Selection of Orifice

Start by stating what the orifice is supposed to do.

i want to know that for which D.P value the orifice will design to achive this flow.

Select any orifice size you want to, it won't make any difference. You have zero flow with or without an orifice plate because you have zero pressure.

An orifice plate does not create pressure, it creates a pressure drop but there's no pressure drop with zero pressure and no flow.

Dear i know An orifice plate does not create pressure, it creates a pressure drop,and it have pressure i.e 1800Pa & line temperature is 350deg.C so we have parameter Flow-2500m3/h Line dia-400mm Line pressure-1800Pa Working temp-350deg C Then for which D.P Value this orifice will design?