Thermoelectric (TE) energy recovery is an important technology for recovering waste thermal energy in high-temperature industrial, transportation, and military energy systems. TE power systems in these applications require high-performance hot-side and cold-side heat transfer to provide the critical temperature differential and transfer the required thermal energy to create the power output. Hot- and cold-side heat transfer performance is typically characterized by hot-side and cold-side thermal resistances, Rh,th and Rc,th, respectively. This heat transfer performance determines the hot-side temperature, Th, and cold-side temperature, Tc, conditions when operating in energy recovery environments with available temperature differentials characterized by an external driving temperature, Text, and ambient temperature, Tamb.
Hot-side thermal resistances (see figure) can be affected by many external factors, including hot exhaust gas contaminations, differential expansion forces, external vibration forces, or changes at key transfer interfaces caused by material diffusions or breakdowns. It is crucial to monitor and track the hot-side thermal performance at all times during TE energy recovery system operation, thereby allowing one to track the system “health,” predict future expected system performance, and anticipate/ prevent system failures.
A perturbation methodology and the direct coupling between TE current, voltage, and hot-side energy flow are used to extract a real-time, in-situ evaluation of hot-side thermal resistances. External measurable TE parameters, either system current or Text, can be perturbed during system operation, and the resulting TE system response can then be coupled mathematically to the hot-side thermal transfer performance (i.e., thermal resistance). This can then assist in developing faster, real-time techniques to alleviate any system performance degradation, or identify and prevent system damage from dramatic changes in hot-side thermal transfer conditions.
This approach provides an internally consistent methodology for identifying and mitigating system performance problems early in critical system testing and validation cycles, thereby providing a real-time methodology for modifying system performance expectations and predictions, as required, and early prevention of potential system-damaging conditions.
This technique can be applied to all spacecraft radioisotope thermoelectric generator (RTG) systems in providing another critical technique for monitoring system health, control system performance, and adjust performance expectations based on real-time, in-situ operational data analysis. It can be applied to any thermoelectric energy recovery system used in automotive and industrial process applications.
This work was done by Terry Hendricks of Caltech for NASA’s Jet Propulsion Laboratory.
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Refer to NPO-49583.