Fan blade pitch

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. 

In the older, induced-draft wooden cooling towers, a common problem is that the wooden slates have broken up. There is usually an access inspection door at the base of the cell. Often, the water distribution holes are plugged or there are large holes broken into the deck. Water is not supposed to overflow around the outside of the cooling tower. On some cooling towers the fans are driven by belts, which can slip or the fan blade pitch is set too low, low being less than 15°, maximum being 23°. 

Fan blade pitch The angle of a fan blade. The bigger the pitch, the greater the air flow. 

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. 

When the mean annual temperature is 16.7°C (30°F) lower than the design dry-bulb temperature and when both fans in a bay have automatically controllable pitch of fan blades, annual power required has been found to be 22, 36, and 54 percent respectively of that needed at the design condition for three process services [Frank L. Rubin, Tower Requirements Are Lower for Air-Cooled Heat Exchangers with AV Fans, Oil Gas J., 165-167 (Oct. 11, 1982)]. Alternatively, when fans have two-speed motors, these dehver one-half of the design flow of air at half speed and use only one-eighth of the power of the full-speed condition. 

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. 

The rate at which each fan circulates air can be varied by changing the pitch of the fan blades. In final drying stages, in which diffusion controls or the product is light and powdery, the circulation rate is considerably lower than in the initial stage, in which high evaporation rates prevail. In the majority of applications, air flows through the... 

The controllable pitch fan provides an infinitely variable air delivery across the K-Fin Sections through automatic changes in the fan blade angle. Temperature can be closely controlled to meet the varying demands of operating conditions and fluctuating atmospheric temperatures with appreciable power savings under low load conditions. For certain control applications, the ability of... 

Temperature control of the process fluid may be accomplished easily through the use of shutters, variable pitch fan blades, variable speed drives, or, in multiple fan installations, by shutting off fans as required. 

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

Pitch The spacing of holes in a flange, or the angle of fan blades. That attribute of auditory sensation depending primarily on the frequency of the sound in terms of which sounds may be ordered on a scale extending from low to high. 

Figure 9-117. Diameter correlation for 16° pitch angle for fan blades. Used by permission of Whitesell, J., Chemical Engineering, Jan. (1955) p. 187, all rights reserved.

Manual (for seasonal changes only) or automatic pitch control operated by air-motor on fan blades. 

Rubin, F. L., Power Requirements Are Lower for Air-Cooled Heat Exchangers with Variable-Pitch Fan Blades, Oil and Gas Jour, Oct. 11, (1982). 

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. 

Air coolers 87-94 Aerodynamic fan blades, decrease rev./min and increase pitch, tip and hub seals, decrease pressure drop. 

---