A testbed for performance studies of gas-liquid thermoelectric generators for waste heat harvesting

We describe a unique test platform for performance studies of thermoelectric generators (TEGs) with gas/liquid heat exchangers. The designed stand allows to simulate the real working conditions of TEG prototypes. It provides accurate measurements of key operational parameters of these devices in high precision laboratory regime. The testbed consists of a hot-gas control unit (HGCU) for examination of the heat exchanger (HHX) of the TEG, a cooling liquid control unit (CLCU), an automated control system (ACS) that allows to precisely set the requested experimental conditions, and a data acquisition system (DAS) that gathers data on temperature, fluids flow, pressure drops and electrical parameters of the TEG. The HGCU unit is a source of hot air, with mass flows in the range of 0-550 m(3)/h, maximum heat power P-H of 15 kW, and temperature range between 15 ? and 800 ?. The CLCU unit controls the flow and temperature of the liquid medium in the range from 10 ? to 110 ? and the mass flow of water m?(water) in the range of 0.006 - 1.2 m(3)/h. The designed testbed allows to evaluate the most important TEG performance parameters, such as: efficiencies of its TE converters, the effectiveness of heat exchangers, power losses due to pressure drops, and net power P-net generated, as well as the statistical uncertainties of the determination of these parameters. The testbed has been used for tests of various TEG prototypes. As an application example, we show results for a prototypical TEG with nominal power of 168 W designed for heat recovery from an automobile exhaust system. The device is based on a hexagonal, internally finned HHX, 24 TEM converters and 24 water-cooled cold heat exchangers (CHXs). The constructed testbed allows for a direct determination of all the factors which may influence the conversion efficiency of the TEG, as well as its net and gross electrical power output under varying heat source and heat sink parameters. The device allows to estimate the performance of the entire thermoelectric generation system as a whole and to identify individual components within the TEG which potentially need to be improved. Such a holistic approach to TEG parameter characterization was not presented or discussed in the literature so far.