Development and Characterization of ITO-Coated Glass Microchannels for High-Speed Flow Visualization

Microchannel heat exchangers (MCHX) with the incorporation of two-phase flow with phase change can achieve the challenge of extracting more amount of heat from concentrating photovoltaics. Flow visualization techniques are necessary to study the performance of MCHX and hindering phenomena like flow instability and flow reversal for large-scale implementation of MCHX. Indium Tin Oxide (ITO) coating facilitates simultaneous flow visualization and heating in flow boiling experiments as it is transparent and works as a heater. ITO coating has been done over a glass slide and square microchannels in the current work. The ITO coating over the substrate was performed using RF sputtering. The optical transmittance of the film was measured with an ultraviolet–visible spectrophotometer and was 95% at 550 nm wavelength. X-ray diffraction confirms the deposition of the cubic bixbyite structure of Indium Oxide. The thickness of the ITO coating, measured using a surface profilometer and atomic force microscopy, was found to be 78 nm. The measured optical transmittance, thickness, and roughness of the coating are in the acceptable range, so the coated microchannels can be implemented in flow boiling experiments.