linear layer thickness evolution

keeper · July 26, 2013, 03:25

Hi all.

I want to include thin material as an thermal resistance but I would like to define linear dependence by the z coordinate. But CFX warns that the value of thin material is defined to be single value.

Is there any option how to set it up properly to have linear dependence for thermal resistance?

Thank you for all your replies.

Best Regards

ghorrocks · July 27, 2013, 07:18

You will probably have to do this manually using source terms. Write a source term to handle the temperature difference over the interface, then you should be able to make it a function of spacial directions.

keeper · July 29, 2013, 04:51

Could you please explain little more what you mean? I don´t have any information about temperatures. I have only data for isolation layer so I would like to add it into the model...

Thank you for reply

BR

ghorrocks · July 29, 2013, 07:55

If you model the thin surface as an interface you can put a thermal resistance on the interface. Have you tried this? Hopefully you can specify the thermal resistance as a function of position.

keeper · July 29, 2013, 07:59

that is exactly what I did. I defined material for isolation and to define thermal resistance, I used thin surface option.
I used linear dependence for definition of layer thickness and I put it as an expression to layer thickness determination.
And then I get message that it is supposed to be single value...
That is why I am wondering that I am able to use expression but not any spatial dependence..?

ghorrocks · July 29, 2013, 08:14

Can you post your CEL and the error message you are getting?

keeper · July 29, 2013, 08:56

sure, here it is..I just have so many domains and interfaces in the model that I attached relevant information only. Please note that I get this error message in CFX Pre.

ghorrocks · July 29, 2013, 21:53

Rather than use "Z Coordinate" just use "z".

keeper · July 30, 2013, 02:46

I used just "z" and it is the same. I was thinking about any expert parameter that changes the "Single Value" definiton that is mentioned in error message...

ghorrocks · July 30, 2013, 06:34

In that case I think you will find spatially varying thermal resistance has not been implemented so that is why you are being stopped from using it.

keeper · July 30, 2013, 06:57

that is exactly what I was afraid of

but anyway thank you for your help

ghorrocks · July 30, 2013, 07:37

I do not understand why, there are not any high order terms created with spatially varying thermal resistance to my knowledge so I would have thought it easy to implement. It might be worth speaking to ANSYS support on this as there might be a simple work-around.

You might also be able to implement a thermal resistance as a source term. Then you will have more control over it and might be able to implement the spatially varying term.

keeper · July 30, 2013, 07:46

yes I had the same idea, it should be simple to define by some expression. So I will try to define it by thermal resistance source term option as you advised. thank you very much

July 26, 2013, 03:25	linear layer thickness evolution	#1
keeper Senior Member Join Date: Jul 2010 Posts: 152 Rep Power: 15	Hi all. I want to include thin material as an thermal resistance but I would like to define linear dependence by the z coordinate. But CFX warns that the value of thin material is defined to be single value. Is there any option how to set it up properly to have linear dependence for thermal resistance? Thank you for all your replies. Best Regards

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July 27, 2013, 07:18		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	You will probably have to do this manually using source terms. Write a source term to handle the temperature difference over the interface, then you should be able to make it a function of spacial directions.

July 29, 2013, 04:51		#3
keeper Senior Member Join Date: Jul 2010 Posts: 152 Rep Power: 15	Could you please explain little more what you mean? I don´t have any information about temperatures. I have only data for isolation layer so I would like to add it into the model... Thank you for reply BR

July 29, 2013, 07:55		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	If you model the thin surface as an interface you can put a thermal resistance on the interface. Have you tried this? Hopefully you can specify the thermal resistance as a function of position.

July 29, 2013, 07:59		#5
keeper Senior Member Join Date: Jul 2010 Posts: 152 Rep Power: 15	that is exactly what I did. I defined material for isolation and to define thermal resistance, I used thin surface option. I used linear dependence for definition of layer thickness and I put it as an expression to layer thickness determination. And then I get message that it is supposed to be single value... That is why I am wondering that I am able to use expression but not any spatial dependence..?

July 29, 2013, 08:14		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	Can you post your CEL and the error message you are getting?

July 29, 2013, 21:53		#8
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	Rather than use "Z Coordinate" just use "z".

July 30, 2013, 02:46		#9
keeper Senior Member Join Date: Jul 2010 Posts: 152 Rep Power: 15	I used just "z" and it is the same. I was thinking about any expert parameter that changes the "Single Value" definiton that is mentioned in error message...

July 30, 2013, 06:34		#10
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	In that case I think you will find spatially varying thermal resistance has not been implemented so that is why you are being stopped from using it.

July 30, 2013, 06:57		#11
keeper Senior Member Join Date: Jul 2010 Posts: 152 Rep Power: 15	that is exactly what I was afraid of but anyway thank you for your help

July 30, 2013, 07:37		#12
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	I do not understand why, there are not any high order terms created with spatially varying thermal resistance to my knowledge so I would have thought it easy to implement. It might be worth speaking to ANSYS support on this as there might be a simple work-around. You might also be able to implement a thermal resistance as a source term. Then you will have more control over it and might be able to implement the spatially varying term.

July 30, 2013, 07:46		#13
keeper Senior Member Join Date: Jul 2010 Posts: 152 Rep Power: 15	yes I had the same idea, it should be simple to define by some expression. So I will try to define it by thermal resistance source term option as you advised. thank you very much