1
UNIVERSITY OF IDAHO & SANDIA NATIONAL LABS
Thermopile Test Bench
Interim Design Document
Adrian Aspinall, David Eld, Tyler Merritt, Paul Sowinski
8/5/2010
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Executive Summary
For our senior design project Sandia National Labs has submitted a project to develop and build a thermopile
test bench. This test bench will measure the electrical characteristics and efficiency of thermopiles. Sandia is
currently working on energy harvesting technology using thermopile, and the ability to determine the
electrical characteristics and thermal efficiency is needed. The test stand will need to take a host of thermal
and electrical measurements under controlled conditions. For the electrical characteristics measurements
the test bench will measure open circuit and load output voltages, internal impedance, and electrical output
power. During the first semester of our project we laid down the foundation for building the test bench. We
conducted initial research into the background of the projects looking into the theory of operation behind
thermopiles and sensor and instruments that would be useful in developing the test bench. The various
systems we would need for the test bench were defined, and we began testing and selecting the sensors and
other hardware that will used. In this report will go over the systems we looked into and finally chose for
heating, cooling, heat flux measurement, and axial loading systems. Ultimately we chose a system using a
ceramic heater, a thermoelectric cooling system, thin film heat flux sensors, and an electrically driven linear
actuator. These systems will be controlled and monitored by a program developed in Labview. We have also
developed a plan and tentative schedule for the following semester.
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Contents
1.0 Background ......................................................................................................................................................4
1.1 Project Introduction ....................................................................................................................................4
1.2 Motivation ...................................................................................................................................................4
2.0 Problem Definition ..........................................................................................................................................5
2.1 Problem Statement .....................................................................................................................................5
2.2 Measurement and Control ..........................................................................................................................5
2.3 Heat Flux Calculation ...................................................................................................................................5
2.4 Voltage Calculation......................................................................................................................................6
2.5 Efficiency Calculation...................................................................................................................................6
2.6 Radiation Calculation...................................................................................................................................8
3.0 Concepts Considered .......................................................................................................................................9
3.1 Heat Flux Sensors ........................................................................................................................................9
3.2 Heaters ..................................................................................................................................................... 10
3.3 Coolers ...................................................................................................................................................... 11
3.4 Axial Load Application .............................................................................................................................. 12
3.5 Vacuum Chamber ..................................................................................................................................... 13
4.0 Concept Selection ......................................................................................................................................... 15
5.0 Design Solution ............................................................................................................................................. 18
6.0 Future Work ................................................................................................................................................. 22
References .......................................................................................................................................................... 25
Appendix A: Sources for Project Learning .......................................................................................................... 26
Appendix B: Axial Load Test ............................................................................................................................... 27
Appendix C: Water Block Cooling Test ............................................................................................................... 29
Appendix D: Thermoelectric Cooler Data Sheet................................................................................................. 32
Appendix E: Heat Flux Sensor Data Sheet .......................................................................................................... 35
Appendix F: Linear Actuator Data Sheet ............................................................................................................ 36
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1.0 Background
1.1 Project Introduction
The premise of the project is to create a test bench for thermopiles. A thermopile is a thermoelectric device.
It converts heat energy into electrical energy. To do this it relies on two thermoelectric effects, the Seebeck
effect and the Peltier effect. When an isolated conductor is exposed to a temperature gradient a voltage is
set up in the material, this is known as the Seebeck effect. When two conductors of different composition are
connected there is a voltage set up in each, but the voltage realized by each is different, thus there is a
change in voltage across the material. When two conductors are connected under a temperature gradient a
voltage is set up and current flows through the material. The opposite is also true, when current runs through
two connected conductors a temperature gradient is setup up across the conductors. Those are the
underlying effects of a thermopile. To further increase the output power of a thermopile many pairs of
conductors are connected in series to create a larger change in voltage. To test the thermopiles they must be
exposed to vacuum so heat loss is minimized and efficiency is maximized. Also, by exposing it to a vacuum
the heat transfer through the material becomes much simpler. Quantities such as heat flux can be measured
more accurately (1D problem instead of 2 or 3D) since there is no error associated with empirical
correlations. The test bench must also exert axial load on the thermopile, this is done to minimize contact
resistance. By minimizing contact resistance the hot side and cold side temperatures of the device can more
accurately be measured.
