Difference Between Seebeck Effect And Peltier Effect Pdf

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Peltier effect , the cooling of one junction and the heating of the other when electric current is maintained in a circuit of material consisting of two dissimilar conductors; the effect is even stronger in circuits containing dissimilar semiconductors. In a circuit consisting of a battery joined by two pieces of copper wire to a length of bismuth wire, a temperature rise occurs at the junction where the current passes from copper to bismuth, and a temperature drop occurs at the junction where the current passes from bismuth to copper. Peltier effect Article Additional Info.

Thermoelectricity is one of the oldest phenomena to be observed in semiconductors, with discovery of the various thermoelectric effects dating back to the early part of the 19th century. These effects can be utilized in devices to generate electrical power from waste heat or to provide solid state cooling, respectively. This chapter reviews the main factors governing thermoelectric effects in solids, and how these factors may be manipulated to produce materials with high thermoelectric figure of merit. The first portion of the chapter covers the main features that determine electrical and thermal transport in crystalline semiconductors, while the latter portion discusses several new approaches to this old problem that hold promise for highly efficient thermoelectric materials in the future.

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This chapter recalls the general principles and main formulations useful in the study of thermoelectric coolers. Starting from the general heat diffusion equation, analytical expressions are introduced for the determination of cooling capacity and rate of heat rejection in steady-state conditions.

When dealing with the whole refrigeration system, the limits of the steady-state analysis of the individual thermoelectric elements are pointed out, indicating the need for transient analysis supported by experimental evaluations. Then, the energy indicators are illustrated by considering the electrical power consumption, the thermal performance described by the dimensionless figure of merit, as well as the coefficient of performance.

Furthermore, the main methods to enhance the thermoelectric cooler performance in refrigeration units are highlighted, with reference to high-performance materials, design aspects and temperature control systems.

Finally, indications are reported on some applications of various thermoelectric refrigeration solutions, considering the technical aspects of the performance of these systems. Bringing Thermoelectricity into Reality. The thermoelectric effect represents direct conversion of the temperature difference into voltage and vice versa and refers to phenomena with which the current flows through the thermoelements or legs of a thermoelectric module. In this case, the electric effects are accompanied by thermal effects and vice versa [ 1 ].

The thermoelectric effects are Peltier effect, Thomson effect and Seebeck effect. The Peltier effect is the phenomenon that converts current to temperature and occurs when an electric current flows through a thermoelectric device. The Peltier effect is a reversible phenomenon, because the Peltier heat depends directly on the direction of the carrier flow or electrical current [ 2 ]. There is interdependence between the sense of the electric current and the temperature difference at the hot and cold ends of a thermoelectric device.

In other words, if the current flow is changed, the temperature at the hot and cold ends is changed as well. The Peltier coefficient determines a cooling effect when the current flows from the N-type semiconductor material to a P-type semiconductor material and a heating effect when the current flows from the P-type semiconductor material to an N-type semiconductor material. The Thomson effect is given by generation or absorption of a heat quantity in a homogeneous conductor by which an electric current flows and where there is a temperature gradient.

The heat absorbed or released depends on the electric current direction and the conductor material. The Thomson effect is a reversible thermoelectric phenomenon and is observed when the charge carriers change energy levels.

The convention for the Thomson effect is: positive Thomson effect, when the hot end has a high voltage and the cold end has a low voltage; the heat is generated when the current flows from the hotter junction to the colder junction, while the heat is absorbed when the current flows from the colder end to the hotter end. Co, Bi, Fe, and Hg [ 3 ]. With reference to Figure 1 , the sign convention of the Thomson coefficient is positive for heat absorbed conductor A and negative for heat dissipated conductor B.

Its expression is given by. If a current density J exists through a homogeneous conductor, the heat production per unit volume or volumetric heat generation is. The Seebeck effect converts temperature to current and occurs like the Peltier effect, but the direction of the electric current is reversed.

The Seebeck effect appears when a temperature gradient along a conductor provides a voltage increment. The Seebeck voltage appearing at the circuit junctions is. The Seebeck coefficient or thermoelectric power is a very important parameter for the thermoelectric materials, determining the performance of Peltier elements. For a good thermoelectric material, the Seebeck coefficient has to be high in order to obtain the desired voltage more easily, the electrical conductivity has to be high, and the thermal conductivity has to be small to reduce the thermal losses in the junctions of the thermocouple [ 4 ].

The sign of the Seebeck coefficient depends on the hole and electron flow: A negative Seebeck coefficient is obtained in semiconductors negatively doped e.

N-type semiconductors. A positive Seebeck coefficient is obtained in semiconductors positively doped e. P-type semiconductors. There is interdependence between the Peltier coefficient and the Seebeck coefficient, as well as between the Seebeck coefficient and the Thomson coefficient, given by the following relationships [ 5 , 6 ]:. A thermoelectric cooler TEC is a semiconductor composed of an electronic component which transforms electrical energy into a temperature gradient.

The TEC consists of one or more thermoelectric couples. The thermoelectric couples are connected in such a way that when the current flows through the device, both the P-type holes and the N-type electrons move towards the same side of the device. The two legs are made of two different thermoelectric materials.

