PASCO ET-8782 Energy Transfer– Thermoelectric - Manual (Page 12)

Energy Transfer –Thermoelectric Conservation of Energy and the First Law of Thermodynamics
12 ®
Observe how the temperatures of the aluminum blocks change.
Run the peltier in Heat Pump mode for about a minute (or until the cold side appears to reach a
minimum temperature), then switch to Heat Engine mode.
Again, observe how the temperatures of the aluminum blocks change.
Power Generated data now appears in the bottom section of the graph display. The area under the
graph equals the energy generated by the heat engine and supplied to the load resistor. The Heat
Engine digits display shows the heat that has flowed out of the hot reservoir (Q
hot
) and the heat
that has flowed into the cold reservoir (Q
cold
).
Continue to record until the aluminum blocks are close to the same temperature.
Analysis
Heat Pump Mode
In Heat Pump mode the peltier does work to pump heat out of the cold reservoir
and into the hot reservoir.
W = work done by the peltier (equal to the area under the Input Power curve),
Q
hot
= heat pumped into the hot reservoir,
Q
cold
= heat pumped out of the cold reservoir.
By the first law of thermodynamics,
Q
hot
= Q
cold
+ W
1) Where did the heat pumped out of the cold reservoir go? Where did the heat pumped into the
hot reservoir come from? Why was more heat pumped into the hot reservoir than was pumped
out of the cold reservoir?
2) Compare your observed values of (Q
cold
+ W) and Q
hot
. If they are not equal, where did the
“lost energy” go?
3) Write an equation in terms of the “lost energy”, E
lost
, and your observed data, W, Q
hot
and
Q
cold
.
Heat Engine Mode
In a heat engine, heat flows out of the hot reservoir, some of the heat is
converted to work, and the rest of the heat flows into the cold reservoir.
W = work done by the heat engine,
Q
hot
= heat flow out of the hot reservoir,
Q
cold
= heat flow into the cold reservoir.
By the first law of thermodynamics,
Q
hot
W
Q
cold
Hot Reservoir
Cold Reservoir
Heat Pump
Q
hot
W
Q
cold
Hot Reservoir
Cold Reservoir
Heat Engine