State-of-the-art optical fiber temperature measurement on a micro-pillar interfacial surface during flow boiling heat transfer

Flow boiling heat transfer is a promising candidate for next-generation cooling technology in thermal management systems, offering superior energy efficiency through latent heat absorption. During flow boiling, transient bubble dynamics lead to non-uniform thermal distributions. This non-uniformity at high heat fluxes can trigger critical heat flux (CHF), posing significant challenges to maintenance and operational stability. In this regard, micro-pillar structures (MPS) have been employed to improve both thermal uniformity and CHF by enhancing re-wetting flow by capillary wicking. This study conducted local thermal analysis to investigate flow boiling heat transfer on the MPS using a state-of-the-art optical fiber temperature sensor. This analysis enabled high-resolution surface temperature measurements (1.49 mm spatial and 125 Hz temporal resolution). The MPS had a pillar diameter of 20 μm, a gap of 20 μm, and a height of 15 μm. The MPS sample exhibited improved thermal uniformity and a high CHF. The re-wetting flow on the MPS contributed to a reduction in surface temperature. The peak surface temperature, indicative of thermal non-uniformity, during vapor backflow was reduced by 10.7 % on the MPS sample compared to the plain surface; furthermore, the liquid inflow following vapor backflow led to a 20.8 % decrease in surface temperature. Based on various experimental conditions, including subcooling, mass flux, and surface structure, we developed a novel CHF prediction model with a mean absolute error of 6.7 %. In conclusion, the local thermal analysis and CHF evaluation in this study provide valuable insights for achieving precise thermal analysis in advanced thermal management systems.