PASCO ET-8782 Energy Transfer– Thermoelectric - Manual (Page 28)

Energy Transfer –Thermoelectric A Model Refrigerator
28 ®
P = IV
where:
P = power (in watts = joules/second),
I = current (in amps),
V = voltage (in volts).
8. From the measured values of applied voltage and current, calculate the energy used to run the
heat pump for one second. How does the energy supplied to the peltier every second compare
to your estimate of the heat transferred from the heat sink to the air every second? Which is
bigger? Explain your observations in terms of conservation of energy.
Insulator, Fan and Heat Sink
9. When the hot and cold blocks have reached equilibrium, write down the temperatures. Did
you make a good refrigerator?
10. Remove the foam insulator (continue recording data). Can you see a change in the cold
temperature? Put the foam insulator back on. Why did the temperature change?
11. Turn off the fan (continue recording data). Observe the effect on the temperatures for a few
minutes. How have the temperatures of both sides changed? How has the temperature
difference between the hot and cold sides changed? Can you explain why?
12. Observe the air temperatures. Have they changed from when the fan was on? Do you think
that the rate of heat transferred from the heat sink to the air has increased, decreased, or
stayed the same? Explain your reasoning.
13. If the blocks were allowed to reach equilibrium with the fan off, what do you think the final
temperature of the “cold” block would be? Would that represent a good refrigerator?
14. Before the hot side reaches 80 °C open the knife switch or turn the fan back on.
15. What part of a real refrigerator is represented by the cold block on your model?
16. In general terms, what does a refrigerator do to make the inside cold? Why does it need
insulation? Why does it need a heat sink?
Further Investigation
1. Let the refrigerator run for several minutes with the insulator removed and the fan switched
on. What is the equilibrium temperature of the cold block in this mode?
2. Without increasing the power supplied to the peltier, can you make the cold side colder?
Propose a modification to your model refrigerator and do an experiment to test it.