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Mixing
Mixing by Dave Dickey, senior consultant, MixTech Inc.
Dave Dickey is senior consultant for MixTech Inc., Dayton, Ohio, which focuses on mixing processes and equipment. He has 25 years of experience in the field, both as a consultant and with equipment suppliers. He gives a number of short courses related to mixing and has written numerous articles and contributed to several handbooks.
Achieve good top to bottom slurry suspension
A general question regarding suspension of fine ore slurries, of the following properties: solids spg=2.9, mean dp=60 microns; liquid is 50wt% sulfuric acid at 100oC. slurry is 45wt% solids. Vessel is 90% full
The vessel is brick lined, approx 16ft diam x 17ft T-T. Bottom head is ASME F&D, OD=204 inches,1/2" thick. There are 3 baffles made into "V" shape using bricks fastened to the vessel walls (ie, no spacing between baffle and vessel wall)
The agitator is 40 HP, and there are 2 hydrofoil type impellers, approx 68 inch diam. I believe that they are A310'S. The impellers are spaced approx 68" apart. I do not know the distance from the bottom to the lower impeller, but I suspect it is about 35 -40". In your expert opinion, is this system adequate to achieve good top to bottom slurry suspension? The desired objective is to achieve as close as possible a uniform suspension within the vessel. Please give me your assessment and recommendations on how to improve this system?
Category: Mixing
Shaft and gearbox size
What should be the required power for agitating a syrup with a density of 1500kg/m3, volume is 15m3, minimum rpm is 350, impeller diameter is 600mm. What should be the size of the shaft and gearbox?
Category: Mixing
Making an agitator for a composting unit
I am interested in making an agitator for a composting unit. The diameter of the compost tub is about 2000 millimeters, while the diameter of the agitator will be about 1500 millimeters. The vertical shaft will be approximately 500 millimeters long, and I want the unit to run at 15 RPM. I need to find out the motor capacity, the shaft diameter and the expected torque for this operation.
Category: Mixing
Redesigning the impeller blade for a batch polyurethane tank
I need to redesign the impeller blade of my batch polyurethane tank. I'm currently using a marine-type impeller, which incorporates a lot of air into the polymer polyol while mixing, causing a lot of bubbles. I need an impeller that mixes well but does not cause turbulence or a lot of bubbles. Please suggest the best option. Polyol has a viscosity of around 420-520 cSt. I'm mixing approximately 50 to 130 kilograms per batch.
Category: Mixing
Reducing dissolving time
We are using a mixing system including v=40000lit,d=1m rpm=56 visc=120-800cst mixer type=pitched turbine kw=2.4. We want to reduce dissolving time by upgrading mixer diameter or rpm. Which one is the best selection for this viscous liquid? What about the other required changes followed selected upgrading? What about the amount of increasing diameter or rpm?
Category: Mixing
Power estimation for turbulent and laminar mixing
Is there a simple rule of thumb for power estimation in either turbulent or laminar mixing?
Category: Mixing
Proposing a suitable tank volume for a specific viscosity
We have experienced when the mixture viscosity increase the proper mixing tank volume would be reduced why is that for theoretically? And how we can propose the suitable tank volume for a specific viscosity by the way how we can specify the required rpm for a specified impeller diameter against viscosity of mixture?
Category: Mixing
HP Motor Size Requirements
If I currently have a mixer that has a one hp motor inputting 3300 rpm to a gear reducer to obtain 800 RPM output, then if I was to remove the motor and reducer to put a VFD driven 1750 motor direct drive to my mixer what size HP motor would be required. If you know please can you also provide the formula.
Category: Mixing
Designing a Support Bracket for a Baffle
I have a vertical 3100mm dia nad 7000 overall length agitator. The baffle supports were failing due to improper loading. I do not have any book so that I can use the formulae for redesign the support. Please provide me a sample calculation for designing support bracket for the baffle.
Category: Mixing
Pilot plant digester mixing
I would like to continually mix 4% DS anearobic sludge in a 1cu.m pilot plant digester(h/d aspect ratio 1.3/1), using an external pump system with 2 nozzle injections. Sludge throughput is 3l/hour. @ 37degC. Max. solids size = 10mm. What would be minimum injection velocity and flow rate required? Any other requirements i.e nozzle angles, nozzle, injection height, baffles, etc.?
Category: Mixing
Vessel | Fixing a Vessel Agitator | Chemical Processing
I want to fix an agitator to a vessel for mixing viscous
chemicals. The viscosity of the fluid range from 600 cPs-800cPs. vessel. The capacity is 3000 gallons. I want to keep the agitator rpm at 60. What should the HP of the motor and gear box be?
