Parallel flow pipe network help 4

[hydronicengr]

Let's say I have a simple parallel flow problem as shown in the attachment. The flow is pressurized and the downstream of the return goes back to a piping system that is negligible. It does not vent to atmosphere.

I've tried reading up on the subject, but I got stuck at a certain point. At point A, I know that the flow going in must equal the flow going out to the two pipes. Therefore, it will look like Q = Q1+Q2. Expanding Q1 and Q2 gives me V*A for each respective pipe.

I also know that the head loss of Pipe 1 must equal the head loss of Pipe 2. Expanding those equations, I find that I am faced with an unknown, which is the friction factor for each pipe. The friction factor can be explicitly calculated using the Swamee and Jain formula, but is dependent on the Reynolds Number, which is dependent on the flow velocity, which is ultimately dependent on the flow rate of each of the pipes. After getting the friction factor, everything else is easy. Simply plug the velocities from the head loss equations back into the Q formula shown above and solve for the unknown.

I know one can attain the correct friction factor value by many iterations, but is there a way without doing iterations by hand or by Excel and not fancy software?

Also, how would I find the total pressure loss of the system?

Thanks!

 

[davefitz]

The static pressure upstream of each of the "dispense pipes" will increase as you move from the center of the header( high velocity, high velocity head, low static pressure) to the dead end of the header( low velocity , low velocity head, high static pressure)Therefore the flow out of the end dispense pipes will be greater than in the middle of the header.

Nasa addressed this issue in the fuel distribution headers to their large rockets ( as you can view at the Houston space center or in the smithsonian A+S museum) by tapering down the header diameter as you proceed from center to end, to maintain a fixed header velocity , fixed velocity head, and constant static pressure at the inlet of each fuel discharge nozzle.

If there is only one flow case to contend with then you can address this by providing differential orificing at the inlet to each dispense pipes.