PASCO ET-8782 Energy Transfer– Thermoelectric - Manual (Page 33)

Model No. ET-8782 Experiment 4: Coefficient of Performance
33 ®
Background
DataStudio has been configured to measure and record the temperature of both aluminum blocks,
and the voltage and current applied to the peltier. From these measured quantities, DataStudio will
calculate and display heat flow, power and work. The following sections explain how DataStudio
makes these measurements and calculations.
Heat vs. Temperature
The digits displays show the heat that flows into the hot block (Q
hot
) and out of the cold block
(Q
cold
). The relationship between heat flow and temperature change is given by
Q = mc
∆T
where:
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
hot
represents heat flowing into the hot block, but a positive value of Q
cold
represents heat transferred out of the cold block.
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
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, W, done by the peltier.
Start Condition
The configuration file contains a start condition; when you click the Start button (with the knife
switch open) DataStudio will display live data, but it will not start recording until you close the
knife switch. This will allow you to monitor the measurements and confirm that both blocks are at
the same temperature before data recording starts.