A Combined Photographic/Thermographic Study of Subcooled Boiling in a Narrow Channel

0933163HOLLINGSWORTHMinichannels(通道间距接近1 mm)为两相冷却的技术应用提供了一个有吸引力的尺度范围。它们足够小，可以产生大量的热流，但也足够大，可以带走大量的热量。此外，它们不像微尺度通道那样存在结垢和维护问题。由于蒸汽生产过程中消耗的潜热，以及由于气泡被限制留在通道表面附近而导致的近壁混合增强，换热系数可能非常高。智能优点：这项研究使用液晶热像仪与高速视频成像相结合来研究毫米级通道内的高度过冷的泡状流。在这种流动状态下，大量非常小的收缩气泡被气流扫过，这为气泡有效地将过冷液体从通道核心向壁面移动的能力而导致的冷却提供了极大的机会。从实验研究中收集到的见解将为更好地理解微通道中过冷泡状流的物理学提供基础，这一理解将导致这一重要过程的新模型。更广泛的影响：这项研究的更广泛的技术影响是它对发现和理解两相毫米尺度器件中的热过程和性能限制现象的贡献。参与该项目的学生将根据需要培养高科技行业的能力：涉及小型设备的实验、高速数字成像、液晶热成像以及两相冷却系统的经验。经验表明，高速成像和液晶热像仪的视觉影响会激发学生的兴趣，并经常激励他们继续研究生学习。以这项研究为载体，少数民族学生，特别是西班牙裔学生，将通过直接参与本科荣誉论文学生的方式被招募到研究生水平学习。该实验室还参加了几项工程学院招生活动，旨在吸引学生进入工程学专业，即工程学开放日和工程学领袖日。

0933163HOLLINGSWORTHMinichannels (those with channel spacing near 1 mm) offer an attractive scale range for technological applications of two phase cooling. They are small enough to create large heat fluxes, but large enough to remove significant quantities of heat. Furthermore, they do not present the fouling and maintenance concerns as do microscale channels. Heat transfer coefficients can be very high due to the latent heat consumed during vapor production, and to enhanced near wall mixing caused by bubbles which are constrained to remain near the channel surfaces. Intellectual Merit: This research uses liquid crystal thermography in concert with high speed video imaging to investigate highly subcooled bubbly flow within a millimeter scale channel. In this flow regime, swarms of very small contracting bubbles are swept along by the flow, presenting the opportunity for greatly increased cooling caused by the capacity of the bubbles to efficiently move subcooled liquid from the core of the channel toward the walls. The insight gathered from this experimental investigation will provide the basis for a better understanding of the physics of subcooled bubbly flow in minichannels, and this understanding will lead to new models of this important regime.Broader Impacts: The technological broader impact of the research is its contribution to the discovery and understanding of thermal processes and performance limiting phenomena in two phase mm scale devices. Students involved in the project will develop capabilities in demand in high technology industries: experimentation involving small scale devices, high speed digital imaging, liquid crystal thermography, and experience with two phase cooling systems. Experience shows that the visual impact of high speed imaging and liquid crystal thermography generates interest in students and often motivates them to pursue graduate study. Using this research as the vehicle, minority students, Hispanic students in particular, will be recruited into graduate level study through direct involvement as undergraduate Honors thesis students. The laboratory also participates in several College of Engineering recruiting activities designed to attract students into engineering, namely the Engineering Open House and the Engineering Leadership Day.