What you are given
- r max (cm): 10
- r min (cm): 5
- Speed (rpm): 10000
Formula: k = 2.53e11 x ln(rmax/rmin) / rpm^2
Physical
How do you calculate centrifuge k-factor?
Rotor clearing factor and pelleting time. The relationship used is k = 2.53e11 x ln(rmax/rmin) / rpm^2.
Worked example
Every number below is computed by the calculator, not typed in
The working
- Radius ratio:
rmax / rmin=2 - Natural log of ratio:
ln(rmax / rmin)=0.6931 - Clearing factor:
k = 2.53e11 * 0.6931 / (10000)^2=1754
This rotor has a k-factor of 1754.
What each symbol means
- k: Clearing factor
- K: Rotor constant
- rₘₐₓ: Radius at tube bottom (cm)
- rₘᵢₙ: Radius at meniscus (cm)
- rpm: Rotor speed (rev/min)
A printable one-page version is on the formula sheet.
Try it yourself
Two problems, with the working revealed
Problem 1 Centrifuge k-factor
Work out the result for centrifuge k-factor.
- r max (cm): 9.5
- r min (cm): 8
- Speed (rpm): 10000
Show the answer and the working
This rotor has a k-factor of 434.8.
- Radius ratio:
rmax / rmin=1.1875 - Natural log of ratio:
ln(rmax / rmin)=0.1719 - Clearing factor:
k = 2.53e11 * 0.1719 / (10000)^2=434.8
Open this in the calculator to change the numbers.
Problem 2 Centrifuge k-factor
Work out the result for centrifuge k-factor.
- r max (cm): 8
- r min (cm): 5
- Speed (rpm): 30000
Show the answer and the working
This rotor has a k-factor of 132.1.
- Radius ratio:
rmax / rmin=1.6 - Natural log of ratio:
ln(rmax / rmin)=0.47 - Clearing factor:
k = 2.53e11 * 0.47 / (30000)^2=132.1
Open this in the calculator to change the numbers.
Do it with your own numbers.
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