CAREER: Enhanced Two-phase Thermal Management Using Self-sustained Flow Oscillations at the Microscale

0748249 narayanan这个CAREER项目的总体目标是在热管理领域建立一个综合的研究和教育框架。在~ 102 ~ 103 W/cm2水平下的热负荷耗散在大功率电子设备的冷却中具有重要意义。目前主要的冷却方法包括喷雾和液体射流撞击蒸发，以及微通道散热器的流动沸腾。虽然这些方法已经证明了去除高热流的能力，但在提高冷却效率方面仍然存在重大挑战。所提出的研究的主要目的是证明，通过使用固有的流动振荡，在没有额外的泵送功率损失的情况下，比目前使用蒸发液体射流和喷雾撞击所实现的单位冷却剂质量通量的传热速率有所提高。风琴管共振机制将用于创建一个自我维持，自激振荡射流（SOJ）。需要考虑的假设包括：(1)流动振荡通过流体动力边界层和热边界层的周期性更新以及表面气泡振荡增加的对流热输送，提高了换热率；(2)由于横向流动振荡对表面的有效再润湿，临界热通量（CHF）可以增加（超过自由表面液体射流和喷雾所达到的）；(3)使用纳米流体时，流动振荡可以减轻纳米颗粒的表面沉积和聚集。为了验证上述假设，提出了一种主要的实验方法来记录传热速率和CHF发作。关键的动量和热输运机制将通过使用激光诱导荧光的流体温度定量成像、使用粒子图像测速法的射流场、使用高速成像的气泡动力学以及使用红外热成像的表面温度来确定。流动振荡对表面微结构和纳米流体的影响也将被研究。该研究的几个方面将通过(a)本科传热课程，(b)拟议的荣誉研讨会和(c) UHC论文整合到大学荣誉学院（UHC）课程中。在研究生阶段，研究成果将通过两个现有课程以及基于研究领域的新专题课程进行传播。每年夏天，有动力的高中生将通过科学与工程学徒计划（www.saturdayacademy.org）参加研究活动。这项研究的学术价值体现在以下几个方面：(a)研究相变条件下的射流振荡现象，(b)将射流振荡与现有的增强机制（如微结构表面和纳米流体）耦合，以及(c)进行详细的成像以描绘对流热传输的物理机制。更广泛的影响包括在热管理领域培养了三名博士，一名硕士和几名本科生和高中生。在两相热管理中，提高传热速率和开发延迟CHF发生的方法对大功率电子设备和航空电子设备以及计算机芯片冷却的性能至关重要。利用被动增强方法来增强热输运和流体输运，可通过有效利用现有资源来减少能源使用。

0748249NarayananThe broad goal of this CAREER project is to establish an integrated research and educational framework in the field of thermal management. Dissipation of heat loads at levels of ~ 102 to 103 W/cm2 is of great interest in the cooling of high-power electronics. Current predominant cooling methods include spray and liquid jet impingement evaporation, and flow boiling in microchannel heat sinks. Although these methods have demonstrated capability of removing high heat fluxes, significant challenges still exist in improving cooling efficiencies. The primary intent of the proposed research is to demonstrate, by the use of inherent flow oscillations, enhancement in heat transfer rate per unit coolant mass flux beyond that currently achieved using evaporative liquid jet and spray impingement, with no additional pumping power penalty. An organ pipe resonance mechanism will be used to create a self-sustained, self-excited oscillatory jet (SOJ). The hypotheses to be considered include the following: (1) Flow oscillations enhance heat transfer rates through both periodic renewal of the hydrodynamic and thermal boundary layers and the increased convective heat transport by bubble oscillations at the surface, (2) Critical heat flux (CHF) can be increased (beyond that attained by free-surface liquid jets and sprays) due to the effective rewetting of the surface by transverse flow oscillations, and (3) Use of flow oscillations mitigates surface deposition and aggregation of nanoparticles when using nanofluids.To test the above hypotheses, a predominantly experimental approach is proposed to document the heat transfer rate and CHF onset. Key momentum and thermal transport mechanisms will be identified by quantitative imaging of fluid temperature using laser induced fluorescence, jet flow field using particle image velocimetry, bubble dynamics using high-speed imaging, and surface temperature using IR thermography. The effect of flow oscillations on surface microstructures and nanofluids will also be studied.Several aspects of the research will be integrated into the University Honors College (UHC) curriculum through (a) an undergraduate Heat Transfer course, (b) a proposed Honors colloquium, and (c) UHC theses. At the graduate level, research outcomes will be disseminated through two existing classes as well as through a new special topics class based on the research area. Each summer, motivated high-school students will participate in research activities through the Apprenticeship in Science and Engineering program (www.saturdayacademy.org). The intellectual merit pertains to the following novel aspects: (a) study of the jet flow oscillation phenomenon under phase change conditions, (b) coupling of jet flow oscillations with existing enhancement mechanisms such as microstructured surfaces and nanofluids, and (c) performing detailed imaging to delineate the physical mechanisms of convective heat transport. Broader Impacts include education of three PhD, one MS, and several undergraduate and high-school students in the field of thermal management. Enhancement of heat transfer rates and developing methods to delay the onset of CHF in two-phase thermal management are of critical importance to the performance of high-power electronics and avionics, as well as for computer chip cooling. Utilization of passive enhancement methods to achieve enhancement in thermal and fluid transport fosters reductions in energy use by effective use of available resources.