## Sudden expansion in duct

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Last edited by Expo on Thu Oct 24, 2013 2:26 pm, edited 1 time in total.

### Re: Sudden expansion in duct

Here is what I have with pressure drop calculator just for sudden expansion:

1. volume flow rate (q):

q : 0.75 m3/s

3. pipe length (L):

L : 1 mm

4. pipe diameter (D):

D : 120 mm

5. pipe roughness (kr):

kr : 0.1 mm

6. density (ρ):

ρ : 1.293 kg/m3

7. kinematic viscosity (ν):

ν : 17.3 mm2/s

8. dynamic viscosity (μ):

μ : 2.2368898E-005 Pas

9. K factor - minor losses coefficient (K ):

K : 1

10. velocity (V):

V : 66.31455 m/s

11. cross section area (A):

A : 11309.734 mm2

12. friction coefficient (f):

f : 0.019525288

13. Reynolds number (Re):

Re : 459985.38

14. pressure on the pipe start (p1):

p1 : 3 kPa

15. pressure on the pipe end (p2):

p2 : 0.15647608 kPa

16. pressure drop (p1-p2):

p1-p2 : 2.843524 kPa

So pressure drop is about 2.8 kPa.

Can you tell me about the calculator you used and provide me inputs?

1. volume flow rate (q):

q : 0.75 m3/s

3. pipe length (L):

L : 1 mm

4. pipe diameter (D):

D : 120 mm

5. pipe roughness (kr):

kr : 0.1 mm

6. density (ρ):

ρ : 1.293 kg/m3

7. kinematic viscosity (ν):

ν : 17.3 mm2/s

8. dynamic viscosity (μ):

μ : 2.2368898E-005 Pas

9. K factor - minor losses coefficient (K ):

K : 1

10. velocity (V):

V : 66.31455 m/s

11. cross section area (A):

A : 11309.734 mm2

12. friction coefficient (f):

f : 0.019525288

13. Reynolds number (Re):

Re : 459985.38

14. pressure on the pipe start (p1):

p1 : 3 kPa

15. pressure on the pipe end (p2):

p2 : 0.15647608 kPa

16. pressure drop (p1-p2):

p1-p2 : 2.843524 kPa

So pressure drop is about 2.8 kPa.

Can you tell me about the calculator you used and provide me inputs?

Pipe flow calculations - since 2000

### Re: Sudden expansion in duct

Thank you for taking the time to reply.

I didn't use any calculator inputs for the expansion of the ducting, other than using the K factor calculator, I was just using the minor loss equation. I have realised that in my previous post I gave a head (loss) of 55m, and then considered this as a water head to get 540kPa. If using air as the media (which I guess is correct) it brings the head loss to around 67Pa (p2 - p1 = h x specific weight).

It's been quite a while since I've done any fluid calculations, so please excuse any stupid assumptions.

Looking at your numbers above, there is a 95% pressure loss as the pipe changes section, which as I understand it means 95% of the energy in the air flow has been dissipated due to friction/turbulence within the flow. This seems like a very large loss, especially as when using the minor loss equation I get a figure of 67Pa (which does seem very small).

To shed a little more light on the application, I require a volumetric flow rate of 0.75m^3/s at a pressure of 2kPa at the end of the ducting. Losses throughout the rest of the ducting and air filter come to about 300Pa, so I was thinking a fan that can provide the required flow at 3kPa should be sufficient.

I didn't use any calculator inputs for the expansion of the ducting, other than using the K factor calculator, I was just using the minor loss equation. I have realised that in my previous post I gave a head (loss) of 55m, and then considered this as a water head to get 540kPa. If using air as the media (which I guess is correct) it brings the head loss to around 67Pa (p2 - p1 = h x specific weight).

It's been quite a while since I've done any fluid calculations, so please excuse any stupid assumptions.

Looking at your numbers above, there is a 95% pressure loss as the pipe changes section, which as I understand it means 95% of the energy in the air flow has been dissipated due to friction/turbulence within the flow. This seems like a very large loss, especially as when using the minor loss equation I get a figure of 67Pa (which does seem very small).

To shed a little more light on the application, I require a volumetric flow rate of 0.75m^3/s at a pressure of 2kPa at the end of the ducting. Losses throughout the rest of the ducting and air filter come to about 300Pa, so I was thinking a fan that can provide the required flow at 3kPa should be sufficient.