topic Re: Problem with result (temperature) in CFD Forum

Problem with result (temperature)

Darius_CAD — Wed, 09 Jan 2019 11:21:08 GMT

Hello!

I am beginner on CFD.

I have part (4 wall, 1 Top, 1 floor, and air). I need to show air distribution on room (by temperature).

At floor I have Heat Exchanger and fan, but on part I not show it. Because I know volume flow rate and temperature. (please look at pictures)

Other data please look at pictures too.

(Volume flow rate 0.17m3/s; temperature 50C.)

I got results, but it is no good because at room have to be about ~25C, but i got ~48C in room.

Maybe anybody can help to mee? any idea?

Thank you very much.

Re: Problem with result (temperature)

frederic.gaillard.7 — Wed, 09 Jan 2019 14:06:08 GMT

Hello Darius,

I think your result are correct regarding to your boundary condition. You apply a temperature boundary condition of 50degC so it's normal that you have a room temperature higher than than 25degC. If you want to decrease the room temperature you will need to add more thermal loss on the wall.

In the model that you share, only one wall has a film boundary condition (0.2W/m2K@18degC). What about the 3 other wall, the celling and the floor ? They must have a film coefficient as well.

***

In a different perspective you should change the geometry of your outlet. I might be usefull to extend your outlet to avoid the recirculation. This phenomena tend to screw your continuity equation that can lead to unrealistic result. In your analysis your 18% off which is significant. See picture below : continuity equation

(((MassflowIn1 +MassflowIn2) - (MassflowOut1 +MassflowOut2)) / (MassflowIn1 +MassflowIn2))*100%
((0.185697+0.185697)-(0.152635+0.153205)/(0.185697+0.185697))*100%

17.65%

This information are available in the result tab in the summary file

Otherwise your simulation look great.

Re: Problem with result (temperature)

Darius_CAD — Wed, 09 Jan 2019 15:28:43 GMT

Frederic,

Thank you for your quick and helping answer. I try fix geometry. (Outdoor wall is one, Other walls are to other rooms.)

1. But should not be seen how the temperature (~18C) of the air mix with the heat temperature (50C)

2. I have example (please look at picture) with similar data and it look diferent. (there are more components, but I think it isn't necessary (maybe necessary would be extract and supply diffusers?).

Thank you very much for your time!

Re: Problem with result (temperature)

frederic.gaillard.7 — Wed, 09 Jan 2019 15:55:17 GMT

Hello Darius,

It's written that you have 30W/m2 heat loss. Do you know where this condition is applied ?
all over the external surface or only on the cold wall ?
Moreover, you have a 0.5ach (air change by hour) which mean you're boundary flow condition must be 0.01125m3/s , not 0.17m3/s. It's probably why you have exterm temperature in your room.

Fred