PASCO ET-8782 Energy Transfer– Thermoelectric - Manual (Page 11)

Model No. ET-8782 Experiment 1: Conservation of Energy and the First Law of Thermodynamics
11 ®
Q = heat transferred,
m = mass of the aluminum block,
c = specific heat of aluminum = 0.90 J/(g·°C),
∆T = change in temperature.
A positive value of Q may represent heat transferred into or out of the aluminum block,
depending on whether the block is on the hot side or the cold side of the peltier, and whether the
peltier is operating as a heat pump or a heat engine.
The temperature of each block is measured by the embedded thermistor. DataStudio calculates the
heat flow from the measured temperature change, and pre-entered values of m and c. Click on the
calculator icon in the tool bar and look at the equations used; note the constants, m and c, in the
bottom section of the calculator window. (The mass of each block is about 19 g. If you would like
to enter your own value for the mass, measure the blocks with calipers and use the density of
aluminum, 2.7 g/cc, to calculate the mass, then enter it in the calculator.)
Input Power and Work Done by the Peltier Heat Pump
In Heat Pump mode, Input Power from the power supply equals the rate at which the peltier does
work to pump heat out of the cold reservoir and into the hot reservoir. The Voltage/Current Sensor
measures the voltage applied to the peltier, and the current that flows through it. DataStudio
calculates the Input Power using the equation: Power = Voltage × Current.
The area under the plot of Input Power versus time equals the energy supplied to the peltier, which
equals the work done by the peltier.
Power Generated and Work Done by the Peltier Heat Engine
In Heat Engine mode, Power Generated is the rate at which the peltier does work on the load
resistor. The Voltage/Current sensor measures the voltage across the resistor and the current
through it. From these measurements, DataStudio calculates the power supplied to the load
resistor. The area under the plot of Power Generated versus time equals the work that the peltier
has done on the resistor.
Procedure
Before you start, the aluminum blocks should both be at room temperature. The knife switch
should be in neutral position (straight up) and the fan should be switched off.
Set the DC Voltage to between 3 and 4 volts.
Start data recording, then set the knife switch to Heat Pump.
You will see Input Power data appear in the top section of graph. The area under the graph equals
the energy supplied to the peltier, which equals the work done by the heat pump. The Heat Pump
digits display shows the heat pumped out of cold reservoir (Q
cold
) and the heat deposited into the
hot reservoir (Q
hot
).