Subscriber access provided by UNIV OF DURHAM
Direct Visualization of Evaporation in a Two-Dimensional Nanoporous Model for Unconventional Natural Gas Arnav Jatukaran, Junjie Zhong, Aaron Harrinarine Persad, Yi Xu, Farshid Mostowfi, and David Sinton ACS Appl. Nano Mater., Just Accepted Manuscript • DOI: 10.1021/acsanm.8b00064 • Publication Date (Web): 06 Mar 2018 Downloaded from http://pubs.acs.org on March 8, 2018
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 16 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Applied Nano Materials
Direct Visualization of Evaporation in a Two-Dimensional Nanoporous Model for Unconventional Natural Gas †
†
†
†
‡
†*
Arnav Jatukaran, Junjie Zhong, Aaron H. Persad, Yi Xu, Farshid Mostowfi, and David Sinton †
Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, Ontario M5S 3G8, Canada ‡
Schlumberger-Doll Research, Cambridge, Massachusetts 02139, United States
ABSTRACT Evaporation at the nanoscale is critical to many natural and synthetic systems including rapidly emerging unconventional oil and gas production from nanoporous shale reservoirs. During extraction processes, hydrocarbons confined to nanoscopic pores (ranging from one to a few hundred nanometers in size) can undergo phase change as pressure is reduced. Here, we directly observe evaporation in two dimensional (2D) nanoporous media at the sub-10 nm scale. Using an experimental procedure that mimics pressure drawdown during shale oil/gas production, our results show that evaporation takes place at pressures significantly lower than predictions from the Kelvin equation (maximum deviation of 11%). We probe evaporation dynamics as a function of superheat and find that vapor transport resistance dominates evaporation rate. The transport resistance is made up of both Knudsen and viscous flow effects, with the magnitude of the Knudsen effect being approximately twice that of the viscous effects here. We also observe a phenomenon in sub-10 nm confinement wherein lower initial liquid saturation pressures trigger discontinuous evaporation resulting in faster evaporation rates. Keywords: evaporation, Knudsen flow, vapor transport, nanoporous, nanofluidics, shale gas INTRODUCTION Evaporation and vapor transport in two-dimensional (2D) nanoporous media plays an important role in many natural processes and synthetic systems such as in biological membranes,1 plant hydrodynamics,2,3 electronic cooling devices,4 steam generation,5–9 water desalination strategies10 and the recovery of hydrocarbons from unconventional oil and gas reservoirs.11–14 There is particular urgency regarding the latter as hydraulic fracturing has reshaped the global energy supply, while there is a lack of understanding of the processes taking place in the nanosized pores. These reservoirs are typically characterized by pores that can be smaller than 10 nm.15 The dynamics of phase change in such nanoporous media are complex, largely unexplored, and critical to quantifying potential recovery and ultimately assessing energy security associated with these resources.11,16 Experimental techniques to study the onset and dynamics of evaporation in porous media at such length scales are urgently required to validate the applicability of classical theories, improve the efficiency of production, and inform policy makers and the public.
ACS Paragon Plus Environment
ACS Applied Nano Materials 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Recent advances in nanofluidic device fabrication has enabled the study of thermodynamics at the nanoscale. Liquid to vapor transitions such as evaporation17–22 and cavitation,23–26 in particular, have garnered significant attention. The majority of studies employ pore or channel dimensions in the range of 100 nm. Experimental techniques to study evaporation at smaller scales are hindered by both the challenge of fabricating precise 2D nanoscopic conduits and the difficulty in directly visualizing vapor and liquid phases in extreme nanoconfinement (
