Elsevier

Applied Energy

Volume 87, Issue 10, October 2010, Pages 3131-3136
Applied Energy

Modeling, experimental study and optimization on low-temperature waste heat thermoelectric generator system

https://doi.org/10.1016/j.apenergy.2010.02.013Get rights and content

Abstract

Thermoelectric generation technology, due to its several kinds of merits, especially its promising applications to waste heat recovery, is becoming a noticeable research direction. Based on basic principles of thermoelectric generation technology and finite time thermodynamics, thermoelectric generator system model has been established. In order to investigate viability and further performance of the thermoelectric generator for waste heat recovery in industry area, a low-temperature waste heat thermoelectric generator setup has been constructed. Through the comparison of results between theoretic analysis and experiment, reasonability of this system model has been verified. Testing results and discussion show the promising potential of using thermoelectric generator for low-temperature waste heat recovery, especially in industrial fields. Several suggestions for system performance improvement have been proposed through the analysis on this system model, which guide optimization and modification of this experimental setup. By integrating theoretic analysis and experiment, it is found that besides increasing waste heat temperature and TE modules in series, expanding heat sink surface area in a proper range and enhancing cold-side heat transfer capacity in a proper range can also be employed to enhance performance of this setup.

Introduction

Thermoelectric generation technology, as one entirely solid-state energy conversion way, can directly transform thermal energy into electricity by using thermoelectric transformation materials. A thermoelectric power converter has no moving parts, and is compact, quiet, highly reliable and environmentally friendly. Due to these merits, this generation technology is presently becoming a noticeable research direction [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14].

However, wide application of thermoelectric power generation has been limited because of its relatively low heat-to-electricity conversion efficiency. Nowadays, a large number of works concerning thermoelectricity focus on how to improve heat-to-electricity transformation efficiency of thermoelectric materials, that is, how to improve the thermoelectric figure of merit ZT of these materials. Nanotechnology [3], [4], [5], [6], novel technology in solid state physics and semiconductor physics [2], [7], [8] are employed to explore this exciting field.

Despite these promising results, efficiency gained at device level has yet to be demonstrated. The scaling of the nanomaterials has proven to be quite difficult and is still in its developing stage. The bulk material has yet to be made commercially available. Bell [1] points out two important pathways that will lead to additional applications of thermoelectric (TE) devices. One is to promote the intrinsic efficiencies of TE materials. The other is to improve the way where existing TEs are currently used. The key factor should be the usage of economic and efficient heat sources.

Currently, there are a large number of waste heats in our surroundings, especially in the field of industrial production, which can not be recycled effectively by conventional methods. TE generation technology appears to have advantages in this area of low-grade waste heat recovery due to its entire solid-state energy conversion mode. Qiu and Hayden [15] develop a self-powered residential heating system using thermoelectric power generation technology. The electricity generated is adequate to power all electrical components of a residential central heating system. Furthermore, considering waste heats are low-cost and even no-cost resources, added with the benefits of energy-saving and emission reduction, the low efficiency problem is no longer the most important issue that we have to take into account. Economic viability of a TE generator may be improved significantly when used for waste heat recovery. Niu et al. [16] have recently done a study concerned.

In the aspect of system analysis and optimization, Rowe and Gao [17] develop a procedure to assess the potential of thermoelectric modules used for electrical power generation. Chen and Wu [18] use an irreversible model to study the performance of a thermoelectric generator with external and internal irreversibility. Esarte et al. [19] apply an NTU–ɛ methodology to study the influence of fluid flow rate, heat exchanger geometry, fluid properties and inlet temperatures on the power supplied by thermoelectric generator. They have analyzed the effect of heat transfer between thermoelectric device and its external heat reservoirs on performance of a single-element thermoelectric generator. In practice, a thermoelectric generator is composed of many fundamental thermoelectric elements. It is a multi-element device.

In this paper, a more reasonable system model of thermoelectric generator has been adopted for system analysis and optimization [20]. Besides, characteristics of a multi-element thermoelectric generator with the irreversibility of finite rate heat transfer, Joule heat inside the thermoelectric device, and the heat leak through the thermoelectric couple leg have been investigated.

In order to investigate viability and further performance of the thermoelectric generator for waste heat recovery in industry area, a low-temperature waste heat thermoelectric generator setup has been constructed. By integrating theoretic analysis and experiment, this paper studies the influence of heat transfer irreversibility on thermoelectric generation performance, and several pieces of advices on improvement of system performance have been proposed.

Testing results and discussion show the promising potential of using thermoelectric generator for low-temperature waste heat recovery in industrial fields. The system model established can be employed in performance optimization and further application of thermoelectric generation.

Section snippets

Mathematical model

A general thermoelectric generator with a load resistance RL connected is composed of several thermoelectric elements (Fig. 1). Each element consists of P- and N-type semiconductor legs which work between high and low-temperature heat reservoirs whose temperature are TH and TL respectively.

QH and QL in Fig. 1 present the heat the generator absorbs from high temperature reservoir and the heat it releases to low-temperature reservoir per unit time respectively, that is, the heat flux between the

Experimental setup

We have designed a flow channel (size: 29 cm by 13 cm by 5 cm, a baffle embedded) to utilize waste heat resource when thermal fluid flows through the channel, namely, using temperature difference between thermal fluid and ambient air to generate electricity by TE modules fixed on the flow channel surface (Fig. 2).

There are ten TE modules (Model No. TEC1-03180T125), arranged in two lines, fixed on one side of the channel surface (Fig. 3) along the fluid flowing direction. The modules are connected

System optimization

In order to optimize and modify this setup, the verified system model has been adopted for further analysis on system performance improvement. Here, a rated condition is set as a benchmark for optimization and the rated condition point (TH = 353 K in forced convection cooling mode) is indicated by “A” in Fig. 5, Fig. 7. Model parameters are the same as that of corresponding theoretic analysis in Fig. 5, Fig. 7.

On the basis of the above discussion, increasing waste heat temperature is a favorable

Conclusion

A low-temperature waste heat thermoelectric generator setup has been constructed. At the same time, a theoretic system model based on basic TE effects and the heat transfer irreversibility has also been build. The comparison of results between theoretic analysis and experiment has approved the reasonability of this model. Therefore, this system model can be used in performance optimization, integrated with experiment, and further application of thermoelectric generation.

The promising potential

Acknowledgment

This work is supported by Natural Science Foundation Project of CQ CSTC (No. 2008BB6167).

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