[Morice]

Originally Posted by vinerm

There are three materials in a case with two components; two materials are the components themselves and one is their mixture. For the mixture, you might be using mass or volume weighted properties; use mass-weighted if density ratio is high. However, for individual components, you can still apply some of the material properties; not all though. So, you can go to Material Properties of Vapor and assign the properties as function of temperature. The material properties that you can assign for individual components depends on the options chosen for the mixture. If mixture property is based on some mixing law, then that particular property has to be given for individual component, otherwise, the property from the mixture is used. Boussinesq is not compatible with Species Transport.

Thank you so much for your responsee. Much appreciated.

I wanted to change the individual specific heat capacity of water vapour to a function of temperature. In you opinion, what is the most effecicient approach? expression or parameter? And if you do not mind, could you please write it out for me. It could provide a foundational insight into changing the properties of other materials that I want to undertake.

Thank you so much.

[vinerm]

The method is not important since all the methods are essentially same; whether you use expression or UDF or methods available within Fluent, result will be same if the dependence or equation is same. Fluent has inbuilt feature to apply specific heat as a function of temperature. You can choose one method and provide the coefficients. The coefficients are available on-line as well as within Fluent database.

[Morice]

thank you very much for your response. much appreciated

will look into it

[mahesh1819]

Dear Vinerm, We have carried out using the transient analysis condition and as of now there are no errors. I thank you so much for your valuable inputs and support. Will let you know in case of any problem faced.

[Morice]

Originally Posted by vinerm

There are three materials in a case with two components; two materials are the components themselves and one is their mixture. For the mixture, you might be using mass or volume weighted properties; use mass-weighted if density ratio is high. However, for individual components, you can still apply some of the material properties; not all though. So, you can go to Material Properties of Vapor and assign the properties as function of temperature. The material properties that you can assign for individual components depends on the options chosen for the mixture. If mixture property is based on some mixing law, then that particular property has to be given for individual component, otherwise, the property from the mixture is used. Boussinesq is not compatible with Species Transport.

Hey Vinerm,

Hope you are well.

Since Boussinesq is not compatible with Species Transport, in the k-e model, what buoyancy effects should be applied? Full or only turbulence production?

I was thinking it should be full?

What do you think?

Thanks, much appreciated

[vinerm]

Buoyancy is not include via turbulence models, rather via density of the substance. Use incompressible ideal gas or ideal gas. The options under turbulence models are sub-models that you may invoke if you want.

[Morice]

Originally Posted by vinerm

Buoyancy is not included via turbulence models, rather via density of the substance. Use incompressible ideal gas or ideal gas. The options under turbulence models are sub-models that you may invoke if you want.

Thanks for your response.

It is something I came across while doing research and I thought I would make an inquiry. I do understand. It seems I still have a long way to go in CFD.

For the density of the water vapour-dry air mixture, I used "volume-weighted" as per the suggestions in this thread.

Does using incompressible ideal gas or ideal gas give a more accurate solution?

Thanks, much appreciated.

[aefe]

Hey there,

I'm trying to model a 2D box with an outlet.

The initial conditions of the air in the box are 45C and 95% RH, and the outlet is opening to an environment with a constant temperature and RH (Assume 20C and 50% RH). I want to see what will happen at the end of the given time.

I can predict that the hot and humid air will exit the box quickly at the beginning, and then the velocity of the exit air will slow down.

I have read all the written comments above, but could not manage to model it.

Is there anyone to help me with this model?

Thanks in advance!

[vinerm]

If the box has only one opening, then the flow would be due to natural convection. That means, you need to enable gravity and the density should be modeled using either Boussinesq (only for single component fluid) or incompressible ideal gas or ideal gas.

[aefe]

Yes vinerm, there is just one opening like you said. Thank you for your reply.

First, I had modeled it exactly like that for temperature, and it worked.

Then I tried to solve the problem with the RH and I could not do it. Do you have any idea about it?

[vinerm]

How are you including RH? Via Species model? Essentially, you need to include the changes in the density due to the difference is species fraction in the mixture. Otherwise, it would behave like a homogeneous mixture and then the solution would be similar to what you got for the first case without RH.

[aefe]

Originally Posted by Ahmed Saeed Mansour

Hello, I want to get the values of the relative humidity for a simulation contains moisture (humid air), I think I have followed the steps that are shown here...I have the steps in the snapshots..Is this right or there is another thing that has to be further done?
Thanks

I made it like Ahmed Saeed Mansour on August 19, 2017.

Yes I am using species model, I give my outlet 296.15K and 0.0096 mass ratio for h2o, which is the mass ratio for 23C and 55% RH.

Also I patch it as 323.15K and 0.0815 mass ratio for h2o, which is for 50C and 95% RH.

[vinerm]

What model are you using for mixture density?

[aefe]

I uploaded the screenshots of my setup to this link if you would like to control

https://drive.google.com/drive/folde...Ma?usp=sharing

Regards

[aefe]

Originally Posted by vinerm

What model are you using for mixture density?

It is ideal gas by the way.

[vinerm]

You have only one cell zone while the scenario you're trying to simulate requires two. If you simulated your first case, the one with only temperature difference, using only one cell zone, then that's also incorrect. For a single cell zone, the flow is only due to pressure difference inside the cell zone and at the outlet boundary. The temperature and the specie mass fraction provided at the outlet do not affect the flow since those values are used by Fluent only during flow reversal. Those values do affect the diffusion near the boundary. You need to have two cell zones, one your regular cell zone and another one connected at the outlet of the first one. Then, initialize inner one with higher RH and outer one with lower RH.

[suiryagowtham]

Originally Posted by Ahmed Saeed Mansour

These are the rest of the snapshots

Thanks for the reference sir.

[m.qodrati8@gmail.com]

salam mohsen. vaght shoma bekheir. shoma tonestion havay martob ro modelsazi konin?salam mohsen. vaght shoma bekheir. shoma tonestion havay martob ro modelsazi konin?