If you take the handle of a hot pot, you may burn sometimes your fingers. The heat of the cooker is transfered via the metal. If the handle is made from plastic, the risk to burn your fingers is minor. Transport of heat varies for different solid materials.
In our climate system we have to take into account not only solid materials but also water and air. How does heat transport happen in this medium? We carry out an experiment in order to investigate the heat transport in this media.
Experimental setup:
Stopwatch
left: Beaker with water in a water vessel.
right: Beaker separated from the water vessel by a larger beaker.
Tools:
2 Experimental boiler, 2 Thermometres, 2 Glass beakers (small), 1 glass beaker (large), 2 large water vessels, ice cubes
Experiment:
1. Fill both of the small beakers with water of the same temperature and heat them with boilers of the same electrical output.
2. One of the beakers is standing in a water vessel, the other one in a larger glass beaker, which itself is standing in a water vessel.Take care, that the temperature in both vessels is comparable. This can be assured by a water-ice mixture.
Tasks:
1. Observe the temperature in both beakers.
2. Change the heat conductivity between the small and the larger beaker by filling in water. Observe the course of temperature in both beakers. Explain this behaviour.
3. What is the relationship towards the climate system?
Measuring the temperature before heating:
Results:
Temperatures as a function of time
| without water between the beakers | with water between the beakers | |||
| Zeit | Temp. beaker 1 | Temp. beaker 2 | Temp. beaker 1 | Temp. beaker 2 |
| [min] | [°C] | [°C] | [°C] | [°C] |
| 0 | 44 | 44 | 36 | 36 |
| 1 | 39 | 44 | 34 | 34 |
| 2 | 35 | 43 | 32 | 32 |
| 3 | 31 | 42 | 30 | 30 |
| 4 | 29 | 41 | 28 | 29 |
| 5 | 27 | 40 | 28 | 28 |
| 6 | 26 | 39 | 27 | 27 |
| 7 | 23 | 39 | 26 | 26 |
| 8 | 21 | 39 | 24 | 25 |
| 9 | 20 | 38 | 24 | 25 |
| 10 | 18,5 | 37 | 24 | 25 |
| 11 | 17 | 36,5 | - | - |
| 12 | 16 | 36 | - | - |
| 13 | 14,5 | 35,5 | - | - |
| 14 | 14 | 35 | - | - |
| 15 | 13 | 34,5 | - | - |
Diagram:
T1 represents the course of temperature in the left beaker directly connected to the water.
T2 represents the temperature course in the right water beaker, surrounded by the air in the larger beaker.
In order to show that it is not the second glass wall which limits the heat transport but really the air between the beakers, we fill the space between them with water.This leads to a comparable temperature course between both of them if we repeat the experiment for these conditions.
T1 represents the temperature in the left beaker in the water vessel.
T2 represents the temperature in the right beaker, now surrounded by water, too.
Interpretation:
1. The quantity of energy transferred as heat is the same in both vessels. In both beakers the water tends to transport energy to the surrounding kept at 0°C. However the temperature is different.
The first beaker is directly connected to the water of 0°C. The second beaker is standing in another one, in the same water vessel of 0°C but separated from the water by the air in the larger beaker. This thin layer of air interrupts the heat transport from the warm water to the cold water. Therefore the temperature in the air-surrounded beaker remains higher than in the one directly connected to cold water.
2. If you replace the air by water the conductivity changes and the course of temperature in both setups is comparable. The isolating layer of air is removed and the heat can be diverted.
Conclusions:
If the supply with energy is given, the temperature is higher when the flowing off of heat is less.
3. Relationship to the climate system:
Water (oceans), air (atmosphere) and the transport of heat from the sun play an important role in the climate system. We saw that the transport of heat is much slower in the air than in water. This means: Heat transport from the warm surface of the earth towards the space is inhibited by the isolating air.
If air has different temperatures in different altitudes (see red temperature diagramm in the chart below), it is only close to the earth’s surface due to the low heat conductivity in the air. With increasing altitude other properties of the air molecules play a role, as the capability to absorb radiation. This is the reason why in the stratosphere (15.-50 km of altitude) the air becomes warmer again. The capability of the air to take up heat by absorption is explained in the greenhouse experiment.
However in the oceans, the temperature decreases with depth. Heat is tranported from the surface to the bottom of the ocean, but does never really reach the enormous depth of several 1000m. Therefore the surface of the oceans, besides from the polar regions, is always warmer.