Hi,
I rarely design anything that needs active cooling so when it comes to fans, my approach is largely inconsistent (read that as: "varies with day of week and phase of moon!).
When it comes to *case* fans ("CPU"s, external disk drives, printers, etc.) I tend to opt to push air
*into* the case drawing it through a filter, first (i.e., pulling air *out* usually results in drawing all sorts of dust and crud into the case from the area surrounding the device -- since most inlets are not filtered).Of course, that depends on what's inside the case "behind" the fan. As well as the roles of any other fans in the case.
I'm adding a couple of (tiny) fans to some external disk enclosures and found myself facing this question, yet again. :-/
So, can anyone offer a nice mnemonic / *rule* that I can just commit to memory and never have to waste time thinking about crap like this again?? :)
Thanks!
--don