Fluent heat trasnfer & coefficient calculation problem

Brandon Han · January 12, 2021, 23:59

Hello, everyone. This is Brandon Han. I have a problem and I really hope someone can help me.

What I'm trying to do is to calculate the heat transfer coefficient of a certain wall(or zone).First of all, the wall is one of the boundaries and I'm wondering how to define its boundary condition. I don't know the temperature of the wall. Should I define the wall as heat flux=0 or something else？

Also, I see there're two heat transfer coefficients in Surface Integrals-Wall Fluxes. One is surface heat transfer coef. and the other one is wall function heat trans. coef.. Under this circumstance I think I should report the surface heat transfer coef. but it seems that the coef. is equal to 0 when the wall is set as heat flux=0. The coef. can be calculated when the wall is set to fixed temperature. What should I do under this circumstance? Should I directly use the coefficient of Fluent, or calculate the coefficient myself?

I really need your help and I really appreciate it.

Brandon Han

Brandon Han · January 13, 2021, 02:29

Can anyone help me please? I really appreciate it.

jlinde · February 3, 2021, 15:05

Hi Brandon,

Fluent needs the total surface heat flux to calculate the HTC, so I think that you should provide some coherent values at this wall.

The next thing I would is to check if you are able to guess the bulk temperature because Fluent also needs a reference temperature in order to obtain the HTC. If you are not able to guess the bulk temperature (complex geometries, irregular heat generation, etc.), you are free to use the wall function temperature along with the first cell temperature. This function uses the temperature wall of the law to estimate the first layer temperature, then the first cell temperature is used as reference temperature. If you use this method, you should check the HTC carefully. The mesh, turbulent model, linearization error could influence this value dramatically. Finally, the wall function HTC is only useful as convective boundary condition as long as you import the first layer temperature too.

GL

January 12, 2021, 23:59	Fluent heat trasnfer & coefficient calculation problem	#1
Brandon Han New Member Join Date: Jun 2020 Posts: 7 Rep Power: 6	Hello, everyone. This is Brandon Han. I have a problem and I really hope someone can help me. What I'm trying to do is to calculate the heat transfer coefficient of a certain wall(or zone).First of all, the wall is one of the boundaries and I'm wondering how to define its boundary condition. I don't know the temperature of the wall. Should I define the wall as heat flux=0 or something else？ Also, I see there're two heat transfer coefficients in Surface Integrals-Wall Fluxes. One is surface heat transfer coef. and the other one is wall function heat trans. coef.. Under this circumstance I think I should report the surface heat transfer coef. but it seems that the coef. is equal to 0 when the wall is set as heat flux=0. The coef. can be calculated when the wall is set to fixed temperature. What should I do under this circumstance? Should I directly use the coefficient of Fluent, or calculate the coefficient myself? I really need your help and I really appreciate it. Brandon Han

January 13, 2021, 02:29	Help	#2
Brandon Han New Member Join Date: Jun 2020 Posts: 7 Rep Power: 6	Can anyone help me please? I really appreciate it.

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February 3, 2021, 15:05		#3
jlinde New Member Jorge Linde Join Date: Feb 2020 Posts: 1 Rep Power: 0	Hi Brandon, Fluent needs the total surface heat flux to calculate the HTC, so I think that you should provide some coherent values at this wall. The next thing I would is to check if you are able to guess the bulk temperature because Fluent also needs a reference temperature in order to obtain the HTC. If you are not able to guess the bulk temperature (complex geometries, irregular heat generation, etc.), you are free to use the wall function temperature along with the first cell temperature. This function uses the temperature wall of the law to estimate the first layer temperature, then the first cell temperature is used as reference temperature. If you use this method, you should check the HTC carefully. The mesh, turbulent model, linearization error could influence this value dramatically. Finally, the wall function HTC is only useful as convective boundary condition as long as you import the first layer temperature too. GL