Water Flow in Kettle
Experiment number : 2255
Goal of Experiment
We will visualize the water flow in a kettle using a thermal imaging camera.
Theory
Flow in fluids, i.e. gases and liquids, is the result of different densities of fluid layers with different temperatures. Usually, with increasing temperature, the density of the fluid decreases due to the volumetric thermal expansion (water with temperature in interval from 0 °C to 4 °C is an exception – also known as the water anomaly); fluid with higher temperature therefore rises.
Equipment
Thermal imaging camera, kettle.
Procedure
In this experiment, we use a thermal imaging camera to monitor the kettle, in which water is being heated, ideally from two perspectives – from above and from the side.
Sample Result
In the top view we can see heated water rise from the heating coil to the surface when the lid is open, the side view shows that although the spiral is located at the bottom of the kettle, the fastest to warm are the top parts of the kettle (due to flow). Heated water rises from the spiral through the centre of the kettle to the surface, here it is “driven” to the walls, cooled down and it sinks along the walls to the bottom. The video below shows a successfully captured experiment.
FLIR i7 thermal imaging camera was used to make this video. The temperature range of the colour scheme was chosen in the interval from 25 °C to 62 °C, emissivity was set to ε = 0.95.
Technical Notes
When scanning the water level from above, do not place the thermal imaging camera to less than 20 cm above the water level to avoid water condensation on the camera chip that would lead to its fogging and wetting.
Pedagogical Notes
It is advisable to use a kettle with the heating spiral visible at the bottom – the students can clearly see that although the heating is done at the bottom of the kettle, the highest temperature is measured at its top.
It is advisable to draw the students’ attention to the fact that, when viewed from above, the thermal imaging camera only measures the temperature of the water level, we have no information about what temperature conditions are under the level; this information is given to us by the side view. However, in this case it is necessary to take into account the fact that the water temperature is not measured directly, but only by measuring the temperature of the kettle walls.