A thermoelectric material is defined as an alloy of materials that generates thermoelectric properties thermal conductivity, electric conductivity and Seebeck coefficient. The quality as a semiconductor material to be cooled strictly depends on the transport properties of the material Seebeck voltage, electrical resistivity and thermal conductivity as well as the operational temperature field between the cold and hot ends [ 5 ]. Considering that the input voltage of a single thermoelectric couple is reduced, many thermoelectric couples are connected to each other by junctions and are sandwiched between two ceramic substrates to form a thermoelectric module TEM.

These ceramic substrates act as insulator from electrical point of view but allow the thermoelectric couples to be thermally in parallel. The number of thermoelectric couples is influenced by the needed cooling capacity and the maximum electric current [ 5 ]. When a low voltage DC power source is applied to the free end of the TEM, the heat flow rate is transferred from one side to other side of the device through the N- and P-semiconductor legs and junctions.

In this case, one side of the TEM is cooled, and the other side is heated [ 7 ]. In the cooling mode, the sense of the electrical current is from the N-type semiconductor to the P-type semiconductor Figure 2.

The Seebeck voltage is generated in the device when there is a temperature difference between the junctions of the thermoelements [ 8 ]. The direction of the current is then essential to establish the functionality of the device. If the direction of the electrical current is reversed, the compartment would be heated instead of being cooled. At the top of every junction, the temperature is the same T c , and at the bottom of every junction, the temperature is the same T h.

Through the cold junction, the electrons are transported from a low energy level inside the P-type semiconductor legs to a high energy level inside the N-type semiconductor legs. This heat is dissipated at the heat sink a passive heat exchanger that cools a device by dissipating heat into the environment , and the free electrons flow to an inferior energy level in the P-type semiconductor. The main components of a refrigeration unit Figure 3 are [ 7 , 9 , 10 ]: the insulated refrigerator cabinet with thermoelectric technology having variable dimensions e.

The TEC can operate in a definite operating range of its temperature difference. To keep this temperature difference inside the specific operating range, a TEC is compulsory to have a heat sink at the hot end to dissipate heat from the TEC to environment.

Sometimes, another heat sink with fins is fixed inside the compartment to improve the heat transfer from the insulated volume which is cooled fluid, solid to the cold side of the TEC. In this case, the heat sink is cooled at a temperature lower than the insulated volume, and the heat flowing between the fins is collected by means of a fan [ 11 , 12 , 13 ];.

The continuity equation is. The general heat diffusion equation for transient state [ 14 ] is. Substituting Eq. Steady-state analysis for a TEC is typically carried out by resorting to a set of approximations. In these conditions, there is no heat transfer from or to the external environment, so that the heat flows occur only between the source and the sink. On these assumptions, Eq.

By replacing in Eq. Let us consider the boundary conditions between the following limits Figure 4 :. Then, Eq. However, this model can be used only at first approximation for the selection of thermocouple materials [ 9 ]. In practice, the semiconductor properties depend on temperature, the contact resistances cannot be avoided, and the Thomson effect cannot be neglected. Moreover, in the steady-state model, the temperatures T h and T c are input values that have to be determined accurately.

If the object to be cooled is directly in contact with the TEC cold surface, the object temperature has the same value as the temperature of the TEC cold surface T c. However, if the object to be cooled is not directly in contact with the TEC cold surface, e. In this case, the cold surface of the TEC has to be some degrees colder than the desired temperature in the refrigerator compartment, and the temperature T c is unknown.

With a similar reasoning, if a heat exchanger is placed at the hot side, the known value is the ambient temperature, and the temperature T h is unknown. The temperature distribution of a complex system refrigerator with TEC is depicted in Figure 5. Therefore, in practical applications in which the TEC is connected to other components e. Thereby, the temperatures at the TEC terminals can be determined by using a dedicated model of the interconnected components.

These temperatures are calculated from the solution of the overall system equations, in which all the temperature-dependent thermoelectric effects Peltier, Seebeck, Thomson and Joule are taken into account [ 17 ]. Thermoelectric refrigerators are controlled devices that operate in transient conditions.

Thereby, it is important to formulate a detailed model taking into account all the thermoelectric effects and the dependence of the model parameters on temperature. The solution of this equation has been obtained in [ 18 ] by constructing an electrothermal equivalent model with resistances and capacities in which the thermoelectric modules are represented through a multi-node structure and the other components are represented by a single node.

The implicit finite difference method has been used to solve the equations. In this model, the input data are the number of modules, the geometric parameters lengths and cross areas , the structural characteristics of the components, the heat flow rate produced by the heat source, the voltage supply from the electrical system and the environment temperature.

The structural characteristics can be given as constant values density, specific heat, surface electrical resistivity of the thermoelectric elements or can be expressed as functions of the temperatures Seebeck coefficient, electrical resistivity and thermal conductivity. Since the model is non-linear, the solution requires an iterative process, so that the initialization of the temperatures at each node of the model has to be provided as well. The outputs of the method with their evolutions in time are the temperatures at all the nodes, the heat flow rates in each component, the power produced by the modules and consumed by the fan and the efficiencies of the modules and of the system.

