Convective Heat Transfer
Definition
Transfer of heat by bulk movement of a fluid (gas or liquid). In compartment fires, the buoyant hot gas plume carries most heat vertically, creating the hot gas layer at ceiling level.
- Mechanism
- Bulk movement of heated gas or liquid
- Result in fires
- Hot gas layer forms at ceiling level
- Contrast
- Conductive and radiative heat transfer
Common questions
Why does the hot gas layer accumulate at the ceiling rather than spreading evenly through a room?+
Buoyancy carries the heated combustion gases upward as a plume, and once they reach the ceiling they spread laterally and bank downward, forming a layer rather than dispersing through the whole space.
Why does convective heat transfer matter for reading fire damage patterns?+
It explains why ceilings and upper walls typically show earlier and heavier thermal damage than the floor, which investigators use when reasoning about the fire's development and area of origin.
Related terms
- Arrhenius Equation
- Mathematical expression relating reaction rate to temperature: k = A × exp(-Ea/RT). The exponential dependence explains the self-accelerating nature of combustion as...
- Auto-Ignition Temperature
- The minimum temperature at which a material ignites spontaneously without a pilot flame or spark. Relevant to the assessment of ignition scenarios...
- Carboxyhaemoglobin (COHb)
- The compound formed when carbon monoxide binds to haemoglobin at the oxygen-binding site, with an affinity 200-250 times greater than oxygen. Produces...
- Conductive Heat Transfer
- Transfer of thermal energy through a solid material by molecular vibration. Rate depends on thermal conductivity, temperature gradient, cross-sectional area, and path...
- Fire Tetrahedron
- The model of sustained combustion requiring four concurrent elements: fuel, oxidiser, heat, and an uninhibited radical chain reaction. Replacing the older fire...
- Flaming Combustion
- Gas-phase oxidation of volatile pyrolysis products above the fuel surface, producing a visible flame at 800-1200°C. Produces less CO than smouldering under...
- Flash Point
- Lowest temperature at which a liquid gives off enough vapour to form an ignitable mixture in air, but the vapour does not...
- Glowing (Smouldering) Combustion
- Surface-phase oxidation of solid char without a gas-phase flame, typically at 400-700°C. Produces large amounts of CO and can persist at lower...
- Radiative Heat Transfer
- Transfer of heat by electromagnetic waves (infrared). Scales as the fourth power of absolute temperature; at near-flashover temperatures it can simultaneously ignite...