Pressurization Time (Nitrogen)

In summary, the conversation discusses the calculation of pressurization time for a part with an internal volume of 24.5mm^3 at environment pressure of 1.01325bar. The question is how long it would take for the internal volume to reach 1.12bar when fed with 1.14bar of nitrogen through an inlet diameter of 0.05mm. The speaker mentions using Solidworks CFD simulation and getting a result of 0.36ms, while in reality it takes around 20ms. The expert calculates a lower limit of at least 8.6ms based on energy conservation and the inflow of gas, but acknowledges that this value may be off due to not considering adiab
  • #1
Lee Chong Chi
2
0
Hi All Expert...

I have a question need help.

I have a part with internal volumme 24.5mm^3 at environment pressure 1.01325bar.

When I feed it with 1.14bar (nitrogen)...with a inlet Dia. 0.05mm

How can I calculate the pressurization time for the internally volumme up to 1.12bar

assume the initial condition at
1.01325bar & 20°CI try to use solidworkd CFD to do simulation, and the result show is 0.36msec
And in actual, the part take update to 20msec

Thanks in advance for all the help.
 
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  • #2
It will depend on the inlet. How do you get 0.36ms in the simulation? A very rough estimate gave me 12ms. Being wrong by a factor of 30 would surprise me.
 
  • #3
mfb said:
It will depend on the inlet. How do you get 0.36ms in the simulation? A very rough estimate gave me 12ms. Being wrong by a factor of 30 would surprise me.
Hi Mfb...

0.36ms get from solidworks CFD simulation.
at 1st i thought my CFD simulation is wrong. Becuase I always get below 1ms.
Then I send my 3D to my Solidworks CFD expert, they run it thru CFD and get 0.36ms (attached the plot i get from the expert)

Possible I know how you get 12ms. I aspect your calculation is close.
Actual 20ms I didn't exclude the sensor respond time and valve respond time.
 

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  • #4
Let's calculate a lower limit:
Energy conservation gives an upper limit on the gas speed, this is given by ##\frac{1}{2} \rho v^2 = \Delta p##. Using the largest available pressure difference and the smallest relevant density, I get v=141m/s. Note that the pressure difference and therefore the speed will go down over time.
Neglecting temperature changes and the small difference between nitrogen and air, you need a mass of ##V\rho \frac{\Delta p'}{p_0} = 3.34\mu g## flowing in. With the given cross-section of ##\pi \cdot (25\mu m)^2##, the speed of 141m/s from above and the density of nitrogen at 1.14 bar (~1.4 kg/m^3), this takes at least 8.6ms.

This value is wrong for two reasons that go in opposite directions:
- I used the maximal pressure difference. Pressure difference will go down, so the inflow will reduce significantly over time which means the whole process takes more time.
- I did not take into account that compression is probably adiabatic (?) or at least not completely isothermal. Filling in 5% additional gas could give of the order of 5% higher temperature (didn't calculate it precisely, some parts are expanding some get compressed), which would lead to the 10% pressure increase you are looking for. So the gas volume that has to flow in can be significantly lower. This is not a factor of 25, however, it is more like a factor of 1.5 to 3.

Your simulated pressure exceeds 1.14 bar and continues to rise afterwards. Do you have an explanation for that? What happens if you run the simulation even longer? In principle oscillations could lead to a higher pressure, but the timescale does not look that long earlier in the process.

Lee Chong Chi said:
Actual 20ms I didn't exclude the sensor respond time and valve respond time.
Can you get measured times for other pressures? That would help to see how long those times are.To get the 12ms I used a guess of 100m/s for the velocity and 0.1 for the delta p/p ratio instead of the real numbers.
 

What is pressurization time?

Pressurization time is the amount of time it takes for a container or system to reach a desired pressure level, typically measured in seconds or minutes.

Why is pressurization time important?

Pressurization time is important because it affects the efficiency and safety of a system. If a system takes too long to pressurize, it can result in wasted time and resources. On the other hand, if a system pressurizes too quickly, it can cause damage or unsafe conditions.

How does nitrogen affect pressurization time?

Nitrogen is commonly used in pressurization because it is an inert gas that is readily available and does not react with other substances. However, nitrogen can also have a slower pressurization time compared to other gases due to its lower compressibility.

What factors can influence pressurization time with nitrogen?

The size and shape of the container, temperature, initial pressure, and flow rate of nitrogen can all influence the pressurization time. The type of valve used and any obstructions in the system can also impact the pressurization time.

How can pressurization time be optimized with nitrogen?

Pressurization time can be optimized by using the appropriate valve and flow rate for the system, ensuring the container is properly sized for the desired pressure, and minimizing any obstructions or leaks in the system. It is also important to consider the temperature and initial pressure of the system when determining the optimal pressurization time with nitrogen.

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