Category: Mixing
Input power of electromotor, power of gearbox and the safety factor
We are going to produce water base resins. These resins have an average viscosity of 60000 cp in a 6-ton industrial reactor, and an anchor mixer has been used for mixing the content of reactor (with the speed of 20-60 rpm). Therefore, we have made the impeller with proper dimensions (shown below). Now we must fix an electromotor and gearbox to the shaft and impeller system. What is your recommend about input power of electromotor, power of gearbox and the safety factor (the agitation system works continuously about 7 hours /day). My calculations show, M2(out put torque) is about 3000N.m and P(motor)= 20 KW and P(gearbox)=20*1.5=30KW, f=1.5
Characteristics of our anchor Impeller with two horizontal arm: D=1.75m, w (blade wide) =0.2 m, H=2m, t (thickness of blades)=0.02m blades are in 45 degree.
Category: Mixing
Jet Mixers vs. Mechanical Mixers
I would like to know the differences between jet mixers and
mechanical mixers. Are there any situation that I have to use jet mixers instead mechanical ones?
Category: Mixing
Efficient Impeller Blade or Mixer
We make a solution of water & benzoyl peroxide (in various percentages - 1%, 4%, 8%, etc...) in a mix tank & transfer it into several poly lined 55 gallon drums to store the solution until we are ready to fill from each drum - one at a time - until empty - into finished product containers. We have to stir each drum for approx. 2 hrs prior to beginning filling to get a homogenous solution in the drum - to get the BP back in suspension. Do you have any suggestions as to a more efficient, specific type of impeller blade or mixer to keep the BP in suspension - so we can keep the drum of solution as homogenous as possible in each drum? We currently have air mixers with a stirrer type 3 blades at the bottom of the shaft. Drum dimensions: int.hgt.= 37 1/16", int.diam. = 21.8 with 2 " Bung/opening with removable lid. Must be kept covered.
Category: Mixing
Designing a Mixing Tank
I want to design a mixing tank to prepare a slurry of very fine
catalysts in water. This tank will have an agitator to keep solids suspended. In this case how would you consider the vortex height generated during mixing?
Category: Mixing
KW Rating | KW Rating and Bearing Size | Chemical Processing
We need to offer a drive ( GearMotor) for a Mixer
with Blade sweep Dia. of 6.56 Ft., Height of Stirrer shaft is 8.202 Ft., rpm - 60, Viscosity - 30 poise, but there is no bearing at the bottom.
The question is what would be the KW rating of the Motor and what size of
Bearing should be there at the Gearbox output shaft ?
Category: Mixing
Mixing Time and Multipropeller
I would like to know if there is a correlation to estimate mixing
time in a vessel with a multipropeller?
Category: Mixing
High efficiency motor ratings
On premium efficiency motors, the FLA is higher on IEEE841 motors than on standard high efficiency motors. Yet the efficiency is higher on 841. More amps is more watts. What makes a premium efficiency motor more efficient? I'm looking at a 50-hp, 1,800, 3/60/460 motor; (a) 841 motor, FLA: 59.9, Efficiency: 94.5% and a (b) High efficiency motor, FLA: 55.9, Efficiency: 93.6%.
Category: Mixing
Horsepower calculations for a specific viscosity
I need to calculate the horsepower required to agitate a solution with viscosity of 0.3 cps and density of 839 kg/m3 at 60 rpm. The tank has an inner diameter of 1,500 mm and tangent-to-tangent length of 4,500 mm. The agitator has three impellers (pitched turbine, I do not know the number of blades) with 900-mm diameter. The tank has four mixing baffles. Using equations from a handbook, I found that the power required is about 1 hp. However, I am not sure if this equation considers the use of multiple impellers.
Category: Mixing
Baffle fabrication
I am presently setting up a micro manufacturing plant for mixing Polymers and other cleaning products. I have two tanks, one that is eight feet,a stainless steel tank and one four-foot poly tank. My question is regarding baffles. Can I fabricate something locally that would work for both steel and poly tanks and is there any tricks to installing these baffles?
Category: Mixing
Calculate "downward force" on an impeller
I am trying to calculate the "downward force" of an impeller. Is this the same a hydraulic force? (e.g. (19,000 x horsepower x service factor)/(rpm x impeller diameter).
Category: Mixing
Blended viscosity and stirred tank content relation
I feel there would be a relation between the blended viscosity of any stirred tank content and the tank volume physically, is that correct? If so, why and what is the rule of thumb criteria for selecting a vessel’s volume with respect to blended viscosity?
