Need some help with a gas flow problem

[steves1080]

I have a steel box that I am trying to purge with gaseous nitrogen (GN2). Just say the dimensions are A x B x C (ft^3). I would like to maintain a continuous purge at a very minimal pressure (~0.5 inH20). To conserve money (i.e. so that I don't need to purchase an expensive flow regulation device), I am simply looking to tie into an already-existent GN2 supply line nearby (to get my flow in) and then add a vent line to get my flow out. The net flow should maintain a very low positive pressure inside the panel. The supply line is pressurized to 100 psi, so I'd need to add an orifice to prevent overpressure. My question is: how can I size my vent and orifice to ensure that my box remains at my requirements (positive low pressure purge)? Do I need a low pressure check valve? Will the outlet diameter or the inlet diameter need to be larger (or does it not matter)?

Thanks for the help!

 

[Navin A S]

To size the vent and orifice to maintain a positive low pressure purge in the box, you'll need to take into account the dimensions of the box (A x B x C), the desired pressure (0.5 inH2O), the flow rate of the GN2 supply line (100 psi), and the gas properties of nitrogen. You can then use Bernoulli's equation to calculate the required flow rate and size the orifice, vent, and check valve accordingly. A low pressure check valve may be necessary to maintain the desired pressure within the box. Generally, the inlet diameter needs to be larger than the outlet diameter to ensure the proper flow rate.