Application of <i>β</i> -FeSi ₂ -based bandpass filters in wavelength-selective infrared drying systems

Abstract This study investigates the enhancement of solvent evaporation rates using wavelength-selective infrared (IR) drying based on a novel tri-layered β -FeSi 2 -based bandpass filter (BPF). Owing to the high refractive index of β -FeSi 2 , which surpasses that of conventional filter materials, the proposed BPFs achieved both high transmittance and an appropriate bandwidth with only three layers. Experimental results demonstrate that IR irradiation at 3.4 μm, corresponding to the absorption band of N-methyl-2-pyrrolidone (NMP), significantly increases evaporation efficiency compared to other wavelengths or broad-spectrum IR irradiation. Notably, wavelength-selective IR heating achieves an evaporation rate up to six times higher than broad-spectrum IR irradiation while improving overall energy efficiency. Thus, β -FeSi 2 -based optical filters with a reduced number of layers are expected to be effective for drying organic solvents in the near-infrared to mid-infrared region.