Blade pitch

The axial-flow fan is inherently a device for moving a consistent volume of air when blade setting and speed of rotation are constant. Variation in the amount of air flow can be obtained by adjusting the blade angle of the fan and the speed of rotation. The blade angle can be either (1) permanently fixed, (2) hand-adjustable, or (3) automatically adjusted. Air delivery and power are a direct function of blade pitch angle. 

The variable-pitch arrangement at constant motor speed changes the pitch of the olades through a pneumatic signal from the leaving-water temperature. As the thermal load and/or the ambient wet-bulb temperature decreases, the blade pitch reduces air flow and less fan energy is required. 

No. Blades Pitch AUTO VARIABLE Enclosure AGMA HP Rating ... 

FLAT BLADE DISC FLAT BLADE PITCHED VANE... 

Variable blade pitch control The impeller blade angle is varied when the fan is in operation, normally only for axial flow fans. 

Louvers are probably the most common type of temperature control device on aerial coolers. They may be either automatically adjusted by sensing the process temperature or manually adju.sled. Blade pitch is probably second most common, and variable speed drive is third. 

Figure 5-51. Flat blade pitched paddle. A simple, low cost design that handles a wide variety of jobs. Operating at low speeds, It gives maximum pumping capacity with a minimum of turbulence. Courtesy of Lightnin (formerly Mixing Equipment Co.), a unit of General Signal.

These fens usually operate with no piping or duct work on either side and move air or gas from one large open area to another. Pressures are usually very low, and volumes depend on size, blade pitch, the number of blades, and speed. 

A 100-gal pilot-plant reactor is agitated with a six-blade pitched turbine of 6 in diameter that consumes 0.35 kW at 300 rpm. Experiments with acid-base titrations showed that the mixing time in the vessel is 2 min. Scale up to a 1000-gal vessel with the same mixing time is desired. 

Scale-up comparison at constant P/V (four-bladed pitch turbine Ds/Dr = 0.5 ... 

Figure 10.58. Power correlation for single three-bladed propellers baffled, (from Uhl and Gray (1967) with permission), p = blade pitch, D = impeller diameter,...

The arming vane may drive a gear train which, after a definite interval, removes safety blocks or aligns the detonator with the next element in the explosive train. Standard arming vanes have blade pitches of 30°, 60°or 90°, but there are also "special" vane assemblies with different blade pitches (Ref 51a, p 5-38)... 

Impeller type DJW IXJII No. of blades Pitch/angle NP Re (approximate values)... 

The fan blades themselves may be adjusted to obtain more airflow. This is done by increasing the fan blade pitch. The pitch can usually be adjusted between 12° (for low airflow) to 24° (for high airflow). Any... 

Cooler weather always increases the airflow produced by a fan. This always increases the amp load on the fan s motor driver. To prevent the motor from tripping off, or simply to save electricity during the winter, you might reduce the fan blade pitch. 

Four blade pitched paddle agitator Vessel fittings omitted for clarity... 

When two six-blade open turbines are installed on the same shaft and the spacing between the two impellers (vertical distance between the bottom edges of the two turbines) is at least equal to Da, the total power is 1.9 times a single flat-blade impeller. For two six-blade pitched-blade (45°) turbines, the power is about 1.9 times that of a single pitched-blade impeller. 

TCV = Temperature Control Valve TE = Temperature Element VAV = Variable Air Volume XP = Positioner for Fan Volume Control, such as a Blade Pitch Positioner... 

PIC-10 is the load-following controller. It compares the optimized set point with the actual header pressure and adjusts the fan speeds or the blade pitch angles of the fans. When its output signal reaches the maximum set on PSH-07, it starts another fan. 

FIGURE 10.17 Flow field behind impeller blades (pitched blade turbine) (from Ranade eto/., 2001a). 

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