4-fold enhancement in energy scavenging from fluctuating thermal resources using a temperature-doubler circuit

doi:10.1016/j.joule.2021.06.007

Joule

Volume 5, Issue 8, 18 August 2021, Pages 2223-2240

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Highlights

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Oscillating thermal resources are common but are underutilized
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Powering a heat engine from such a resource normally requires a second thermal terminal
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The “temperature doubler” needs only the single, oscillating, thermal terminal
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The electrical power output is 4 to 8 times higher than a traditional approach

Context & scale

Fluctuating thermal resources, e.g., periodic solar heating, are ubiquitous but are significantly underutilized. Oscillating temperatures can also be found in nonsolar settings such as vehicles, materials processing, power electronics, and aircraft flight operations. Traditionally, for energy scavenging from a periodic solar thermal resource, electricity is generated only during the hot daytime hours. However, by limiting the heat sink to be the terrestrial ambient temperature, this misses an opportunity to exploit the even colder nighttime temperatures as a heat sink. The temperature doubler begins to access the best of both worlds—by sampling and holding both extreme temperatures (hot and cold) of the resource, this thermal circuit provides heat to the engine with a nearly constant temperature approaching the resource’s maximum temperature while simultaneously receiving heat rejected from the engine at a nearly constant temperature approaching the resource’s minimum temperature.

Summary

Oscillating thermal resources are ubiquitous thanks to the diurnal cycle and are also found in nonsolar settings. Yet in isolation, oscillating thermal resources cannot normally generate electricity because standard heat engines require two thermal terminals, a source and a sink, and hence the engine’s second terminal is typically connected to some nearby constant-temperature reservoir. As an alternative, here we introduce the “temperature doubler” thermal circuit, based on two thermal diodes and two thermal capacitances. Modeling reveals how the electrical power output depends on the thermal diodes and masses. Benchtop experiments match the modeling well with no free parameters. Experiments further show that the temperature doubler generates four times more electricity than a conventional approach using a static heat sink, with a theoretical limit of an 8-fold enhancement for perfect thermal diodes and large thermal masses. This study shows how high-performance nonlinear thermal elements enable new approaches to more effective thermal-to-electrical energy conversion.

Graphical abstract

Keywords

thermal H bridge

temperature doubler

energy scavenging

thermal diode

thermal rectifier

Cited by (0)

⁴: Present Address: Form Energy, Somerville, MA 02143, USA

⁵: These authors contributed equally

⁶: Lead contact