Replacing commercial thermoelectric generators with a novel electrochemical device in low-grade heat applications
Introduction
A TEG converts heat into electricity, it is a solid-state electronic device without any mechanical moving element [1]. The primary concept of a TEG was firstly introduced by Thomas Johan Seebeck in 1821 [2]. Some applications of TEGs in different areas of engineering such as geothermal energy [3], biomass [4], automotive industry [5] and solar collectors [6] have been reported in the literature. A TEG is composed of two surfaces, a hot-side surface and a cold-side surface. A TEG maps the difference of temperature between its two surfaces to its output electric power. To produce electricity by a TEG, it is necessary to establish a reasonable temperature difference between the two surfaces [7]. As a consequence, for low-grade heat harvesting applications where temperature difference ranges below 50 °C, TEGs cannot be used alone. In this regard, some relatively expensive devices such as concentrators and heat pipes should be also utilized [8]. For instance, to harvest solar energy, different methods which all require peripheral devices can be achieved [[9], [10], [11]]. There are two methods to feed solar heat to the hot-side surface of a TEG; direct method [12] and indirect method [13,14]. In direct method, lens (fresnel) and/or concentrators are required for solar heat feeding [15,16], while in indirect method, heat pipe systems positioned in vacuum glass tubes or the waste heat of PV modules are usually utilized to heat the hot-side surface [[17], [18], [19], [20], [21]]. The TREC is an electrochemical cycle composed of four steps, in which an amount of electric energy is released in the fourth step [22]. Two similar small scale low-power membrane-free and charging-free TREC cells with an efficiency of less than 3.5% were designed and reported in Refs. [23,24]. Some other researches have been carried out to optimize the physical factors of a TREC cell [25].
As mentioned the main defect of a TEG that makes it useless for low-grade heat harvesting is its very low output power. For these types of applications, some extra devices are also required that there is often no technical and economical justification for utilizing them. In this study, utilizing a proposed novel electrochemical device operating based on the TREC is suggested for low-grade heat harvesting applications instead of TEGs. The proposed electrochemical device is theoretically analyzed, and experimental results obtained from the operation of a prototype of the device constructed in this study are presented. The device is also compared to a commercial TEG module TEG1-1263-4 that verifies the superiority of the proposed electrochemical device in low-grade heat harvesting. TEG technology is concisely introduced in Section 2. The proposed electrochemical device is theoretically analyzed in detail in Section 3. The details of the constructed electrochemical device along with experimental results are presented in Section 4, and the paper is concluded in Section 5.
Section snippets
Thermoelectric generators
A TEG is a solid-state electronic device composed of a p-type semiconductor and an n-type semiconductor, one side of the two semiconductors forms the hot-side surface of the TEG, while the other side of them forms the cold-side surface. The open-circuit voltage () of a TEG is proportional to difference between the temperatures of the two surfaces, and is expressed as:where is called “Seebeck coefficient”, and and are the temperatures of the hot-side and
Proposed electrochemical device: theoretical analysis
A TREC cell basically includes a positive electrode and a negative electrode which are separated by an anion membrane. The TREC consists of four processes: heating up, charging, cooling down and discharging as shown in Fig. 3. There is a difference between two voltages charged in the two electrodes during the charging process, so electric power is produced by the TREC cell in the discharging process. The positive electrode is made of solid CuHCF immersed in 6 M NaNO3 aqueous solution, while the
Proposed electrochemical device: construction and experimental results
A prototype of the proposed electrochemical device has been constructed. The dimensions and weight of the built device are, respectively, and 3.1 kg that makes it portable, and so, suitable for industrial applications. The photo of the constructed electrochemical device attached on the back of an opaque glass to harvest solar heat is depicted in Fig. 6. The opaque glass was exposed to the sun rays to harvest solar energy as a low-grade heat harvesting application, and the electric
Conclusion
In this paper, a novel electrochemical device operating based on the TREC was proposed to replace TEGs in low-grade heat harvesting applications. The device was theoretically analyzed, a prototype of the device was constructed and experimental results were presented. The comparison between the proposed electrochemical device and a commercial TEG module TEG1-1263-4.3 demonstrated that the output power and current of the electrochemical device is extremely more than that of a commercial TEG
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