Stirrer Power Calculations And Examples - Getinge Applikon my-Control Hardware Manual

6.4.5 STIRRER POWER CALCULATIONS AND EXAMPLES

The computations in this section are derived from the theory for single impeller configurations and are
therefore the most accurate for those configurations. A subsequent version of this manual may include the
calculations for multiple impeller configurations.
The power (Watt) of the stirrer motor that is required depends on the number, type and diameter of the
impellers, density of the medium and the stirrer speed. The required power per impeller of a stirrer motor in
non-aerated media is given by the equation:
where:
P
ρ
N
D
N
p
*) Rushton turbine impellers:
Applikon marine impellers:
When mounted according to the given configuration, a second or third impeller on a shaft requires only 90 %
of the power of the first impeller. This means that the equation above is multiplied with the factor 1.9 for two
impellers and with a factor 2.8 for three impellers.
Required Torque
The required torque of the stirrer motor is related to its power according to the following equation:
where:
M
P
N
Impeller Tip Speed
The Tip Speed (m/s) of an impeller at a certain stirrer speed is given by the equation:
Where:
N
D
The examples section shows several calculations of required power, torque, and impeller tip speed.
Hardware Manual my-Control MiniBio
P = ρ x (N/60)
Required Power of the Stirrer Motor (W)
Density of the Medium (kg/m
Stirrer Speed (rpm)
Diameter of the Impeller (m)
Power Number of the Impeller*)
Np = 6
Np = 1.5
M = P x 60 /(2 π N)
Required Torque of the Stirrer Motor (Nm)
Required Power of the Stirrer Motor (W)
Stirrer Speed (rpm)
Tip speed = (N / 60) x π x D
Stirrer Speed (rpm)
Diameter of the Impeller (m)
REACTORS AND AUXILIARIES
3 5
x D x N
p
3
)
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