Experimental study of mixing in a closed room by doorway exchange flows.

We present a series of analogue laboratory experiments of the transient exchange flow between a room filled with warm air and a cold exterior following the opening of a doorway. Our experiments suggest that the time-scale for mixing the fluid in the room below the top of the doorway is independent of the door height. We then describe the steady-state two-layer stratification that is established when, in addition to the exchange flow, a localised heat source provides heat at the base of the room. Our experiments suggest that the height of the steady interface depends primarily on the aspect ratio of the doorway and is independent of the strength of the source of heat.