## General Mechanical

Topics relate to Mechanical Enterprise, Motion, Additive Print and more

#### Internal heat generation

• David Satala
Subscriber

Hello!

Not so long ago I started using Mechanical APDL to solve thermal conductivity problems and I had one question. I am modeling a two-dimensional temperature field on a slice of a multi-chip module made of different materials, where the chips are internal heat sources. The chip sizes are 0.012 x 0.0005 m (12x0.5 mm). I want to set their power equal to 10 watts. In order for me to get a solution close to reality, I have to set the power of internal sources in Mechanical APDL somewhere around 10^9. Why is this happening? What is this value?

• Chandra Sekaran
Ansys Employee

I am not quite following the question. The value in SI units for heat generation would be (10/Volume) W/m^3. In the 2D analysis you can specify the thickness (Z direction). So the volume would be (0.012*0.0005*thickness) m^3.

• Rahul Kumbhar
Ansys Employee

Seems like unit issue. What command are you using to define heat?

• David Satala
Subscriber

I work in Mechanical APDL ecosystem. Simply setting a heat generation on purple areas. On the bottom edge I set a constant temperature 300K, on the upper edge convection with air. Problem is solved in SI units, all material properties are also set in SI. If I set HGEN value as 10^9 I get a result as shown on the picture. Result is close to reality, but HGEN value is extremely high. For example, if I set HGEN as 10^8, there will be temperature difference something around 1 K in all module. So, I don't clearly understand what is represented by that value. I thought, that it is density of heat generation, but it doesn't seems like that.