We present preliminary results from an examination of the capture and
venting of a buoyant plume by a chimney.
The aim is to enable improved management of indoor pollutant sources
–
for instance, the plume rising from a
cooking pan in a kitchen or a cooking fire in a hut. Using the principle of dynamic similarity, we precise
ly and
controllably model the behaviour of indoor plumes by using saline solutions ejected into an enclosure containing
freshwater. These well
-
established laboratory analogue techniques enable the location and concentration of tracer
in the plume to be eas
ily tracked, reflecting the evolution of pollutants carried in the plume. Focusing on a plume
within a room containing a quiescent ambient environment, we identify two physical mechanisms potentially
responsible for driving the removal of pollutants. The f
irst, we describe as the
capture
of the plume, a process
driven by the direct interaction between the plume and the evacuation opening; the second, we describe as the
draining
flow driven by a buoyant layer of fluid which may accumulate at the ceiling and
is then evacuated through
the effects of buoyancy. We first demonstrate that the addition of a simple cylindrical chimney that hangs
downwards from an opening in the (analogue) ceiling increases the venting efficiency of these potentially polluting
plumes.
We go on to examine how the capture efficiency of these simple chimneys varies as the relative size of
the plume and the chimney are altered, and demonstrate that simple model can provide
predictions
of the observed
variation in capture efficiency.