Nozzle Design Help: 6 bar Outlet Pressure, 36L/m Flow Rate

[NeiLL]

Nozzle designing help !

hii .
i am supposed to design a converging nozzle for water flow
Its outlet pressure should be 6 bar and flow rate is 36L/m
. no. of nozzles are 3 .
this is the only data i have .
.i don't know how to proceed . i think its less data but its only i have . so what assumption i have to take ?

 

[jehan60188]

you need information on the input

thermodynamics of a nozzle (at steady state)

0 = Q-W - m(h1-h2 + ke1-ke2 + zg1-zg2)

Q = heat exchange = 0
W = work = 0
ke = kinetic energy = NOT ZERO
zg = potential energy = zero change
h = enthalpy = NOT ZERO
m = rate of mass flow = p*A*V = density * area (of nozzle)* velocity (of water)

you need to know h or KE of the input to be able to do a TD analysis

 

[jehan60188]

i guess you can assume 36 L/min will be input. at room temperature, for "slow enough" water, the specific volume will be .001 m^3/kg at 1 atm (10^5 pa, 1 bar)
but this will change depending on the input pressure

i don't remember if enthalpy and specific volume are closely related, but you can look up steam tables for water. near those results, you can probably find the properties for liquid water
http://www.engineeringtoolbox.com/water-thermal-properties-d_162.html
(might have what you need, but poke around and you'll find something better)

without making large assumptions, I don't think I can be much more help
good luck!

 

[Travis_King]

I don't know if you meant this, but the only way to control pressure out of a nozzle is to drop it. If your system is supplying 5 bar, then you won't see your required 6 bar. What you need is a system that's at, say, 7 bar supplying your nozzles.

From this, knowing the flow rate required, you can size an appropriate nozzle for a Cv (or appropriate term for nozzles). Basically, you can size the nozzle such that, for a given flow rate you will get a 1 bar pressure drop.

Obviously, you will also need to ensure that the system is supplying approximately 108 L/min (so that each of the 3 nozzles will see 36 L/min).
If it does not, then your problem is trickier.

You need to know:
Capacity (L/min) of existing system
Head/Pressure (ft / psi / bar /etc) of existing system at the point of use