Object
The objectives of this experiment are as follows:
(i) to observe the evaporation and boiling phenomena in a drop after it falls onto a heated surface,
(ii) to measure the lifetime of the drop, and
(iii) to determine the heat-transfer characteristics in the sessile drop-boiling system.
Apparatus
Figure 20.1 is a schematic of the experimental setup. It consists of a dropgenerating system and an electrically heated testing surface with a thermal measurement device.
The liquids used in the drops are carbon tetrachloride, benzene, methyl alcohol, and distilled water.
A liquid fills a bottle equipped with a stopcock which is attached to a support and hangs over the heated surface. A needle valve regulates the rate of dripping flow from the bottle through a no.-1/4 hypodermic needle. The liquid is released from the needle in the form of drops 2 to 3 mm in diameter which fall at regular intervals.
In order to generate drops of identical size, a drop receiver is used to collect the drops until they fall at a steady, desired rate.
At the start of the experiment, the receiver is quickly displaced via the action of a spring to allow only a single drop to fall onto the center of the heated surface.
A center rest-pin is installed on the drop receiver to produce two-dimensional movement (in order to prevent drop-receiver vibration).