CFD heating simulation

[Anonymous]

Hello everyone. I am designing a hydroponic greenhouse as a university project. Along with all the other features, I am optimizing heating and cooling system doing CFD simulations. Heating is provided by fan which blows air on a PTC cell (110°) . I followed this guide ( https://knowledge.autodesk.com/support/cfd/learn-explore/caas/CloudHelp/cloudhelp/2019/ENU/SimCFD-Tu... ) to simulate this scenario and it works decently. What I am not sure about is if this way to simulate takes into accout the air motion along with heating diffusion. I mean, first I computed steady state air velocity and after a transient heat diffusion, heat spreads over the volume but the way it does looks like a natural convection rather than a forced one (the forced auto convection is set in the simulation) . I tried to simulate heat and motion simultaneously with transient simulation but I get messy results (the volume heats up but often there is strong incoherence between adiacent time steps either suddenly heation or cooling a lot ). I attach some images of the two steps simulation. Thanks for your precious help! 

p.s. for a bit of context, the volume to heat is 20x30x40 cm, the initial air volume is at 20°, the fan has a volumetric flow rate of 5 m^3/h and the air taken from the outside is at 20° too; the temperature target is set at 27°-30° (the green region in the simulated plane)

[frederic.gaillard.7]

Hello 

can you share your cfz file ?

thx 

fred

[Anonymous]

Hello! In the end I managed to get good results using transient simulation for both heating and flux (which seems to me the most appropiate way to act since they both develop simultaneously). I am getting some problems with the cooling though. I can't understand if I set wrong boundaries/initial condition or it other. I attach the .cfz file where you can find the cooling section (where I am having issues at the moment) and the heating one so you could check if everything seems right in that section too. The problem I am getting is that the whole air volume suddently change temperature (withing 0.1 second); hopefully it is an issue related to simulation settings. Thank you for your precious help! (sorry I couldn't include the results because the file would be too heavy to upload)

p.s. the forum doesn't let me attach the .cfz file because it says "content type does not match its file extension" and I can't upload it; I created a shareable onedrive link, hopefully you should still be able to get it  ( https://polimi365-my.sharepoint.com/:u:/g/personal/10559467_polimi_it/EQ9PQpDgwOJJuZ-5G1XJYn0Bw23o6s... )

[frederic.gaillard.7 · Accepted solution]

Hello Lorenzo, 

I find suspicious that your intlet boundary condition has a value of 5m3/s. What it means concretly is the presence of a supersonic flow inside your greenhouse. I don't know what type of plant grow inside your greenhouse but it seems unlikely that life can grow peacefully in those condition.

Thank for clarify 

Fred

[Anonymous]

Wow you are totally right! It is supposed to be 5 m3/h not second! Not it looks definetely better. Let me ask just one more question. Is "auto forced convection" option to be enable when you studying an actual forced convection model? I read something on autodesk site but I couldn't get much about it. Thank you again! You saved me probably hours to find the issue.

Lorenzo

[frederic.gaillard.7]

Hello Lorenzo, 

Auto Forced Convection are usually used for steady state analysis.  It solve the flow field first and once it converged, thermal solution is added to the existing solution. 

Hope it helps 
Fred

[Anonymous]

I thank you a lot for your help. 

Kind regards,

Lorenzo