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Table of Contents 1 Mission Statement 2 Thermoelectric Physics 2.1 Seebeck and Peltier 2.2 Thermoelectric Figure of Merit, ZT 2.3 The Physics of Thermoelectrics 2.4 The Seebeck Coefficient 3 Thermoelectric Applications 3.1 Seebeck ''Power Generation'' Thermoelectric Operation 3.2 Peltier ''Heating and Cooling'', Thermoelectric Operation 3.3 Thermoelectric Systems 3.4 Thermoelectric Cooling Systems 4 Benchmarking - Vendors and Developers 4.1 Researchers and Developers of Thermoelectric Materials 4.2 Commerical Vendors of Thermoelectric Modules 4.3 Commerical Vendors of Thermoelectric Systems 5 Methods for Testing and Evaluation of Thermoelectric Modules and Systems 5.1 Codes and Standards 5.2 Testing programs at Other Institutions 5.3 Scholarly Articles 6 Family Development Roadmap 6.1 General References, Background Information, and Web Resources 7 Customers Supporting this Family of Projects 8 Stakeholders having an interest in this Family of Projects 8.1 Senior Design Students at RIT 8.2 Students Enrolled in the Energy and The Environment Option in ME 8.3 Students Enrolled in the Sustainability Minor in the KGCOE

The Next Generation Thermoelectric Systems - Family of Projects is built upon Dr. Robert J. Stevens' professional development interest in support of the Energy and the Environment Option within the mechanical engineering department at RIT. This project family focuses on the application, performance testing evaluation, and development of emerging and next generation thermo-electric modules and devices for use in both heat transfer and power generation applications.

Mission Statement

The mission of this family of projects is three-fold.

1. To engage students in meaningful design, development, and research activities related to the technology field of thermo-electrics, with a particular focus towards students enrolled in th Energy & Environment Option of the ME Department, the Sustainability Minor administered by the ISE department, and the Power Systems Concentration in the EE Department.
2. To provide a foundation for the continued professional development of Dr. Robert J. Stevens, and other faculty who may develop collaborative research interests with Dr. Stevens.
3. To enhance the reputation of the Kate Gleason College of Engineering in the broad field of thermo-electric technology development.

Family of Projects

Project Number	Project Description	Start Term	End Term
P07441	Thermoelectric Test Stand	20062	20063
P07442	Thermoelectric Demo Device	20062	20063
P07443	TBA	20072	20073
P07444	TBA	20072	20073
P07445	TBA	20072	20073

Thermoelectric Physics

Thermoelectric devices work due to a phenomenon called the thermoelectric effect which is the direct conversion of a temperature gradient across two dissimilar metals into electricity. The thermoelectric effect is also reversible directly converting electricity into a temperature gradient.

Seebeck and Peltier

The thermoelectric effect is based on a combination of the Seebeck effect and the Peltier effect. In 1821, German physicist Thomas Seebeck accidentally discovered the Seebeck effect when he observed a voltage differential between the ends of a bar, composed of two dissimilar metals, when one end was heated and the opposite was cooled. Thirteen years after Seebeck, John Peltier observed the reverse phenomenon which is now referred to as the Peltier effect. The Seebeck effect has been implemented for decades in thermocouples, but it was not until recent advances in semiconductor technology that the thermoelectric effect was applied to heating, cooling and power generation applications.

Thermoelectric Figure of Merit, ZT

Thermoelectric power generation efficiency is determined by a non dimensional figure-of- merit, ZT=S²RT/k, where S is the Seebeck coefficient, R is electrical conductivity, T is absolute temperature, and k is thermal conductivity. Over the years efficiency was increased by increasing the ratio of electrical conductivity to thermal conductivity using specialized metals and assembly techniques bringing the maximum ZT value to around one. Recently, major advances in engineered thermoelectric materials via optimization of proton and electron transport, through superlattices and quantum dot superlattices, have significantly increased the maximum ZT value. Future material discoveries implementing nanostructures, such as nano wires and nanotubes, are expected to raise the maximum ZT value to far greater levels.

The Physics of Thermoelectrics

The Thermoelectric effect is created in the presence of a temperature difference between two dissimilar metals or semiconductors due to a varied response in temperature change between the two metals. The difference in temperature from one material to the other causes current to flow in conductors if they form a current loop. The voltage generated in the current loop is generally in the order of several microvolts per degree temperature difference.

The following image is of a common thermoelectric circuit configuration comprised of Semiconductor materials P and N. Semiconductors are the common material of choice in thermoelectric devices because they possess a higher Seebeck coefficient that other metals. P and N designate the electron affinity or hunger for electrons of the semiconductor material. Th and Tc represent the hot and cold side.

