What happens inside the nitrous oxide bottle at the critical temperature?
When nitrous oxide transitions to a supercritical fluid at 97.5F, distinct liquid and gas phases no longer exist. All of the nitrous oxide in the bottle becomes a homogeneous fluid phase. Above the critical temperature, orientation of the siphon tube is irrelevant. However, what happens as the nitrous oxide transitions to a supercritical fluid is very relevant. Click on the following link to the University of Leeds Supercritical Fluids site for pictures of carbon dioxide undergoing phase transition. Nitrous oxide will behave in a similar manner. Near the critical temperature, the liquid meniscus starts to disappear and the liquid and gas phases become less distinct. If you are operating your nitrous system with the bottle just below the critical temperature, the siphon tube will not consistently draw liquid and you can expect surging as the nitrous oxide mass flow rate varies. The conclusion is that the system should never be operated just below the critical temperature. Since temperat
