Fans Problems

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1. A pressure of 1.5 in. of water is required to move air up through a bin of grain at 20 cu ft per (min sq ft) of floor. If the floor has an area of 175 sq ft, what fan horsepower is required assuming 75 percent efficiency?

2. The air system C of Fig. 5.10, which is carrying 10,000 cu ft per min, is altered so that the resistance is less and the fan delivers 11,000 cu ft of air per min. Determine the speed at which the fan must operate to deliver exactly 10,000 cu ft per min, and the static pressure and horsepower. What is the percentage reduction in power requirement?

3. A fan geometrically similar to that of Fig. 5.10 must operate at 2.0 in. pressure, 6000 cu ft per min, and an efficiency of 75 percent. Specify the wheel diameter, speed, and power required.

4. Determine the discharge velocity of the fan of Fig. 5.10 from the outlet area and from the velocity pressure, both at 10,000 cu ft per min.

5. A forward curved blade fan delivers 380 cfm at free discharge at 1725 rpm. The rotor is 6 in. diameter, 3.25 in. wide; and the discharge edge of the vanes is 45° relative to the radius. Show the velocity vectors for the air leaving the rotor. Show the velocities by dotted vectors if the flow is throttled to 190 cfm.

6. Plot pressure gradients (static, velocity, total) for the system shown below.

7. Assume that the fan of Fig. 5.10 is connected to a long flexible tube with resistance features that permit a capacity of 7000 cfm. Now connect the discharge end of the tube to the fan inlet. The areas are the same. Discuss the effect on operating conditions-pressures, air rate, power.

8. Compute the basic shut-off or zero flow static pressure for the Fig. 5.10 fan. Explain the difference between the observed and the computed values.

9. A room is to be ventilated by an axial flow fan as shown below. Compute the conditions required for selecting a fan and the required horsepower. Assume 70% efficiency.

Buy the solutions: PM @ Engineering Daily

Buy the solutions: PM @ Engineering Daily

Buy the solutions: PM @ Engineering Daily