1.2 Motivation
Sandia National Laboratories has sponsored this project, to acquire a test bench, allowing thermopile devices
to be tested in a controlled environment. As the previous solution has been described to our team, the prior
test bench was a rudimentary setup and was not very user friendly. Heat flux could not be directly measured
so efficiency could not be accurately determined. Also the Lab view VI was poorly put together and did not
have good documentation. The new test bench will be beneficial to Sandia because it will allow users to test
these devices and determine their overall efficiency, which they are not currently able to do effectively.
Sandia also hopes that this project design will allow them to test their devices at various test conditions.
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2.0 Problem Definition
2.1 Problem Statement
To design and fabricate test equipment to accurately and easily determine efficiency and electrical
performance of thermopiles under an imposed temperature gradient. The device must withstand vacuum,
apply axial load, and display and record relevant data.
2.2 Measurement and Control
The Test Bench will need to accurately measure and control the conditions of the test to determine the
thermopile characteristics and efficiency. The test bench will measure the following values.








Open circuit and load voltage produced by the thermopile
The impedance of the thermopile
The load resistance
Electrical power produced by the thermopile
Heat flow through the thermopile
The temperature of the hot and cold sides of the thermopile
The axial load applied to the thermopile
The pressure of the vacuum chamber
Along with measuring the test conditions the test bench must carefully control several aspects of the test
these include.




The hot and cold side temperatures
Heat flow through the thermopile
The axial load applied to the thermopile
The load resistance
2.3 Heat Flux Calculation
Estimate of heat flux, compare to measured heat flux.
By taking T_hot and T_cold as constants and knowing an effective thermal conductivity k we can estimate the
heat flux through the material with the following equation:
𝑞 ′′ = 𝑘 ∗
𝑑𝑇
𝑑𝑥
(1)
6
q''
[W/m^2] k [W/m-K] dT [K] dx [m] s [m]
A [m^2]
q [W]
6769
1.1
80
0.013
0.018 0.000324 2.193
21150
1.1
250
0.013
0.025 0.000625 13.221
13750
1.1
250
0.02
0.025 0.000625 8.594
9167
1.1
250
0.03
0.025 0.000625 5.729
6875
1.1
250
0.04
0.025 0.000625 4.297
5500
1.1
250
0.05
0.025 0.000625 3.438
Table 1 Calculated values for varying thermopile sizes and temperatures
Probable flux for first unit
Possible fluxes for next unit
(depends on dx and
effective thermal
conductivity)
These estimates can be used to validate what our heat flux sensors return, though our flux out will be lower
than our flux in as some energy will be converted to electrical energy. These values are rough estimates
based on approximate thermal conductivity and approximate dimensions.
2.4 Voltage Calculation
Estimate voltage from thermopile, compare to measured voltage
The output voltage should agree with the following equation:
𝑉=𝛼∗
𝑛𝑝𝑖𝑙𝑙𝑎𝑟
∗ ∆𝑇 (2)
2
Where alpha is the Seebeck coefficient of the material, n_piller/2 would represent the number of junctions in
the thermopile. This is an approximation as the Seebeck coefficient depends on the proportion of Bi and Te in
the material, also not all the thermo-electric elements are in series.
2.5 Efficiency Calculation
Estimate thermopile efficiency, compare to efficiency based on measurements
An equation for theoretical efficiency is as follows:
(Taken from the CRC Handbook of Thermoelectrics [1])
𝜂=
𝑇1 − 𝑇2 𝑀 − 1
∗
𝑇
𝑇1
𝑀 + 𝑇2
1
(3)
𝑤ℎ𝑒𝑟𝑒 𝑀 = (1 + 𝑍 ∗ 𝑇𝑚 )0.5 (4)
𝑇𝑚 = 𝑚𝑒𝑎𝑛 𝑡𝑒𝑚𝑝. =
𝑇1 + 𝑇2
2
(5)
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Figure 1 AT for different materials [2]
For smaller unit 𝑇𝑚 =40°C
For larger unit 𝑇𝑚 =125°C
ZT will be read off the above graph rather than calculated as we do not have the required
information to calculate it for our specific material. For both TE units ZT ~ 0.95
First Unit
Efficiency
4.14%
T1 [C]
T2 [C]
M
80
0
T1 [K]
T2 [K]
353
1.396
ZTm
Tm
0.95
40
273
Second Unit
Efficiency
9.87%
T1 [C]
T2 [C]
M
250
0
T1 [K]
T2 [K]
523
ZTm
Tm
1.396 0.95 125
273
Table 2 Calculated values for the first and second units
Above are the calculations for efficiency, these will be used later to help validate our measurements.
