How to write a udf for temp dependent emissivity

Oula · December 9, 2018, 12:26

Hi everyone

In my model there are some boundaries (walls) that their emissivities change with temperature. For example

at a specific wall
at T=200 C emissivity = 0.80
T=400 C emissivity = 0.82
T=600 C emissivity = 0.84

How can I write the suitable UDF for this case?

Any help is much appreciated

Oula · December 10, 2018, 11:00

I'm a bit confused about which macro can be used to change the material property that is changing with temperature?, is it DEFINE PROPERTY or DEFINE PROFILE?

I have found the thread below which used DEFINE PROFILE. can anybody explain to me what is the difference.

Temp dependent emissivity udf

Any help is much appreciated

AlexanderZ · December 10, 2018, 21:10

DEFINE PROPERTY macro is used to define material properties
DEFINE PROFILE is used to define a custom boundary profile or cell zone condition

emissivity is not material property, but property of surface, so you should use DEFINE PROFILE

best regards

December 9, 2018, 12:26	How to write a udf for temp dependent emissivity	#1
Oula Member Oula Join Date: Apr 2015 Location: United Kingdom Posts: 81 Rep Power: 11	Hi everyone In my model there are some boundaries (walls) that their emissivities change with temperature. For example at a specific wall at T=200 C emissivity = 0.80 T=400 C emissivity = 0.82 T=600 C emissivity = 0.84 How can I write the suitable UDF for this case? Any help is much appreciated

December 10, 2018, 21:10		#3
AlexanderZ Senior Member Alexander Join Date: Apr 2013 Posts: 2,363 Rep Power: 34	DEFINE PROPERTY macro is used to define material properties DEFINE PROFILE is used to define a custom boundary profile or cell zone condition emissivity is not material property, but property of surface, so you should use DEFINE PROFILE best regards Oula likes this.

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December 10, 2018, 11:00		#2
Oula Member Oula Join Date: Apr 2015 Location: United Kingdom Posts: 81 Rep Power: 11	I'm a bit confused about which macro can be used to change the material property that is changing with temperature?, is it DEFINE PROPERTY or DEFINE PROFILE? I have found the thread below which used DEFINE PROFILE. can anybody explain to me what is the difference. Temp dependent emissivity udf Any help is much appreciated