Initial Conditions or Boundary Conditions? 1

[TJK1]

In a thermal problem, if an electronic heat generating device (100Watts) is inside of a cabinet and initially the air in the cabinet and outside the cabinet, in the room, is 72F, before the device is turned on, what would be the boundary conditions and what would be the initial conditions? The cabinet is sheet metal. There are no fans. The front and rear doors of the cabinet are perforated 64%. The cabinet sides, top and bottom are solid (no perforations). I am using an FEA called JLAnalyzer.

 

[kmount]

A boundary condition lasts the length of your analysis (or step), so if you are looking for transient effects, you will want to apply the 72F as an initial condition. Your heat source (with whatever heat conditions you choose, ie convection, radiation, or conduction) will then dictate temperatures throughtout your analysis.

 

[TJK1]

Thanks kmount. If I wanted to know what the steady state temperature would be, would I still use the 72F as an initial condition, or do you just use it if you are looking for transient effects? Do you always need to input both boundary and initial conditions in every analysis? Is it permissible to have more than one boundary and initial condition in each analysis?

 

[kmount]

Generally boundary conditions in a thermal analysis are used to prescribe temperatures at a surface. Therefore YOU control the surface's temperature. An initial condition on a surface is free to change throughout the analysis based on the environment you prescribe around it. I don't think you always need to input both types of conditions in every analysis. It all depends on what you're analyzing. How are you representing the heat generating device?

 

[TJK1]

I am representing the heat generating device as "nodal heat" at one particular node. The units are BTUs / sec.