The voltage developed within this circuit is derived from:

equation 1

S_P and S_N are the Seebeck coefficients (also called thermoelectric power or thermopower) of the semiconductor materials P and N. The Seebeck coefficients are non-linear, and depend on the conductors' absolute temperature, material, and molecular structure.

The Seebeck effect is due to two effects: charge carrier diffusion and phonon drag.

The Seebeck Coefficient

The Seebeck Coefficient used in calculating thermoelectric power is commonly derived in the following manner.

When the temperature difference between the materials is relatively small:

Then the lumped Seebeck coefficient of the entire thermocouple may be defined by the voltage generated by the thermoelectric system DeltaV as follows:

equation 2

The Seebeck coefficient may also be derived by the relation of the electric field E and the temperature gradient by the equation:

equation 3

Superconductors are commonly used to determine individual Seebeck coefficients because superconductors have a Seebeck coefficient of zero. Due to this phenomenon the Seebeck coefficient derived in equations 2 and 3 for superconductor/semiconductor thermocouples is simply the coefficient of the individual semiconductor material.

Thermoelectric Applications

Most commercially available modules consist of an array of either Lead Telluride or Bismuth Telluride semiconductor pellets. Some Specialized power generation modules may also use Silicon Germanium. Lead Telluride modules are generally used for power generation applications due to their ability to operate near combustion gas temperatures of 500 C while Bismuth Telluride modules are most often used for heating and cooling applications for temperatures less than 200 C. Thermoelectric module size is limited due to thermal material expansion between hot and cold sides. Bismuth Telluride modules are generally between 0.25 to 2 square while large power generating Lead Telluride modules may be slightly larger.

Semiconductor arrays are configured in pairs of N and P pellets where N pellets are doped with N type impurities so the majority carriers are electrons and P type pellets are doped with P type impurities so the majority carriers are holes. The configuration of the N/P pellet paring determines the direction of current flow within the module. N/P pellet pairs are configured so that they are connected electrically in series, but thermally in parallel as seen in the thermoelectric voltage figure. The pellet array is sandwiched between a metalized ceramic substrate which holds the pellets and provides conductive tabs that connect them together. The ceramic substrate also serves as an electric insulator and heat transfer medium between the pellet arrays owing to the requirement for specialized material. Multiple thermoelectric modules may be arranged in groups with either series, parallel, or series/parallel electrical connections or in some specialized applications used stacked series multistage heat transfer configurations. All thermoelectric modules may be used for power generation from a heat gradient or for heating and cooling under power.

Seebeck Power Generation Thermoelectric Operation

For most power generation configurations a large heat sink is coupled to both sides of the thermoelectric device. When a temperature gradient is created across the thermoelectric device, by heating one side in relation to the other, a DC voltage develops across the terminals. When a load is properly connected, electrical current flows. The figure of merit, ZT, for the majority of modern bismuth Telluride power generation modules is approximately 1, while lead telluride modules carry a ZT value of approximately 0.8-0.9. Regardless of the lower ZT value, in comparison to bismuth telluride, lead telluride modules are more efficient in power generation owing to their ability to operate at a greater temperature gradient.

Thermoelectric power generation modules are currently in use on remote telecommunication devices, for navigation, and for remote petroleum installations.

Peltier Heating and Cooling, Thermoelectric Operation

Applying direct current to a thermoelectric module causes the charge carriers within the P/N pellets to absorb heat from one side of the ceramic substrate and transfer it to the opposite side. This creates a cold surface on the substrate where heat is absorbed and a hot surface where heat is released similar to a heat pump.

The figure of merit, ZT, for the majority of modern bismuth Telluride modules is approximately 1. Thermoelectric heating and cooling modules are widely used for mini cooling applications, small refrigerators, vibration free cooling applications, and precision heating and cooling.

Thermoelectric Systems

The efficiency of a thermoelectric system is governed by the first law of thermodynamics:

For thermoelectrics the first law is reversible depending on cooling and heating or power generation. Often thermoelectric systems are used to increase the thermodynamic efficiency of other systems. Power generation thermoelectric systems may be used for example to power fans or pumps in heat exchangers using electricity generated by the temperature differential accross the heat exchanger.