Measurements have yet to be performed as we have just acquired our flux sensors. Rough
measurements will be made starting late august. More accurate measurement can be made when we
acquire a vacuum chamber.
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2.6 Radiation Calculation
Use flux and power (based on measurements) to estimate energy lost to radiation and determine if radiation
shielding must be used.
By using measured heat fluxes and calculating electrical power out we can check to see if there are other
losses.
𝑃𝑜𝑢𝑡 =
𝑞𝑖𝑛 = 𝑞"𝑖𝑛 ∗ 𝐴
&
𝑉2
𝑅
(6)
𝑞𝑜𝑢𝑡 = 𝑞"𝑜𝑢𝑡 ∗ 𝐴
(7) & (8)
If there are no losses from the system to convection (should not be losses to convection if in a vacuum) or
radiation then:
qin − Pout = q out (9)
If equation (9) does not hold largely true it is likely that there are appreciable losses to radiation.
The equation would then take the form:
qin − Pout − qradiation = qout (10)
If Q_radiation is large enough to throw the efficiency calculation (9) off by say a percent or two, then the
thermopile must be shielded as to minimize radiation loss.
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3.0 Concepts Considered
Figure 2 shows the initial visualization of the test bench and outlines basic components. Components in this
figure correspond to the concepts considered in this section.
Figure 2 Initial visualization of test bench
3.1 Heat Flux Sensors
All of our heat flux sensors operate on the same principle. This principle is best described on the RdF
corporation website: http://rdfcorp.com/anotes/pa-hfs/pa-hfs_02.shtml. Here are some excerpts from this
page that describe the construction and operation of the heat flux sensor. “The principle of operation of the
sensor is a differential thermocouple type sensor which utilizes a thin foil type thermopile bonded to both
sides of a thermal barrier as shown below. The temperature difference across the thermal barrier is
proportional to the heat flow through the sensor… Only one pair of junctions is required for a completed
sensor; however the output signal and sensitivity are directly proportional to the number of paired
junctions… Multiple pairs of junctions in series are used to increase signal and resolution.”
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Figure 3 diagram of a heat flux sensor [3]
∆𝑇 = 𝑄
𝑆
𝐾
Where ΔT is temperature difference across the thermal barrier, Q is the heat flux through the thermal
barrier, S is the thickness of the thermal barrier, and K is the thermal conductivity of the thermal barrier. For
best results maximize thermal conductivity and minimize thickness.
3.2 Heaters
All of our heaters operate on the same principle: Joule heating. Pass current through a wire and it will
produce heat. Minimizing the cross sectional area will affect the current density allowing for lower current
draw and higher voltages to attain direct conversion of electrical energy into thermal energy.
The performance of our heaters therefore depends largely on the material that contains the resistive
elements, in all cases some sort of etched foil. This substrate has a certain breakdown temperature after
which it fails when that temperature is exceeded. Four substrates were considered: ceramic, polyimide,
Teflon, and silicone.
The ceramic being the only non rubber substrate can obviously withstand higher temperatures but is limited
in its construction by the high temperature solder applied to attach the leads. Another drawback to the
ceramic heater is that it is brittle. The rubber heaters vary in breakdown temperature and malleability and as
such have inherent problems. The breakdown temperature of the rubber substrates are below our specified
temperature of the heater. The picture below shows a visualization of the ceramic heater with its foil heating
element.
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Figure 4 Diagram of the ceramic heater [4]
3.3 Coolers
Three principle effects where considered for our cooling device. We considered thermoelectric coolers, heat
sinks, and water bath cooling. The thermoelectric cooler operates on the Peltier effect, cooling one side of
the device while heating the other thus creating a temperature difference proportional to the electrical
power through the device. This allows a certain amount of controllability but requires another device to
remove heat from the heated side of the device. Next we considered water bath cooling with a water block
removing the heat, transferring it to the water. Water can contain a lot of thermal energy, but ideally this
also requires an additional device to remove thermal energy from the system. The third type of device we
considered is the heat sink. The heat sink removes heat through convection and this is not ideal for our
application as we intend to minimize convection within our test fixture.
