Question

I'm currently dealing with an application involving gases. I have pure nitrogen as a pressurizer and eventually water vapour (only if condition for evaporation or boiling are met). I wanted to ask to which extent can I consider pure species or mixture as ideal gases. I know that nitrogen reaches critical condition when pressure is about 33 bar. My application would have initially a small amount of nitrogen pressurized at 17 bar approximately. Is it better to switch to a cubic equation of state like the Peng - Robinson one? Would that justify the additional complexity with respect to the ideal case?

Answer 1

The ideal gas law can be used for nitrogen at standard conditions but may become inaccurate at the pressurized conditions indicated. If high precision is needed in the application, using the Peng-Robinson equation to account for non-ideal behavior may be more appropriate, whereas for minor deviations from ideality, the ideal gas law may suffice.

Step-by-step explanation:

When dealing with gases in an application, it is essential to evaluate whether to treat the gases as ideal or to use a more complex equation of state. Nitrogen can often be approximated as an ideal gas at standard conditions, but in your case where the nitrogen is pressurized at 17 bar, which is above atmospheric pressure, its behavior may deviate from ideal gas law predictions.

While the ideal gas law is a good approximation at high temperatures and low pressures, it may not be accurate under all conditions, such as when gases are near their critical points or at high pressures. The Peng-Robinson equation of state is a more sophisticated model that can more accurately predict the behavior of gases under non-ideal conditions by considering the size of gas particles and intermolecular forces.

If precision in your application is critical, and you anticipate that the properties of the gas have a significant impact on its performance or safety, then it may be better to use the Peng-Robinson equation. However, if the expected deviations from ideal gas behavior are small and would have a negligible impact on the application's outcome, the added complexity may not be justified.