Yes, I set all regions to have the same pressure. But I believe I should check my simulation setting again. I will check again with your suggestions such as speed or 1D problem. Thanks for your reply.
Thank you for your answer.
I agree the simulation doesn't show the noticeable bulk convection.
So do you think that simulation doesn't look like real nature?
I hoped to model real gas which is around us.
This is a fluid dynamic simulation.
The top area has 100 degrees Celsius.
The bottom area has 0 degrees Celsius.
And both are filled with an ideal gas which is 1-atmosphere pressure.
Two areas are connected through the left small line. Another part is blocked.
So heat transfer can only happen...