BAE 2023 Physical Properties of Biological Materials Spring 2009

Exam 2

Name:______

Answer all of the questions below. The last question is an extra credit question. Each is worth 10 points (including the extra credit question). Partial credit is possible so show your work, please.

1.  Find the NPSHa of the following system…. (show your calculations)

2.  Operating at 3600 rpm, a centrifugal pump produces 950 gpm at 160 ft total head. What would the capacity and total head be if a motor running 1760 rpm was used to drive the pump (direct coupled, no gear reduction)?

3.  A ventilation system has a circular 18” outlet. The fan produces 9850 cfm at 5.4 inches (density = 4.30 x 10-5), powered by a 30 hp electric motor. Determine the total pressure of the system, total efficiency and static efficiency.

4.  What would the overall sound power level be if 4 identical fans, each with a sound rating of 89 dB, operated at the same time? Would this overall level meet OSHA standards for an 8 hour work day? Why or why not?

5.  Calculate the TDH for this system:

6.  What is the minimum amount of air required to sort corn kernels from corn cobs?

7.  Why is it difficult to sort wheat heads (threshed) from wheat straw?

8.  Four fans are installed in parallel with each other. Fan one produces 2400 cfm at 7”. Fan two produces 3200 cfm at 7” and Fan three and Fan four each produce 1500 cfm at 7”. What is the resultant airflow (cfm) and pressure (inches)?

9.  What kind of fan exhibits self-limiting power characteristics?

10.  Calculate the HP required for a bucket elevator that lifts wheat (60 lb/bu) 99 feet with 8 inch wide buckets similar to figure 8.10(a). There are 125 buckets included on the chain and the belt speed is 35 ft./min.

Extra Credit Problem:

A company wants to move Styrofoam packing materials (peanuts) from a large box on the floor into the top of a hopper 20 foot tall that feeds the dispensing mechanism (see figure below) to fill their shipping boxes upon demand. What kind of a conveyor would you suggest they use to accomplish this task and why?