Impeller design

Frame-Mounted. For medium and severe appHcations, when nozzle loads and thermal transients tend to impose high stresses and internal deflections inside the pump, frame-mounted designs are used. Typically, these designs use conventional impellers, but recessed impeller designs are also available (Fig. 5). 

Practically, the NPSH required for operation without cavitation and vibration in the pump is somewhat greater than the theoretical. The actual (NPSH)r depends on the characteristics of the liquid, the total head, the pump speed, the capacity, and impeller design. Any suction condition which reduces (NPSH ) below that required to prevent cavitation at the desired capacity will produce an unsatisfactoiy installation and can lead to mechanical dimculty. 

As shown in Eq. (10-48), the head depends upon the velocity of the fluid, which in turn depends upon the capability of the impeller to transfer energy to the fluid. This is a function of the fluid viscosity and the impeller design. It is important to remember that the head produced will be the same for any liquid of the same viscosity. The pressure rise, however, will vary in proportion to the specific gravity. 

Wear-ring clearances are excessive (closed impeller design). 

Limit agitator power input and provide proper impeller design Limit shaft speed Monitor shaft speed Provide adequate cooling system Design system to accommodate maximum expected temperature, and pressure... 

Excessive mixing Limit agitator power input and provide proper of reactants or impeller design impurities which, Return process to pilot or development to rede-promotes process to eliminate or minimize this emulsification. problem Poor phase separa- tion resulting in L it shaft speed problems in subse- Monitor shaft speed quent processing, phase separation steps or in down- stream equipment. I" " de-emulsifiers CCPS G-29 Lees 1996... 

The Ns is useful in analyzing a problematic pump and in purchasing a new pump. When the parameters of a new pump are determined, the speed, flow, and head can be worked through the Ns formula to give a value indicating a certain type impeller design. Sec Figure 6-22. 

An impeller designed for air ean be tested using water if the dimensionless parameters, Reynolds number, and speeifie speed are held eonstant... 

EMI Incorporated Manufacturer of fluid mixing equipment, including impeller designs for flow controlled applications in chemical processing, coatings, food, and pharmaceutical, http //www.emimixers.com... 

Fan, non-clogging A fan with an impeller designed to reduce the clogging of the material being handled. 

Figure 3-47. Impeller designs and corresponding specific speed range. (By permission. Standards of the Hydraulic Institute, 10th ed.) Also see [17], Hydraulic Institute, 13th ed., 1975.

For change in speed with a geometrically similar family of fixed impeller design, diameter and efficiency, the following conditions and characteristics change simultaneously [25] ... 

The action of the impeller design produces flow of the fluid, head on the fluid, or shear in the fluid, all to varying degrees depending on the specific design. A general identification of these characteristics for several types of impellers is given by [27]. (Note Use consistent dimensions). 

Oldshue [29] points out that to identify the turbulent range as beginning at a specific may not be exactly correct, as it actually varies with different impeller designs. This range may vary from = 10 to = 10, so for common use = iO" is taken as the turbulent range for all impellers. 

Figure 5-12. Power vs. RPM with impeller diameter parameters. Illustration of impeller input power versus speed for a family of Impeller designs, but only of various diameters, showing uniformity of performance. By permission, Oldshue, J. Y, Fluid Mixing Technology, 1983, Chemical Engineering, McGraw-Hill Publications Co. [29].

In general, just about any material that can be worked into the impeller design is available, including steel, stainless alloys, copper alloys, nickel and alloys, hard rubber, and lead, rubber and plastic coatings on impellers and shafts. 

Figure 11-60. Typical closed and open impeller designs for use in a mechanical expansion turbine. (Used by permission Bui.

Figure 12-46H. Advanced datum impeller design reduces operating stresses and improves flow velocity. (Used by permission Dresser-Rand Company. All rights reserved.)...

Speed cannot be increased indefinitely due to mechanical stresses developed in the rotating impeller and due to the limit of Mach 1 for the tip speed and gas velocity. The limitations will vary according to the impeller designs of the various manufacturers. 

Sonic flow, safety relief, 438 Rupture disk, 460, 461 Sub-sonic flow, 461 Sonic or critical flow, 115, 125 Calculations, 125 Velocity, 126 Specific speed, 194-197 Impeller designs, 194 Upper limits, chart, 195-197 Specifications,... 

The main functions of the impeller are to subdivide the entering gas into small bubbles, to disperse them throughout the liquid, and to maximize the gas residence time. Several impeller designs have proved to promote optimum... 

Figure 7.21. Variation in turbine impeller designs (a) Flat blade (b) Disc flat blade (c) Pitched vane (d) Curved blade (e) Tilted blade (/) Shrouded (g) Pitched blade (h) Pitched curved blade (7) Arrowhead...

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