Axial-Flow Propeller Pumps

Axial-Flow (Propeller) Pumps (Fig. 10-44) These pumps are essentiahy very-high-capacity low-head units. Normally they are designed for flows in excess of 450 mVh (2000 gal/min) against heads of 15 m (50 ft) or less. They are used to great advantage in closed-loop circulation systems in which the pump casing becomes merely an elbow in the line. A common installation is for calandria circulation. A charac teristic cui ve of an axial-flow pump is given in Fig. 10-45. 

Axial flow impellers, 16 672-673, 684 Axial-flow propeller-type pumps, 22 67, 68 Axially split pumps, 22 67, 68 Axial Peclet number, 10 763 Axial undulations, in hemodialysis, 26 830-831... 

Figure 7.10. Some types of impellers for centrifugal pumps, (a) Open impeller, (b) Semiopen impeller, (c) Shrouded impeller, (d) Axial flow (propeller) type, (e) Combined axial and radial flow, open type, (f) Shrouded mixed-flow impeller, (g) Shrouded impeller (P) in a case with diffuser vanes (V). (h) Turbine impeller.

Axial-Plow Propeller-Type. The axial-flow propeUer-type pumps are used to handle large volumes of pumped Hquid at low head. Flow rates of >12 m /s (>200,000 gal/min) can be accommodated. 

FIG. 10-44 Axial-flow elbow-type propeller pump. Cowtesy of hawrence Pumps, Inc.)... 

The pump impeller receives the pumped liquid and imparts velocity to it with help from the electric motor, or driver. The impeller itself looks like a modified boat or airplane propeller. Actually, boat propellers are axial flow impellers. Airplane propellers are axial flow impellers also, except that they are adapted to handle air. 

Turbine pumps mix features of a simple propeller (axial flow) pump with a centrifugal pump and are often referred to as units with mixed flow. A simple turbine pump carries curved vanes on a central rotating spindle. Such pumps are often immersed in the liquid and find use in closed-loop circulation systems, in condenser circulating water, and in sumps and wells. Turbine pumps have noteworthy pumping capacity, and like positive displacements pumps are often used for heads up to about 100 ft/stage with capacities of up to several hundred gallons/minute. 

Figure 4.4 shows various types of impellers that are used in centrifugal pumps. The one in a is used for axial-flow pump. Axial-flow pumps are pumps that transmit the fluid pumped in the axial direction. They are also called propeller pumps, because the impeller simply propels the fluid forward like the movement of a ship with propellers. The impeller in d has a shroud or cover over it. This kind of design can develop more... 

Propeller pumps—The same as axial-flow pumps. 

The flow pattern from a pitched blade turbine is shown in Fig 7.7. The flow pattern is dominated by a large axial flow through the impeller. This pumping does not provide any mixing of the fluid, but the mixing is accomplished by the vortex system formed from the blade tip. The flow from the pitched blade turbine spreads out both axially and radially. The flow pattern developed by a propeller is quite similar to that produced by the pitched blade turbine, but in the propeller discharge mostly axially. 

The action of a turbine or propeller in a Newtonian liquid of low viscosity can be likened to that of the impeller in a radial or axial flow pump respectively. That is, we can regard the mixer as being a caseless pump. The use of the flow rate (or discharge), Q, from a pump and the fluid head, //, is well known. Thus for a pump of unit efficiency these variables can be related to the power input... 

Propeller types pump li( uid. Every revolution of a square pitch prop discharges a column of liquid approximately equal to the diamf ter of the propeller. The flow is iixial. Such pumps are used primarily for high-speed applications and side-entry mixers. Duel propellers are used on vessels with H/D ratios greater than 1. The axial flow decreases mLx time. They are heavier and cost more than pitched-blade turbines. Propeller-to-vessel-diameter ratio is usually Vs- A propeller-type impeller is used for high flow. 

Pumping the liquid volume pumped by the impeller = kp N where kp is a constant dependent upon the impeller Dj is the diameter of the impeller and N = rpm. For a three-bladed marine propeller whose pitch = Dj, kp = 0.5 many other types of impellers have smaller values, and therefore the marine propeller is one of the good axial flow impellers. In general, impellers giving axial flow are used in about 70 % of the mixing applications. 

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