Radiant heat · perpendicular

Radiant heat flux along a wall at 90° to an opening

Our wall runs away from the emitter's plane at a right angle, so openings in it see the emitter sideways. This gives the flux all along the wall, the solid return wall needed before an opening can start, and the effect of a wing wall or an offset.

Inputs

Emitter

Emitter width b

Emitter height a

Geometry

Wing wall, if any W

Offset of the corner from the emitter plane s

Return wall, if any R

Other points along our wall (m from the corner, optional)

Fire and criterion

Emitter temperature T

°C

Emissivity ε

Acceptance criterion q_crit

kW/m²

Round lengths up to

Physical constants (σ in W/m²K⁴)

The values shown are an example. Use the emitter temperature, emissivity and acceptance criterion adopted for your project. IFEG 2005 notes that ε may conservatively be taken as 1.0.

Result

Peak flux along our wall

–kW/m²

Solid length needed from the corner L

–m

Flux at the end of the return wall

–kW/m²

Received flux along our wall, measured from the corner. Dashed lines: the criterion, the solid length L and the return wall R.

For your report

Item	Value

Working

Step	Symbol	Expression	Value	Unit

Method

Plan view. x is measured along our wall from the corner, and the distance from the emitter's plane is c = x + s. The receiver is at the emitter's mid-height.

The emitter is a uniform rectangle at temperature T with emissivity ε, emitting E = σεT⁴. A receiver on our wall faces sideways towards the emitter. With the receiver at the emitter's mid-height, the emitter splits into equal upper and lower halves of height h = a/2. Each half uses the factor for an element at 90° to a rectangle, level with its corner: φ_p(X, Y) = 1/(2π) [atan(1/Y) − Y/√(X²+Y²) atan(1/√(X²+Y²))], with Y = c/h.

Configuration factors add over area, so a wing wall is handled by subtraction: φ = 2 [φ_p((W+b)/h, c/h) − φ_p(W/h, c/h)]. This is exact when the emitter is on the plane of the wing wall. If the emitter is also set back from the corner (s > 0), a wing wall on the boundary hides more of the emitter than its own length, so the result is conservative.

The solid length L is the distance from the corner beyond which the flux stays at or below the criterion. It is solved exactly and then rounded up. A common slip is to use the formula for a receiver lying flat. Openings are in a vertical wall, so both ratios are divided by the emitter's half-height h. See validation.