PASCO TD-8564 THERMAL EFFICIENCY APPARATUS - Manual (Page 5)

012-05443A Thermal Efficiency Apparatus
1
Introduction
The Thermal Efficiency Apparatus can be used as a
heat engine or a heat pump. When used as a heat
engine, heat from the hot reservoir is used to do work
by running a current through a load resistor. The
actual efficiency of this real heat engine can be ob-
tained and compared to the theoretical maximum
efficiency . When used as a heat pump to transfer heat
from the cold reservoir to the hot reservoir, the actual
coefficient of performance and the theoretical maxi-
mum coefficient of performance can be obtained.
The apparatus is built around a thermoelectric con-
verter called a Peltier device. To simulate the theoreti-
cal heat engines found in textbooks which have infinite
hot and cold reservoirs, one side of the Peltier device
is maintained at a constant cold temperature by pump-
ing ice water through the block and the other side of
the Peltier device is maintained at a constant hot
temperature using a heater resistor imbedded in the
block. The temperatures are measured with ther-
mistors which are imbedded in the hot and cold blocks.
Additional Equipment Needed
To perform the experiments in this manual, you will
need the following equipment in addition to the
Thermal Efficiency Apparatus.
• 1 DC power supply capable of 2.5A at 12V
(SF-9584)
• 3 kg (7 lbs) ice and a bucket for the ice-water bath
• Ohmmeter (SB-9624)
• 1 Ammeter (up to 3A) (SB-9624A)
• 2 Voltmeters (SB-9624A)
• Patch Cords (SE-9750-51)
History
The principle upon which the Thermal Efficiency
Apparatus operates has been known since the 1800’s
but has only become practical since the recent devel-
opment of semiconductors.
In 1821 the Russian-German physicist Thomas Johann
Seebeck discovered that when a junction of dissimilar
metals is heated, a current is produced.
1
This phenom-
enon is now known as the Seebeck Effect and is the
basis of the thermocouple.
Then, in 1834, Jean-Charles-Athanase Peltier discov-
ered the opposite of the Seebeck Effect, that a current
flowing through a junction of dissimilar metals causes
heat to be absorbed or freed, depending on the direc-
tion in which the current is flowing.
2
Since the Ther-
mal Efficiency Apparatus is operated in this manner
the thermoelectric converter is called a Peltier device.
However, the Thermal Efficiency Apparatus also
exhibits the Seebeck Effect because the two sides of
the device are maintained at different temperatures.
Today the Seebeck Effect is achieved using pn junc-
tions. The arrangement of the dissimilar semiconduc-
tors is as seen in Figure 1. If the left side of the device
is maintained at a higher temperature than the right
side, then holes generated near the junction drift across
the junction into the p region and electrons drift into
the n region. At the cold junction on the right side, the
same process occurs but at a slower rate so the net
effect is a flow of electrons in the n region from the
hot side to the cold side. Thus there is a current from
the cold side to hot side in the n region.
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Hot
(T
h
)
Cold
(T
c
)
p
n
p
n
Copper
I
I
I
I
Load resistor
I
Figure 1: Arrangement of Thermocouples
1
Timetables of Science, by Alexander Hellemans and
Bryan Bunch, Simon & Schuster, NY, 1988, p.281.
2
IBID, p.301.
3
Circuits, Devices, and Systems, 3rd ed., by Ralph J.
Smith, Wiley, 1976, p.543.