Cannot mesh volume

Wendy Tjan

Hi, can someone help me please. I am currently on a project to model a bio reactor. Basically I have a L pipeline channeling the inlet to the vessel, and have 2 pipes to reject whatever effluent. I have split the volume of the reactor with the inlet pipelines, and try to mesh the volume of the reactor. and Gambit shows an error, "volume could not be meshed without face succesfully meshed" and "Meshing volume aborted due to poor face mesh quality". Does this means that I have to mesh the face before I mesh the volume. If so, which face I have to mesh.

Can anybody tell me what is difference between merge and unite? Thank you.

Wendy Tjan