As discussed previously, AFT Fathom uses a Newton-Raphson matrix method to obtain a system level mass balance and energy. When the Solver (the part of AFT Fathom that applies the governing incompressible flow equations to obtain a solution to the pipe system) is finished, the Continuity Equation and Energy Equation are satisfied at all branching sections. Once solved, it is a simple matter to go back and sum up all mass flows and energy at each branch to verify that these equations are satisfied. In fact, AFT Fathom does just that.

After the Solver converges, AFT Fathom loops over each junction and adds up the inflow and outflow of mass and energy and compares the sum to the solution tolerances. If it appears that any junction is out of tolerance, a warning is given in the output.

In the Solution Balance Summary table AFT Fathom provides additional information on the balance at each junction. This table can be displayed by selecting the option in the Output Control window General tab. Figure 1 shows an example of the Solution Balance Summary table.