Figure 5 picture of the water block(left) [5] and Thermoelectric module(right) [6]
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3.4 Axial Load Application
Concepts Considered
1. Pneumatic Actuator
2. Linear Actuators (Electric)
3. Mechanical Application
Overview of Pneumatic Actuator
The load would be applied with a pneumatic cylinder; the load would
have to be calculated by the Labview VI based on the input of a
pressure sensor. Besides a pressure sensor, air lines, valves, and an air
compressor would be needed (unless shop air was available). If the
actuator was double acting or spring loaded that would be convenient,
otherwise an external spring might need to be used to retract the
actuator when thermopiles needed to be switched. Since the forces
exerted by the pneumatic actuator would not be directly proportional
to its displacement, measures may need to be taken to prevent damage
to thermopiles- unless the actuator was sized so max load was not
Figure 6 Pneumatic Actuator [7]
much beyond 300 lbf with max pressure supplied
A load would be generated by an electric motor with a gear
reduction extending a rod. For a range of loads to be applied a spring
in series may need to be used to ramp on the load. Determining load
would be trivial if a spring was used in that many linear actuators
have linear potentiometers built in so a force could be calculated
based on a known spring constant. Alternatively, a force or pressure
transducer could be used to determine the force. Either way, the
signal could be passed to the Labview VI and the input to the
actuator could be varied to further extend or retract.
Figure 7 Electric Linear Actuator [8]
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Overview of Mechanical Application (arbor press or clamp)
The last, and obviously worst idea for axial load
application is some sort of mechanical/manual load
application. This could be carried out as an arbor press or
a clamp with a built in mechanical advantage. The obvious
problem with this from the start is that it would be
difficult to control by software. For an arbor press a
stepper motor or servo could possibly be implemented,
for some sort of clamp a servo or solenoid could be used
(with no capability of automatic load adjustment with the
latter). Either way such a solution would be clumsy and
roundabout. So it was not looked into too seriously from
the start.
Figure 8 Arbor Press [9]
3.5 Vacuum Chamber
Concepts Considered
1. Custom Fabricated Chamber
2. Bell Jar
3. Pre-fabricated Chamber
Overview of Custom Fabricated Chamber
The vacuum chamber has not been considered at great depth
yet, however these are the options considered thus far.
There are a number of options for making a vacuum chamber.
1.
2.
3.
4.
5.
Thick plastic sheets adhered (acrylic, Plexiglas, etc)
Thick plastic tubing
Round metal tubing (probably steel)
Square metal tubing
Modifying a pressure vessel
Figure 9 Materials for fabrication
With either round option sealing the door may be awkward as it may need to be on the curved side due
to the likely proportions and layout of the rest of the apparatus. So the door could consist of a section of
a pipe with an ID equal to the OD of the wall. The door for either material would ideally be transparent.
Besides using a section of slightly larger pipe for a door (may be hard to find compatible sizes) a sheet
could be thermal formed. The advantage of the plastic sheets is that sealing the doors would be trivial as
they would just be flat sheets.
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Overview of Bell Jar
This would be a simple option which would require less time
designing and fabricating so time could be spent elsewhere on
the project. A bell jar of about the size we would need would
cost roughly $700. However, there would still be fabrication
required for some sort of base plate for mounting, passing
wires, and passing tubing. While the amount of fabrication for
the bell jar may be less, the fabrication may have to be done by
us, where as fabrication of a vacuum chamber, say from round
or square steel tubing, may be outsourced largely to some sort of
Figure 10 Bell Jars [10]
fabrication shop- so this is yet another aspect to further consider.
Overview of Pre-Fabricated Chamber
A prefabricated vacuum chamber may be
purchased that would require little to no
modifications (including vacuum pass thrus and
inspection windows). However, along with that
convenience is a hefty price tag and the
inability to closely choose size and proportion
(which may not be fully known until later in the
project). A very rough estimate of cost would
be $3000+.
Figure 11 Pre-fabricated Chambers [11]
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4.0 Concept Selection
When considering our heat flux sensors our most important attributes included the ability to withstand our
maximum temperature, operate within our power range, and have low thermal impedance. Our table below
shows that again we have one option that can withstand our maximum temperature, but there are other
options that come close to our specifications.
Table 3 Decision matrix for flux sensor options
When considering heaters our most important attributes included the ability to reach our maximum
temperature, deliver thermal energy in our power range, and have a large usable area. Our decision matrix
below shows that only one heater fits our maximum temperature requirement although there are a few
options that come close.
