Defining a new material in FLUENT

liying02 · October 25, 2019, 02:49

Hi all,

I am trying to use ideal R134a gas in FLUENT for my simulation but it is not within the FLUENT database. As such, I am trying to create a new material by setting my own fluid properties.

I did so by setting density to be ideal-gas, molecular weight to be 102.03kg/kmol (for r134a) and cp, thermal conductivity and viscosity to be 4th order polynomial functions, which I obtained from fitting my data to a polynomial function in excel.

After calculating, this gave me a mass flow rate of around 4e-5 kg/s. However, when I changed the viscosity to a different polynomial function (eg. 3rd order), the mass flow rate changes greatly to 2e-4 kg/s! I have double checked my polynomial functions in excel and they give almost the same viscosity, so it is not a problem with the functions.

Does anyone have an idea of what is going on here?? How can it be that my mass flow rate varies so much with the viscosity function used?

Would greatly appreciate any inputs. Thanks so much.

crubio.abujas · October 29, 2019, 11:23

Without further details of the geometry or the assumptions is difficult to assest the importante of the viscosity in your model. You can try checking the viscosity of your model by displaying it and ensure that it has the proper values..

Make sure that you are using the proper units, tipically fluent uses K degres not Celsius and that could be a huge difference in the correlations.

Hope it helps.

LuckyTran · October 29, 2019, 16:10

Maybe provide some screenshots of what you inputted into Fluent.

October 25, 2019, 02:49	Defining a new material in FLUENT	#1
liying02 New Member Liying Lim Join Date: Oct 2019 Posts: 3 Rep Power: 6	Hi all, I am trying to use ideal R134a gas in FLUENT for my simulation but it is not within the FLUENT database. As such, I am trying to create a new material by setting my own fluid properties. I did so by setting density to be ideal-gas, molecular weight to be 102.03kg/kmol (for r134a) and cp, thermal conductivity and viscosity to be 4th order polynomial functions, which I obtained from fitting my data to a polynomial function in excel. After calculating, this gave me a mass flow rate of around 4e-5 kg/s. However, when I changed the viscosity to a different polynomial function (eg. 3rd order), the mass flow rate changes greatly to 2e-4 kg/s! I have double checked my polynomial functions in excel and they give almost the same viscosity, so it is not a problem with the functions. Does anyone have an idea of what is going on here?? How can it be that my mass flow rate varies so much with the viscosity function used? Would greatly appreciate any inputs. Thanks so much.

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October 29, 2019, 11:23		#2
crubio.abujas Senior Member Carlos Rubio Abujas Join Date: Jan 2018 Location: Spain Posts: 127 Rep Power: 9	Without further details of the geometry or the assumptions is difficult to assest the importante of the viscosity in your model. You can try checking the viscosity of your model by displaying it and ensure that it has the proper values.. Make sure that you are using the proper units, tipically fluent uses K degres not Celsius and that could be a huge difference in the correlations. Hope it helps.

October 29, 2019, 16:10		#3
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,674 Rep Power: 65	Maybe provide some screenshots of what you inputted into Fluent.