Characterisation of industrial crossdrafts and their effect on hood capture efficiency.

Standard design methods for local exhaust hood design require the selection of the necessary capture velocity and then application of empirical equations relating capture velocity with hood flow rate. The selection of capture velocity depends on hood geometry, source generation rate, and disturbances in the vicinity of the local exhaust hood. Current design techniques for vapor degreasers require a hood flow rate of 0.25m3s-1 per m2 of tank area.(1) The design method does not account quantitatively for crossdrafts, but instead recommends eliminating crossdrafts. The little published data (1) on crossdrafts (velocity through "cracks" for various pressure differentials), is insufficient for design purposes. A more detailed analysis of industrial crossdrafts is necessary.