السلام عليكم و رحمة الله و بركاته،

I was reading about vertical separator with wiremesh demister sizing, they said that the criteria for the inlet nozzle sizing is that the feed momentum should not exceed prescribed levels, but the criteria written was:
pv2<1400 if no inlet device is used
( Note that p is the density)
(2means square )
and for a half open pipe the criterion is pv2<2100
for schoepentoeter pv2<4100
My question is that I know that the term pv2 represents the momentun but I do not know how, the momentum is mv so how did they use pv2 to show the momentum?
Also, why should not the momentum of the inlet feed exceed certain levels? and if we want to increase it then we have to use inlet devices?
Can some body expalain this for me, I know that the first separation occurs at the inlet of the vessel , the difference in the momentum that occurs due to the change in the direction is responsible for the primary separation of the gas and liquid. But what are these levels and why shouldn't we exceed them?

Thank you in advance and sorry for the english I prefer to wirte in Arabic but this is due to a problem in my computer that makes it difficult to shift from Arabic to English when I want to write the scientific terms.