Single-Dye Multispectral PLIF (SDMS-PLIF) For Quantitative Thermographic Visualisation Of Nucleate Boiling

The boiling of dielectric fluids in miniaturised channels has emerged as one of the most promising solutions to high- density electronics cooling. Although significant breakthroughs have been made, a fundamental understanding of the hydrodynamic and thermal performance in relevant flows is still lacking, which calls for further development of state-of-the-art measurement techniques and their deployment for the provision of high-quality, detailed experimental information. To this end, we conducted an experimental investigation of flow boiling in a miniaturised vertical square channel with a hydraulic diameter of 5 mm, using HFE-7100 as the working fluid. A whole-field thermographic imaging approach referred to as single-dye multispectral planar laser-induced fluorescence (SDMS-PLIF) was developed and applied to measure spatiotemporally-resolved temperature fields. For its implementation, Nile Red, a thermosensitive lipophilic dye, was dissolved in HFE-7100 as a fluorophore. The measurements were taken at selected conditions to achieve a nucleate boiling regime in a laminar flow. Time-lapse temperature maps provided direct evidence for bubble-induced mixing observed as thermal plumes, where a portion of hot fluid is advected above the thermal boundary layer at the heated wall and penetrates the colder bulk phase in the flow core.