RSS
Print pageHome » What is the formula for laminar mixing?
What is the formula for laminar mixing?
Q: I wanted to know the formula for power for laminar mixing.
I have read the “Handbook of Industrial Mixing” as you previously advised. But it doesn’t have a clear formula for laminer flow stirrer (power, shaft design, gearbox design, etc.)
tank inner diameter = 36 inches
impeller diameter = 15 inches
impeller type = pitched blade (45 degree)
Reynolds no. = 3
specific gravity = 1.2
cp;(viscosity coefficient)= 10000, nearly. (tomato suspension in boiling water)
tank height = 84 inches
RPM = 15
A:
I stand by my initial advice. The “Handbook of Industrial Mixing” has about as much information as you are going to find in any literature reference, without a more complete background in mixing. A short course on mixing might fill some of those gaps. In the laminar range, Reynolds number less than 10, the power number for a pitched-blade turbine is 52.6 divided by the Reynolds number. The other answers to torque and bending requirements for shaft design and gearbox design can be found in Chapter 21, Mechanical Design of Mixing Equipment, in the “Handbook of Industrial Mixing”.
Beyond that information, the mixer you describe will not effectively mix the "tomato suspension in boiling water" you describe. The table Mixer Design Total - small shows that one 15-inch diameter pitched-blade turbine running at 15 rpm puts only 0.0025 hp into the process, for a mixing intensity of 0.15. A mixing intensity of 1.0 is required to effectively move all of the contents in the tank.
The table Mixer Design Total - small 2 shows using three pitched-blade turbines operating at 125 rpm will possibly mix the contents. Actually, pitched-blade turbines are probably not the best impeller choice for low Reynolds number (36) applications. At least more larger impellers are required to handle viscous fluids.
Here are more of the latest questions on: Mixing
How do I select the optimal location for an impeller inside a tank?
I am new to tank mixing and I have a question about selecting the optimal location (and orientation) for an impeller inside a tank. I am dealing with a tank that contains very light materials (0.7 and 0.8 SG). The contents have been sitting in the tank and are stratified. Please let me know if there is some sort of general process for selecting the proper impeller position.
The tank is 120 ft. in diameter, 45 ft. high. It is allowed to only have one mixer. The first layer of material has a specific gravity of 0.75 is 32 ft. high. The second layer of the tank has a specific gravity of 0.67 and is 10 ft. high; making the total contents of the tank 42 ft. high. The purpose of the mixer is to have complete mixing within 6 hours.
Is a UDIF impeller suitable?
We have been using a UDIF agitator for emulsion polymerization mixing for 1cp to 8,000 cp. Is this type of agitator suitable for mixing?
What kind of agitator is suitable for a range of viscosities?
Our process dissolves several types of polymers in appropriate solvents. During the solving process, the viscosity might reach to the value of 8,000 cp. Our vessel dimension is 30 cm in diameter and 70 cm in height. What kind of agitator is suitable for this purpose?
What is the best way to approach gas-gas mixing?
I want to mix two low viscous gas streams in laminar regime. I am planning to mix them by passing through a pipe filled with spherical pebbles or some structured packing. I want to calculate the length required for the mixing expected. My required process stream details are as follows:
Q = 1Nm3/hr
He= 0.99
H2= 0.01
P= 1.2 bar
Dia of pipe = 1/2 inch
Temp= 25 degrees C
I have gone through the text book "Handbook of Industrial Mixing." But that textbook has procedure for only commercially available static mixers. Please guide me through the design. Is dispersion model helpful in finding the length? If so, how?
We would like to have a general idea of pumping number for our reactors. Can you help us with blend-time calculations?
To characterize one of the reactors at plant scale, we use the discoloration method. The parameters for the mixing time are calculated based according to the following formula:
t_mix= K/(aN(D/T)^b (T/Z)^0.5 )
N = impeller speed
D = diameter stirrer
T = diameter tank
Z = liquid height
The divisor is known as Kmix
Because we don't really know the uniformity (U) reached with this method we don't replace K with
K = -ln (1-U)
But get the best fit for K, a and b by means of the least square method. It is known that the pumping number can be determined by
N_Q= (Vk_mix)/(ND^3 )
We would like to have a general idea of pumping number for our reactors. So if we would like to deviate the pumping number from the above method would it be correct that for T=Z (so at a fixed volume based on the reactor geometry) we use the following formula.
N_Q= (VaN(D/T)^b)/(ND^3 )
Working in a turbulent regime, this result in a constant pumping number related to the tank geometry. Would the above approach be correct to compare pumping and mixing time capabilities of different reactor set ups? I think that not working at a fixed uniformity results in a gap in the above approach.