Category: Mixing
Agitator design procedures
I want to know the selection criteria and standard design procedure for all types of agitators, mainly anchor and turbine). Please also suggest some books.
Category: Mixing
Sizing mixers
How do you select the type of impeller for different applications? How do you determine the measurement of the impeller size and dimension?
Category: Mixing
Pump shaft size and driver relation
What would a general rule of thumb be for pump shaft size related to driver horsepower? I have used the following rule: The minimum pump shaft diameter would be 1 in. for every 100 hp. The minimum pump shaft for a 300 hp driver would be 3 in. to avoid shaft issues. This seems to indicate when a mismatch may occur. Is there another rule of thumb to use that may be better at indicating potential pump issues?
Category: Mixing
Suitable reactor capacity
We have installed a cylindrical dish-end type of SS reactor with a capacity of 1,500 L, diameter of 1,200 mm; height of 1,350 mm; depth of 50 mm; total height of 1,650 mm; and the required rpm at the agitator end is 500-600 rpm. Process details are: paste type liquid (free flowing); specific gravity around 1.0; viscosity of liquid is 350-600 cSt.; agitator is vertical with four, 45-degree vertical turbine-type impellers. Suggest the suitable capacity of torque with its rpm selection to have the desired rpm at the end of the impeller withstanding the torque generated by the liquid during the mixing. Can we operate the same system with gear motor?
Category: Mixing
Agitator capable of dispersing air through the shaft/blades
I am looking for an agitator that can disperse compressed air through the agitator shaft/blades. Is there a manufacturer out there that makes an agitator like that?
Category: Mixing
Motor requirements for varying fluid viscosity
I have an agitator with a 40-hp motor. The service fluid viscosity is 1,000 cp. I want to use the same shaft and motor for a 10,000-cp fluid. Can I use same shaft, and if so, what parameters need to be changed?
Category: Mixing
Partial discharges, condition monitoring
Considering partial discharges related to condition monitoring in electrical equipment: On which type of equipment is this technology applied?; What are the parameters monitored?; What are the equipments/sensors used to monitor partial discharges?; What about indicators/statistics of that monitoring?
Category: Mixing
Power requirement for a constant stirring vessel
What is the power requirement (motor specification, gearbox size and the shaft size) for a constant stirring vessel that is an open type with a 60-degree inclined pitched blade agitator running at 14-15 rpm? The contents of the vessel can be UF (Urea Formaldehyde resin), Melamin formaldehyde resin, MUF, phenol formaldehyde resin, etc. The diameter of the tank is 3,500 mm and the height is 5,500 mm. The stirring is required to not let the liquid gel-up.
Category: Mixing
Power requirement for a gearbox
I have a 1,000-mm diameter and 1,800-mm high tank. Material to be mixed with an agitator is 76% solid and 24% water (calcium carbonate slurries), with a viscosity of 350-450 cps. I want to use a gearbox for mixing with output speed between 18-36 rpm. How much power (kW) do I need for the gearbox? How many blades must be made in order to make slurries?
Category: Mixing
Agitator type for batch reactor
I would like to know what kind of agitator in a batch reactor I should use. Reactor dimensions are 1160 mm in height and 800 mm in diameter. Reactor contents are 250 Kg of 853 Kg/cubic meter dense liquid and the gas is purged to the liquid through dip tube at 75Kg/hr. What kind of agitator should we introduce to this batch reactor?
Category: Mixing
Power consumption equation
I would like to know the formula for calculating power consumption for an agitator and grinding mill. I have all the process data information for this equipment, but I don’t know how to calculate approximate power from the data.
Category: Mixing
Follow-up to previously answered impeller diameter question
A few days ago, I posed this question: Q: I have a vessel with a top entering agitator without baffles. The vessel height is 2 m and vessel inside diameter is 1.5 m. The impeller type is three 60-degree pitched blades. Each blade has an inclination of 60-degress in respect to the agitator shaft too. The impeller diameter is 880 mm. The pitched blades are fixed to a cylinder that is 122 mm in height and with a 125 mm diameter. The width of the blade at the cylinder is 112 mm and at the end is 80 mm. The shaft diameter is 100 mm. The agitator has a velocity redactor of 1 to 10. The agitator has no driver and has no characteristics label. I want to use this vessel in the production of 50% calcium nitrate solution with a density of 1,450 Kg/cubic meters and a dynamic viscosity of 1.35-1.8 cp. What will be the calculated power at 180 rpm and 360 rpm?
