Thermodynamic irreversibility and performance characteristics of thermoelectric power generator Ahmet Z. Sahin * , Bekir S. Yilbas Mechanical Engineering Department, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia article info Article history: Received 3 December 2012 Received in revised form 13 March 2013 Accepted 14 March 2013 Available online 17 April 2013 Keywords: Thermoelectric generator Performance Entropy generation abstract Thermodynamic irreversibility and performance characteristics of a thermoelectric power generator are investigated. The influence of the external load parameter, the thermal conductivity ratio, the figure of Merit, and the conductance ratio on the efficiency, the output power, and the entropy generation rate is predicted for various device operating parameters. It is found that the device efficiency increases to reach its maximum at the critical value of the output power and operating the device beyond the critical output power lowers the thermal efficiency and enhances the entropy generation rate significantly in the device. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Thermoelectric generators are one of the potential candidates for renewable energy conversion. Although their efficiency is low, their environment friendly nature, simple design, and operation are the driving forces for the current research interest of these devices. The recent developments in thermoelectric materials improve notably the figure of Merit and the device efficiency. However, the performance of the thermoelectric generators can be further improved through minimization of thermodynamic losses during the operation. One of the methods to maximize the thermal effi- ciency of the thermoelectric device is to minimize the entropy generation rate in the thermoelectric system. Therefore, investi- gation into entropy generation rate and the performance of the thermoelectric generators becomes essential. Considerable research studies were carried out to examine thermal characteristics of thermoelectric systems. Optimization study for low-temperature waste heat thermoelectric generator system was carried out by Gou et al. [1]. They demonstrated that expanding heat sink area in a proper range and enhancing cold-side heat transfer capacity, thermoelectric device performance improved notably. Performance of two-stage thermoelectric refrigerator sys- tem was studied by Meng et al. [2]. They presented analytical ex- pressions for the electrical current in terms of the cooling load versus the electrical current and the coefficient of performance versus the electrical current of the combined devices. The thermoelectric generator and multi-scale irreversibility were investigated by Meng et al. [3]. They presented the effects of external irreversibility on the performance of the thermoelectric generator. The constructal design of a thermoelectric device was examined by Pramanick and Das [4]. They demonstrated that the maximum permissible length was dependent on applied temperature gradient whereas the minimum allowable length was independent of the temperature gradient. Topping cycle and thermoelectric power generation were studied by Sahin et al. [5]. They showed that for a certain combination of operating and thermoelectric device pa- rameters, thermal efficiency of the topping cycle became slightly higher than that of the same system without the presence of the thermoelectric generators. Thermoelectric device for optimum external load parameter and slenderness ratio for the maximum efficiency was investigated by Yilbas and Sahin [6]. They indicated that for a fixed thermal conductivity ratio, the external load parameter increased with increasing slenderness ratio while the electrical conductivity ratio of the p and n pins reduced in the device. Optimization of thermoelectric generating process was carried out by Garcia and Zorraquino [7]. They presented the future of the cogeneration system incorporating the thermoelectric devices. The integrated assessment of energy conversion processes through thermodynamic, economic, and environmental parameters was carried out by Tonon at al. [8]. They presented detailed analysis to evaluate economic and exergetic behavior of the energy conversion processes including the thermoelectric devices. The analytical model for parallel thermoelectric generator was proposed by Liang et al. [9]. They showed that the thermal contact resistance reduced the output power by reducing the temperature difference between * Corresponding author. E-mail address: azsahin@kfupm.edu.sa (A.Z. Sahin). Contents lists available at SciVerse ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy 0360-5442/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.energy.2013.03.064 Energy 55 (2013) 899e904