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Relative Humidity

Posted 29.11.2011, 15:32 GMT-5 Heat Transfer & Phase Change Version 4.2 6 Replies

Rilya Rumbayan
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Hi Comsol user,

I am a beginner Comsol user, and i plan to study more about this interesting software.

Now, i am involving in a project about modeling of environmental effects on concrete bridge. i plan to combine the solar radiation, ambient temperature, wind speed and relative humidity as environmental conditions in my model. I used 3D transient heat transfer to simulate this condition, but now i get a problem with "relative humidity' effect. I do not know how to put my relative humidity data in the model.

I used data of solar radiation as (Qo) in "heat flux"
I used data of ambient temperature as (Texternal) in "convective cooling1"
I used data of wind speed as (Uexternal) in "convective cooling 2"
I put data of ambient temperature and emissivity of concrete in "surface to ambient radiation"
Also, i used the thermal properties of concrete (density, thermal conductivity and specific heat) in 'heat tranfer in solid"

My question is, where i should put data of relative humidity in my model?
Would you please share your understanding about this.

I really appreciate and thank you for your consideration!

-Lia-
6 Replies Last Post 30.08.2014, 09:42 GMT-4
Francois Gregoire
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Posted: 1 decade ago 29.11.2011, 23:45 GMT-5
Hi Rumbayan,

How is the RH supposed to interact in your model?

Does it just affect the air properties? If yes, I think you just have to adjust the air properties (density, viscosity, etc.) in order to take account for humidity (humidity function of time and air properties function of humidity in a list of variables).

Hi Rumbayan, How is the RH supposed to interact in your model? Does it just affect the air properties? If yes, I think you just have to adjust the air properties (density, viscosity, etc.) in order to take account for humidity (humidity function of time and air properties function of humidity in a list of variables).
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 30.11.2011, 02:27 GMT-5
Hi

I would also advice: start one physics at the time.
Multiphysics simulations is somewhat like cooking: if you mix everything in one go, and then turn on the heat, the results is not always as expected. It's easier to add one physics at the time and get an estimate of what does what independently, then together

--
Good luck
Ivar
Hi I would also advice: start one physics at the time. Multiphysics simulations is somewhat like cooking: if you mix everything in one go, and then turn on the heat, the results is not always as expected. It's easier to add one physics at the time and get an estimate of what does what independently, then together -- Good luck Ivar
Rilya Rumbayan
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Posted: 1 decade ago 30.11.2011, 11:07 GMT-5
Thank you for your feedback, i really appreciate it.

I simulated one by one for each variable, and the end i mixed all variables (except the relative humidity effect) , to see the result. The fact is in my simulation, i used the same geometry and environmental condition data available from previous field experimental study.

In this case, i want to verify the results of my model with the results of field experimental testing. So far, my model (just account solar loading, ambient temperature and wind speed surrounding a large concrete block ) seems having a good agreement with the field results. And now i want to improve my model with included relative humidity effect.

So far, i had relative humidity data and the actual air temperature which are recorded in the field experimental study. However, i need to figure it out, how to put this relative humidity data on my model. The idea of adjustment of the air properties seems make sense to me. However, i need to learn more about that.

Thanks
Thank you for your feedback, i really appreciate it. I simulated one by one for each variable, and the end i mixed all variables (except the relative humidity effect) , to see the result. The fact is in my simulation, i used the same geometry and environmental condition data available from previous field experimental study. In this case, i want to verify the results of my model with the results of field experimental testing. So far, my model (just account solar loading, ambient temperature and wind speed surrounding a large concrete block ) seems having a good agreement with the field results. And now i want to improve my model with included relative humidity effect. So far, i had relative humidity data and the actual air temperature which are recorded in the field experimental study. However, i need to figure it out, how to put this relative humidity data on my model. The idea of adjustment of the air properties seems make sense to me. However, i need to learn more about that. Thanks
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 01.12.2011, 01:51 GMT-5
Hi

try to search on the web, or in air material database (NIST ...) about the functional development of air+RH% characteristics and then you need to make functions for the material data in COMSOL. The RH must be defined as a variable and then at least the air properties (k, Cp, rho, ...) become dependent of all T, P, RH.

now if your humidity enters also the solid materials, you need to consider diffusion and the related equations to balance RH and material moisture, it adds a level of complexity and RAm need

--
Good luck
Ivar
Hi try to search on the web, or in air material database (NIST ...) about the functional development of air+RH% characteristics and then you need to make functions for the material data in COMSOL. The RH must be defined as a variable and then at least the air properties (k, Cp, rho, ...) become dependent of all T, P, RH. now if your humidity enters also the solid materials, you need to consider diffusion and the related equations to balance RH and material moisture, it adds a level of complexity and RAm need -- Good luck Ivar
Rilya Rumbayan
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Posted: 1 decade ago 01.12.2011, 02:00 GMT-5
Hi Ivar,

Thank you for the advise. I will search it.

Now, i know how complicate if i put the relative humidity effect in my model, but i will try my best to do it.

Thanks!

Rilya
Hi Ivar, Thank you for the advise. I will search it. Now, i know how complicate if i put the relative humidity effect in my model, but i will try my best to do it. Thanks! Rilya
Solmaz Farzaneh
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Posted: 1 decade ago 30.08.2014, 09:42 GMT-4
Hi Rilya

Could you share your experience with me about defining RH as a boundary condition? Now I have the same problem.
Thank you
Solmaz
Hi Rilya Could you share your experience with me about defining RH as a boundary condition? Now I have the same problem. Thank you Solmaz

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