Influence of Heat Pipe Operating Temperature on Exhaust Heat Thermoelectric Generation

Abstract

Increasingly stringent targets on energy efficiency and emissions, as well as growing vehicle electrification are making attractive the electric recovery of the energy normally wasted through the tailpipe of Internal Combustion Engines. Recent developments in thermoelectrics (TE) may soon make them a viable solution for such applications [1]. This team has been exploring the potential of using TE modules in combination with variable conductance heat pipes for transferring the exhaust heat to the generator with very low thermal resistance and at a constant, prescribed temperature. This passive temperature control eliminates the need for bypass systems in the event of temperature overshoots. The operating temperature of a generator should be as high as possible in order to maximize the Seebeck effect. However, currently available modules are temperature limited. Moreover, the higher the HP temperature the less the usable thermal power at the exhaust will be (heat can only be transferred to from a hotter to a colder body). The present work assesses both theoretically and experimentally the influence of the HP temperature in the electric output of a thermoelectric generator. A small diesel engine and a generator were tested and it was found that a high HP operating temperature is only limitative for performance in the cases where low exhaust temperature and low engine power are present. In those cases it is possible to estimate an optimal HP temperature in order to maximize power output. The combined use of Seebeck modules and heat pipes was found to be highly advantageous in various ways.

Compact automotive thermoelectric generator with embedded heat pipes for thermal control

“…This pressure would vary within controlled values depending on the volume of the system. The authors performed the modelling of aforementioned system, first under fixed pressure and including full experimental validation [11], [12], [14]. Subsequently, the model was applied to realistic driving cycles with fixed pressure/temperature [13] and finally allowing also for realistic pressure variation during the driving cycle [15].…”

Thermoelectric conversion of waste heat from IC engine-driven vehicles: A review of its application, issues, and solutions

“…Power performance test is conducted under 3 conditions, ie, HP pressure/temperature of, viz., (i) 1 bar/100°C, (ii) 2.7 bar/130°C, and (iii) 6 bar/160°C. Optimum condition is attained at 2.7 bar/130°C where a peak electric power of 25 W is achieved at system efficiency of around 1.2% . Orr et al used HP heat exchanger and 8 commercially available Bi 2 Te 3 modules in a 3.0 l fuel injected V6 engine (vehicle: Holden Commodore).…”

“…B, HP‐exhaust thermoelectric generator assembly. C, Top view and lower view of condenser blocks (adapted from Brito et al) [Colour figure can be viewed at wileyonlinelibrary.com]…”

“…Optimum condition is attained at 2.7 bar/ 130°C where a peak electric power of 25 W is achieved at system efficiency of around 1.2%. 38 Orr et al used HP heat exchanger and 8 commercially available Bi 2 Te 3 modules in a 3.0 l fuel injected V6 engine (vehicle: Holden Commodore). Eight thick-walled water HPs (30°C-300°C) are placed in exhaust duct of the heat recovery system.…”

Heat Pipe-Assisted Thermoelectric Power Generation Technology for Waste Heat Recovery

“…Brito et al 22 presented an experimental and theoretical study on the influence of the heat pipe temperature in the electric output of a TEG connected to a small diesel engine. Their research demonstrated a possible method for estimating an optimal variable conductance the heat pipe's temperature to maximize the power output.…”