Pressure drop 1

[Engprofile]

Hi,

I am trying to determine the pressure drop across a pipe reduction, from 6" pipe to 1" pipe. The volumetric flow rate is 4.5m3/min.

Is there a k value for a reduction of this size? or is there an equivalent length for a reduction in pipe of this magnitude?

I would like to see how the pressure varies as the flow rate varies.
assume kinematic viscosity = 0.0000011m2/s
Density = 998kg/m3

Any help with this problem would be greatly appreciated

 

[Artisi]

I would be more interested in the friction loss in 1" pipe than any pressure drop from 6" to 1" at 4.5m3/min. or is this a typo and it should be 0.45m3/min.

 

[micalbrch]

Agree with Artisi. Depending upon the length of the 1" section the friction loss there will be much more of importance.

 

[Engprofile]

Should have been more clear. the 6inch line has a 1" nozzle on the end. I am interested to find out how much backpressure or restriction the nozzle has. And yes I do mean 4.5m3/min.

 

[Artisi]

Yes considering the head loss at this flowrate(approx 1200USgpm) thru 1" dia. pipe is somethging like 700ft loss for a 1'(one foot) length of pipe.

 

[Engprofile]

there is not a length of 1" pipe it is simply a nozzle (1inch in diamter) on the end of the 6inch pipe. This device is used for cutting rock. I am working out all the pressure losses through the pipe (i.e valves etc.) and would like to know how much pressure loss will result from the reduction due to the nozzle.

 

[Artisi]

Sorry was sending my last message as you were posting-
suggest you google flow through nozzles - a heap of info there for you.

 

[Artisi]

"I would like to see how the pressure varies as the flow rate varies."

The pressure varies as the square of the flowrate.

Double the flowrate the presure increeases x 4

 

[micalbrch]

2720 psi at 4.5 m³/min and 1" nozzle size.

 

[ione]

Rearrange the formula in the link below and solve it for the pressure drop ?p

http://www.lmnoeng.com/Flow/SmallOrificeLiq.htm#equations

 

[Engprofile]

Can you explain how you got 2720psi? seems very high for a line component pressure drop even at this high flow rate.

 

[katmar]

Engprofile, please also see my post in the thread "Flow through pipe at 40 psi".

To accelerate the water to give 4.5 m[sup]3[/sup]/min through a 1" nozzle (i.e. 440 ft/sec) takes 1300 psi. The pressure drop through the 6" to 1" reducer will depend on the profile of the reducer. A 30 degree conical reducer would give a pressure drop of about 300 psi. So I would say you need about 1600 psi in the 6" pipe to give this flow.

All numbers are approximate because we do not have accurate dimensions.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[micalbrch]

I used velocity² x density/2. That gives me the pressure. But I just discover that I made a mistake when calculating the velocity. 1585 psi is now what my calculation leads to. Sorry! I used 25.4 mm nozzle diameter.

 

[ione]

Katmar,

Don’t know whether you’ve read my post (ref. 23 Jun 10 5:41). Using the approach reported there I got approx 2900 psi pressure drop (with a coefficient of discharge C = 0.95). Cannot understand how you’ve calculated 1600 psi, could you expand?

 

[katmar]

ione, I used the same approach as micalbrch, except that I took my ID as 26.64 mm and got 1300 psi as the velocity head. If I use 25.4 mm I get the same value as as micalbrch. I got 300 psi for the reducer using a correlation by Hooper (the 2K man) for a conical reducer. If I substitute a sudden reduction for the reducer I get 930 psi. Adding the sudden reduction to the velocity head (for 25.4 mm) gives 1585+930=2515 psi. You and I are within 13% of each other. Without detailed drawings of what it all looks like I would not argue over that difference.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[ione]

katmar,

thanks for your swift and detailed (as always) reply.

 

[Engprofile]

Thanks everyone for this very useful information. Problem solved.