Conversion of waste heat to electricity using a high performance pyroelectric converter

The pyroelectric coefficients of a 60/40 P (VDF-TrFE) film under high voltage were measured as a function of temperature. When heating at 28 MV/m (700 V/25 μm), they increased almost linearly from 110 μC/m2K at 35°C to 730 μC/m2K at 60°C but they decreased to as low as 480 μC/m2 K between 60°C and 80°C. However, they increased rapidly again above 80°C and reached as high as 1035 μC/m2K at 92°C where 60/40 P (VDF-TrFE) underwent phase transition. Similar measurements at 20 MV/m (500 V/25 μm) showed the phase transition near 70°C. However, pyroelectric coefficients during cooling were much lower and similar both at 8 MV/m (200 V/25 μm) and 28 MV/m. They were less than 70 μC/m2K at 95°C and linearly increased with decreasing temperature and they reached the highest value 485 μC/m2K at 65°C. The transition temperature during cooling was hardly affected by the applied electric field. It remained near 65°C both at 8 MV/m (200 V/25 μm) and 28 MV/m. Subsequent to the above measurements, pyroelectric conversion was examined at various operating conditions using a single 25 μm thick 60/40 P(VDF-TrFE) film. A pyroelectric conversion cycle conceived by Olsen was adopted. External control voltage was cycled between high and low in synchronization with cycling of film temperature. When cycled between 700 V and 100 V and between 30°C and 70°C, electrical output to electrical input ratio reached 1.8. When this ratio is greater than one, it reflects the conversion of heat to electricity through pyroelectric conversion. The net power output density at these conditions before subtracting parasitic losses was 250 J/L of copolymer used. As the difference between high- and low-control voltage increased the electrical output to input ratio also increased. This paper reviewed how the pyroelectric effect could be applied to convert heat to electricity and presented experimental results.