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

微尺度超临界流体高通量加热的计算与实验研究当温度和压力足够高时，流体变为超临界流体。当超临界流体被加热时，它不会像常见的沸腾过程那样经历从液体到蒸汽的相变。相反，流体经历了从“类液体”到“类气体”的连续转变，不会形成气泡。在这种“准临界”转变过程中，每升高一度温度，流体就可以吸收大量热量，这可能会使新的高强度传热技术成为可能，而不会出现导致两相沸腾解决方案面临挑战的不稳定性、临界热流密度和分布不均问题。通过利用超临界流体的独特性质，有可能进一步开发出更高功率、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，在微尺度流动几何结构的准临界区域(7.5？8.5兆帕，30？40°C)使用超临界二氧化碳(SCO2)。在这些条件下，SCO2具有极高的体积热容和导热系数，能够管理高热流密度(~500W cm-2)。在这项研究中形成的新的工程资源和模型将使超临界冷却在现实世界的技术中迅速采用。此外，提高对微尺度超临界流体传输的了解可以促进各种技术的进步，包括强化石油开采、接近零的全球变暖潜势(GWP)超临界制冷和电力循环以及溶剂/浸渍工艺。该研究小组将进行一项综合的实验和计算研究，以阐明在微尺度几何形状的准临界条件下，SCO2和一般超临界流体加热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这一尺度上关键超临界现象的存在，并量化其影响，包括伪沸腾、固有流动脉动、由于急剧物性变化而导致的换热强化和/或恶化、销钉-翅片尾迹相互作用以及共轭换热效应。实验将在高压(75 P 200 Bar)和热流密度下使用超临界二氧化碳进行，并将利用微制造技术来探索电子冷却和太阳能热应用中感兴趣的先进几何形状。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来补充实验，并使泛化超越特定的工作流体和操作条件。DES代表了一种研究超临界对流输运的新方法，它捕捉到了通道主体中的关键非定常湍流现象，不像以前研究中使用的雷诺平均公式，但没有LES/DNS的极端计算成本，它也完全解决了近壁区的问题。一旦实验验证，模拟将被用于将结果扩展到具有不同构型和几何形状的超临界流动。在这些研究中，单独的流体性质趋势将被独立地调制，以隔离和量化以前仅通过集中参数描述来表征的关键影响。这种方法将使结果能够推广到更广泛的超临界流体家族，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集成将产生统一的分析传输模型，促进基础研究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.