Table 4 Decision matrix for heating options
The most important aspects for the cooling to the team were the minimum temperature, length of cooling
and controllability. The minimum temperature was the most important because the cold side of the
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thermopile can be no higher 15°C. The length of cooling refers to how long the cooling source can maintain
its cold temperature. For example, an aluminum block would eventually reach the temperature of the
system. The last aspect of importance was controllability. This was important because we wanted the user
to be able to control the cold side temperature and not just have it fixed.
Table 5 shows the different options we considered for cooling the cold side of the thermopile. All the options
except the thermoelectric cooler were used by themselves. The thermoelectric cooler had to be cooled on
its hot side somehow though, so we used the water block in series with it. The aluminum and stainless steel
blocks and the aluminum heat sink were not chosen because they have no controllability over how cold they
are and eventually would become the same temperature of the system, since they cannot rely on convective
cooling in a vacuum. The water block and thermoelectric cooler were excellent choices, but using the
thermoelectric cooler with the water block allowed us to have fine control over the temperature as well as
having the water block consistently removing heat with water.
Table 5 Decision matrix for cooling options
The two most important aspects for the axial loading device were the ability to apply a 300 lbf and that it was
software controlled. Table 6 shows the different options we considered for the axial load. The arbor press
was not selected due to the fact that we could not think of a way to easily control it with software. The
pneumatic and linear actuators were both adequate choices since both of them provided all the functions
and worked in similar ways.
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Table 6 Decision matrix for axial loading options
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5.0 Design Solution
The design of our test stand is based on the scores from our design matrices. Through these design matrices
we were able to select the best components to use in our design based on how well they performed the
necessary tasks. Not all components of our design have been fully considered yet, but are included in our
future work to be accomplished next semester. Figure 11 shows the components that we have selected so
far.
Cooling
Axial Loading
Heat Flux
Sensors
Heaters
Thermoelectric Cooler with
Water Block
Linear Actuator
[12]
RDF
hfs-a
[13]
Thermostone
Beryllium Oxide
Heater [4]
Figure 12 Selected components for design
Since we do not have all the parts yet, we modeled a three-dimensional view of what the design will look like,
this can be seen in figure 13. Below the thermopile is the thermoelectric cooler and water block. Above the
thermopile is the heating block (copper or some other highly conductive material), the heater isolation block,
and the linear actuator. This is all contained in a vacuum chamber, which we will be researching next
semester.
+
Figure 13 Current 3D design of test stand (not all parts proportional)
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To confirm that the thermoelectric cooler and water block meet our specifications, we tested the cooler
against different options of cooling the hot side. The detailed results can be found in the Water Block Test
write-up in the appendices, but using room temperature water with the water block, we achieved
-7.5°C. This exceeded our goal temperature of 10°C at the beginning of the project. This setup is also ideal
because the thermoelectric cooler allows the tester to accurately control the temperature by regulating the
voltage to the cooler and the water block keeps a consistent temperature on the hot side of the cooler. The
cooler and thermal paste used in testing is shown in figure 14.
Figure 14 the thermoelectric cooler and thermal paste
To heat the hot side of the thermopile, we have chosen the Thermostone ceramic heater. The main reason
for choosing this heater is because it can reach the necessary temperature of 250°C. The heater also has a
thickness of 0.04 inches which allows us to easily isolate it from the load.
To apply the axial load, we have decided to use a linear actuator. We had considered pneumatic and electric
actuators, but due to client preference, we choose the electric linear actuator. The reasons that linear
actuators were appealing were because they could be controlled by the software and some have
potentiometers built-in them, which will help with interfacing it with the software.
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The heat flux sensor that we want to use is the hfs-a Micro-Foil Heat Flux Sensor from Rdf Corporation. The
reason we want to use this heat flux sensor is because it was the only one that we could find that could
withstand a temperature of 250°C. This is a crucial component to determine the overall efficiency of the
thermopile and must be able to reach our max temperature. This sensor also has a thickness of 0.003 inches
and a response time of 0.05 seconds, which will help keep the design compact and gather data quickly and
accurately. These sensors also have thermocouples built into them, allowing the software to record the
temperature and not just the heat flux.
