PASCO TD-8564 THERMAL EFFICIENCY APPARATUS - Manual (Page 26)

Thermal Efficiency Apparatus 012-05443A
22
Procedure
➀
Connect a DC power supply and a voltmeter and ammeter to the heater block terminals.
Turn on the voltage to about 11 V.
➤ NOTE: This is just a suggested value chosen to make the hot temperature nearly at the
maximum allowed. Any voltage less than 12 V is suitable. The Thermal Efficiency
Apparatus should not be run for more than 5 minutes with the hot side above 80°C. A
thermal switch will automatically shut off the current to the heater block if it exceeds
93°C to prevent damage to the device.
➁ Connect the 0.5W load resistor with a short patch cord as shown in Figure 11. Connect a
voltmeter across the load resistor.
➤ NOTE: Alternatively, a variable power resistor (rheostat) may be used in place of the load
resistors supplied with the Thermal Efficiency Apparatus. This has the advantage of being
able to continuously vary the load resistance. However, it will be necessary to measure
the resistance of the load.
➂ Allow the system to come to equilibrium so that the hot and cold temperatures are constant.
This may take 5 to 10 minutes, depending on the starting temperatures. To speed up the
process, increase the voltage across the heating resistor momentarily and then return it to 11
V. If it is desired to cool the hot side, the voltage can be momentarily decreased. Remember
that the thermistor resistance goes down as the temperature increases.
➃
Measure the temperature resistances of the hot side and the cold side by using the toggle
switch to switch the ohmmeter to each side. Record the readings in Table 5.1. Convert the
resistances to temperatures using the chart on the front of the device or Table 1 as explained
in the Measurements section.
➄
Record the voltage (V
H
) across the heating resistor, the current (I
H
), and the voltage across
the load resistor (V
W
) in Table 5.1.
Table 5.1: Heat Engine Data and Results
R(
Ω
) T
H
(k
Ω
) T
C
(k
Ω
) T
H
(°K) T° (°K) V
H
I
H
V
W
P
H
P
L
e
0.5
1.0
1.5
2.0
2.5
3.0
3.5