Chemistry Reference
In-Depth Information
Figure 3 shows the mean temperature of a rectangular area of the water
surface during an experiment. Images were acquired once every 0.8 sec-
onds. Initially, the laboratory is unventilated and the surface temperature is
very close to both the bulk water temperature and the room temperature
(images 0 - 180). When the laboratory is ventilated by dry air the mean
temperature drops rapidly until the surface heat loss is balanced by heat
supplied to the surface by free convection within the container. (There are
fluctuations in surface temperature associated with free convection pat-
terns, but in common with numerous other observations of free convection,
every surface element is much cooler than the underlying water). At image
328, the peristaltic pump was switched on and bubbles began to surface
near the centre of the selected area. The temperature rose steadily as the
region disrupted by the surfacing bubbles expanded, until this region en-
compassed the entire selected area. Thereafter the surface temperature de-
creased as a result of heat loss, which was enhanced by the bursting bub-
bles.
Fig. 11.
Temperature of water surface in the course of an experiment
Examination of individual frames of thermal and video imagery reveals
details of disruption processes. Individual bubbles produce local warming,
indicating some disturbance of the surface microlayer, but only partial re-
newal of the surface. A plume of bubbles acts in concert to produce rapid
surface renewal within a well-defined area of the surface. The area affected
by the plume expands well beyond the region where bubbles are surfacing.
It is important to note that the particular experiment described here was
conducted with a very low airflow into the bubble generator yielding a
bubble plume that was barely perceptible in close-up video images of the
water surface. Stronger airflow and a substantial bubble plume produced
