Design, empirical modelling and analysis of a waste-heat recovery system coupled to a traditional cooking stove Rachsak Sakdanuphab a , Aparporn Sakulkalavek b,⇑ a College of Advanced Manufacturing Innovation, King Mongkut’s Institute of Technology Ladkrabang, Bangkok 10520, Thailand b Department of Physics, Faculty of Science, King Mongkut’s Institute of Technology Ladkrabang, Bangkok 10520, Thailand article info Article history: Received 9 November 2016 Received in revised form 20 February 2017 Accepted 21 February 2017 Keywords: Waste-heat recovery (WHR) system Response surface methodology (RSM) Thermoelectric generator Cooking stove Heat pipe abstract In this work, a waste-heat recovery (WHR) system was designed and implemented to utilise the waste heat from a cooking stove. The WHR system was designed to preserve maximum thermal energy effi- ciency, use passive cooling, and produce a system that did not alter the body of the cooking stove. The thermal energy from the cooking stove was converted into electrical energy by a thermoelectric gener- ator (TEG) and used in a waste-heat hot water boiler. The cold side of the TEG was cooled by heat pipes immersed in a water box that offers a high heat transfer rate. The heated water can be used for domestic purposes. Dependent variables were the heater temperature and the volume of water. The heater temper- ature was varied between 130 and 271 °C, and 4.2–9.5 L of water was investigated. At equilibrium, response surface methodology based on a central composite design was used to empirically model the influence of the heater temperature and the volume of water on the electrical power generation and the hot water temperature. Experimental results of the system efficiency showed that the heater temper- ature was more influential than was the volume of water. The total efficiency of the WHR system was more than 80%. Thermal contact resistance was analysed to improve the WHR system performance. Finally, the thermal efficiency of a cooking stove, both with and without the WHR system, was measured. Results showed that the thermal efficiency of the cooking stove decreased by less than 5% when the WHR system was attached. Ó 2017 Elsevier Ltd. All rights reserved. 1. Introduction A serious problem for people in the rural areas of developing countries is a lack of reliable access to electricity. A sustainable solution to this problem is the ability to independently generate electrical power, preferably from routine activities, such as using a cooking stove. Various types of cooking stove have been widely used, and 90% of people in rural areas of developing countries use a biomass cooking stove [1]. Several countries in Southeast Asia, such as Thailand, Lao, Cambodia, Malaysia, the Philippines, and Vietnam, use a similar mechanical form of the cooking stove [2]. For example, the Thai cooking stove comprises a galvanised iron bucket and an inner ceramic firebox. The bucket has an open- ing cut into its side from the bottom and an integrated grate with equally distributed holes 15–20 mm in diameter [2]. Wood or charcoal can be burned on the grate. Thermal energy from the cooking stove can be converted to electricity by the thermoelectric module contained in a thermoelectric generator (TEG). Thermo- electric has long been too inefficient to be cost effective in energy conversion application compared with solar cells and wind tur- bines. The application is not currently available for people in devel- oping country. However, theoretical predictions suggested that thermoelectric efficiency could be greatly enhanced through nano-structural engineering and low-dimensional system [3,4]. Thermoelectric generator looks very promising and can contribute to applying the application. Energy conversion of a part of waste heat from stoves using TEG system has been developed. Efforts are already underway to combine a thermoelectric generator on various types of stove in many countries. The TEG has the advan- tages of being a maintenance-free system, containing no moving or complex parts, and being compact in size [1,5–11]. Although photovoltaic solar and wind systems are more efficient than TEGs, they depend on favourable natural conditions. Lertsatitthanakorn [10] analysed the electrical performance of the Thai cooking stove with an integrated TEG system. The side wall of the cooking stove was removed and a TEG system was installed. The system had a power output of 2.4 W at a temperature difference of http://dx.doi.org/10.1016/j.enconman.2017.02.057 0196-8904/Ó 2017 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: aparporn.sa@kmitl.ac.th (A. Sakulkalavek). Energy Conversion and Management 139 (2017) 182–193 Contents lists available at ScienceDirect Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman