simple fluid flow question I hope

[what4]

I need to maintain a fairly constant flow rate of liquid nitrogen out of an orifice. The liquid nitrogen is contained in a tank that has an internal pressure of 22psig. My budget is minimal, so I plan on attaching a fitting with a hole drilled though it to the the outlet of the tank to restrict the flow. The flow needs to be 250 mL/min or 0.250 L/min. I need to estimate the diameter of the hole/orifice to produce that flow rate.

I found the following thread on this forum

http://www.eng-tips.com/viewthread.cfm?qid=119094

One response noted the following equations for water:

dL = sqrt(.0444)(QL / sqrtDP)
wheredL = Diameter of orfice / in
sqrt = Square root
QL = Required water flow / gpm
DP = P1 - P2 / psi
P1 = Inlet pressure / psi
P2 = Outlet pressure / psi

or this for other liquids I'm assuming:

dL = sqrt(QL / .0001423 sqrt(DP / r))
wheredL = Orifice diameter / micrometers
QL = Liquid flow rate / mL / min
r = Liquid density

I have a few questions about the 2nd set of equations. I changed all of the units to m-kg-s. In the 2nd set of equations, the units come out to length^2/time instead of just length. Does the constant (0.0001423) have any units that might change this?

Alternative solutions or suggestions would be appreciated.

 

[BigInch]

wow, that's one heck of a conversion factor.

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