How do I calculate filling a heat exchanger with nitrogen? Need help?
Thread Content
This post was last edited by Desert Fish on 2015-8-27 at 14:11. Nitrogen was introduced into the heat exchanger until the pressure reached 0.4 MP (gauge pressure), after which the nitrogen supply was turned off and helium was used to raise the pressure in the heat exchanger to 0.5 MP (gauge pressure). Before nitrogen is filled in, the heat exchanger is at atmospheric pressure and contains air. May I ask what the helium concentration is? What is the helium partial pressure?
Is it nitrogen pressure or helium pressure? Because there is nitrogen in the air itself. How can the pressure increase in the later stages?
It is helium. First, fill it with nitrogen to 0.4 MPa, then fill it with helium to 0.5 MPa
The helium partial pressure is 0.1 MPa ................
Helium 0.1/0.6, nitrogen 0.479/0.6, oxygen 0.021/0.6; other components in air are ignored. 0.6 is absolute pressure.
If it’s a vacuum inside, then is it not necessary to apply 0.1 MPa?
It was already said that the inside contained air at normal pressure before nitrogen was filled in. The values of 0.4 and 0.5 MPa mentioned later refer to gauge pressure again.
Let’s start with two assumptions: 1. Before pressurization, the container contains 20% oxygen and 80% nitrogen, with all other components being negligible； 2. The pressurization process is a constant-temperature process. Since the final total pressure is 0.6 MPa g, which is below 1.0 MPa a, it can be considered an ideal gas. Before pressurization, the pressure is at atmospheric level, with a total pressure of 101.325 kPa. The partial pressure of oxygen is 101.325*20% kPa = 20.265 kPa, while the partial pressure of nitrogen is 101.325*80% kPa = 81.060 kPa ； During the first pressurization, nitrogen was introduced until the pressure reached 0.4 MPa g, resulting in a total pressure of 501.325 kPa a. The partial pressure of oxygen remained unchanged at 20.265 kPa, while the partial pressure of nitrogen increased by 400 kPa, reaching 481.060 kPa. During the second pressurization, helium was introduced until the pressure reached 0.5 MPa g, giving a total pressure of 601.325 kPa a. The partial pressures of oxygen and nitrogen stayed the same at 20.265 kPa and 481.060 kPa respectively, while the partial pressure of helium increased by 100 kPa. The final partial pressure of helium was 100 kPa. The volume fraction of helium is calculated by dividing its partial pressure by the total pressure: 100/601.325*100% = 16.6 v%