Learning Forum

[Hamid Dehkordi]

I am trying to simulate vortex tube. Vortex tube is a mechanical device that separates a compressed gas into hot and cold streams.

The flluid flow setting I used:

Incompressible flow, K-e, tetrahedral mesh, velocity inlet, pressure outlet, steady state, apply energy equation but I have two problems:

Convergence is not very good

and the heat transfer does not happen in the pipe, I could not get  neither temperature drop nor reverse flow in the pipe

 

[Federico Alzamora Previtali]

Hello Amid, 

why do you say convergence is not good? It looks pretty good to me, you just might need a few more iterations.

[NickFL]

Wow you chose a challenging problem. Or did it chose you?

The convergence looks fine. If this was my final run I would continue to solve until the residuals "flatline", but for model development and debugging this is good enough.

I do not see a control at the end, usually a cone or something, that forces some of the stream back. Is this in your model? Also we do not see temperature here. But what causes the temperature to change. And how is that reflected in your model? There is a big something in the physics that seems to be missing.

Also I would review your turbulence model. I would recommend looking at what people typically use for hydrocyclones--these have similar high swirl properties.

[Hamid Dehkordi]

Hi

Thanks for the reply. I will modify the end to create a stagnation point and create a reverse flow. 

Question 1: should not consider the flow as compressible instead of incompressible?

Question 2: The main physical phenomenon of the vortex tube is the temperature separation between the cold vortex core and the warm vortex periphery fully explained with the work equation of Euler.

What we considered was incompressible flow, turbulence equation, solving Navier-Stokes, and energy equation. I am not an expert in the dynamics of gases. Is there anything or any equation we need to consider other than what I mentioned?

Thanks

 

[NickFL]

Q1: Are you running fully incompressible (constant density)? What is the temperature and pressure difference you are expecting?

Q2: Let me ask it a different way. What are the boundary conditons you are using?

I suggest you look over the following (I believe this one is free): https://doi.org/10.1038/s41598-022-19779-0

[Hamid Dehkordi]

Hi

Total Pressure inlet, environmental pressure hot end and cold end. I let the software calculate the hot end and cold end temperatures.

input: total pressure: 600kpa

Out put both hot and cold ends: 100kpa

for the total pressure 600kpa, -10C cold end and 87C hot end

I read many papers but I am not sure if I applied physics properly. there are two problems: 1. I can not obtain the temperature mentioned above 2. I can not see reverse flow from hot end towards cold end too.

[NickFL]

 

You are expecting a temperature difference of 97 degrees and a pressure drop less than 0.5 bar? Unless have something going on that is much more efficient than a traditional vortex tube, that does not sound reasonable.

EDIT: If the Prof., who is 2019 received a $20k project to study vortex tubes, had used that money for ANSYS training or to support a good post-doc who could model this in a couple of months, maybe he wouldn't be on here asking for help from volunteers. Unfortunately, given the circumstances, I will step away from a project that I found interesting at the beginning.

 

[Hamid Dehkordi]

I did not find your reply relevent to what we asked here. The tradintional vortex tube simulation is working just fine. These data are the experimental data obtained from filed measurement of the vortex tube.