Learning Forum

[admin]

How to specify the latent heat for gas-liquid phase change in FLUENT?

[admin]

The standard state enthalpies of vapor and liquid phase are set such that their difference equals to latent heat of vaporization. The unit of standard state enthalpy is kj/kmol and usually the latent heat value is available in kj/kg. While specifying it here, multiply that value by molecular weight. We recommend using the saturation temperature as the reference temperature and the values of standard state enthalpy and other material properties at this saturation temperature for vapor and liquid or building their difference which leads to the latent heat at the saturation temperature. If the values of standard state enthalpy as well as the isobaric heat capacities are known at another temperature we can set this known temperature as reference temperature and employ the related enthalpy and other material properties values. In this case we have to provide the system pressure.

[farizanluthfi]

The standard state enthalpies of vapor and liquid phase are set such that their difference equals to latent heat of vaporization. The unit of standard state enthalpy is kj/kmol and usually the latent heat value is available in kj/kg. While specifying it here, multiply that value by molecular weight. We recommend using the saturation temperature as the reference temperature and the values of standard state enthalpy and other material properties at this saturation temperature for vapor and liquid or building their difference which leads to the latent heat at the saturation temperature. If the values of standard state enthalpy as well as the isobaric heat capacities are known at another temperature we can set this known temperature as reference temperature and employ the related enthalpy and other material properties values. In this case we have to provide the system pressure.

 

for the highlight in above sentence, is it related entalphy means to the standard state enthalphy of saturation temperature or known temperature as reference temperature? and why?

thank you.

[DrAmine]

Yes that is related to standard state enthalpies.

[farizanluthfi]

Yes that is related to standard state enthalpies.

 

Could you please tell me more specific about this one Sir? because I'm still new one on the ansys fluent and I'm taking a project on working boiling heat transfer multiphase flow.

I've seen in many tutorials said that, when we apply the material properties, on the reference temperature we should put 298.15K. Meanwhile, when I take a look on the standard state of enthalpy value is not coming from the value of reference temp (298.15K). The value of standard state enthalphy pointed out on the saturation temperature for both phases. Need your fully support Sir, is it correct or what?

Thank you,

Best Regards,

Luthfi

[Karthik R]

Hello,

Here is a screenshot from the Fluent theory guide about standard enthalpy.

As you can see, the standard state enthalpy is estimated based on the chosen reference temperature. This standard state enthalpy is used to estimate the total enthalpy at any temperature T. On subtracting the enthalpy of liquid phase from vapor, Fluent obtains the latent energy. 

Fluent by default takes 298.15K as the reference temperature (as seen from the material properties). It is not necessary to use this value. If you like, you can change this value. But be very careful to input the correct standard state enthalpy corresponding to your reference temperature. 

I hope this helps.

Best Regards,

Karthik

[farizanluthfi]

Thank you so much for your explanation, but I think for this standard state enthalphy you give me is for model evaporation-condensation. However, it really helpful for my better understanding.

Best Regards,

farizanluthfi

 

[Karthik R]

Hi,

I am glad it helped. Good luck with your modeling.

Best Regards,

Karthik

[nagasudhan]

Where to specify Latent Heat for (Solid to liquid phase change ) of PCM(Phase change materials) ?

 

Greetings,  

I am try to simulate solidification/melting model of PCM (Phase change materials) While creating a new PCM material Fluent I can specify density, thermal conductivity,Specific heat as a piecewise-polynomial property. Now, along with that I have Latent heat for the PCM during melting phase. Is there any possible ways to specify Latent heat in terms of specific heat or how should I proceed.

I have attached my PCM thermo physical properties below.Those values are in temperature range of piecewise-polynomial.  

 

Thankyou.

Regards,

Nagasudhan

[DrAmine]

You specify that in terms of Solidification and Melting model as Fusion Heat in the PCM material. If you want to use Thermal Phase Change Model then you do it like for vapor liquid systems: you put the whole latent heat on the side with higher standard state enthalpy.