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International Heat Transfer Conference 16

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

IN SITU TEMPERATURE MEASUREMENT OF EVAPORATION IN MICROPILLAR WICK STRUCTURES USING MICRO-RAMAN SPECTROSCOPY

Lenan Zhang
Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA

Yangying Zhu
Massachusetts Institute of Technology, Cambridge, MA 02139, USA; Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305, USA

Sameer Raghavendra Rao
Rensselaer Polytechnic Institute, Troy, NY, USA; Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA

Kevin R. Bagnall
Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA

Dion S. Antao
Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843, USA; Massachusetts Institute of Technology, Cambridge, MA 02139, USA

Arny Leroy
Device Research Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02149, USA

Lin Zhao
Device Research Laboratory, Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA

Bikram Bhatia
Device Research Laboratory, Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA

Colin C. Kelsall
Device Research Laboratory, Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA

Evelyn N. Wang
Device Research Laboratory, Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA

DOI: 10.1615/IHTC16.bae.023152
pages 763-771


KEY WORDS: Boiling and evaporation, Nano/Micro scale measurement and simulation, thin film evaporation, Raman spectroscopy, heat transfer enhancement with micro/nano structures

Abstract

Micro and nanostructures to enhance liquid-to-vapor phase change heat transfer for cooling high-performance electronics have attracted significant attention owing to their ability to generate capillary flow and thin-film area. Typically, heat transfer measurements are performed remotely (i.e., away from the three-phase contact line) due to limitations of conventional contact-mode temperature sensors such as thermocouples and resistance temperature detectors (RTDs), or averaged over an area of 20-50 µm with infrared cameras. However, as evaporation mainly occurs in the thin-film region near the three-phase contact line, fundamental understanding of the enhancement mechanism requires a microscopic measurement technique capable of probing temperature near the contact line with high spatial resolution. Here, we report a novel platform using micro-Raman spectroscopy to perform in situ temperature measurement of micropillar structures during thin-film evaporation. We built a custom micro-Raman spectroscopy with a spatial resolution of 1.5 µm. We calibrated the Stokes peak positions of silicon with its temperature and observed a linear relationship and an uncertainty of approximately ±0.9 °C, which agrees well with literature. We fabricated silicon micropillar arrays (diameters of 20 µm, heights of 50 µm and pitches of 40-100 µm) and built a thermo-fluidic test block to house the sample and to interface with the micro-Raman system. De-gassed and de-ionized water was used as the test fluid. We measured temperature on the top of silicon micropillars near the liquid-vapor interface at various locations on the sample and heat flux conditions. The results indicate that the local wall temperature reduced as the pitch of micropillars reduced, which is a result of increased thin-film area. The experimental results provide a guideline for optimizing the wick structures to increase evaporation heat transfer coefficient. The local, in situ temperature measurement platform presented in this study serves as a new tool to aid mechanistic understanding of phase change heat transfer.

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