Fluid flow in ultrasmall structures

Jiangtao Cheng, Purdue University

Abstract

We describe studies of the pressure driven flow of several classical fluids through lithographically produced channels in which one dimension, the channel height h, is in the micron or nanometer size range. The measured flow rates are compared with theoretical predictions assuming no-slip boundary conditions at the walls of the channel. The results for water agree well with this prediction for h as small as 40 nm (our smallest channels). However, for hexane, decane, hexadecane, and silicone oil we find deviations from this theory when h is reduced below about 100 nm. The observed flow rates for small h are larger than theoretical expectations, implying significant slip at the walls, and values of the slip length are estimated. The results are compared with previous experimental and theoretical work. We have also developed an improved method of making micro-models for the study of multiphase flow in porous media. A central theme of our work is to use model systems to gain new insights into the geometrical aspects of multiphase flow. We would like to better understand how the geometry of the open pore space affects the geometry (fractal or otherwise) of the wetting and non-wetting phases, and how these geometries vary during a drainage/imbibition cycle. In addition to flow rate measurements at various levels of saturation, we have used photographic studies of the geometries of the wetting and non-wetting phases, in our case decane and nitrogen gas, to measure the interfacial area per unit “volume” (IAV) separating these phases. While the relation between saturation (S) and capillary pressure (Pcap) during these cycles is hysteretic, the IAV appears to be a single valued function of S and Pcap. This observation confirms, at least qualitatively, theoretical predictions of Gray and coworkers concerning the importance of IAV as a fundamental quantity necessary for understanding and characterizing multiphase flow. We believe this to be the first experimental measurement of the IAV for multiphase flow.

Degree

Ph.D.

Advisors

Giordano, Purdue University.

Subject Area

Fluid dynamics|Gases

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