The pressure in a reactor fluctuates between 10 and $30 \mathrm{psig}$. It is necessary to feed air to the reactor at a constant rate of $20 \mathrm{lb}_{\mathrm{m}} / \mathrm{h}$ from an air supply at $100 \mathrm{psig}, 70^{\circ} \mathrm{F}$. To do this, you insert an orifice into the air line that will provide the constant flow rate. What size (diameter) should the orifice be?