Q:
A: Your question is a bit incomplete.
It's a system duct design question.
Q = m(dot)Cp(delta)T
i have to choose an axial fan to provide
I might be missing out because your info is a bit vague, but this is what I'd think:
-Q would be the amount of heat that has to be led away.
for example if you need to cool a power transistor producing 60W of heat, Q would be 60
You will soon discover that the possibilities are almost endless: to start with, should you buy an axial fan, a centrifugal fan, or even an inline fan. Surely a fan is just a fan I hear you ask. You have a brand new bathroom, and building regulations require you to install a bathroom extractor fan....