# Run-time Calculations¶

## Auto Blend Calculation¶

Users can automatically calculate the tank blend time using the
*Calculate Tank Blendtime* command. After selecting this option from the
Menu, users will be prompted to enter a particle injection point, number
of particles, and injection time. These values represent the location,
quantity, and time at which tracer particles are added to the system.
Next, users will be prompted to specify a number of sub volumes in the x-, y- and
z-directions. These sub-volumes are used to calculate the coefficient of
variation of particles across the tank. The extents of these bins, the
amount of fluid inside each bin, and the equilibrated particle count are
reported in the solver log file prior to the first iteration.

At a time interval equal to the Slice Output time interval, the solver reports the instantaneous Blending COV and the normalized particle concentration in each bin.

The precision of the COV calculation is related to the number of bins and the number of particles. In general, users should inject at least 5000 particles per sub-volume.

For free surface simulations, the particle injection point should be below the fluid height.

- Number Bins X
Number of bins in X direction

- Number Bins Y
Number of bins in Y direction

- Number Bins Z
Number of bins in Z direction

- Start Time
Auto blend calculation start time [s]

- Number Of Particles
Number of particles

- Particle Injection Point
Start point of particles [Template Units]

- Particle Density
Density of the particles used in the autoblendtime calculation

- Particle Diameter
Diameter of the particles used in the autoblendtime calculation [Template Units]

- Visible
Enable/disable the visibility of this component

## 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

## Local Residence Time Distribution¶

This is an advanced component used to compute a local residencne time distribution (RTD) within a given sub-set of the tank

- Start Time
RTD Start Time [s]

- Box Lower Corner
Bounding box lower corner

- Box Upper Corner
Bounding box lower corner