Impeller variable speed

Figures 8.7(a) and (b) illustrate variable-speed couplings which can provide a stepless speed variation over a wide range. The impeller and runner of the couplings are housed in a stationary housing with a built-in oil sump. Oil is...

If the condition should be oecasional, the solution could be to install a variable speed motor. If the condition is permanent, the solution could be to reduce the impeller diameter, replace the pump, or increase the diameter of the pipe. If normal operations require living with the condition, then increase the diameter of the pump shaft to improve the L/D factor. 

There is no constant scale-up factor for each specific mixing system/process [29]. The two independent impeller variables come from speed, diameter, or power, because once the impeller type/style has been selected. 

The variables involved in the performance of a centrifugal pump include the fluid properties (p, and p), the impeller diameter (cl), the casing diameter (/)), the impeller rotational speed (N), the volumetric flow rate of the fluid (0, the head... 

Note The purchaser may consider the use of variable speed drive capability and/or the use of blank stages (to add impellers in the future) for multistage pumps to meet this requirement. 

Pumps shall be capable of at least a 5% head increase at rated conditions by replacement of the impeller(s) with one(s) of larger diameter or different hydraulic design, variable-speed capability or use of a blank stage. 

Fig. 3 shows the experimental apparatus. The feed tank had a 50 gallon capacity and was equipped with a variable speed mixer. The feed pump was a flexible impeller, positive-displacement pump to minimize shearing of the feed emulsion. The pumping rate was regulated by a Graham Variable Speed Transmission. Each flotation tank was 11.5 in. ID with 6.5 in. liquid depth maintained by a CE IN-VAL-CO conductometric level controller with a pneumatically actuated control valve in the effluent line. The fourth cell was not equipped with an air inducer. The outer diameter of the air downcomers was 1.5 in. The rotor in each air inducer was a turbine taken from a 2 in. turbine flow meter. Each rotor was belt driven by a 10,000 rpm, 1/30 hp motor and all three motors were governed by the same variable transformer. Another pulley on each rotor shaft was attached to a non-powered belt connecting all three shafts to ensure that each rotor turned at the same speed. 

Recently, one of the most practical results of these studies has been the ability to design pilot plant experiments (and, in many cases, plant-scale experiments) that can establish the sensitivity of process to macroscale mixing variables (as a function of power, pumping capacity, impeller diameter, impeller tip speeds, and macroscale shear rates) in contrast to microscale mixing variables (which are relative to power per unit volume, rms velocity fluctuations, and some estimation of the size of the microscale eddies). 

Other pump data included in manufacturer s engineering information include characteristic curves for various diameter impellers in the same casing (Fig. 6.19) and variable-speed head-capacity curves for an impeller of given diameter (Fig. 6.20). Note that the required power input is given in Figs. 6.18 and 6.19 and may also be given in Fig. 6.20. Use of Table 6.25 is explained in the table. 

The use of variable-speed drives in pilot plant and manufacturing plant vessels is recommended for development and scale-up of crystallization processes. This capability provides the opportunity for critical experimentation at the pilot plant scale to determine the effect of impeller speed on PSD and other variables. On the manufacturing scale, the ability to change impeller speed is the most readily adjustable parameter for manipulation on scale-up. Modem variable-frequency drives provide an excellent means to vary speed over a wide range. The added cost of variable-speed capability is minimal compared to all other methods of changing mixing... 

Pilot plant vessel to include variable-speed drive, subsurface addition at impeller, online measurement devices, variable-temperature jacket services, controlled seed addition as slurry, antisolvent/reagent addition at controlled rate. 

Solid-liquid mixing involves the suspension, distribution, and the drawing down of solids by agitation. In addition to vessel geometiy, impeller variables include type, diameter, number, speed, and location. Process results include the desired level (quality) of suspension, such as just off-the-bottom, complete uniformity, or any intermediate condition. The slurry properties, density difference (solid/liquid), viscosity, and solids concentration all determine how difficult the task may be. As alternatives to stirred vessels, jets (see Section 9.10) can be used for light-duty suspension. Literature references deal mainly with settling solids as opposed to floating solids. We will try to address both conditions. 

With variable-speed drive and replaceable impellers. 

Using moderate agitation (800 rpm) provided by a Lightnin Mixer or similar variable speed unit and an impeller suitable for general mixing and blending operations, disperse or screen the Carbopol resin into the DI water. 

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