Derivation of capture efficiency of kitchen range hoods in a confined space

An existing derivation of capture efficiency of a kitchen range hood in a confined flow system, based on a two-zone mixing model, is shown to be inconsistent and inadequate. A new derivation is proposed, which shows that the capture efficiency equals the ratio of captured flow rate to the total plume flow rate at the front canopy height. The new capture efficiency equals the direct capture efficiency, if we assume that the hood captures contaminant directly from the source as efficiently as it captures contaminant that is entrained from the room.