Compressed air flow predictive math model?

Is anyone out there aware of software, or a relatively easy to use set of formulae, that could be programed into an Excel spreadsheet to model flow of compressed air through a piping system. A colleague and I are need to develop a method to predict performance of various configurations of open ended piping systems intended as a filter blow-down mechanism. We would like to be able to predict orifice final flow, pressure drops, and blow-down burst times based on pressure drop in the receiver (vessel) at the entry end of the pipe system. Any help would be appreciated. Received on Thu Jul 26 13:46:00 2001