I received this answer: A: The answer is don’t do it. There is no way an impeller that large should ever be rotated at 180 rpm in a vessel that size. Without baffles, the liquid contents would swirl over the top to the tank an splash everywhere around the tank. At 180 rpm, without baffles, the impeller power draw would be about 7.8 kW, that's kilowatts, not watts. At 360 rpm, the power jumps to 61 kW. The mixer described is suitable for a much larger tank, not for one 2 m tall and 1.5 m in diameter, regardless of the contents. Baffles only make the design >worse, because the power levels are about three times the levels without baffles. Do not attempt to operate the mixer in the manner described!
Of course, I am satisfied with the answer, but now I have a new idea. Can I do the blades of my impeller shorter, keeping up the original design, except the diameter? If I can do it, what would be the optimum impeller diameter to avoid having the liquid contents swirl over the top of the tank and splash? What would be the consumed power in this case? I attempted to calculate it, using the Perry’s Manual, but there wasn’t any similar impeller in the figure.
Category: Mixing
Motor horsepower equation
I have to select a motor for a mixing tank. The tank is 7-ft in diameter and 4-ft high. Two-thirds of the tank will be filled with polymer slurry. I expect the impeller diameter to be 3 ft with a rotational speed of about 300 rpm. Can you please tell me how to calculate the horsepower requirement of the motor? I would appreciate if you could quote a formula.
Category: Mixing
Agitator speeds for different fluids
Can I get the same maximum agitator speed for a given motor for different types of fluid?
Category: Mixing
Calculating rpm power
I have a vessel with a top entering agitator without baffles. The vessel height is 2 m and vessel inside diameter is 1.5 m. The impeller type is three 60-degree pitched blades. Each blade has an inclination of 60-degress in respect to the agitator shaft too. The impeller diameter is 880 mm. The pitched blades are fixed to a cylinder that is 122 mm in height and with a 125 mm diameter. The width of the blade at the cylinder is 112 mm and at the end is 80 mm. The shaft diameter is 100 mm. The agitator has a velocity redactor of 1 to 10. The agitator has not driver and has not characteristics label. I want to use this vessel in the production of 50% calcium nitrate solution with a density of 1450 Kg/cubic meter and a dynamic viscosity of 1.35-1.8 cp. What will be the calculated power at 180 rpm and 360 rpm?
Category: Mixing
Agitator design
How do you design the shaft diameter, impeller rpm and power required to drive an agitator?
Category: Mixing
Agitator efficiency equation
I am looking for a formula to calculate the efficiency of an agitator. I am currently designing a mixing impeller for the dissolution of ammonium persulphat in denim water. Now I want to compare between the efficiencies of the propeller and the turbine impeller designs with respect to their efficiencies. Can you help with the formula? The shaft is a top, off-center entering at an angle in a closed hemispherical tank.
Category: Mixing
Pitched-blade impeller direction
I would like to know the direction of 60-degree angle pitch-blade impeller and whether it should be facing upward or downward while the agitation is in clock-wise direction. I also am seeking information on how much distance is required from the bottom dish of the reactor to the bottom impeller. As far as I know, if the pitch-blade impeller's angle is facing upward during its clock-wise rotation, the material lifts from bottom to top and gets radial and axial agitation to lift the reaction mixture. If the pitch-blade impeller's angle is facing downward during its clock-wise rotation, the material pushes down and may be not getting proper mixing effect. In either case what should it be?
Category: Mixing
Agitator design
I have a tank of 4.5m diameter and 2m height containing water. I want to install an agitator consist of two blades of sweep diameter 2 m. The agitator's speed should be 20 rpm. Gear ratio is 60:1. Motor is of 3.7 kW. Please tell me how I should design this agitator? Also tell me the specification of the gear box and motor.
Category: Mixing
Suspension agitation
In several parts of our process we are making suspensions of solids in mixing tanks with agitators. Some solids tend to float on the surface. Some suspensions also tend to create a lot of foam on top of the water surface causing problems (flooding). A higher rotation speed creates a better mixing but creates also more foam. We use antifoam chemicals to reduce the foam. Is there a way to prevent or reduce foam? By using another agitator or agitator position or another trick?
Category: Mixing
Design for an off-centered agitator shaft
I am trying to design an off-centered agitator shaft. The shaft would be offset 20% of the tank’s inner diameter. What service factor would I need to use for the off-center?
Category: Mixing
Hydraulic load factor for water, oil mix
What is the hydraulic load factor for a fluid made up of oils and water being stirred by a three-blade propeller with the blade fully submerged under the mixer? Can you also help with the diameter of the shaft? Details are: power equals 2.2 kw; length of shaft equals 2.228s; speed equals 460 rpm; and impeller diameter is 390 mm.
