how to create vacuum in fluent
 

hi,
i am new in cfd. my thesis is on simulation of mitral heart valve.
problem is to create a vacuum atrial chamber with -15 mm hg pressure and a ventricular chamber with 650mm hg. i have taken the chamber as a quarter of a cylindrical pipe. now while designing in GAMBIT the software shows the whole chambers full of blood. i cannot create a vacuum chamber and a blood full chamber
can anyone help me out.