Blimey! What's wrong with using those already on the market? Dirt cheap and compliant with all the current Standards....

hello! im in final year mechanical and doing project on designing of fire fighting system so later i will be picking frm market but as for now basic design is required.

........So go to the current standards and start from there. Unless you want me to nick one from Basildon Fire Station? Eh?

A simple convergent nozzle is just that: Simple. It's cone shaped. More sophisticated ones have a short, straight section at the small end, and the end is typically radiused (or at least chamfered) to eliminate a sharp edge at the exit.