Model radiators and porous media¶

Bramble models a radiator core as a Darcy–Forchheimer porous region. You define it on the Template Case's Radiators tab, and Bramble can fit the coefficients from pressure-drop test data.

Before you start

Nothing needs enabling. The Radiators table is in Template Cases of the OpenFoam and OpenFoam with CHT Methodology Groups. Star-CCM+ Template Cases use Radiators (CCM) instead.
Decide how the core's upstream and downstream faces will be found (the Up/Down mode below), because it decides how you name the core zones.

Prepare the geometry¶

Each radiator needs a frame and a core. Use only letters, digits, _ and - in the radiator name.

Frame: a watertight solid round the core, so flow can't bypass it. Name it <zone>-<radiator name>, for example eb-rad-main or body-rad-water-lhs.

Core: the zones depend on the Up/Down mode:

Up/Down	Core zones	Example for radiator `rad-water-lhs`
`Auto`	One zone, `toint-<name>`. Bramble finds the upstream and downstream faces itself	`toint-rad-water-lhs`
`Manual`	Two zones: `toint-<name>-up` and `toint-<name>-down`, thin surfaces covering the whole core	`toint-rad-water-lhs-up`, `toint-rad-water-lhs-down`
`Off`	One zone, `toint-<name>`	`toint-rad-water-lhs`

For Manual, oversize the up and down faces by a few mm so they extend slightly into the frame and seal.

See toint zones.

Add a radiator¶

In the Template Case editor, go to the Radiators tab. In Radiators, click New.

Fill in the row:

Field	Enter
Name	The radiator name used in the zone names, for example `rad-water-lhs`
Inside Point	A point in the core, in metres (or mm if the editor is set to Use (mm)). Disabled for `Auto`, which works it out
Darcy Coefficient, Forchheimer Coefficient	The porous coefficients. Click the cog to fit them from test data
Through Vector	The unit normal to the core face, pointing with the flow
Orthogonal Vector	A unit vector across the face (usually right–left), orthogonal to the through vector. Three or four decimal places are enough
Factors	Multipliers on the coefficients in the through direction and the two directions across the core. The default `1, 10, 10` makes the resistance across the core ten times the through resistance
Up/Down	`Off`, `Manual` or `Auto` (see above)
Export	Exports a slice through the core after the run
Fields	The variables in the slice export

For Auto, the vectors only need to be roughly aligned with the core. Bramble takes the flow direction from the vectors.

Optionally, click Show Grid Settings to export a probe grid across the core: Grid Rows, Grid Columns, Grid Width (m), Height (m), Horizontal Edge (m) and Vertical Edge (m).
Click Save, then Save in the header. If a field is wrong, the editor shows "Radiator Error: Radiator data must be filled in correctly".

When you save a radiator, Bramble adds monitors for it to Forces → Solve Monitors: the mass flow, and the area-weighted total pressure and pressure, on toint-<name> (or toint-<name>-up). For Manual, it also adds the pressures on toint-<name>-down.

Fit the coefficients from test data¶

In the radiator row, click the cog next to Darcy Coefficient or Forchheimer Coefficient. Porous Data opens.
In the Porous Data table, enter at least three test points, each a Velocity (m/s) and a dp (Pa). With fewer, the dialog shows "Enter a minimum of three porous data values" and Save stays disabled.
In Porous Property, enter:
- Thickness (m): the core depth along the through vector
- Dynamic Viscosity (kg/m.s) and Density (kg/m3): the air properties at the test conditions
Check the fitted curve and the Darcy Coefficient: and Forchheimer Coefficient: values, then click Save. Both coefficients are filled in.

Bramble fits dp = a₀ + a₁v + a₂v² to your points, then sets D = a₁ / (thickness × μ) and F = 2a₂ / (thickness × ρ).

Porous and fan jumps¶

For thin porous or fan surfaces that don't need a porous volume, use the Interior Zones tab instead:

Porous Jumps: Name (the zone), Permeability, Pressure Jump Co-efficient, Thickness, Max Velocity (m/s), Tags, Force Group
Fan Jumps: Name (the zone), Function (polynomial coefficients), Direction, Min Velocity and Max Velocity (m/s), Tags, Force Group

For heat rejection from a radiator, the Macro Heat Exchanger (the thermometer icon in the Radiators table) sets its air and coolant properties.

Check the set-up¶

Check	Fails when
Radiator Coordinate System Orthogonality	A radiator's through and orthogonal vectors aren't orthogonal
Radiator Coefficients	D is outside 1e4–1e8, or F outside 1–10,000, for example "Porous region … does not have a sensible D coefficient (1e4 < D < 1e8)"
Check for unused or missing toints	A radiator's `toint` zone is missing from the geometry, or a `toint` Part isn't used

To see each radiator, choose it in Select Pre-check Plots on the Run Checks tab. The Radiator Plots show the through vector in red and the normal vector in blue.

After the solve, Check Cell Zone Sizes flags a porous zone whose cell count differs from the baseline's by more than 10 %.