Modeling condensation in species

mohsen_23 · November 2, 2017, 14:50

Hi all
I want to model dehumidification of air in a big room and I don't want to use multiphase modeling (because my room is so big and this method is so expensive in calculation).
I want to model this with species transport and neglect the water that produced. dehumidification isn`t in species library and I don't know how to add this.
Anyone can help me?
Thanks in advance

mohsen_23 · November 3, 2017, 02:50

Any Idea?!?

e_cfd · November 17, 2017, 12:21

Hi Mohsen,
I guess that by means of species model you just can model the humid air (by solving an additional transport equation for the water vapor). For dehumidification, you need to define proper source terms for continuity, momentum and energy equations based on the mass transfer rate.

You might be able to avoid multiphase models considering that you can define this mass transfer rate (which is based on the gradient of the water vapor concentration) properly.

mohsen_23 · November 18, 2017, 12:28

Quote:

Originally Posted by e_cfd

Hi Mohsen,
I guess that by means of species model you just can model the humid air (by solving an additional transport equation for the water vapor). For dehumidification, you need to define proper source terms for continuity, momentum and energy equations based on the mass transfer rate.

You might be able to avoid multiphase models considering that you can define this mass transfer rate (which is based on the gradient of the water vapor concentration) properly.

Hi dear ehsan
Thanks for your responce
Yes,its very good idea but i have 2 question about it
Wator vapor can define in species and also by using uds, which is better?
How can i define gradient of water vapor in boundaries?
Thanj you in advance

e_cfd · November 20, 2017, 06:21

Dear Mohsen,

To me the easiest way to define water vapor is using Species model.

Moreover, if you are looking for a realistic mass transfer rate at the walls, you need to use multiphase models (due to condensation or de-sublimation), and define proper udfs for source terms. In this way, there is no need to define water vapor gradient at the walls explicitly. Otherwise, if you want to avoid multiphase models, you might define spiecies boundary condition at walls for h2o and specify h2o mass fraction which is quite tricky (I have not tried this).

November 2, 2017, 14:50	Modeling condensation in species	#1
mohsen_23 New Member Mohsen Join Date: Sep 2017 Posts: 20 Rep Power: 9	Hi all I want to model dehumidification of air in a big room and I don't want to use multiphase modeling (because my room is so big and this method is so expensive in calculation). I want to model this with species transport and neglect the water that produced. dehumidification isn`t in species library and I don't know how to add this. Anyone can help me? Thanks in advance

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November 3, 2017, 02:50		#2
mohsen_23 New Member Mohsen Join Date: Sep 2017 Posts: 20 Rep Power: 9	Any Idea?!?

November 17, 2017, 12:21		#3
e_cfd Member ehsan Join Date: Sep 2014 Posts: 38 Rep Power: 12	Hi Mohsen, I guess that by means of species model you just can model the humid air (by solving an additional transport equation for the water vapor). For dehumidification, you need to define proper source terms for continuity, momentum and energy equations based on the mass transfer rate. You might be able to avoid multiphase models considering that you can define this mass transfer rate (which is based on the gradient of the water vapor concentration) properly.

November 20, 2017, 06:21		#5
e_cfd Member ehsan Join Date: Sep 2014 Posts: 38 Rep Power: 12	Dear Mohsen, To me the easiest way to define water vapor is using Species model. Moreover, if you are looking for a realistic mass transfer rate at the walls, you need to use multiphase models (due to condensation or de-sublimation), and define proper udfs for source terms. In this way, there is no need to define water vapor gradient at the walls explicitly. Otherwise, if you want to avoid multiphase models, you might define spiecies boundary condition at walls for h2o and specify h2o mass fraction which is quite tricky (I have not tried this).