Why does fluid pressure decrease with higher density in narrow pipes?

[Lurker_Letum]

So I was playing around with Fluid Pressure and Flow over on PHET animations and noticed something odd. When a fluid with high flow rate is going from a large pipe to a small pipe a lower density increases the pressure. And a higher density lowers the pressure in the narrow part of the pipe. My knowledge would say that the higher the density the higher the pressure with other variables constant.

Was wondering if some one could let me know if this is a software issue or could point me in the right direction to read about this a bit more.

 

[BvU]

Hello Lurker,

Your intuition is correct:

with other variables constant

so just follow it up with the logical conclusion that there must be something else not constant. The velocity, for instance.

Read up on Bernoulli and Navier-Stokes.

 

[boneh3ad]

I'm not really sure what you mean by higher or lower density in this case. Usually when discussing pipe flow like that the density is assumed constant. Do you have a link to what you were viewing?