pressure drops, void fraction, slip, hold up, velocity, conentrations, shape,size and density of the particles. etc.....
A two phase line is split phase. That's the same as in you home.Hot 1 is 120VAC to Neutral.Hot 2 is 120VAC to Neutral, and is 180 degrees aways from Hot 1.Hot 1 is 240VAC to Hot 2.Neutral is grounded...
360 degrees or 2(pi) radians
Diastole (relaxation)Systole (contraction)
They must be precisely in phase. If connected out of phase current would flow uncontrollably between the two alternators as a short circuit.