**Abstract**

In this chapter, experimental analysis of the direct conversion of thermal energy into electric energy was carried out, in order to encourage the conscious use of energy and to reduce waste. The conversion of thermal energy into electrical energy occurs in a thermoelectric generator through the Seebeck effect. This effect is associated with the appearance of an electric potential difference between two different materials, placed in contact at different temperatures. This relation between temperature and electrical properties of the material is known as thermoelectricity. This experimental study has as objective the obtaining of operating characteristic curves of the thermoelectric generator TEG1-12611-6.0, for different temperature gradients and under constant pressure between the heater plate and the heat sink. Resistors were used to heat the thermoelectric generator, which simulates the residual heat, and insulation material to minimize the dissipation of heat to the environment. For cooling, a heat exchanger was used in order to maximize the temperature difference between the sides of the thermoelectric generator. In this way, it was possible to perform an experimental analysis of the obtained electric power for different temperature ranges between the faces of the generator and, with this, verify the applicability in real systems.

**Keywords:** waste heat recovery, thermoelectric generator, Seebeck effect, thermal energy

## **1. Introduction**

In 2017, total world energy consumption was approximately 13,511 million-ton equivalent of petroleum (MTEP). With the fast industrial growth of developing nations over the last decade, the industrial sector consumed approximately 2852 MTEP. It is estimated that in 2035, the world consumption of energy will increase by more than 30% [1].

Approximately 33% of the total energy consumed in the industry is rejected as residual heat, presenting as a major problem the fact that the most of this rejected energy is identified as low-quality residual heat [2]. This type of waste heat has a

small working potential, and the temperatures are below 230°C, which implies a low energy density [3]. Concurrently with the concern for global warming and the issues of diminishing oil consumption, there is a strong incentive for the development of more efficient and clean technologies for heat recovery and energy conversion systems using waste heat.

In order to minimize the waste of energy with residual heat, energy recovery systems have been more explored. These systems can become an important object of research and/or application if, at least, part of the thermal energy expelled by industrial equipment to the atmosphere can be reused [4]. In this context, experimental analysis of the direct conversion of thermal energy into electric energy, using thermoelectric generators, was carried out.

The Seebeck effect is related to the appearance of a difference of electric potential between two different materials, placed in contact, however, at different temperatures [5]. Basically, this is the same effect that occurs in thermocouples, where two different materials are connected and submitted to a temperature difference, causing a potential difference to be generated and translated into a temperature reading. In addition to this application, the thermoelectric effect can be explored in the generation of energy for wristwatches and aerospace applications or, even, in the generation of electric energy from the heated gases released in the internal combustion of engines, boiler gases, and/or the geothermal sources. The thermoelectric generators (TEG) have as main characteristics the reduced dimensions, easy adaptation in complex geometry, and very low maintenance [6]. Its conversion efficiency is about 5%; however, studies conducted at the NASA laboratory have reached 20% efficiency for high temperatures [2].

The studied thermoelectric generator consists of an arrangement of small blocks of bismuth telluride (Bi2Te3) doped with *n*-type and *p*-type, mounted alternately, electrically in series, and thermally in parallel between two plates of good thermal conduction [7], as shown in **Figure 1**.

The top of the *p-n* junction is heated, and the bottom of the set is cooled; in this way, a temperature gradient is generated. The free electrons of the *n*-type doped elements and the interstices of the *p*-type elements begin to move toward the cold part, that is, the lower part of the system. In the cold part, the *n*-type doped elements acquire negative polarity, while the *p*-type elements get positive polarity. Closing the circuit between the *p*-*n* elements, an electric potential is generated [7], and, with the electron accumulation at the cold side, an internal electric field is created, causing the Seebeck voltage.

**85**

**Figure 2.**

*Heat Recovery and Power Generation Using Thermoelectric Generator*

The experimental apparatus and procedure developed for this research are

The experimental bench developed to obtain the thermoelectric generator characteristic curve, shown in **Figure 2(a)**, consisted of a laptop (*Dell*™), an uninterruptible power supply (*NHS*™), an aluminum block containing electrical resistors in cartridge, a thermoelectric generator (TEG1-12611-6.0), a water-cooled heat exchanger, a controlled automated resistive load variation system controlled by an *Arduino*™, data logger (*Agilent*™ 34970A with 20 channels), a power supply unit (*Politerm*™ 16E), an ultrathermostatized bath (*SOLAB*™ SL-130), and a variable area flowmeter with throttle (*Omega Engineering*™ FL-2051). In **Figure 2(b)**, the heating and cooling system of the thermoelectric generator and the data acquisition system to obtain generated power by the thermoelectric generator TEG1-12611-6.0 are shown in detail. The thermoelectric generator used in this experiment is made of bismuth telluride (Bi2Te3) and has dimensions of 56 mm by 56 mm with a height of 3.3 mm,

main specifications can be seen in **Figure 3** and **Table 1**, respectively.

*Experimental apparatus. (a) Experimental bench. (b) Test section and data acquisition system.*

. An illustration of the generator and, also, its

*DOI: http://dx.doi.org/10.5772/intechopen.85122*

described in details in this section.

totaling a surface area of 0.003136 m2

**2.1 Experimental apparatus**

**2. Methodology**

**Figure 1.** *Schematic diagram of a thermoelectric generator.*

*Heat Recovery and Power Generation Using Thermoelectric Generator DOI: http://dx.doi.org/10.5772/intechopen.85122*
