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International Heat Transfer Conference 16

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

EVAPORATION FROM ULTRATHIN NANOPOROUS MEMBRANES INTO LIQUID-MOIST AIR SYSTEMS

Zhengmao Lu
Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA

Kyle L. Wilke
Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA

Daniel J. Preston
Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA

Ikuya Kinefuchi
Department of Mechanical Engineering, University of Tokyo, Bunkyo, Tokyo 113-8656, Japan

Evelyn N. Wang
Device Research Laboratory, Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02149, USA

DOI: 10.1615/IHTC16.bae.023305
pages 1357-1362


KEY WORDS: Boiling and evaporation, Mass transfer and drying, Ultrathin, Nanoporous, High flux

Abstract

Evaporation, a phenomenon commonly found in nature, is of fundamental interest and has many practical applications. In previous studies, evaporative transport is often limited by the thermal resistance and viscous loss in the liquid phase. To reach high interfacial heat fluxes during evaporation, which is desirable in most applications, we designed and microfabricated an evaporator made of ultra-thin membranes with nanopores patterned in them. In this configuration, the heat conduction length in the liquid scales with the pore radius (~65 nm) and the flow length in the nanopores reduces to the membrane thickness (~200 nm). Consequently, we demonstrated ~500 W/cm2 steady state heat fluxes across the liquid-vapor interface using this nano device with pure evaporation into an air ambient, outperforming the fluxes reported in previous work by over 500%. Our experimental data agreed very well with the prediction of the Maxwell-Stefan equation which takes into account both the diffusive and convective flow. The present work improves the fundamental understanding of evaporation into liquid-moist air systems, provides a reliable platform for studying intensive interfacial transport, and paves the way for high flux phase-change devices that can be applied to thermal management, steam generation, desalination, and beyond.

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