Category: Mixing
Liquid mixing equation
I know there is an equation that can be used to determine the adequate mixing time of two liquids (viscosity of water). Can you give me the name of the equation? I saw it once a long time ago and, if I remember correctly, it was a person's name.
Category: Mixing
Agitator force
I have an agitator which is used to mix the dough. The agitator is running at 150 hp motor at 84 rpm. Taking 1005 efficiency, how do I calculate how much force will the dough exert on a fixed cold bar? The idea is that the dough gets squeezed between the agitator and the fixed cold bar.
Category: Mixing
Hydraulic load calculations
An agitator has a steady bearing (a PTFE bush bearing),
a radial bearing (rolling element bearing) and a locating bearing (rolling element bearing - in the gear box). How do you calculate the reaction loads at each of these bearings due to hydraulic load and other loads. Do you have any examples for this type of problem?
Category: Mixing
Mix throttled liquid/flash gas and hot gas
What is a good way to mix throttled liquid/flash gas and hot gas in the low side of a refrigeration system to achieve a uniform superheated vapor? Both the feed streams are currently injected at a common point and then allowed to run through about 20 ft of tubing with four 180-degree return bends. There is a liquid stream rolling along the bottom of the pipe where incomplete evaporation is evident. There is insufficient room to add much additional piping. Would static mixers, which I believe are typically used for liquid blending, be of any benefit?
Category: Mixing
Calculating torque exerted by liquid
We have a vessel of 6,500-L capacity. It needs to be driven by a top agitator with 2 Nos. of turbine impeller with four 300-diameter blades. I want to know the torque exerted by the liquid. The viscocity of the liquid is 250 cp.
Category: Mixing
Service factor for an unbalanced hydraulic load
The following is the data for an application:
Can you please give the service factor that needs to be used while computing the hydraulic unbalanced load?
Category: Mixing
Calculating unbalanced hydraulic force
When calculating the unbalanced hydraulic force on an agitator impeller, one of the articles says that the calculation of force can be done by the formula:
Force = (2000*Output hp*12*Position factor)/(rpm*DIa. of turbine in inches). What does that position factor stand for, and what are the values for a top entry type agitator, with a 11kW motor? In another text it was written that the force can be computed by the formula F = Torque/(0.75*Radius of blade in mm). Which of the two gives an accurate result?
Category: Mixing
Suspending salt mixtures in a PVC solution
I am interested in keeping a mixture of 30% salt suspended in a liquid PVC material. The goal is to produce products that are heavy and weigh the same without any salt collecting on the bottom.
Category: Mixing
Installing an agitator in a reactor | Chemical Processing
We represent a company that sells second - hand equipment, our customer needs a practical way to mix a viscous product and the agitator is a 36 hp - 120 RPM, but the structure to handle this agitator in a 1200 gal SS reactor is very complicated according to our main engineer in USA. We do not have more in the inventory, what could be the mechanical structure suitable to install the agitator in the reactor?
Category: Mixing
Recommendation for small pilot plant batch mixer
I'm looking for a recommendation for small pilot plant batch mixer (idal capacity target 1 to 4 liters) that handles powder and can be heated to about 80 C. Mixing should be possible at low speed.
Category: Mixing
Formula for position of impeller
We have a pilot mixing plant here on site. Ever since it was stripped down and rebuilt due to its PM schedule, it hasn't worked properly. We use the tank to mix a powder and a liquid. Now when it runs, no vortex is created (or be it a very poor one) and the powder does not go into solution, it just sits on the top of the liquid. We have tried moving the impeller up and down the shaft but to no avail. Unfortunately, the original dimension drawing are missing and so we do not know the original position of the impeller and its dimensions etc.
Are there formula that might help us to determine the optimum position for the impeller etc. if we measure the various aspects of the tank, baffles etc.?
Category: Mixing
Solid particle size distribution
Can give me the various general solid particle size distribution used in chemical industries in various applications or a link or reference where i can get this data?
Category: Mixing
Blade RPM speed
I have a tank (7-meter diameter 8.5-meter told), with and old agitator for milk of lime suspension and a double blade 84 inches wide each. At what RPM do I have to turn the blades in order to keep the lime in suspension at 8 or 10% of solid?
Category: Mixing
Mixing powders of similar micron sizes
I would like to know what are the factors to consider when mixing two types of powder with similar micron sizes.
What would be the most cost effective way to mix big volume quantity in the rangeof 500 000 to 1 million lbs a year?
This mix will have to be filled in individual products, and I would like to know if there is a group out there that can guide us in the design and implementation of a production system.
Category: Mixing
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