PASCO TD-8564 THERMAL EFFICIENCY APPARATUS - Manual (Page 18)

Thermal Efficiency Apparatus 012-05443A
14
Mode T
H
(k
Ω
) T
c
(k
Ω
) T
H
(°C) T
c
(°C) V
H
I
H
V
w
V
S
Engine
Open
Table 2.1 Data
B. Connect the 2
Ω
load resistor with a short patch cord as shown in Figure 2.1. Connect a
voltmeter across the load resistor.
C. 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.
D. 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 3. Convert the
resistances to temperatures using the chart on the front of the device or Table 1 as
explained in the Measurements section.
E. Record the voltage (V
H
) across the heating resistor, the current (I
H
), and the voltage
across the load resistor (V
W
) in Table 2.1.
➁ Open
A. Disconnect the patch cord from the load resistor so no current is flowing through the
load and thus no work is being done. Now all the power delivered to the heating resistor
is either conducted to the cold side or radiated away. Leave the voltmeter attached so
that the Seebeck voltage (V
s
) can be measured. (see figure 7)
B. Decrease the voltage applied to the hot side so that the system comes to equilibrium at
the same hot temperature as in the Heat Engine Mode. Since the temperature difference
is the same as when the heat engine was doing work, the same amount of heat is now
being conducted through the device when there is no load as when there is a load.
(It may not be possible to exactly match the previous cold temperature.)
C. Record the resistances in Table 2.1 and convert them to degrees.
Also record V
H
, I
H
and V
p
.
Calculations for the Heat Engine
➀ Actual Efficiency: Calculate the actual efficiency using
e =
P
W
P
H
,
where P
W
=
V
W
2
R
and P
H
= I
H
V
H
.
Record the powers in Table 2.2 and the efficiency in Table 2.3.