Air Pass Through a wall passage

[shmar]

Hi,
i have a problem calculating the pressure drop through an opening, air comes into a plenum and exist through a narrow opeining - what is the best method

 

[quark]

Describe the problem clearly. There is a thread down here which discusses about it (air flow through 2" pipe)

 

[shmar]

there is a duct that supplies air to a plenum, from the plenum the air is going out through a small hole (slots)
how do you calculate the pressure drop in the slots?