GOALI: Local thermoreflectance measurement of evaporative heat transfer in the thin film region of a dynamic meniscus

蒸发冷却广泛应用于重要的工业和发电过程中。提高对蒸发传热的理解将为热管理行业带来更节能的设备设计。本项目旨在以前所未有的空间分辨率测量半月板薄膜区域的局部蒸发传热。理论上认为，热通量会在半月板的薄蒸发区域出现峰值，但先前的实验无法充分解决这一关键特征。热管理技术利用扩展半月板的微/纳米结构表面来开发这一区域。测量局部蒸发的新实验对于改善热管理行业的纳米结构设计至关重要，但对于半月板驱动的过程（如沸腾和脱盐）也具有基本价值。这些教育活动将通过课程开发、客座研讨会和实习，让学生接触到行业驱动的学术研究。通过与当地非营利组织的合作，将定期向代表性不足的中学生提供拓展机会。蒸发热通量将使用频域热反射（FDTR）测量，同时将使用干涉测量法测量半月板厚度。薄膜区域的微尺度范围(100-102 ？面内（100- 103nm厚）和亚开尔文的液-气温差（过热）挑战了传统的测温方法，而寄生传导到底层衬底的现象混淆了实际的蒸发热通量。因此，先前的测量有效地整合了大片液-气界面上的蒸发速率，允许一系列令人满意的理论解释。热反射方法已经彻底改变了热传导研究，将有助于克服薄膜蒸发计量中的这些障碍。这些对蒸发热通量(？B10%)将独特地识别表面吸引力和调节系数对薄膜蒸发的作用。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Cooling by evaporation is used in a wide range of important industrial and power-generation processes. Improved understanding of evaporative heat transfer will lead to more energy-efficient equipment designs for the thermal management industry. The objective of this project is to measure local evaporative heat transfer in the thin film region of menisci with unprecedented spatial resolution. Theory suggests that heat flux will spike in the thin evaporating region of the meniscus, yet prior experiments cannot adequately resolve this key feature. Thermal management technologies exploit this region using micro/nanostructured surfaces that expand the meniscus. New experiments that measure local evaporation are critical to improve such nanostructure designs for the thermal management industry but are also of fundamental value to meniscus driven processes like boiling and desalination. The educational activities will expose students to industry-driven academic research through curriculum development, guest seminars, and internships. Through collaboration with a local non-profit, regular outreach opportunities will be formalized with underrepresented middle school students. Evaporative heat fluxes will be measured using frequency domain thermoreflectance (FDTR) and simultaneous measurements of meniscus thickness will be made using interferometry. The microscale extent of the thin film region (100-102 ?gm in-plane, 100-103 nm thick) and sub-Kelvin liquid-vapor temperature differences (superheats) challenge conventional thermometry, while parasitic conduction into the underlying substrate obfuscates actual evaporative heat fluxes. As a result, prior measurements effectively integrate evaporation rates over large swaths of liquid-vapor interface, permitting a range of satisfactory theoretical interpretations. Thermoreflectance approaches, which have revolutionized heat conduction research, will help to overcome these barriers in thin film evaporation metrology. These accurate measurements of the evaporative heat flux (?b10%) will uniquely discern the role of surface attractive forces and accommodation coefficients on thin film evaporation.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.