Exchange principles

Results

Below are some screenshots captured during the experiment. The Y-axis shows temperature in degrees C at the four different measuring points along the heat exchanger.

Figure 4: Con–current results

Figure 4 above was generated using the con–current setting with warm and cold water both coming into the heat exchanger from the right. It is evident from the experiment that the maximum exchange that takes place is 50% — as soon as the two temperatures are equal no further net exchange is possible.

Figure 5 below shows the results from a counter–current experiment with a low flow rate through the exchanger. The warm water is entering the exchanger from the right while the cold water enters from the left. As shown this is a very efficient way of exchange. The warm water enters at 29 °C and leaves at 10 °C while the cold water enters at 8 °C and leaves at 28 °C.

Figure 5: Counter–current results (low pump speed)

In the final results (Figure 6) the counter–current setting is used but this time with a higher flow rate through the exchanger. In this case it is clear that at this high flow rate the exchange is not as efficient as with the low flow showing that the exchange is flow-dependent.

Figure 6: Counter–current results (high pump speed)

Teachers’ notes

Safety issues
None.

Time required

• 1 day to set up and verify the experiment.
• 2–3 hours to perform the experiment.

Target age groups
This experiment is aimed at university level students, but can be adopted to different levels depending on the questions asked.

Results
The results from the experiments should be discussed with the students so that they fully understand the principles and what effects flow rate and flow directions have on the exchange and then put this in the context of biological systems.

Distance education studies
The exchange principles experiment is ideally suited for running as part of a distance education programme.

A working example of the experiment is currently set up in the University of Göteborg in Sweden. The lab can be accessed and the experiment performed over the Internet.

For further information about this experiment please contact Professor Michael Axelson of the University of Göteborg.