Design and Experimental Investigation of Thermoelectric Generators for Wearable Applications. Issue 7 (20th April 2017) - Lee, Yun Goo
Abstract : 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 (∆ T ext ) is typically less than 10 K. Furthermore, the thermal resistance ( R th ) at the TEG–air interface often overwhelms R th of TEG itself, which makes the temperature differential within the TEG merely a small fraction of ∆ T ext . Here, the designs of TEG systems for wearable applications based both on theory and systematic experiments are studied. First, this study fabricates the TEGs having different fill factors (equivalently, varied internal R th of the TEGs) and finds an optimum fill factor that is determined by both thermal matching condition and the electrical contact resistance. Next, to investigate the effects of heat sink and external air flow, this study combines plate fin heat sinks with the TEGs and evaluates their performance under three different convection conditions: natural convection, and convection with either parallel or impinging flow. Lastly the effect of R th at the skin–TEG interface is studied. Although the TEG system produces an output power of 126 µW cm −2 (∆ T ext = 7 K) on a smooth heat source (Cu heater), it generates reduced power of 20 µW cm −2 (∆ T ext = 6 K) on wrist (uneven heat source). Abstract : An optimizing method for wearable thermoelectric generators (TEGs) is presented, that is validated through characterizations under three different convection conditions. To maximize the temperature differential across a TEG, thermal resistance related parameters such as fill factor and heat sink geometry are optimized. With an impinging flow (1.4 m s −1 ) and ∆ T ext = 7 K, the developed TEGs generates up to 126 µW cm −2 .