A buoyancy-capture principle is firstly revisited as the most important fluid dynamics mechanism in kitchen range hoods. A recent new derivation of the capture efficiency of a kitchen range hood, which eliminates the inconsistencies and inadequacies of existing derivations, shows that the capture efficiency equals the ratio of capture flow rate to total plume flow rate in a confined space. The result is applied here, together with the buoyancy-capture principle, to derive a simple formula for determining capture efficiency.
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