8: Thermoelectrics
- Page ID
- 18991
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)A thermoelectric device is a device which converts a temperature differential to electricity, or vice versa, and it is made from a junction of two different conductors or semiconductors. To understand thermoelectric devices, we need to understand the fundamentals of heat transfer and thermodynamics. This chapter begins by discussing these fundamental ideas. Next, thermoelectric effects and thermoelectric devices are discussed.
Many common processes heat an object. Rubbing blocks together, for example, heats them by friction. Burning a log converts the chemical energy in the wood to thermal energy, and applying a current to a resistor also heats it up. How can we cool an object? If we supply electricity to a thermoelectric device, one side heats up and the other cools down. We can place the object we want to cool near the cooler side of the thermoelectric device.
Thermoelectric devices, pyroelectric devices, and thermionic devices all convert energy between a temperature difference and electricity. Pyroelectric devices were discussed in Sec. 3.1. They are made from an insulating material instead of from a junction of conductors or semiconductors. Thermionic devices are discussed in Sec. 10.1, and they involve heating a cathode until electrons evaporate off. Thermoelectric devices, discussed in this chapter, are much more common than pyroelectric devices and thermionic devices due to their efficiency and durability.
- 8.1: Thermodynamic Properties
- This page discusses energy storage in confined air, highlighting the interplay of volume, pressure, and temperature. It introduces four key thermodynamic properties: volume, pressure, temperature, and entropy, along with their classifications. The page also provides important units of pressure and volume, clarifies absolute versus gauge pressure, and defines temperature and entropy.
- 8.2: Bulk Modulus and Related Measures
- This page discusses the bulk modulus (\(\mathbb{B}\)), a measure of a material's resistance to compression, defined by the change in pressure and volume. It highlights the modulus's positive value and its relation to isothermal compressibility, permittivity, and specific heat. Furthermore, it covers the Joule-Thomson coefficient, which describes temperature changes with pressure at constant energy, and volume expansivity, concerning volume changes with temperature at constant pressure.
- 8.3: Ideal Gas Law
- This page explains simple compressible systems, emphasizing the relationship between thermodynamic properties (volume, pressure, temperature, and entropy) where knowing three allows calculation of the fourth. It introduces the ideal gas law (PV = nRT) as a model for gases and its applicability to liquids and solids, detailing how these properties interact.
- 8.4: First Law of Thermodynamics
- This page explores the first law of thermodynamics, focusing on energy conservation and its various storage forms, like capacitors and batteries. It highlights simplified concepts often presented in introductory courses, categorizing energy transformations as heat transfer or mechanical work. The law is mathematically expressed, demonstrating energy conservation in closed systems with examples of energy interplay and mechanical work.
- 8.5: Thermoelectric Effects
- This page covers the Seebeck, Peltier, and Thomson thermoelectric effects, which explain the conversion between thermal and electrical energy at metal or semiconductor junctions. It emphasizes electrical conductivity for effective thermoelectric devices, the need for low thermal conductivity, and introduces the figure of merit \(Z\) for evaluating material efficiency, influenced by key parameters like the Seebeck coefficient.
- 8.6: Thermoelectric Efficiency
- This page explains Carnot efficiency as the theoretical maximum for energy conversion devices and includes its formula, emphasizing temperature dependence. It covers how energy is managed in thermoelectric devices while noting that practical efficiency is hindered by energy losses like resistive heating. Additionally, it mentions that the power output is significantly low, illustrating that even minor efficiency losses can adversely affect performance.
- 8.7: Applications of Thermoelectrics
- This page discusses thermoelectric devices and their importance in cooling systems for electronics, food, and individuals, enhancing reliability for heat-sensitive components. They are used in applications like thermoelectric refrigerators and cooling systems for imaging technologies. Despite their lower efficiency compared to traditional systems, their environmentally friendly nature is a key advantage.
- 8.8: Problems
- This page discusses thermodynamics and thermoelectric materials, emphasizing gas pressure calculations, energy transfer, and thermoelectric device properties. It covers gas temperature-pressure relationships, methods for measuring electrical and thermal conductivity, and thermoelectric coefficients. The content also includes calculations for figures of merit and efficiency in thermoelectric devices like skutteridites, along with their practical applications in refrigeration and energy generation.
Thumbnail: Illustration of the thermoelectric effect with a simple thermopile made from iron and copper wires. (CC BY-SA .0 International; Cmglee via Wikipedia)