Enhancing Thermoelectric Energy Recovery via Modulations of Source Temperature for Cyclical Heat Loadings

Recent improvements in thermoelectric (TE) materials have expanded the potential to use this technology to generate electricity from waste heat in a variety of applications. The performance of a TE generator improves when the temperature difference across the generator is as large as possible given the constraints associated with its application. This paper considers the use of a “thermal switch,” located physically between the heat source and the TE device, to modulate the heat flow through the TE device. A control schema is envisioned which permits heat to flow from the source to the TE device only when the source temperature is near maximum, yielding a higher time-averaged temperature drop across the TE and therefore a higher efficiency. A numerical model is used to evaluate the benefits of an active thermal switch in series with a TE generator relative to a baseline case defined by the absence of a thermal switch for both time-varying and constant heat inputs. The results demonstrate that modulating the heat flow through the TE device and maintaining the source temperature at a near constant maximal value is capable of improving the time-averaged TE device energy recovery efficiency. For some conditions, improved efficiencies of more than five times are realized. The requisite physical conditions necessary for achieving these improvements are also identified.