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Heat Transfer Application examples of using fins

  • #1
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Hello,
Im struggling a bit with this problem. (uploaded)
Unbenannt.JPG



I dont know how to sketch the equivalent thermal circuit for any of them. Does it have to look like anything like that?
TZL111_Effective_Thermal_Fig_2.jpg

the thermal circuits are for b) parallel connectd right? and for aswell?
And im getting wrong answers for a). Shouldnt it be like this?
Q= he*Ab2*55 + 1/((1/hi)+(Lb/kb))*Ab2*55
or are they all parallel? like this Q=Ab2*1/((1/hi)+(Lb/kb)+(1/he)) .
My first thought was that the heat rate dissipating on the chip side is the same as the heat rate on the board side. why is this thought wrong? im confused :D
thank you for your answers
Best regards
 

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