My question comes from exercises with parallel pipes such as this.
I know that to analyse internal flow, we use general energy equation which origins from the 1st law so each time we apply it we are using a Control Volume. However for this type of question, if I apply a CV that goes from 1 to 2, part of the mass flows toward C and so starting from the 1st law the equation should become like this:
However the solution tells me that it is:
I dont understand why you can procede as the solution. It ignores the mass flow toward 3, almost as if there is only mass flow from 1 to 2 which permits it to cancel out completely the mass flow.