The advancements in nanotechnology and quantum optics have drawn great interest in the spectral control of thermal radiation due to its promising applications in infrared sensing, thermal imaging, radiative cooling, and in thermophotovoltaics.
Shinichiro Tsuda and colleagues at Tohoku University in Japan proposed a method that works by utilizing the polymer infrared optical window in passive thermal management. The method uses spectral control of thermal radiation and can improve the transfer of heat in polymers that have a reduced thermal conductivity as a result of their low phonon mean free path. Their work is now published in Applied Thermal Engineering.
The authors used a heater embedded between a heat insulator on the bottom side and an emitter on the top side, and this was placed below an acrylic resin plate that was supported using alumina pipes. This setup was encased within a vacuum chamber that had an infrared optical window. It was assumed that there was a quasi-one-dimensional heat transfer path, such that there was conduction between the heater and the emitters, then thermal radiation between polymer plates and emitters and finally via the infrared optical window. The optical system which included the Fourier-transform infrared spectroscopy was used to measure the transmitted thermal radiation via the infrared optical window which enabled the authors to characterize thermal radiation through various thicknesses of polymer plates.
The impact of the transmission of thermal radiation through the polymer was characterized by using acrylic resin polymer plates of different thicknesses at the optical window. The distribution of surface temperatures on polymer plates was evaluated using their thermal images and a similar emissive power was used to obtain the radiative spectrum from each emitter. It was assumed that the polymers did not experience thermal dissociation therefore, the effect of temperature is negligible on the optical window.
The researchers observed that the spectrally selective emitter has a lower average emittance and this causes it to have a higher temperature as compared with the high emissivity emitter. The effective spectral matching caused a greater radiative intensity in the spectrally selective emitter as compared with the high emissivity emitter and this is irrespective of the thickness of the plate. From this, it was evident that the spectrally selective emitter is more efficient in heating the polymer plate as compared by the high emissivity emitter.
They also observed that the selectively enhanced thermal radiation on the polymer’s optical window improved the spreading of heat and reduced hotspots. From the experimental results, the coefficient of temperature variation in the spectrally selective emitter was lower as compared with that of the high emissivity emitter which showed that the former enhanced the spreading of heat and reduced hotspots, and this is not heavily dependent on the thickness of the plate.
From the research conducted in the paper, it can be concluded that the method proposed by the authors increased the spreading of heat, reduced hotspots, and the spectra of the proposed emitters improved the dissipation of heat through thermal radiation.
Shinichiro Tsuda, Makoto Shimizu, Fumitada Iguchi, Hiroo Yugami. Enhanced thermal transport in polymers with an infrared-selective thermal emitter for electronics cooling. Applied Thermal Engineering 113 (2017) 112-119.Go To Applied Thermal Engineering