如何计算针阀CV值及孔径

遇到如下问题不知该如何计算
请指教，谢谢
have some requests more about needle valves :

1 – What is the hole diameter the needle valves needs for a flow rate of 2500 litres/hour with a pressure of 4.2 bars.


2 – what is the flow rate for a hole diameter of 6.8mm with a pressure of 4.2 bars
     what is the flow rate for a hole diameter of 8mm with a pressure of 4.2 bars



1.压力为4.2BAR，CV值是2500L/H的情况下，孔径是多少。

2．压力为4.2BAR，孔径为6.8MM，CV值是多少

  压力为4.2BAR，孔径为8MM，CV值是多少