[khoopes]

I am simulating air flow through a pipe. I am setting the wall temperature at 20 [K] less than the inlet temperature. My issue is that the massflow average temperature steadies out near the end of the pipe, and has the logarithmic shape axial distribution that I anticipated, but it steadies out at about 0.5 [K] above the wall temperature, I thought that it would approach the wall temperature and the delta T would approach 0. Is massflow average the correct temperature to use? Also, my mach number is ~0.05, should I use thermal or total energy, or does it mater? The flow is laminar. RE based on pipe diameter of about 400.

Thanks,

Kevin

[Opaque]

May I ask what is odd in the results ?

The fluid will reach the wall temperature at the "infinite length" of the pipe. Is the pipe long enough for the fluid to reach uniform temperature across the section of the pipe. Otherwise, there is a radial profile, and the mass flow average will never be Twall.

Hope the above helps,

[khoopes]

Originally Posted by Opaque

May I ask what is odd in the results ?

The fluid will reach the wall temperature at the "infinite length" of the pipe. Is the pipe long enough for the fluid to reach uniform temperature across the section of the pipe. Otherwise, there is a radial profile, and the mass flow average will never be Twall.

Hope the above helps,

I think what I do not like about the results is that the temperature difference between the wall and the massflow average temperature does not get to zero, but the axial temperature gradient does get to zero. So there is still a 0.5K dt between wall and fluid, but there is no temperature drop in the fluid.

If I am understanding you correctly you are saying maybe it just needs more time to get closer to the wall temp, but I think what I am seeing is that the temperature is not changing anymore.

This leads me to get a zero htc near the end of the tube since I have a finite delta t (from mass flow average) and a vanishingly small q (from enthalpy change). Is this the correct approach to calculate htc?

Thanks for your help.

Kevin

[Thomas MADELEINE]

how do you get these result ? (with a plane, a curve ?)

For me supposing you have the average temperature over a small area (massFlowAve), and you get that area closer and closer to the wall it will get closer and closer to your wall temperature.

But your fluid is only at wall temperature at the first integration point of your first cell (in wall direction) so if you want to see the exact wall temperature I will not use an massFlowAve function but directly the temperature (along a radius by example).

[ghorrocks]

Are you looking at the total temperature? That will be higher that the static temperature, and the static temperature should match the wall temperature.

[sircorp]

Originally Posted by khoopes

I am simulating air flow through a pipe. I am setting the wall temperature at 20 [K] less than the inlet temperature. My issue is that the massflow average temperature steadies out near the end of the pipe, and has the logarithmic shape axial distribution that I anticipated, but it steadies out at about 0.5 [K] above the wall temperature, I thought that it would approach the wall temperature and the delta T would approach 0. Is massflow average the correct temperature to use? Also, my mach number is ~0.05, should I use thermal or total energy, or does it mater? The flow is laminar. RE based on pipe diameter of about 400.

Thanks,

Kevin

Kevin

Did you try to set facet vector temp rather average ? Also near the end of the pipe refine the mesh(Adapt) & check it if you still get 0.5K difference. As the sample size(data points) increases, average may get better.

Shane