torque required to stir liquid?

Liquid viscosity is 1.04 ?[units]?

Rory

hob wrote:

inadequate information. A stirrer could be a flat plate, or it could be a wire square. No viscosity unit.

Still, the torque is likely to be less than 5 lb-ft At 30 rpm we are talking pi X 0.2 m/rev X 0.5 rev/sec X 5 lb X 9.8 N/kg / 2.2 lb/kg =

Brian W

thanks. the figure of 1.04 is the original gravity (not the viscosity as i previously said!). the stirrer will be a flat plate of total length 200mm, width 30mm.

Answer depends on impeller design and baffle configuration. Impeller/stirrer manufacturer should be able to supply these data.

Alternatively, see Perry's Chemical Engineering Handbook (pages 19-6 through 19-8 in the

What you will see is a plot of the dimensionless "power number" versus impeller Reynolds number. Calculate Reynolds number, look up power number for your specific impeller design, and then find power. Torque is power/angular velocity in appropriate units. (If power is in ft-lbf/s, and angular velocity is in radians/s, then torque will be in ft-lbf.)

See also:

IMHO that is the kind of thing where an old engineer looks for a like product and then does a quick test - only students have to actually figure such things

I would agree however even young (freshly minted grads) engineers cling to "we can calc it". They just love that false precision.

THey don't have the experience; one good test is worth a thousand expert opinions (or 100 pages of calcs)

:)

Bob

One good source of information is a company that makes mixers and impellers. Try: