Blade pitch setting

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. 

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. 

Example 9.5. An agitated vessel 6 ft (1.8 m) in diameter with a working depth of 8 ft (2.44 m) is used to prepare a slurry of 150-mesh fluorspar in water at 70 F. The solid, has a specific gravity of 3.18, and the slurry is 25 percent solids by weight. The impeller is a four-blade pitched-blade turbine 2 ft (0.61 m) in diameter set 1.5 ft above the vessel floor, (a) What is the power required for complete suspension (b) What is the critical stirrer speed ... 

A fairly similar flow pattern is produced by the four-bladed pitched turbine with its blades set at a 45° angle. The radial component, however, is already more evident with this design. 

Setting the blade pitch cannot be done with great precision, and it s not too critical. I once increased the blade pitch from 15° to about 22°. Air flow increased by only 5 percent measured by the increased amperage load on the motor driver. 

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°. 

Fixed pitch The blade angle cannot be altered from the manufacturers. setting. 

Fill the beaker with 1000 ml of standard hard water at 30°C + 2°C. The stirrer should be centrally located in the beaker and positioned in such a way that the lower edges of the stirrer blades are 60mm above the base of the beaker. The pitch of the stirrer blades and the direction of rotation are such that the propeller pushes the water upwards. Add the tablet to the water without stirring. Wait for 1 minute. Switch on the stirrer with the speed set to about 300 rev/min... 

The maximum dissipation rates for the dispersion of droplets and gas bubbles with different stirrer types such as turbine and pitched-blade stirrers, Lightnin A 310 and Cheminer HE 3 was determined using ID-LDA measurements, and the resulting turbulent fluctuating velocities were calculated using a model based on dimensional analysis. The essential parameters were identified using statistical analysis supported by sensitivity analysis. It was found that in the relationship e oc the stirrer speed dependence with n is correct, but that for the stirrer diameter with was set too low. The number of baffles was of secondary importance [608]. 

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