Emberline

Radiant heat · parallel

Radiant heat flux from an opening facing your wall

The flux received at a wall that faces an opening (the emitter) across a gap, at the point opposite the centre of the opening, which is the worst point on the receiving wall. It also gives the separation at which the flux equals your criterion.

Inputs

Emitter and separation
m
m
m
Fire and criterion
°C
kW/m²

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

Received flux q
–kW/m²
Configuration factor φ
–
Separation that meets the criterion
–m

For your report

Emitter b × a (m)Separation c (m)φq (kW/m²)Criterion (kW/m²)Result

Working

StepSymbolExpressionValueUnit

Method

c b emitter (b wide, a high) receiving wall receiver
Plan view. The receiver is on the receiving wall opposite the centre of the emitter.

The emitter is a uniform rectangle at temperature T with emissivity ε, so it emits E = σεT⁴. The flux received by a small element of the facing wall is q = φE, where φ is the configuration (view) factor.

Seen from the point opposite its centre, the emitter splits into four equal quarters. Each quarter is a rectangle with the receiver on the normal through one corner, for which φc = 1/(2π) [X/√(1+X²) atan(Y/√(1+X²)) + Y/√(1+Y²) atan(X/√(1+Y²))], with X = (a/2)/c and Y = (b/2)/c (SFPE Handbook; IFEG 2005, Figure 2.4.2.3a). Then φ = 4φc.

The separation that meets the criterion is found by solving φ(c)E = qcrit, and is rounded up to the next 0.01 m. See validation for the checks behind these formulas.