Collaborative Research: Computational and Experimental Investigation of High-Flux Heating of Supercritical Fluids in Microscale Geometries

微尺度几何中超临界流体高通量加热的计算和实验研究在足够高的温度和压力下，流体成为超临界流体。当超临界流体被加热时，它不会像熟悉的沸腾过程那样经历从液体到蒸汽的相变。相反，流体经历从“类液体”到“类气体”性质的连续转变，而不形成气泡。在这种“伪临界”转变期间，流体可以在每度温度升高时吸收大量的热量，这可能使新的高强度传热技术成为可能，而不会出现引起两相沸腾解决方案挑战的不稳定性、临界热通量和分布不均问题。通过利用超临界流体的独特性质，有可能进一步开发更高功率、紧凑的计算机芯片和更高效的高温太阳能热系统。为了探索这些可能性，研究小组将研究一种新的热管理框架，采用超临界二氧化碳（sCO 2）在伪临界区（7.5？8.5 30兆帕？40°C）在微尺度流动几何形状中。在这些条件下，sCO 2具有极高的体积热容和热导率，能够管理高热通量（~500 W cm-2）。本研究中制定的新工程资源和模型将使超临界冷却在现实世界的技术中得到快速采用。此外，对微尺度超临界流体运输的更好理解可以在各种技术方面取得进展，包括强化石油开采，近零全球变暖潜能值（GWP）超临界制冷和动力循环以及溶剂/浸渍工艺。该研究小组将进行综合实验和计算研究，以阐明在微尺度几何结构中在伪临界条件下加热sCO 2和一般超临界流体过程中的复杂控制现象。局部快速响应温度测量和红外热成像将解决关键超临界现象的存在，并量化这种规模的影响，包括伪沸腾，固有的流动脉动，传热增强和/或恶化，由于急剧的属性变化，针翅尾流相互作用，共轭传热效应。实验将进行超临界二氧化碳在高压（75 P 200巴）和热通量，和微加工技术将被利用来探索先进的几何形状感兴趣的电子冷却和太阳能热应用。将进行广泛的分离涡模拟（DES）计算，以提供详细的局部流动数据，以补充实验，并使泛化超出特定的工作流体和操作条件。DES代表了一种新的方法来研究超临界对流传输，捕捉关键的非定常湍流现象的通道散装，不同的雷诺平均公式在以前的研究中，但没有极端的计算成本LES/DNS，也完全解决近壁区。一旦经过实验验证，将采用模拟将结果扩展到具有不同配置和几何形状的超临界流。在这些研究中，单独的流体特性趋势将被独立地调制，以隔离和量化以前仅通过集总参数描述表征的关键影响。这种方法将使结果推广到更广泛的超临界流体，而不仅仅是实验中使用的特定流体。详细的实验和计算数据的整合将产生统一的分析传输模型，促进基础研究的快速转化为实用的热管理技术。

Computational and Experimental Investigation of High-Flux Heating of Supercritical Fluids in Microscale GeometriesAt a sufficiently high temperature and pressure, fluids become supercritical. When a supercritical fluid is heated, it does not undergo a change in phase from a liquid to vapor like in familiar boiling processes. Rather the fluid undergoes a continuous transition from "liquid like" to "gas like" properties without the formation of bubbles. During this "pseudo-critical" transition, the fluid can absorb a great quantity of heat per degree of temperature increase, which potentially enables new high-intensity heat transfer technologies without the instabilities, critical heat flux, and maldistribution issues that cause challenges in two-phase boiling solutions. By harnessing the unique properties of supercritical fluids, it may be possible to further develop higher power, compact computer chips and more efficient high temperature solar thermal systems. To explore these possibilities, the research team will study a new thermal management framework employing supercritical carbon dioxide (sCO2) in the pseudo-critical region (7.5 ? 8.5 MPa, 30 ? 40°C) in microscale flow geometries. Under these conditions sCO2 has extremely high volumetric heat capacity and thermal conductivity, enabling management of high heat fluxes (~500 W cm-2). New engineering resources and models formulated in this study will enable rapid adoption of supercritical cooling in real-world technologies. Additionally, improved understanding of microscale supercritical fluid transport can yield advances in diverse technologies including enhanced oil extraction, near-zero global warming potential (GWP) supercritical refrigeration and power cycles, and solvent/impregnation processes. The research team will conduct an integrated experimental and computational investigation to elucidate the complex governing phenomena during heating of sCO2 and general supercritical fluids at pseudocritical conditions in microscale geometries. Local fast-response temperature measurements and infrared thermal imaging will resolve the existence of, and quantify the effects of key supercritical phenomena at this scale, including pseudo-boiling, intrinsic flow pulsations, heat-transfer enhancement and/or deterioration due to sharp property variations, pin-fin wake interactions, and conjugate heat transfer effects. Experiments will be conducted with supercritical CO2 at high pressure (75 P 200 bar) and heat fluxes, and microfabrication techniques will be leveraged to explore advanced geometries of interest for electronics cooling and solar thermal applications. Extensive detached eddy simulation (DES) computations will be performed to provide detailed local flow data to complement experiments, and enable generalization beyond specific working fluids and operating conditions. DES represents a new approach to study supercritical convective transport that captures key unsteady turbulent phenomena in the channel bulk, unlike Reynolds averaged formulations employed in previous studies, but without the extreme computational costs of LES/DNS that also fully resolve near-wall regions. Once experimentally validated, simulations will be employed to extend results to supercritical flows with diverse configurations and geometries. In these studies individual fluid property trends will be modulated independently to isolate and quantify critical effects that have previously only been characterized through lumped parameter descriptions. This approach will enable generalization of results to the broader family of supercritical flows, rather than just specific fluids employed in experiments. Integration of detailed experimental and computational data will yield consolidated analytical transport models, facilitating rapid translation of fundamental research to practical thermal management technologies.