Change in drag, apparent slip and optimum air layer thickness for laminar flow over an idealised superhydrophobic surface

Busse, Angela, Sandham, Neil, McHale, Glen and Newton, Michael (2013) Change in drag, apparent slip and optimum air layer thickness for laminar flow over an idealised superhydrophobic surface. Journal of Fluid Mechanics, 727. pp. 488-508. ISSN 0022-1120

This is the latest version of this item.

[img]
Preview
PDF (Article)
Reprint_Busse_JFM_vol_727_p488_2013.pdf - Published Version

Download (1MB) | Preview
Official URL: http://dx.doi.org/10.1017/jfm.2013.284

Abstract

Analytic results are derived for the apparent slip length, the change in drag and the optimum air layer thickness of laminar channel and pipe flow over an idealised superhydrophobic surface, i.e. a gas layer of constant thickness retained on a wall. For a simple Couette flow the gas layer always has a drag reducing effect, and the apparent slip length is positive, assuming that there is a favourable viscosity contrast between liquid and gas. In pressure-driven pipe and channel flow blockage limits the drag reduction caused by the lubricating effects of the gas layer; thus an optimum gas layer thickness can be derived. The values for the change in drag and the apparent slip length are strongly affected by the assumptions made for the flow in the gas phase. The standard assumptions of a constant shear rate in the gas layer or an equal pressure gradient in the gas layer and liquid layer give considerably higher values for the drag reduction and the apparent slip length than an alternative assumption of a vanishing mass flow rate in the gas layer. Similarly, a minimum viscosity contrast of four must be exceeded to achieve drag reduction under the zero mass flow rate assumption whereas the drag can be reduced for a viscosity contrast greater than unity under the conventional assumptions. Thus, traditional formulae from lubrication theory lead to an overestimation of the optimum slip length and drag reduction when applied to superhydrophobic surfaces, where the gas is trapped.

Item Type: Article
Uncontrolled Keywords: drag, slip, superhydrophobic, Leidenfrost, Core Annular Flow
Subjects: F200 Materials Science
F300 Physics
H100 General Engineering
Department: Faculties > Engineering and Environment > Physics and Electrical Engineering
Related URLs:
Depositing User: Glen McHale
Date Deposited: 02 Jan 2014 11:21
Last Modified: 17 May 2017 22:57
URI: http://nrl.northumbria.ac.uk/id/eprint/14932

Available Versions of this Item

  • Change in drag, apparent slip and optimum air layer thickness for laminar flow over an idealised superhydrophobic surface. (deposited 02 Jan 2014 11:21) [Currently Displayed]

Actions (login required)

View Item View Item

Downloads

Downloads per month over past year

View more statistics


Policies: NRL Policies | NRL University Deposit Policy | NRL Deposit Licence