# Conjugate heat transfer problem

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 October 28, 2009, 11:54 Conjugate heat transfer problem #1 New Member   Susan Join Date: Oct 2009 Posts: 26 Rep Power: 16 Dear All, I have a problem where I have a fluid surrounded by different solids and want to solve the heat transfer in the solids. The solids are surrounded by still air and I need to specify the outer boundary as Convection and give the Heat Transfer Coefficient. I can find different normal values by searching but I can see that I get different results depending on which value I use The higher heat transfer coefficient I use the more heat flux out of the outer boundary. I don't know what the heat flux should be, but want to find out. How do I determine the correct heat transfer coefficient. Thanks in advance

October 29, 2009, 08:08
#2
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Volker Pawlik
Join Date: Mar 2009
Location: Germany
Posts: 25
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Quote:
 Originally Posted by hvem10 Dear All, I have a problem where I have a fluid surrounded by different solids and want to solve the heat transfer in the solids. The solids are surrounded by still air and I need to specify the outer boundary as Convection and give the Heat Transfer Coefficient. I can find different normal values by searching but I can see that I get different results depending on which value I use The higher heat transfer coefficient I use the more heat flux out of the outer boundary. I don't know what the heat flux should be, but want to find out. How do I determine the correct heat transfer coefficient. Thanks in advance
So you are dealing with a free convection boundary. Heat transfer coefficient for free convection problems of horizontal or vertical plates can be found in several textbooks or handbooks (e.g. VDI Wärmeatlas).

Typically you' ll find values of about 1 up to 10 W/m2K for air and typical temperature gradients.

If you need a more exact value, see textbooks or: Maybe you can enlarge your modell and include the "outer heat transfer" into your model and convert it to an inner one..

 October 29, 2009, 17:31 #3 New Member   Susan Join Date: Oct 2009 Posts: 26 Rep Power: 16 Dear Volker, Thanks for your reply. I have been looking in text books, but my geometry is a bit out of the range of standard examples. But I wanted to be sure that I had not overlooked any smart approach, so thanks for the reply. I have now extended the domain such that I have the surrounding air included. I did find a heat transfer coefficent on 8, whcih is within the range you mentioned. Thanks