vented enclosure heat transfer

[nonails44]

Hi all, new to the forum and heat transfer problems in general. I have a 3"diameter, 3" tall electronics enclosure that will be mounted on the end of a DC motor. I know how much heat the motor will put into the enclosure's bottom and also know the heat generated by a few of the enclosed electronic components (FETs). The enclosure has several holes - thus it is not sealed. My quest is to find the resulting temperature of a few of the enclosed components. I have the FEA tools - but not CFD. My primary question is how to simulate the enclosed air. I am tempted to treat all internal and external surfaces with natural convection but worry that I may not be capturing the effect of any "trapped heat". This type of problem is outside my comfort zone so would appreciate any inputs.

Thanks

 

[chicopee]

Assuming that you have enough holes in the enclosure and no dead air spaces, then you would have convective heat transfer from air flowing into the lower holes and escaping thru the upper holes, conduction from motor housing thru base of enclosure and internal heat generation from the components, all of which could be added into one heat transfer equation.
So now what are you trying to figure out? Are you looking at the internal components as generating heat and not as regions of trapped heat? are you trying to figure out the escaping air temperature or the surface temperature of the electronic components?

 

[nonails44]

Thanks for the inputs. There is a PCB inside the enclosure and I am trying to see the resulting temperature of a couple of components on that board. The other internal components that generate heat are not my concern; they are mounted off of the PCB and are affixed to the inside wall. Given that I don't have CFD capability I think this plan of considering all interior and exterior surfaces as convective may be the only thing I can analyze. However, it seems there would be no temperature rise on any of the PCB's components - since they just live in this convective space. Yes, they may see radiation - but that seem minimal.

A worst case approximation might be to consider all the vents plugged. In that case there is interior convection of the trapped air. How is that typically handled in a heat transfer FEA?