MCEN 3032
3/15/2011
Thermoelectric Cooler Lab
Thermoelectric Coolers (TECs) are solid-state heat pumps that are widely used in
electro-optical research and industrial, analytical instruments as well as some
commercial products. They are mainly used to keep optics and electronics from
overheating and malfunctioning. They provide precise cooling (and heating) where
space is scarce, and do not require the complex fluid-mechanical setup of a
conventional refrigeration cycle. The general thought is that they are rather inefficient
at converting the electrical-power input to heat, i.e., a few sources claim the efficiency is
around 10%. However, manufacturers of these coolers claim the efficiency is near 40%.
This lab will investigate the efficiency of a TEC system to determine if the
manufacturers’ claims are feasible.
Figure 1 presents a thermoelectric cooler. The cooler is formed from two n-type and
two p-type semiconductors with low thermal conductivity, five metallic interconnects
with high electrical conductivity and high thermal conductivity, two electrically
insulating ceramic substrates, and a power source. When power is supplied, current
flows through the resulting electric circuit, giving the refrigeration effect: a heat transfer
of energy from the cold region. This phenomenon is known as the Peltier effect.[1]
The p-type semiconductor material has electron vacancies called holes. Electrons move
through this material by filling individual holes, slowing electron motion. In the adjacent
n-type semiconductor, no holes exist in its material structure, so electrons move freely
and more rapidly through that material. When power is provided by the power source,
positively charged holes move in the direction of current while negatively charged
electrons move opposite to the current; each transfers energy from the cold region to
the warm region.[1]
Figure 1: Thermoelectric Cooler Diagram.[2]
MCEN 3032
3/15/2011
Thermoelectric Cooler Circuits Background:
The overall objective of this lab is to determine the efficiency and operational
characteristics of a TEC using an experiment with a setup similar to the illustration in
Figure 2.
5V and 12V
Figure 2: Experimental set up (Part A).
The TEC will be powered from a voltage supply, and by tracking the voltages and
electrical input power, one can calculate the thermal efficiency of the TEC using heat
balance equations. The experiments will be transient (time dependent), and, for one
experiment, both masses (bodies) will be insulated from the environment (assume
adiabatic when defined as insulated).
For determining the temperatures of the hot and cold regions in parts A and B of the
experiment a basic understanding of the circuits involved is needed. Fig.3. illustrates
the circuit which provides the LabView VI with the voltage being supplied to the TEC for
parts A and B of the experiment.
MCEN 3032
3/15/2011
Figure 3: Visual Representation of circuit used to deliver the voltage input of TECS 1&2 to LabView.
In Figure 3, VPower Supply is the voltage selected by the switch on the electrical box of the
experiment (see Figure 6). R* is equal to 0.1 Ohm and serves as a current sensor. The
current through R* may be found using the voltage measurements of V1 and V2. V1
and V2 represent the actual voltage drop across the 0.1 Ohm resistor. The TEC box
represents the TEC that is connected between V2 and ground (V=0). The LabView VI
displays V1 and V2 directly.
In part A of the lab, the temperatures of the two heat bodies need to be determined
using the resistance of a thermistor attached to each body. Figure 4 presents the
voltage-divider circuit associated with the thermistors for part A.
Figure 4: Voltage divider circuit used for determining the resistances of both the hot region and cold region
thermistors.
MCEN 3032
3/15/2011
Thermistor 1 is connected to the cold region of experiment A, and thermistor 2
measures the hot region. Knowing the voltage supplied, the voltage measured, and the
resistor that serves as the upper leg of the voltage divider, the resistance of the
thermistors can be calculated.
Experimental Procedure:
This experiment consists of two parts; Experiment A and Experiment B are illustrated in
Fig.5.
Figure 5: Illustration of the two different experimental set ups for the TEC
The laboratory equipment used in this experiment is illustrated in Figure 6.
MCEN 3032
3/15/2011
Figure 6: Visual representation of the Thermoelectric Cooler Lab Module
Part A, 5V:
1. Connect the USB cable to the computer at a LabStation.
2. Open the NI Measurement and Automation Explorer (MAX) software. On the
left side of the screen within the Devices and Interfaces tree, a NI USB 6008
device should be listed. Make sure this device is labeled as “Dev3,” and if it is
not, re-label it to be “Dev3” (right click on the deviceRename). This is
necessary for the LabVIEW program to work properly.
3. Plug in the 5V/12V power supply and turn it on via the switch on its back panel.
4. Open the Lab View VI: “Thermoelectric Cooler.VI” which is located in the H:\ITLL
Documentation\ITLL Modules\Thermoelectric Cooler folder.
5. On the electrical box, set the voltage switch to 5V. Flip the experiment-selection
switch is set to Experiment A. Start the VI and record data for 10 min.
6. Once you have collected 10 minutes of data, stop the VI. SAVE YOUR DATA! Set
the experiment-selection switch to the middle (off) position. You will come back
to Part A of the experiment after completing Part B, so remove the insulation
from underneath experiment A and replace it with the aluminum plate. This is
to help the temperature of the two bodies equilibrate.
MCEN 3032
3/15/2011
Part B:
1. Set the voltage switch to 12V.
2. Flip the experiment-selection switch to Experiment B and start recording data
with the LabVIEW VI.
3. Turn the temperature set screw (using provided screwdriver) on the controller so
that the set point temperature equals 20C. Keep recoding data until steady state
is reached. Adjust to 17.5C, wait for steady state, then 15C and finally 10C.
4. Once you have all the data and have been able to reach steady state for all
temperatures, stop the VI. SAVE YOUR DATA!
5. Set the lab switch to the middle (off) position.
Part A, 12V:
1. On the electrical box, set the voltage switch to 12V. Flip the experimentselection switch is set to Experiment A. Start the VI and record data for 10 min.
2. Once you have collected data for 10 minutes, stop the VI. SAVE YOUR DATA! Set
the lab switch to the middle (off) position and turn off the power supply via the
switch on the back.
3. Unplug the power supply and USB cable. Return the experiment to its storage
rack.
Data Analysis:
Part A
1.1 Write down the overall heat balance in the system and state any assumptions.
Expand all equations in detail, and explain you reasoning.
1.2 Convert the voltages for the two thermistors to temperatures using Figure 4 and
information from the data sheet of the thermistor.
1.3 Discuss the results of the experiment in terms of:
- The heating and cooling balance to input power
- Ratio of cooling to heating for different times (1min, 2min, 5min, and 10min)
1.4 What are the uncertainties in this experiment?
MCEN 3032
3/15/2011
Part B
2.1 Illustrate the energy balance in this setup, including the body of interest, the TEC
and the heat sink. Assuming a constant temperature for body 1, write down the heat
transfer equation between the ambient air and the body. How can you get a good
approximation for the body surface temperature?
2.2 The typical application involves keeping the temperature in body 1 constant. Record
the power supplied to the TEC, and calculate the heat flow into the body from the
surrounding environment, Q, for the five different temperatures.
3.3 Find the ratio of the TEC input power to the heat transfer into the body, and discuss
any relation to the body temperature. When is the TEC working hardest?
3.4 What are the uncertainties in this experiment?
Lab References
[1] Book
[2] TEC Diagram, http://www.ferrotec.com/technology/thermoelectric/, March 15th
,2011