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P_vapor is calculated with CoolProp by solving for nitrous temperature given manifold pressure and density, then using temperature and a quality of 0 to solve for saturation pressure. This result, combined with a low orifice length/diameter ratio implies that flow will remain SPI. The Dyer Model was chosen primarily because it was designed to account for supercharge, as opposed to purely self pressurized. On Osiris, nitrogen is used to supercharge the nitrous.
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From these results, the flow regime was assumed to be SPI and the coefficient of discharge 0.8. From these assumptions, the ideal orifice area could be calculated and used to determine orifice geometry. An additional orifice was added at the base of the pintle tip to prevent flow instabilities and heat damage. It tip melting; if no hole there, nitrous will stagnate and be trapped underneath the radial orifices, causing it to flash boil, which then lets the hot gas melt the tip. The hole was sized based on the difference between ideal and actual orifice area.
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