Flow boiling enhancement in microtubes with crosslinked pHEMA coatings having different coating thicknesses

In this experimental study, flow boiling in mini/microtubes was investigated with surface enhancements provided by crosslinked polyhydroxyethylmethacrylate (pHEMA) coatings, which were used as a crosslinker coating type with different thicknesses (50 nm, 100 nm and 150 nm) on inner microtube walls. Flow boiling heat transfer experiments were conducted on microtubes (with inner diameters of 249 µm, 507 µm and 998 µm) coated with crosslinked pHEMA coatings. pHEMA nanofilms were deposited with initiated chemical vapor deposition (iCVD) technique. De-ionized water was utilized as the working fluid in this study. Experimental results obtained from coated microtubes were compared to their plain surface counterparts at two different mass fluxes (5,000 kg/m2s and 20,000 kg/m2s), and significant enhancements in Critical Heat Flux (up to 29.7 %) and boiling heat transfer (up to 126.2 %) were attained. Thicker pHEMA coatings resulted in larger enhancements in both CHF and boiling heat transfer.