Clearing factor
In centrifugation the clearing factor or k factor represents the relative pelleting efficiency of a given centrifuge rotor at maximum rotation speed. It can be used to estimate the time t {\displaystyle t} (in hours) required for sedimentation of a fraction with a known sedimentation coefficient s {\displaystyle s} (in svedbergs): t = k s {\displaystyle t={\frac {k}{s}}} The value of the clearing factor depends on the maximum angular velocity ω {\displaystyle \omega } of a centrifuge (in rad/s) and the minimum and maximum radius r {\displaystyle r} of the rotor: k = ln ( r m a x / r m i n ) ω 2 × 10 13 3600 {\displaystyle k={\frac {\ln(r_{\rm {max}}/r_{\rm {min}})}{\omega ^{2}}}\times {\frac {10^{13}}{3600}}} As the rotational speed of a centrifuge is usually specified in RPM, the following formula is often used for convenience: k = 2.53 ⋅ 10 5 × ln ( r m a x / r m i n ) ( R P M / 1000 ) 2 {\displaystyle k={\frac {2.53\cdot 10^{5}\times \ln(r_{\rm {max}}/r_{\rm {min}})}{({\rm {{RPM}/1000)^{2}}}}}} Centrifuge manufacturers usually specify the minimum, maximum and average radius of a rotor, as well as the k {\displaystyle k} factor of a centrifuge-rotor combination.