topic Re: Moist Air Mixing in CFD Forum

Moist Air Mixing

Anonymous — Thu, 17 Mar 2016 19:03:42 GMT

Greetings,

I'm running a simulation of mixing two moist air, airstreams, classic HVAC mixing box. One stream at 75F, 50% RH and the other at 40F, 60% RH. When using the "moist air" material model, the scalar quantity (which is the absolute humidity) does not project into the mixing box as expected. The results show almost the same scalar value throughout the box, roughly equal to what is expected for the mixture. Sharp gradients in the box do not exist.

If I run the model using a general scalar and the diffusion coefficient for water vapor in air, I get results that I would expect to see with all of the sharp gradients in the box until the two streams can mix.

Is this the expected behavior when using the "moist air" model?

I've attached images from both scenarios.

Thank you.

Cory

Re: Moist Air Mixing

KubliJ — Sat, 19 Mar 2016 00:37:45 GMT

Hi Cory,

If I understand correctly, using the mosit material model and following the directions in the help generates poor results with no gradient within the mixing volume. However using a scalar mixing and running the analysis shows a gradient mixture in the volume, correct?

Can you share your model? Otherwise give me some time to build a test model and run.

Thanks,

James

Re: Moist Air Mixing

Anonymous — Mon, 21 Mar 2016 12:22:41 GMT

Support file is attached.

Thanks.

Re: Moist Air Mixing

KubliJ — Mon, 21 Mar 2016 16:53:06 GMT

Hi Cory,

Thanks for uploading the model. Unfortunately, I was not able to replicate the issue. I simply went through the model, verified that everything was setup correctly and ran it. The moist air looks like it is mixing correctly, though the analysis is not complete yet.

Out of curiosity, can you tell me what build version of CFD you are running?

Thanks,

James

Re: Moist Air Mixing

Anonymous — Mon, 21 Mar 2016 17:10:47 GMT

Build is 20151006

-Cory

Re: Moist Air Mixing

KubliJ — Mon, 21 Mar 2016 18:37:16 GMT

Hi Cory,

I found the issue. It appears there is a bug in service pack 2 for version 2016. I was running service pack 1 when I tested the model. It seems the only way to work with the moist air material model would be to unistall service pack 2. There are instructions in the help on how to uninstall.

I apologize for the inconvenience of this.

Thanks,

James

Re: Moist Air Mixing

Anonymous — Fri, 22 Jul 2016 12:51:09 GMT

Just installed CFD 2017. Same issue as with 2016 SP2. Moist air does not mix correctly. Scalar works.

Re: Moist Air Mixing

KubliJ — Fri, 22 Jul 2016 18:13:23 GMT

Hi Cory,

I apologize again, the bug was not fixed in 2017. But it is looking good for it being resolved in the first service pack for CFD. Right now there is no ETA for its release.

Thanks,

James