The heat flux sensors will be placed on the top and bottom of the thermopile, on the faces of the heating
block and thermoelectric cooler. We have a tentative solution to use a heater isolation block that is just a
hollowed out piece of metal that allows the heater to sit under it, without taking any of the axial load so that
it does not break. Not shown in figure 13 are the electrical wires and water tubing from the water block
routing out of the vacuum chamber. Since we have not decided on a vacuum chamber yet, we still have not
decided how to route these items.
The software we have decided to use is LabVIEW. We have chosen this software because of its simplicity and
it is user-friendly. Data will be acquired from the test stand, through a data acquisition system, and recorded
in LabVIEW. From the software interface, users will be able to monitor the test and change certain aspects of
the test. Figure 15 shows the current concept of what the LabVIEW interface will look like. Users will be able
to monitor the real time measurements for the electrical, heat transfer, and environmental aspects of the
test in the ‘Measurements’ section. The calculations being performed by the software will be displayed in
the ‘Calculations’ section. The parameters to be set by the user will be controlled in ‘Test Control Inputs’
section. Figure 16 shows the layout of how the Labview program will acquire input from the test stand and
control and measure the experiment.
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Figure 15 Current concept LabVIEW interface
Figure 16 system control map
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6.0 Future Work
As we move forward into the next semester there is a significant amount of work ahead of us. To help
maximize the effectiveness of our remaining time we have planned out the rest of our project and
established a preliminary time line and schedule for next semester. First after returning from the break
between semesters we will have a teleconference with our client to update everyone on the current state
and future tasks of the project. In early September we will be finishing the testing of components to become
familiar with their functions and verify that they will work for our application. We will make our test writeups available for review. We will want to have finalized the specifications for the data acquisition and control
system around the same time we complete initial component testing. We will be using out newly acquired
flux sensor to set up PID temperature control in Labview. An image of our flux sensor is shown in figure 17.
Figure 17 Thin film heat flux sensor
With the flux sensor we will also be able to start gathering some preliminary data on heat flux and efficiency.
We have also acquired a thin film thermocouple for testing purposes. We will use this for preliminary
measurements and to test the effects of axial load on contact resistance. Our thin film thermocouple is
shown in figure 18
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Figure 18 thin film thermocouple
Since the cross section of the thermopiles, the flux sensor, and the thermocouple are all different we will be
using polyimide tape to fill in any gaps to maintain a flux as uniform as possible. The two sensors are
constructed largely from polyimide, so we can maintain a near constant thermal conductivity. The polyimide
tape is shown in figure 19.
Figure 19 Polyimide tape
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The next phase of the project will be developing the detailed design. We will need to create a drawing
package, detailed list of hardware, and cost estimate for approval of the final design. Upon approval of the
design construction of the prototype would begin in late September. The prototype is to be complete and
testing its functionality by mid October. Once the functionality is verified a manual draft for the test bench
will be written and submitted for review.. From this point the remaining time will go into writing the final
design report and preparing for the final snapshot day. Below is table 7 with our current schedule.
Client Meeting
Late August
Complete initial testing
Mid September
Complete Detailed Design
Mid September
Detail design review
Mid September
Finish Prototype
Late October
Finish Verification Tests
Mid November
Submit Manual Draft
Mid November
Final Snapshot
12/3/10
Final Report
12/15/10
Table 7. Schedule for next semester
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References