This formulation is consistent with an experimental application, such as the one presented in [ 17 ]. The energy indicators useful for the design and the performance of TEC are the cooling capacity, the rate of heat rejection, the input electrical power, the dimensionless figure of merit ZT and the coefficient of performance COP. The input electrical power P el or electrical power consumption [ 19 ] is. An important physical property of the TEM is the figure of merit Z.

It depends on the transport parameters Seebeck coefficient of the thermoelectric couple, total electrical resistivity and total thermal conductivity :. The thermal performance of a thermoelectric cooler is given by dimensionless figure of merit ZT. The parameter ZT represents the efficiency of the semiconductor materials of N-type and P-type thermoelements. In this case, a thermoelectric semiconductor with a higher figure of merit is advantageous because it gives a superior cooling power.

To obtain a higher figure of merit, a thermoelectric material optimization is required. This means to optimize the ZT dimensionless parameter by a maximization of the power factor, which depends on material properties like electrical conductivity and Seebeck coefficient, as well as a minimization of the thermal conductivity [ 1 ]. The best materials with high ZT are high doped semiconductors. Metals have relatively small Seebeck coefficients, and insulators have low electrical conductivity.

The thermoelectric cooling materials are alloys which contain bismuth telluride Bi 2 Te 3 with antimony telluride Sb 2 Te 3 like p-type Bi 0. The figure of merit of thermoelectric modules rises with the Seebeck coefficient, while the cooling capacity of the heat sink becomes narrow [ 26 ]. Much more, the figure of merit of a thermoelectric element limits the temperature differential achieved between the sides of the module, while the length-to-surface ratio for the thermoelements defines the cooling capacity [ 3 ].

Thermoelectric effect

In the s, three effects were experimentally observed. At first, it was not obvious that these experiments were related, but soon they were found to be three aspects of the same phenomenon [5, p. The first effect, now called the Seebeck effect, was discovered in by Thomas Seebeck [5, p. It is observed in a junction of two different metals or semiconductors. As discussed in Section 6.

Peltier Effect. With frame. First of all, in considering thermoelectric effects, we have to realize that we are dealing with a non -equilibrium situation. A general theory of non-equilibrium is beyond our means, suffice it to say that Lars Onsager , with a paper entitled " Reciprocal relations in irreversible processes " induced some fundamental insights as late as ; he received the Nobel price for his contribution to non-equilibrium thermodynamics in - for chemistry, of all things. However, what we should be aware of, is the essential statement of non-equilibrium theory:.

Giant Seebeck effect across the field-induced metal-insulator transition of InAs

A benchtop unit to examine the performance of a thermoelectric device for Peltier or Seebeck tests as a heat pump or generator. The increasing need for smaller and more portable electrically powered equipment has produced a need for low maintenance, smaller and more portable cooling. To satisfy this need, manufacturers now use solid-state thermoelectric devices in computers, portable refrigerators and cool boxes. The Peltier and Seebeck Effect demonstrator shows how one of these devices work and tests its performance when connected in a choice of two modes:. Students then learn to analyse its performance in both modes, analysing several factors including coefficient of performance COP and energy balance.

Thermoelectric effect

The thermoelectric effect is the direct conversion of temperature differences to electric voltage and vice versa via a thermocouple. Conversely, when a voltage is applied to it, heat is transferred from one side to the other, creating a temperature difference.

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This chapter recalls the general principles and main formulations useful in the study of thermoelectric coolers. Starting from the general heat diffusion equation, analytical expressions are introduced for the determination of cooling capacity and rate of heat rejection in steady-state conditions. When dealing with the whole refrigeration system, the limits of the steady-state analysis of the individual thermoelectric elements are pointed out, indicating the need for transient analysis supported by experimental evaluations. Then, the energy indicators are illustrated by considering the electrical power consumption, the thermal performance described by the dimensionless figure of merit, as well as the coefficient of performance. Furthermore, the main methods to enhance the thermoelectric cooler performance in refrigeration units are highlighted, with reference to high-performance materials, design aspects and temperature control systems.

The thermoelectric effect is the direct conversion of temperature differences to electric voltage and vice versa via a thermocouple. Conversely, when a voltage is applied to it, heat is transferred from one side to the other, creating a temperature difference. At the atomic scale, an applied temperature gradient causes charge carriers in the material to diffuse from the hot side to the cold side. This effect can be used to generate electricity , measure temperature or change the temperature of objects. Because the direction of heating and cooling is affected by the applied voltage, thermoelectric devices can be used as temperature controllers. The term "thermoelectric effect" encompasses three separately identified effects: the Seebeck effect , Peltier effect , and Thomson effect.

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5 Comments

  1. K1C2 20.04.2021 at 07:01

    Any thermoelectric effect involves the conversion of differences in Effect is a phenomenon in which a temperature difference between two.

  2. Ignace R. 20.04.2021 at 12:36

    Peltier Effect: Heating or cooling a junction by electric current. by elastic collisions between the particles and the piston [9]. B. Seebeck Effect: Direct power generation from temperature difference.

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