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Convective Air Flow - Single Heat Source

Calculate the vertical air flow and air velocity generated by a single heat source.

A heat source, like an engine, stove, melting pot or a person, will generate a convective vertical air flow as indicated in the figure below.

Air Velocity

The air velocity in the center of the air flow at a distance above the floor can be calculated as

vc = c1 (P / l)1/3                                              (1)

where

vc = air velocity in center of the air flow (m/s)

c1 = constant characterizing the actual application, typical values ranging 1 to 2

P = heat power from the source (kW)

l = distance above the floor and the heat source (m)

Air Flow Volume

The air flow volume in a distance above the the floor can be calculated as

Q = c2 P1/3 l5/3                                       (2)

where

Q = air flow volume (m3/s)

c2 = constant characterizing the actual application, values ranging 0.05 to 0.15 (typical 0.06)

Example - Convective Air Flow above an Engine

The heat loss from the surface of an engine is 10 kW. If c1 = 1.5, the air velocity 3 meters above the engine can be estimated to

vc = 1.5 ((10 kW) / (3 m))1/3

= 2.2 m/s

With c2 = 0.06 the volume flow can be estimated to

Q = 0.06 (10 kW)1/3 (3 m)5/3

= 0.8 m3/s

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Citation

• The Engineering ToolBox (2005). Convective Air Flow - Single Heat Source. [online] Available at: https://www.engineeringtoolbox.com/convective-heat-source-d_1007.html [Accessed Day Month Year].

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7.8.15

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