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	Volume 2, Issue 2 Pg 117 - 238 (October 2007)
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Volume 1 (2007)

Advances and Applications in Fluid Mechanics

Advances and Applications in Fluid Mechanics
Volume 2, Issue 1, Pages 59 - 70 (July 2007)

FILM THICKNESS FOR TWO PHASE FLOW IN A MICROCHANNEL
Ronan Grimes (Ireland), Colin King (Ireland) and Edmond Walsh (Ireland)

Abstract:
The issue of contamination of micro channel surfaces by bio fluids is a significant impediment to the development of many biomedical devices. A solution to this problem is the use of a carrier fluid, which segments the bio fluid and forms a thin film between the bio fluid and the channel wall. A number of issues need to be addressed for the successful implementation of such a solution. Amongst these is the prediction of the thickness of the film of carrier fluid which forms between the bio sample and the channel wall. The Bretherton and Taylor laws relate the capillary number to the thickness of this film. This paper investigates the validity of these laws through an extensive experimental program in which a number of potential carrier fluids were used to segment aqueous droplets over a range of flow rates. The aqueous plugs were imaged using a high speed camera and their velocities were measured. Film thicknesses were calculated from the ratio of the velocity of the carrier fluid to the velocity of the aqueous plug. The paper concludes that significant discrepancies exist between measured film thicknesses and those predicted by the Bretherton and Taylor laws, and that when plotted against capillary number, film thickness data for the fluids collapsed onto separate curves. By multiplying the capillary number by the ratio of droplet to carrier fluid viscosity, the data for the different fluids collapsed onto a single curve.

Keywords and phrases: film thickness, two phase flow, micro fluidics, carrier fluid.

Communicated by Shahrdad G. Sajjadi.

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