I understand that vortexing will result in mixing / re-suspension of particles, and that centrifugation will result in the separation of particles. However, what is the difference in the physics that makes this happen? (Since in both cases, we are spinning a solution.)
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2 Answers
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A vortex is a local disturbance caused by turbulent flow. It carries fluid and particles inward toward a central axis of rotation. The central axis is not fixed. It moves within a larger body of fluid. The speed of the vortex is greater near the axis of rotation and decreases toward the edge of the vortex.
Unlike a vortex, a centrifuge creates centrifugal force perpendicular to a fixed axis of spin. Centrifugal force is directed outward from the axis of spin, and carries fluid and particles away from the central axis.
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$\begingroup$ +1 The difference is in the angular velocity as a function of radius. In a vortex the angular velocity decreases as $1/r$, while in a centrifuge it is constant, so in a centrifuge the centripetal acceleration $\omega^2r$ increases with radius, so things more rapidly float/sink to their preferred depth. $\endgroup$ Commented Feb 4, 2016 at 21:28
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On a vortex mixer the liquid is swirling inside a test tube. In a centrifuge, the test tubes (containing the liquid) are held in a fixed position inside a rotor, and the rotor is spinning inside the centrifuge.
