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First Thermal and Fluids Engineering Summer Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

EXPLORING THE "NANO-FIN EFFECT" IN POOL BOILING ENHANCEMENT USING TEMPERATURE NANO-SENSOR ARRAYS

DOI: 10.1615/TFESC1.mph.012953
pages 1811-1821

Hongjoo Yang
Texas A&M University, Mechanical Engineering, MS 3123 TAMU, College Station, TX 77843-3123, USA

Debjyoti Banerjee
Texas A&M University, Mechanical Engineering, MS 3123 TAMU, College Station, TX 77843-3123, USA


KEY WORDS: nanotechnology, nanofabrication, phase change, heat transfer

Abstract

Singh and Banerjee (2013) coined the term "nanoFin Effect (nFE)", which implies that critical heat flux (CHF) should scale inversely with the magnitude of Kapitza Resistance "Rk" (between a nanofin and the working fluid). Thus thermal conductivity (or diffusivity) of the nanofin material itself plays a secondary role. Banerjee and Dhir (2001) reported that non-linear growth of 3-D Taylor instabilities cause temperature transients ("cold spots") on a plain heater surface. Cold spots can drain 60~90% of the total heat flux. Size of cold spots depends on the thermal conductivity (and diffusivity) of the heater material. Experimental validation of the numerical predictions for the nanofin effect was performed in this study using various nanofin materials. Inorganic nanofins (e.g., silicon, silica, metals, etc.) were nanofabricated with diameter of 100~200 nm, pitch of 800~900 nm and heights ranging from 10~700 nm. Wall superheat measurements were performed using temperature nanosensors of 200~400 nm nm thickness (K-type Thin Film Thermocouples or "TFT") that were microfabricated in-situ on the nanofin arrays. Molecular simulations were performed to estimate Rk (Unnikrishnan et al., 2008). The trends for total thermal impedance (and also Rk) were found to scale with the measured values of CHF in the experiments. Hence, this study validates the "nano-fin" hypothesis which models the surface nanostructures using an electrical network analogy for thermal resistance, thermal capacitance and thermal diode.

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