Is there any kind of formula that exists or I can put together that will allow me to determine airflow from a fan being funneled into a tube that decreases in size over the length of the tube? Something specifically that would allow me to determine the air pressure (psi ?) coming out the end of the tube? An example: a 5" diameter fan that consumes 30 watts of power and spins at 4,000 RPMs. Directly attached to the fan is a funnel that channels the air flow into a 2" tube that gradually tapers down to a 1/4" tube. At what rate would the air come out of the 1/4" opening? How could I measure the PSI? Does length of tube have an impact? Whats the best method to channel as much of the air as possible into the 2" opening reducing push back, or drag (?), that might reflect back into the fan because the air can't all fit into the 2" opening at once (so it must go somewhere right?)? Essentially, I am trying to create a low tech air compressor that regular room temperautre air forced at high rates of speed to create a high (or higher) pressure through a series of channeled tubes. Any thoughts or insights into the project, beyond the answers to the above questions, would greatly be appreciated. Thanks.