[1] CRC Handbook of Thermoelectrics, Edited by D.M. Rowe, 1995
[2] The Science of Thermoelectric Materials,
http://www.thermoelectrics.caltech.edu/science_page.htm
[3] RdF, Heat Flow Measurement (construction and principal of operation),
http://rdfcorp.com/anotes/pa-hfs/pa-hfs_02.shtml
[4] Thermo-Stone, Thin Film Heaters, http://www.thermostone.com/index.cfm/products.htm
[5] Newegg, Thermaltake CL-W0075 Liquid Cooling System,
http://www.newegg.com/Product/ImageGallery.aspx?CurImage=35-106-077-S01&SCList=35-106-077S01,35-106-077-S02,35-106-077-S03,35-106-077-S04,35-106-077-S05,35-106-077-S06,35-106-077-S07,35106-077-S08,35-106-077S09&S7ImageFlag=2&Item=N82E16835106077&Depa=0&WaterMark=1&Description=Thermaltake%20CLW0075%20Liquid%20Cooling%20System
[6] Parts Express, Peltier Thermo-Electric Cooling Module 3 Amp,
http://www.parts-express.com/pe/showdetl.cfm?partnumber=320-252&source=googleps
[7] RS, P1D 2 acting pneumatic cylinder,63x100mm, http://radionics.rsonline.com/web/search/searchBrowseAction.html?method=getProduct&R=4939564#header
[8] Supertech Machinery & Electric Co., Linear Actuator-IMD3 (GD23),
http://www.ecvv.com/product/1411025.html
[9] Northern Tool & Equipment, JET Arbor Press — 1 Ton, Model# AP-1 333610,
https://www.northerntool.com/shop/tools/product_200406671_200406671
[10] Great Glass, Pyrex Bell Jars, http://www.greatglas.com/PyrexBellJars.htm
[11] Terra Universal, Vacuum Chambers,
http://www.terrauniversal.com/environmental_chambers/vacuum_chambers_index.php
[12] Surplus Center, Electric Linear Actuators, https://www.surpluscenter.com/item.asp?item=5-15772&catname=electric
[13] Rdf, Heat Flux Sensors, http://www.rdfcorp.com/products/hflux/hfs-a_01.shtml
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Appendix A: Sources for Project Learning
Websites:
Topic
Website
Transtutors
URL
Seebeck Effect
Seebeck Coefficient
Electronics Cooling
http://www.electronicscooling.com/2006/11/the-seebeckcoefficient/
Heat Flux Sensors
RdF
Temperature Controllers
Omega
http://www.rdfcorp.com/anotes/
pa-hfs/pa-hfs_01.shtml
http://www.omega.com/prodinfo
/temperaturecontrollers.html
Thermopiles
PID Theory
Wikipedia
National Instruments
Peltier Effect
Transtutors
Thomson Effect
Transtutors
Thermoelectrics
The Science of
Thermoelectric Materials
Books:
CRC Handbook of Thermoelectrics (Edited by D.M. Rowe)
http://www.transtutors.com/phy
sics-homework-help/currentelectricity/seebeck-effect.aspx
http://en.wikipedia.org/wiki/Thermopiles
http://zone.ni.com/devzone/cda/tut/p/id/378
2
http://www.transtutors.com/physicshomework-help/current-electricity/peltiereffect.aspx
http://www.transtutors.com/physicshomework-help/current-electricity/thomsoneffect.aspx
http://www.thermoelectrics.caltech.edu/scie
nce_page.htm
27
Appendix B: Axial Load Test
Axial Load Test- Peltier Cooler
Purpose: The purpose of this experiment is to make sure our pettier cooling units can withstand axial loads
up to 300 pounds. The other reason was to see how high of loads they can withstand- which would be
important if there were a failure (of a sensor or in software) which may cause a higher than desired load.
Experimental Setup:
Arbor Press Rack
y
Arbor Press Arm
Force Gauge
W_rod
W_rack
Al Plate
Cooler
Base
W_scale+W_applied
An equation for the axial force would be:
𝑟𝑎𝑡𝑖𝑜
𝐹𝑎𝑥𝑖𝑎𝑙 = 𝑊𝑟𝑎𝑐𝑘 + (
2
) ∗ 𝑊𝑟𝑜𝑑 + 𝑟𝑎𝑡𝑖𝑜 ∗ (𝑊𝑎𝑝𝑝𝑙𝑖𝑒𝑑 + 𝑊𝑠𝑐𝑎𝑙𝑒 )
Measurements:





The weight of the rack was estimated to be 11.7 lbf
The weight of the lever arm was measured to be 5.20 lbf
The weight of the scale was measured to be 3.46 lbf
One revolution of the arm was made for a ∆𝑦 of 6.825”, with a arm length of 22.5” from axis,
the ratio between axial force and force applied to the lever arm is 20.7.
The aluminum plate used (placed between the cooler and rack) was cut to 1”x1” to
represent the largest thermopile the test fixture will use.
Plugging values into the previous equation yields:
𝐹_𝑎𝑥𝑖𝑎𝑙 = 137 + 20.7 ∗ 𝑊𝑎𝑝𝑝𝑙𝑖𝑒𝑑
28
Results:
Applied Load (lbf)
0.64
3.0
5.44
7.84
20 (max)
Axial Load
(lbf)
150
200
250
300
551
Compression Stress (psi)
150
200
250
300
551
After these loads were applied, the 1”x1” block was replaced with a 0.7”x0.7” block effectively
doubling the amount of stress the cooler could experience- this was done because the force gauge
could not read out more than 20 lbf. The data corresponding to the smaller block is as follows:
Applied Load (lbf)
0.64
3.0
5.44
7.84
20 (max)
Axial Load
(lbf)
150
200
250
300
551
Compression Stress (psi)
300
400
500
600
1100
Under these loads (in either case) no damage was obvious upon visual inspection.
