Manifold flow distribution: choice of outlet BC
 

Hi, I am having an inlet stream splitted in 4 other stream, one is a straigth line aligned with the inlet, and the 3 others are vertical tube going at different hight. Thos 4 streams pass a heat exchnager and them are joined to evacuate the fluid. Simulating the whole thing would be way too intense in term of computation demand. Thus i have simulated only the manifold but have some concern about what outlet BC to use, knowing that i dont have any information on what is the pressure at the outlet and if the flows are splitted equally. A pressure outlet would split all the streamm automatically and indicate me there is mal-distribution. Using an outflow would require me to know how the stream are splitted but this i dont know it. Is anybody would have a wise comment to share on this subject. Thanks in advance! thomas