Contents lists available at ScienceDirect Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman Thermoelectric generation for waste heat recovery: Application of a system level design optimization approach via Taguchi method Dongxu Ji a , Zhongbao Wei b , Stefano Mazzoni b , Marco Mengarelli b , Srithar Rajoo e , Jiyun Zhao c , Josep Pou a, ⁎ , Alessandro Romagnoli d, ⁎ a School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore b Energy Research Institute @ NTU, Nanyang Technological University, Singapore c Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Hong Kong, China d School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore e UTM Centre for Low Carbon Transport (LoCARtic), Universiti Teknologi Malaysia ARTICLE INFO Keywords: Thermoelectric generator Waste heat recovery Taguchi method System optimization Thermoelectric module ABSTRACT Thermoelectric generator is a solid-state energy converter which can convert waste heat directly into electricity. During the past decades, thermoelectric materials have been widely investigated whereas the integrated design of thermoelectric generators have been less studied. This paper proposes and implements a framework for the design of thermoelectric generators, consisting of thermoelectric modules and heat exchangers, based on the Taguchi method. As compared with previous researches which optimize the thermoelectric module alone and assume fixed temperature or fixed heat fluxes for the thermoelectric modules, this work proposes a methodology to optimize the thermoelectric module and the heat exchanger together. Five design parameters (namely the height, the fill-ratio, the ratio of cross-sectional area of n-type material over p-type material of thermoelectric module, the length and the material of the heat exchanger) were analyzed for two different applications, waste heat recovery from marine and automotive engines. In order to perform the analysis, a L 27 (3 5 ) orthogonal array was employed to assess all of the design parameters returning the maximum output power. By analysis of variance, it is found that the thermoelectric module height is the most important design parameter contributing for the 69.6% and 30.25% in automotive and marine application, respectively. And the optimal design para- meter set are also determined in both applications. 1. Introduction The emerging concerns over the fossil-fuel depletion, global warming and environmental pollution have promoted the use of effi- cient energy processes [1,2]. A vast amount of energy in industrial process is dissipated as waste heat. In the United States alone, around 5–13 quadrillion kJ/year of energy is lost as waste heat [3]. Numerous technologies have been proposed to utilize the waste heat, including organic Rankine cycle (ORC), Kalina cycle, steam Rankine cycle and thermoelectric generator (TEG) [4]. TEG is a solid-state technology that converts waste heat directly into electricity by exploiting the Seeback effect [5]. TEG is usually made by a few known materials, such as Bismuth Telluride (Bi 2 Te 3 ) and lead telluride (PbTe). Compared with other waste heat recovery technologies, TEG has many unique ad- vantages, including no gas emission, no moving parts, and no noise, so that it has attracted a lot of attention for real applications. The TEG has been widely used in space and military applications [6] and many major automotive manufacturers, such as Ford, BMW, GM and Volks- wagen, have developed TEG waste heat recovery systems to improve the fuel economy of their automobiles, with reported output power from TEG ranging from few hundreds watts to one kilowatt [7]. A typical TEG waste heat recovery system is shown in Fig. 1. A TEG is composed by multiple thermoelectric modules (TEMs) and heat ex- changers (HEXs). Each TEM comprises many thermoelectric (TE) cou- ples, which consist of n-type TE legs and p-type TE legs. The exhaust gas flows through the HEX, passing the exhaust energy in the form of heat flux to the hot side of the HEX by convective heat transfer. Then the heat is transferred by heat conduction to the hot side of the TEMs. The cold side of the TEMs is usually cooled down by cooling water. A temperature difference is maintained between the cold and hot side of TEMs, in order to generate electricity [8]. One major challenge for the wide application of TEG for waste heat https://doi.org/10.1016/j.enconman.2018.06.016 Received 11 April 2018; Received in revised form 3 June 2018; Accepted 5 June 2018 ⁎ Corresponding authors. E-mail addresses: j.pou@ntu.edu.sg (J. Pou), a.romagnoli@ntu.edu.sg (A. Romagnoli). Energy Conversion and Management 172 (2018) 507–516 0196-8904/ © 2018 Published by Elsevier Ltd. T