# Mean Age¶

For open systems, users can automatically calculate the transient mean age distribution using the Calculate Mean Age command. After selecting this option from the Menu, users will be prompted to select an age source from among the inlets, a calculation start time, and an age diffusion coefficient. The age diffusion coefficient is related to the molecular self-diffusion coefficient. The spatial variation in the mean age is printed to volume and slice output files. The mean age at each outlet is printed to output.

The transient mean age represents two physical values. First, it represents the average age of molecules at a given point inside the tank, relative to the time these molecules entered the system via the selected inlet. Second, the represents the mean residence time of molecules at a given point inside the tank. For systems with a single outlet, the mean age at the outlet is equal to the volume averaged mean-age. The volume averaged mean age is also equal to the mean residence time of the system.

Start Time

Start Time, [seconds]

Time at which to begin the mean age calculation

Diffusion Coefficient

Age diffusion coefficient, [m^2/s]

Diffusion coefficient of the age variable. Typically equal to the molecular diffusion coefficient.

Selected Inlet

Selected inlet for mean age calculation