论工作的方向。该项目旨在通过实验探索ORR在多大程度上适用于热电（TE）物理学来填补这一空白。在TE系统中，ORR预测珀耳帖系数与热功率的比率等于绝对温度。本项目将通过在违反ORR基本假设的条件下测量该比率来测试ORR。这些条件包括达到足够大的温差以符合远离平衡的条件，并在具有内在非线性力流关系的半导体二极管上测试ORR预测。需要回答的主要问题是，即使在其基本假设之外，ORR是否仍然有效，如果不是，ORR是否可以修改，以将其推广到更广泛的条件。这项研究的结果将建立定量的指导任何这样的修订，从而扩大非平衡态热力学的理解。这个奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

Nontechnical Abstract:Management of heat flow to control temperature plays a critical role in the proper operation of a wide variety of modern processes, ranging from running computer chips to heating/cooling a house to cryptocurrency mining. Interestingly, the physics of heat flow is well understood only for what is known as “near-equilibrium” situations, where temperature differences and heat transfers between hot and cold regions are small. However, many large-scale processes, such as generating electrical power or running a modern data center, involve sizeable heat flows between objects at very different temperatures. It is unclear whether existing understanding of near-equilibrium processes can be used to model accurately such “far-from-equilibrium” conditions. The main goal of this project is to conduct experiments on heat flow that violate the main assumptions of the near-equilibrium theory and test whether its conclusions continue to hold or need to be amended in far-from-equilibrium situations. The results will provide a foundation on which to build advanced models to manage far-from-equilibrium heat flows produced in the industrial production of almost all goods and services. Being an NSF GOALI partnership between industry and academia, this project will expose students to an industrial perspective and approach to research, which will be particularly valuable training to both students and society when they enter the workforce.Technical Abstract:Nonequilibrium thermodynamics is concerned with evolution of heat and entropy when energy, mass, and charge flows result from various driving forces. A central question is how macroscopic energy dissipation and entropy production develop when the microscopic particle dynamics are time reversible and dissipationless. The principle known as the Onsager reciprocal relation (ORR) is considered a cornerstone of current understanding in nonequilibrium thermodynamics but was derived assuming the simplest of conditions: microscopic time-reversal symmetry, linear force-flow dynamics, and a macroscopic system in near-equilibrium. More complicated cases have been examined theoretically but with no agreement on whether the ORR can be applied. No reliable empirical guidance exists to steer the direction of theoretical work. This project aims to fill in this gap by experimentally exploring to what extent the ORR, as applied to thermoelectric (TE) physics, continues to remain valid. In TE systems the ORR predicts the ratio of Peltier coefficient to thermopower equals the absolute temperature. This project will test the ORR by measuring this ratio under conditions that violate the ORR’s basic assumptions. These conditions include going to large enough temperature differences to qualify as far-from-equilibrium and testing the ORR prediction on semiconductor diodes that have an intrinsic nonlinear force-flow relation. The main questions to be answered are whether the ORR continues to be valid even outside its foundational assumptions and, if not, whether the ORR can be revised to generalize it to a wider range of conditions. Results of this research will establish quantitative guidance on any such revisions and thus broaden the understanding of nonequilibrium thermodynamics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.