Enhanced Pool Boiling Heat Transfer of FC-72 and Ethanol on Inclined Microchannel Surfaces

Boiling is one of the most effective mechanisms for heat transfer enhancement and is therefore widely applied in high-performance cooling systems for electronic devices, power electronics, and compact heat exchangers. A comprehensive understanding of the relationship between surface microstructure geometry and boiling dynamics enables the design of advanced surfaces with improved thermal performance and enhanced operational stability. This study presents an experimental investigation into the effect of inclined microchannel geometry on the pool boiling characteristics of FC-72 and ethanol, two working fluids with significantly different thermophysical properties. The experiments were conducted on copper surfaces with parallel microchannels of various widths, depths, and inclination angles, with the obtained results compared with those for a technically smooth reference surface. The experiments were performed under atmospheric pressure conditions with a gradually increasing heat flux. Boiling curves, heat transfer coefficients (HTCs), and critical heat flux (CHF) values were determined. The results demonstrate that properly designed microchannel geometries can significantly enhance boiling heat transfer by increasing the number of active nucleation sites and modifying the conditions of vapor bubble growth and departure. The most favorable thermal performance was achieved for surfaces with the smallest channel width, confirming the important role of microstructure geometry in governing boiling heat transfer mechanisms. For FC-72, the HTC increased by more than 200% compared with the reference surface, whereas ethanol exhibited higher HTC values and a more stable nucleate boiling regime over the entire investigated heat flux range. The results confirm that optimization of inclined microchannel geometry provides an effective strategy for designing surfaces dedicated to enhanced boiling cooling, while the effectiveness of surface modification depends on both microstructure characteristics and the thermophysical properties of the working fluid.