mass flow rate through a pipe
mass flow rate through a pipe
(OP)
I have a 6000 psig nitrogen cylinder. I'm not sure the setting of the regulator outside of the cylinder. The nitrogen flows to a nitrogen accumulator tank, and fills it so that the pressure in the accumulator is the same as the pressure in the cylinder. On the outside of the accumulator is a fast acting valve. We use this valve to pulse nitrogen into our system. The pipe coming from the fast acting valve is a 3/4' schedule 80 pipe. I need to figure out how to find the flow rate of nitrogen if the fast acting valve goes from closed to 100% open and then closes again in .75 seconds. Any help would be appreciated!!





RE: mass flow rate through a pipe
With the accumulator's volume you can work out the mass change and divide by the number of valve cycles and the time each cycle the valve is open.
RE: mass flow rate through a pipe
There are a lot of unknown features down there. I've gave you the stripped formula. I'm not such a bright student in pneumatics, although I deal with this field a lot, but only when I make the control the rest I leave it to the best
TD2K is right, at least pressure gauge is needed in both chambers. Maybe the best way is to get a flow meter, but you have pretty big pressure involved there.
The flow exactly cannot be found easily, perhaps a simulation in Solidworks / Cosmos flow analysis can help with that.
Cheers!
It's nice to be important, but it's more important to be nice!
RE: mass flow rate through a pipe
Ap[sqrt[(k/RT)*{(k+1)/2}^-{(k+1)/2/(k-1)}]
K=1.4
R=55
T= absolute temp accumulator
RE: mass flow rate through a pipe
All that aside, if you want to know the mass flow rate (which I'm assuming from the title of the thread), then you have to know starting and ending pressure in the accumulator, volume of the accumulator, and possibly pipe volume if it is material. With that, you can determine the mass of nitrogen that transferred in the 0.75 seconds and divide mass by time to get mass flow rate.
David
RE: mass flow rate through a pipe
First, answer the above questions. There are too many unknowns to calculate the answer to enough detail.
Let the tank pressure steady at a known temperature.
Put an ACCURATE calibrated gage on the tank, and record temperature and tank pressure.
Then, cycle the valve once into an empty accumulator exactly as you would do for a normal cycle. Vent the accumulator, reset your piping and system. Record tank pressure.
Repeat the valve cycle, vent the accumulator, reset the system. Repeat 30 times.
Compare start pressure to end pressure.
RE: mass flow rate through a pipe
do you want the mass flow rate as a function of time, or just the mass flow for an opening event ? the previous post is a good way to experimentally derive the latter. i think, with more information, you could mathematically derived the steady state mass flow rate, but some varibles (coefficient of discharge of the valve, viscosity effects of your tubing) are difficult to accurately quantify.
RE: mass flow rate through a pipe
RE: mass flow rate through a pipe
Thanks again for all the help!