[arjun71]

I put my pipe in a cylinder-shaped enclosure to figure out how hot the leak was.
My enclosure (opening) contains 21% O2 and 79% N2.
I set up my leak zone as an inlet for hydrogen. I tried different types of mass flow rates in my hydrogen inlet, and the simulation is running well, but the temperature is not changing in my enclosure.


What should I do now?

[Gert-Jan]

What do you expect? Cooling as a resullt of expansion? Then turn on Total Energy.

[arjun71]

Generally, we know that hydrogen increases temperature when it flow through a leak (the Joule-Thomson effect).
My leak's temperature is not changing from 25 degrees C.
If the temperature does not increase, my result will be worthless.

[Gert-Jan]

Then it should indeed incease in temperature. So, are you running with Total Energy?
If it does not work, I have no idea. No specific experience with hydrogen......

[arjun71]

How can I turn on total energy ?


because I am a beginner in Ansys World.

[Gert-Jan]

ANSYS CFX is not a kind of Chat GPT in which you throw some stuff from a distance and then get an outcome that fits you well.
Therefore you should first do several tutorials on thermal problems and them come back here.

[ghorrocks]

The Joule-Thomson effect is a real gas effect. You cannot model this with ideal gases, so you are going to have to use a real gas model. So this is more complex than "just" a compressible flow simulation, it is real gas compressible flow simulation, probably with a high pressure ratio and high Mach numbers. This is a complex model which will require careful development, and does not sound like a simulation for a beginner to attempt.

[arjun71]

I run with total energy, but there has been no change in temperature.
Moreover, I am using real gas. It's also the same.


According to the Letaure evaluation, I must use N2 and O2 at STP.
I tried this one, too, with high pressure and a high Mach number.


In every method, there was still no temperature change. But velocity is showing good results.

[ghorrocks]

If you are going to try to attempt this complex model then you need to approach it as you would approach any complex model. You need to start with a simple model and add the complex physics one step at a time (or preferably in a series of separate simulations) before doing the final simulation with all the physics you need, and hopefully giving you something close to the correct answer.

I would start with an ideal gas and a simple geometry where it goes through a nozzle. Make sure the pressure difference does not generate supersonic flow (so stay subsonic). Once you have this working, then add the hydrogen real gas. Then model the crack as ideal gas at the actual pressure ratio, before finally modelling the crack at full pressure with hydrogen real gas.

You need to get all the physics sub-models working by themselves before you combine them together. If you run it with everything and it fails, how do you know where the problem is?

[arjun71]

Thank You.I solved my previous problem.


Now,how can i set external ignition on cfx ?

because experiment has an external ignition.

[ghorrocks]

Have a look at the spark ignition model, Theory manual section 7.15.

[Opaque]

Originally Posted by arjun71

Thank You.I solved my previous problem.


Now,how can i set external ignition on cfx ?

because experiment has an external ignition.

How did you solve it? The forum is a two-way street, and everyone benefits from everyone's else experiences.

[arjun71]

I set total thermal energy and made my air domain bigger ,then it works well.

[Opaque]

Originally Posted by arjun71

I set total thermal energy and made my air domain bigger ,then it works well.

Thank you for the feedback.

Sure you mean "Total Energy" since it cannot be both because Total Energy = Thermal Energy + Kinetic Energy