The need for off-grid renewable electricity sources has long driven research on thermoelectric (TE) generation using wasted heat, and this need continues to grow. Most research on TE generation has focused on improving the TE properties of the materials, particularly the figure of merit ZT. However, such improvement in ZT only contributes a small increase (few percent) in generation efficiency. As an alternative to ZT improvements, the TE research community has begun to focus on methods to improve the system efficiency through novel designs of TE generators (TEG).

Low-temperature TE generation has attracted attention, since its energy source, heat, is abundant around us, i.e. body heat, solar radiation, and heat wasted from electric devices. The goal of this research topic is to make the generation from such ubiquitous heat sources practical by applying advanced manufacturing processes and novel system designs. The novel geometry and its realization using advanced manufacturing methods resulted in a temperature distribution in the TEG that improved the TE output, and also increased the efficiency of heat transfer efficiency between the heat source and the TEG.

Thermoelectric Generator Optimized for Harvesting Body Heat

A critical challenge in using thermoelectric generators (TEGs) for charging the portable or wearable electronics has been their limited outputs, as available temperature differential on human body (ΔText) is typically less than 10K. Furthermore, the thermal resistance at the TEG–air interface often overwhelms the thermal resistance of TEG itself, which makes the temperature differential within the TEG merely a small fraction of ΔText. We studies the designs of TEG systems for wearable applications based both on theory and systematic experiments. Next, to investigate the effects of heat sink and external air flow, this study combines heat sinks with the TEGs and evaluates their performance under different convection conditions.

Publications:

Y.G. Lee, J. Kim, M.-S. Kang, S.-H. Baek, S.K. Kim, S.-M. Lee, J. Lee, D.-B. Hyun, B.-K. Ju, S.E. Moon, J.-S. Kim, and B. Kwon*, “Design and Experimental Investigation of Thermoelectric Generators for Wearable Applications” Advanced Materials Technologies, 1600292, 2017.

Thermoelectric Generators Optimized for Non-Planar Surface

Many heat sources have complex surface shapes and/or nonuniform temperature distributions along the surface. However, TEG shapes are almost always planar and have rarely been modified from their rectangular shape mainly due to the poor manufacturability of TE alloys. Especially, weak mechanical strengths of conventional TE materials have limited the shape and aspect ratio of the TE elements. Recently, there have been efforts to improve the contact between TEGs and curved heat sources by either employing flexible substrate or fabricating conformal forms of TE materials. Conformal TEGs offer significant system level performance enhancements by efficiently mating to the heat transfer source. Such TEGs could also provide improved heat transfer interfaces with cold reservoirs for heat rejection.

Publications:

F. Kim, B. Kwon (co-first author), Y. Eom, J.E. Lee, S. Park, S. Jo, S.H. Park, B.-S. Kim, M.H. Lee, T.S. Min, K.T. Kim, H.G. Chae, W.P. King, and J.S. Son, “3D Printing of Shape-Conformable Thermoelectric Materials Using All-Inorganic Bi₂Te₃-Based Inks” Nature Energy, 3, 301, 2018.