Need help to find average velocity and pressure drop in duct

In summary, to meet the required volume flow rate of 5000 l/s, the average velocity of the air must be 13.88 m/s in a duct size of 600 mm x 600 mm. To overcome frictional losses in the duct, a fan would need to produce a pressure of 110.63 KPa and would require a power of 555 Kw.
  • #1
mchi6aa2
2
0

Homework Statement



1. the average velocity of the air to meet the required volume flow rate,
2. the pressure a fan needs to produce to overcome the frictional losses in the duct,

2. Relevant Information

Duct size - 600 mm x 600 mm which operates at 3 Pa/m.
The air path is 87 meters from intake to discharge including allowances for grilles, bends and dampers.
The pressure drops per meter are for the required volume flow rate of 5000 l/s. Average velocities in the duct can be calculated by considering the volume flow rate and cross sectional area of the ducts.

Please help. Thanks

Danny
 
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  • #2
Thats the way I did. I am not sure is it right or wrong:

First , Head required to overcome friction Losses and to maintain
velocity head is to be calculated.

Q= 5000 l/s = 5 m³ /s , A= 0.6 * 0.6 = 0.36 m² , Av . Velocity = Q/A =13.88 m/s

Velocity head = V²/2g = 9.83 m of air coloumn ,
frictional head to overcome by the fan = 3*87=267 Pa

Fan pressure = 1.145 * 9.83 * 9.8 KPa + 267 Pa = 110.63 KPaFan power required = PQ = 110.63 * 5 = 555 Kw
 

FAQ: Need help to find average velocity and pressure drop in duct

What is the formula for calculating average velocity in a duct?

The formula for calculating average velocity in a duct is: V = Q/A, where V is the average velocity, Q is the volumetric flow rate, and A is the cross-sectional area of the duct.

How do I measure the pressure drop in a duct?

To measure the pressure drop in a duct, you will need a differential pressure gauge. This device measures the difference in pressure between two points in the duct. Place one end of the gauge in the duct and the other end outside of the duct to get an accurate reading.

What factors can affect the average velocity and pressure drop in a duct?

Some factors that can affect average velocity and pressure drop in a duct include the size and shape of the duct, the type of fluid flowing through the duct, and any obstructions or bends in the duct. Air temperature and humidity can also impact these measurements.

How can I improve the average velocity and pressure drop in a duct?

If you are looking to improve the average velocity and pressure drop in a duct, you may want to consider increasing the diameter of the duct, reducing any obstructions or bends, or using a smoother material for the duct walls. Additionally, choosing a fluid with a lower viscosity can also help increase velocity and decrease pressure drop.

Can I use the same formula to calculate average velocity and pressure drop in any type of duct?

Yes, the same formula can be used to calculate average velocity in any type of duct. However, the pressure drop may vary depending on the type of fluid and any other factors that may affect the flow of the fluid. It is important to take these factors into consideration when calculating pressure drop.

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