For power generation systems efficiency is determined by the thermoelectric figure of merit ZT and delta T from hot sink to cold. The plot below shows efficiency verses deltaT for a variety of current and projected ZT values

Thermoelectric Cooling Systems

For applications in heating and cooling the term efficiency is generally not used due to its specific thermodynamic definition relating to heat generated to work applied. This definition often does not apply to heating and cooling applications due to heat pumping which involves the movement of heat from place to another. For many household heat pumps the calculated thermodynamic efficiency would appear to be well over 100%, however, this is a misnomer based on the fact that the work applied is simply used to pump heat from another source and not directly for heat generation. The Coefficient of Performance COP, which is the ratio of useful heat movement to work input, is most often used to determine heating and cooling performance. COP is defined for heating and cooling by the following equations:

Currently, the majority of available thermoelectric modules vary between 0.4 to 0.7 COP which varies based on DeltaT and ZT. Typically, modern refrigerators have a COP of 3-4.

Because of the relatively low COP for current thermoelectric cooling devices large thermoelectric refrigerators and heat pumps are still cost prohibitive. For small cooling applications, such as wine coolers, thermoelectric devices are actually highly competitive in price and performance to vapor compression refrigerators. Thermoelectric refrigerators also have advantages over standard refrigerators in that they are silent, more compact, and vibration free.

Benchmarking - Vendors and Developers

Hi-Z has published numerous papers on thermoelectric technology and is one of the pioneers of the industry. Currently supplies a range of high quality modules and is the only established thermoelectric company with near production prototype superlattice modules.

Global Thermoelectric Corp specializes in high power thermoelectric generators and is the only supplier of lead telluride modules in the US.

Marlow Industries develops thermoelectric technology for the United States Military.

Melcor Corporation is the leader in quality low cost thermoelectric modules in China.

Nextremethermal is the only commercial manufacturer of superlattice thermoelectric modules.

Researchers and Developers of Thermoelectric Materials

The Thermal Electric Institute is a leader of thermoelectronic technology in Ukraine.

MIT Nanoengineering is a leader in thermoelectric quatum dot and nanotube material research.

Clarkson University has developed several thermoelectric waste heat recovery systems.

Michigan State is working on thermoelectric technology with Tellurex corp

University of Texas, Austin has made several breakthroughs and continues work on thermoelectric nanotechnology.

Clemson University is focused on themoelectric materials research for heating and cooling applications

Commerical Vendors of Thermoelectric Modules

A list of all known commercial thermoelectric vendors throughout the world may be found here

The following Companies supply thermoelectric systems to the US

Tellurex sells bismuth telluride modules for power generatinos as well as heating and cooling, they have very good information on thermoelectic design available on their site.

Advanced Thermoelectric sells both thermoelectric modules and accessories to research institutions. One may also find another brief introduction to thermoelectric technology on their webpage.

Ferrotec is a global supplier of customized thermoelectric modules and supplies

San Diego, California based Hi-Z Technologies Inc. offers various power generation thermoelectric modules for sale on their website in addition to a small selection of accessories and supplementary equipment.

Marlow Industries Inc. sells a range of thermoelectric coolers, including single and multistage solutions.

Thermoelectricsupplier.com offers a wide assortment of thermoelectric supplies, including but not limited to interface materials, senors, power supplies, and sub-assemblies.

http://www.inbthermoelectric.com/index.html Supplier of a wide variety of thermoelectric products

http://www.tetech.com/

Commerical Vendors of Thermoelectric Systems

http://www.globalte.com/ is the only US company that offers High power lead telluride generating systems.

Supercool of Sweden offers numerous industrial thermoelectric systems.

Methods for Testing and Evaluation of Thermoelectric Modules and Systems

The Thermoelectric module family of projects must abide by all standards that govern the testing and operation of thermoelectric devices set forth by the American Society of Mechanical Engineers (ASME) and the Institute of Electrical and Electronics Engineers (IEEE). Due to the limited nature of research conducted in this area, and limited commercial application of thermoelectric devices, the body of literature available on standards for this field of electro-mechanical devices is relatively limited. However, some literature is available for review and guidance. Moreover, meaningful guidance can be extracted from literature on similar processes (e.g. heat exchangers, transducers, etc.).

As this body is developed, sections will be recategorized and amended to reflect the addition of new information. A first attempt at creating a body of regulations for the implementation of testing thermoelectric modules follows.

Codes and Standards

ASHRAE offers codes and standards for heat exchangers and testing relating to the HVAC&R industry the standard for air to air heat exhangers ANSI/ASHRAE 84-1991 is found here.

ASME Standards for air to air heat exchangers may be purchased here.

ASME Heat exchange commitee offers a list of ASME contacts IEEE Power generation standards

UL Testing Proceedures and certifications for HVAC, Electrical insulation and Engine generation may be found here.

