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各种重要的工业和发电过程中。更好地理解蒸发换热将为热管理行业带来更节能的设备设计。本项目的目标是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换热。理论表明，热通量将在薄薄的半月面蒸发区域达到峰值，但先前的实验不能充分解决这一关键特征。热管理技术利用微/纳米结构表面扩展半月面来利用这一区域。测量局部蒸发的新实验对于改善热管理行业的这种纳米结构设计至关重要，但对沸腾和海水淡化等弯月面驱动过程也具有基本价值。教育活动将通过课程开发、嘉宾研讨会和实习让学生接触到行业驱动的学术研究。通过与当地非营利性组织的合作，将正式为代表性不足的中学生提供定期外展机会。蒸发热流将使用频域热反射(FDTR)进行测量，同时将使用干涉测量进行半月面厚度的测量。薄膜区域的微尺度范围(100-102GM面内，100-103 nm厚)和亚开尔文液汽温差(过热)挑战了传统的测温方法，而寄生到衬底的传导混淆了实际的蒸发热流。因此，以前的测量有效地积分了大片液-汽界面上的蒸发速率，允许一系列令人满意的理论解释。热反射方法使热传导研究发生了革命性的变化，它将有助于克服薄膜蒸发计量中的这些障碍。这些对蒸发热流的准确测量(？B10%)将独特地辨别表面吸引力和容纳系数在薄膜蒸发中的作用。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.