Temperature increasing for cooling operation in transient CFX

TharunSK · March 26, 2019, 08:44

I have a model of an octagonal room with a machine tool in it. The initial air temperature inside is 34 °C . The inlets have static temperature of 15°C and transient simulations are performed to observe the cooling process. For a rough approximation, I use time steps of 0.5s and total time is 60s. Now, I observe some weird results. The temperature graph on a point inside the air domain (not on machine tool ) shows the starting temperature as 15 °C and increases to 17°C in 60s, even though I had initialized the domain with 34°C and this is a cooling operation.

Please comment on the following:

1. Why is the starting temperature not somewhere near 34°C on the graph?
2. Why is the temperature increasing from 15 when actually it should cool down from 34 to 15.

Gert-Jan · March 26, 2019, 09:44

Usually this is not a problem. So, either your initial guess is wrong or your monitoring point is in the wrong location, or...... Could be anything

ghorrocks · March 26, 2019, 16:45

Please attach your Output file and an image of what you are modelling.

March 26, 2019, 08:44	Temperature increasing for cooling operation in transient CFX	#1
TharunSK New Member Tharun Suresh Join Date: Mar 2019 Location: US Posts: 7 Rep Power: 7	I have a model of an octagonal room with a machine tool in it. The initial air temperature inside is 34 °C . The inlets have static temperature of 15°C and transient simulations are performed to observe the cooling process. For a rough approximation, I use time steps of 0.5s and total time is 60s. Now, I observe some weird results. The temperature graph on a point inside the air domain (not on machine tool ) shows the starting temperature as 15 °C and increases to 17°C in 60s, even though I had initialized the domain with 34°C and this is a cooling operation. Please comment on the following: 1. Why is the starting temperature not somewhere near 34°C on the graph? 2. Why is the temperature increasing from 15 when actually it should cool down from 34 to 15. Last edited by TharunSK; March 26, 2019 at 09:55.

March 26, 2019, 16:45		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Please attach your Output file and an image of what you are modelling. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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March 26, 2019, 09:44		#2
Gert-Jan Senior Member Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,827 Rep Power: 27	Usually this is not a problem. So, either your initial guess is wrong or your monitoring point is in the wrong location, or...... Could be anything