Unformatted text preview: CBE 320 September 28, 2009 Transport Phenomena Problem Session V Part A: Equations of Change 1. Electroosmosis. Electroosmosis is the flow driven by an electric field acting on charges within a fluid. You will analyze such a flow in this problem. A fluid is contained in a slit formed by a plastic and a glass surface, as illustrated in the figure below. The glass naturally attains a negative charge, creating positive charges within the fluid very near the glass surface. x h L P P z f (x) z v (x) z + + +---------------- + + + + + glass plastic g When an electric field is applied in the z direction, an electric force acts on the positive charges— and thus the fluid—in the positive z direction. For this setup, the force per unit volume of the fluid (a vector) is given by f = A exp ( − κx ) δ z , (1) where A is a known constant, and κ is another known constant that characterizes how rapidly the force diminishes with increasing distance away from the glass surface. In this problem it is reasonableforce diminishes with increasing distance away from the glass surface....
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- Fall '08
- Electric charge, glass surface, velocity profile vz, steady-state velocity profile, electric body force