Testing programs at Other Institutions

Thermoelectric modules have been used in industry for some time. A significant amount of research was conducted in the field during the 1960's and 1970's, while interest dropped / tappered in the following decade. Relatively recently, interest has focused on applying newly engineered materials to modules. However, very little literature exists about testing methodology and performance rating of competing modules.

Hi-Z has developed a Themoelectric Testing Proceedure

Tellurex offers an in depth analysis of techniques used to compare their thermoelectric systems to other manufactures

The University of Maryland has developed testing programs in partnership with Melcor

UK Based Cardiff Thermoelectric Group offers thermoelectric testing and consulting services

The NASA Jet Propulsion Lab has proceedures for testing deep space SiGe themoelectric generators

Peltier-info.com offers links and information to just about everything else related to thermoelectrics

Scholarly Articles

Several Papers are available through IEEE on Thermoelectric characterization and standards

Search Term (thermoelectric standards) and (thermoelectric characterization) in Compendix

Papers Include:

A simple experimental technique for the characterization of the performance of thermoelectric-coolers beyond 100 deg C

Authors:Nabi, Aharon; Asias, Amiad

Serial title: Annual IEEE Semiconductor Thermal Measurement and Management Symposium

Accession Number: number:05499523543

---

Thermodynamic modelling of a solid state thermoelectric cooling device: Temperature-entropy analysis

Authors: Chakraborty, A.; Saha, B.B.; Koyama, S.; Ng, K.C.

doi.org

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Methodology for extracting thermoelectric module parameters

Authors: Mitrani, D.; Tome, J.A.; Salazar, J.; Turo, A.; Garcia, M.J.; Chavez, J.A.

Accession Number: 04418404346

Family Development Roadmap

The family of projects begins with the launch of two related projects this winter, P07441 A Thermo-Electric Module Test Stand and P07442 A Thermo-Electric Demo Device. The future goal is to launch several projects within this area over the next couple of years, with the allocation of approximately $15,000 offered from the funds of Dr. Stevens to the projects.

General References, Background Information, and Web Resources

A wealth of information relating to thermoelectrics, refrigeration, semiconductors, Thermodynamics, Seebeck, and Peltier with text referances is available at Wikipedia

Tullurex Corporation is Michigan based manufacturer of thermoelectric products. A section of their website has been committed to a reasonably detailed explanation of the thermoelectric effect, common application, and some engineering modeling.

Presentation on Material Issues for the Next Generation of Thermoelectrics (PDF)

Presentations at a Department of Engergy conference in 2004 (collection of PDF)

JPL Report on Thermoelectric Efficiency Explains how thermoelectric efficiency is defined

Green Car Congress offers news, updates and information on thermoelectric technology for vehicles

Electronics Cooling gives an in depth information on thermoelectric engineering and formulas for thermoelectric cooling

RMT Ltd presents a very good explanation of how thermoelectric devices are manufactured

Information on Quatum dot thermoelectrics may be found at Evident Technolgies

MIT has alot of information available on their website about thermoelectric Nanotechnology

Customers Supporting this Family of Projects

The initial customer of this family of projects is RIT, represented by Dr. Edward Hensel, Head of the ME Department. RIT is investing funds to aid Dr. Stevens in establishing his career at RIT, and as such, has a vested interest in getting a measurable return on that investment as measured by student engagement, faculty pbulication, and subsequent external sponsorship support of the project family.

Anticipated future customers include corporate, government, and academic research sponsors and collaborators.

Stakeholders having an interest in this Family of Projects

The primary stakeholders in the Thermoelectric family of projects are also its customers Dr Robert Stevens, Dr Edward Hensel. Additional stakeholders are design students enrolled in any of one of the family of projects, and to a large extent the Kate Gleason School of Engineering. Project Stakeholders are usually directly involved and have a vested intrested in the project completion for educational, intellectual, monitary and resouce based benifits. Stakeholders in the Thermoelectric project have a stake in advances made to thermoelectric technology, and research publicity generated for the school by thermoelectric projects and publications completed at RIT.

Senior Design Students at RIT

Anticipated Student Enrollment in Senior Design

Term	ME Students	EE Students	ISE Students	CE Students	uE Students	Total Students
AY 2006-07 Projected Enrollment
2006-3 Spring	36	21	0	12	0	58
2006-4 Summer	0	21	0	12	0	33

Students Enrolled in the Energy and The Environment Option in ME

Students Enrolled in the Sustainability Minor in the KGCOE

Author: Joseph Pawelski 2006