Beng 130 Lecture 7

Beng 130 Lecture 7 - Molecular Motion Transport Processes...

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Molecular Motion Transport Processes and Properties Transport Processes Transport Processes Diffusion Diffusion - Thermodynamic driving force Thermodynamic driving force - Frick Frick ’s first law. s first law. - Frick Frick ’s second law. s second law. - Stokes Stokes -Einstein Equation Einstein Equation Viscosity Viscosity Molecular Physical Chemistry – Lecture 7 Reading: Chapter 6 and Lecture Notes Reading: Chapter 6 and Lecture Notes • Till recently we focused on systems at equilibrium where there is no net flow of heat, work, or matter. At the microscopic level, what we have been studying is time averaged behavior . • There are cases where time average of forces acting on a system results in a flow of material –This leads to transport phenomena Transport Processes • 4 such phenomena we encounter are: – Diffusion – Electrical conduction – Fluid flow (convection) – Heat flow (conduction) • Each of these represents net movement in the direction of the gradient from a higher to a lower potential Transport Processes • The gradients arise from differences in – Chemical potential – Electrical potential – Temperature – Pressure • The general equation for all forms of transport: • The flow (J) of material in the x-direction is proportional to the gradient of force of type A in the x-direction . B is a constant. A BF dx dA B J 0 0 Transport Processes
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•F o r diffusion - Fick’s Law B=D, the diffusion constant •F o r electrical conduction - Ohm’s Law B= ț , the conductivity •F o r fluid movement - Poiseuille’s Law B=C, the hydraulic conductivity •F o r heat transfer - Fourier’s Law B=K T , the thermal conductivity coefficient A BF dx dA
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This homework help was uploaded on 04/07/2008 for the course BENG 130, 103B, taught by Professor Gough during the Spring '08 term at UCSD.

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Beng 130 Lecture 7 - Molecular Motion Transport Processes...

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