duct system flows

Application of the principle of the balance of mechanical energy gives a constraint on the possible values of the junction coefficients at a duct system junction. In some cases the recorded junction coefficients in the literature do not satisfy this constraint. The values given may then be questionable. The terminology in connection with junctions is discussed and the role of the principle of balance of mechanical energy in duct system flow modelling is considered in some detail.

The governing equations in duct system flow analyses are nonlinear, and iterative solution methods must be used. A suitable initial flow rate guess may be needed to start the calculations so that a converged solution can be finally achieved. A method to obtain a reasonably accurate initial flow rate guess is presented. In it the duct system is analyzed first in a strongly simplified setting assuming a linear (imaginary laminar) duct flow problem. The continuity equations at the junctions are satisfied.