Thermoelectric Exhaust Energy Recovery with Temperature Control through Heat Pipes

Abstract

Currently, a great deal of the automotive industry's R&D effort is focused on improving overall vehicle environmental and energy efficiency [1]. For instance, one of the things that Electric Vehicles (EVs) and Hybrid cars (HEV) have in common is the recovery of waste energy, namely during braking. But, when an I.C. engine is operating (e. g. as a range extender in an EV), a large amount of energy is also wasted within the exhaust gases and with engine cooling, energy that could otherwise be recovered by different methods. This paper reports on the recovery of waste thermal energy using thermoelectric generators (TEG) for application in hybrid, extended range electric vehicles and more generally in any vehicle that could benefit from the generation of a small amount of electric current that would reduce the alternator operation time.Although some manufacturers are trying to develop TEGs to use at exhaust temperatures, there are still no commercially available TEG modules capable of withstanding these extreme temperatures. The present work assesses the potential of the use of heat pipes (HP) as a means of transferring energy from the hot exhaust gases to the TEG modules at a compatible temperature level while minimizing the loss of efficiency due to temperature downgrading. The type of HP used in this study is called Variable Conductance Heat Pipe (VCHP), and its deployment has the advantage of inducing good temperature control.Various types of HPs were designed, manufactured, tested and improved with the aim of enhancing the overall heat transfer process, enabling an optimal level of electric energy recovery from the referred TEG modules. This was accomplished by the testing of different fluids inside the HP and by regulating the pressure of the gas chamber. Although the system is still under improvement, the results indicate that the use of VCHPs in conjunction with thermoelectric generators is a convincing technique for recovering otherwise wasted energy from the exhaust gases.

Characterization of a Thermoelectric Generator (TEG) System for Waste Heat Recovery

“…Their results were validated by a performance analysis by the authors of [8], which was additionally validated by the comparison by the authors of [26,28,30] and other references that were cited throughout this chapter. Other applications of the evaluated technology (TEGs) gave gains of up to 52 W in residential chimneys [51], generation rates of up to 10.9 kWh/m 2 per year in of solar ponds [52], potential power to near 50 W in driving cycle conditions of diesel light-duty engines [53], and allowed efficiencies to reach 55% By analyzing the power output (P out ) curve as a function of the output current (I out ), shown in Figure 6, it was possible to determine the maximum current and power that were supplied by the thermoelectric generator for different temperature gradients (∆T).…”

“…From the point of view of application, thermoelectric materials have been widely used in cooling processes, transforming electric energy into thermal energy (Peltier effect) [24,28,30,37]. However, the use of the reversible thermoelectric effect (i.e., transforming thermal energy directly into electrical energy) (Seebeck Effect) had still not been explored much for the purposes of electric energy generation, as shown in [13][14][15]; in this way, the proposed device provided a valuable contribution to the implementation of this new technology.…”

Temperature Controlled Exhaust Heat Thermoelectric Generation

“…Another paper detailed some of the results obtained with simplified proof-of-concept installations [29]. A more recent work dealt with the theoretical modelling of a TEG-heat pipe system [30].…”

Integrated Energy and Thermal Management for Electrified Powertrains

“…Hence, recuperating a certain amount of that energy, which would otherwise be dissipated into the environment, is a promising way to improve powertrain efficiency. Two types of waste heat recovery (WHR) technologies can be found: Thermoelectric generators [12][13][14][15][16] and Rankine cycle-based WHR systems [17][18][19][20]. A thermoelectric generator consists of various P-type and N-type semiconductor materials, which convert heat into electricity directly, based on the Seebeck effect [21].…”