Learning Forum

[claudiabogdan]

Hello ANSYS Community,

I have some doubts regarding my model. I am running a countercurrent gas to gas heat exchanger with working fluids - helium and hydrogen. The mesh has the skewness lower around 0.85. I am using k-epsilon model and Simplec method. As BC i have for inlet - velocity and temperature and for outlet - pressure outlet with gave pressure. Mention that the heat exchanger is around 50mm high. The residuals after 100 iteration looks like in the image bellow.

My question is, should i trust this result? Seems like the temperature drop is to high. Mention that no warning have shown during running the solution.

Secondly, for solids - i use steel and copper OFHC with 1200 W/mK thermal conductivity, but if I switch to 386 W/mK not a substantial change - around 1,5K. Shouldn't there be a bigger difference considering that the conductivity is about 3 times lower?

[Rob]

100 iterations may not be enough, run 1500 and see how it is. The only models that run within 100 iterations are the tutorials! nCheck the mesh, and add monitor points: how is the quality, resolution and monitor stability? nRe the conductivity; what governs the rate of heat transfer in a unit? n

[claudiabogdan]

Well, I completed with the interfaces that I omitted and now the heat transfer works better.nAbout the conductivity, it is still on hold; I use copper with higher conductivity to accelerate heat transfer. Can not understand why I do not have different results regarding temperature,

[Rob]

Have a careful look at the heat transfer: what is the limiting step to this? Ie which of the heat transfer mechanisms dominates (fluid to solid, solid conductivity or solid to fluid)? n