In this Science experiment, about 10 litres of hot water were placed inside the drum and the drum was heated using portable gas cookers until the water had boiled vigorously for a few minutes. The drum itself was very hot to touch also.
The heat was removed and when water vapour stopped coming out of the hole, the screw cap was fastened on.
The drum was hosed down in an attempt to cool the inside (cooling the bottom seemed to work well as the water in the bottom of the drum was still close to boiling point and so cooling that cooled the drum quite quickly).
The drum then suddenly "imploded" with a loud bang.
The simple explanation is that in heating the water in the drum the water changes phase from liquid to gas. Continuous heating drives the air out and water vapour continues to occupy and begin to leave the drum. After a while the contents of the drum is mainly water vapour at a temperature of 100 deg C or above.
When the cap is closed the system is sealed off from the outside. So as the contents begin to cool the vapour begins to condense. In the phase change there is a volume change - liquid occupies less space than gas. This decrease in volume results in a decrease in pressure. With atmospheric pressure being significantly greater than the pressure inside the walls of the container are not able to withstand the pressure differential and move to relieve the stress. So the drum collapses in on itself.
12 мар 2013