Conclusion: After the first tests were done the cooler was supplied with power and it was verified
that is still functioned correctly. Again, after the smaller block was used, the cooler was again
supplied with power and it was verified that is still functioned. It was initially thought that with a
300 pound load the brittle ceramic material might be crushed- though that seems to not be the
case. Upon reflection it makes sense that the cooler could resist at least 1100 psi in that the load
was completely compressive. Not only does it seem likely the coolers will not have any problem
resisting loads the apparatus is likely to operate under, but it could also resist loads in excess of
what the linear actuators under consideration could produce.
Verification of Method: Initially there was some doubt that the arbor press could produce 65 lbf
with only the weight of the rack and rod (horizontal) alone. The spring rate of a coil spring was
experimentally determined. The spring had a rate of 28.4 lbf/in. With no load applied (and the scale
removed) the arbor press could compress the coil spring from its free length of 2.9” to its solid
length of 1”. This corresponded to a force of at least 54 pounds (at which time the spring bottomed
out, at which point the lever arm was no longer horizontal which would correspond to a shorter
effective lever arm) - so it was determined that our model was at least sufficiently accurate.
29
Appendix C: Water Block Cooling Test
Water Block Cooling Test
Purpose: The purpose of this experiment is to make sure our water block cooling system would be able to
provide enough cooling to the peltier cooler so that low temperatures could be maintained on the cold side of
the thermopile. We wanted to see that if ambient temperature water flowing through the water block would be
adequate enough or if we would have to circulate water through an ice bath. It also served as a test to see that
if this setup would work as our cooling solution for our design. We were also able to regulate the voltage
through the peltier cooler and compare our experimental outputs with the data supplied from the manufacturer.
Experimental Setup:
Water Block
Pump
5 gal Bucket
16 oz. Cup
Ice
Aluminum Block
Stainless Steel Block
Potentiometer
Peltier Cooler
12 V Power Supply
Type K Thermocouple (with LabView VI)
Thermal paste
Water Block Test Setup
Thermoelectric Cooler Attached to Water Block
Measurements:
●
●
●
Water at room temperature was around 20°C
Water with ice was around 0°C
The voltage output from the potentiometer ranged from 3-10V
Experiment: The power supply that we used to power the system (the peltier cooler and water pump) was a
12V computer power supply. To be able to control the voltage to the peltier cooler, we used a potentiometer,
which allowed us to control the voltage from 3-10V. Although we could get 10V from the potentiometer, it
would start to heat up quickly, so we kept the voltage level around 7V. To compare the effectiveness of the
water block, we found two other metals to use as a heat sink. For all the cooling blocks, we used thermal paste
between the cooling block and the peltier cooler to help conduct heat better.
30
Results:
Cooling Block
Temp. (°C)
Time to Steady State
Temp. (s)
Aluminum
Stainless Steel
Water Block
Water Block (Ice
Bath)
~ -5
~2
~ -7.5
~ -10
~ 60
~ 60
~ 60
~ 35
Conclusion: The specifications given to us, by our client, was to have the cold side of the thermopile at 1015°C, which was obtained by all the cooling blocks we tested. Since our final design will be in a vacuum, we
will have to rely on conduction for cooling, since there will be no convection heat transfer and all of our
cooling blocks in this test did remove heat by conduction. If a single thermopile test will take a couple of
hours though, using just conduction into a material will eventually raise the temperature of the material to the
hot side of the thermoelectric cooler. This is why the water block was an appealing solution, since the water
flowing through the system will remove heat from the block and our data shows that it will still work with
room temperature water and give comparable results to the other cooling blocks tested.
Plots of Temperature vs. Time
Plot of Temperature vs. Time for Stainless Steel Block
Plot of Temperature vs. Time for Aluminum Block
31
Plot of Temperature vs. Time for Water Block with Room Temperature Water
Plot of Temperature vs. Time for Water Block with Ice Bath Water
32
Appendix D: Thermoelectric Cooler Data Sheet
33
34
35
Appendix E: Heat Flux Sensor Data Sheet
36
Appendix F: Linear Actuator Data Sheet