Flow of air in ducts

Problem Statement: You are assigned a project to design an exhaust system for a laboratory fume hoods where acids are used. The hood has an opening that is 6' wide x 1' high. The minimum face velocity must be 150 ft/min (average across the face). The entrance loss for the hood is 1.78 x face VP and the loss where the hood connects to the duct is 0.40 x duct VP.

The duct, fittings, and fans are fabricated from FRP (fiberglass reinforced polyester). The duct between the exhaust fan inlet and the exhaust hood outlet is 150' long. There are 3 - 90 degree elbows in the 150' run plus one butterfly dumper near the hood.

There may be a round-to-round transition on the fan inlet and discharge. (You can assume the transition will be 12 inch in length and the loss coefficient can be determined using the information. Once you have the loss coefficient, the fitting head loss is calculated.)

On the fan outlet, there is also 1 - 90 degree elbow, and 10' of duct.

All 90 degree elbows are "smooth round" type. Assume the duct layout is done well and there are no "system effects".

An acid fume scrubber is installed to remove the acid from the exhaust. Assume the pressure loss across the scrubber is 2.5 inch wc including the inlet and outlet transitions.

The duct should be sized to a pressure loss per 100 feet of no more than 0.3 inch w.c. Keep in mind that FRP has a lower loss than sheet metal duct. When using sheet metal duct size tables or charts, you can assume the FRP friction loss is only 90% as great as for sheet metal.

Assume the air temperature is 70^oF.

The layout is given, below:

Provide calculations to justify your answers:

1. Specify the diameter of the duct. Choose the nearest even inch diameter that meets the criteria, above.

2. What is the actual loss per 100' for the size duct selected?

3. Indicate the total pressure loss from the hood entrance to the exhaust discharge. Use an Excel spread sheet to do the calculations.

4. Specify an exhaust fan from the New York Blower website. Include flow, static pressure, model, impeller diameter and type (airfoil, forward curved, backward curved, etc.) brake up, rotational speed, motor hp, and inlet/out sizes.

Attachment:- 529579_2_Duct-design-Excel-Sheet6.xls