Effects of composite coatings on pool boiling performance characteristics in demineralized water

Nucleate boiling is known for its high heat transfer capacity which occurs at a reasonably low temperature difference between the surface and saturated liquid due to the rapid vaporization process. The vaporization process and boiling heat transfer (BHT) primarily depend on surface morphology and wettability. In this article, surface morphology and wettability of smooth copper surfaces have been altered by coating with binary oxide nanoparticles. Three different combinations of composite coatings: TiO2/SiO2, TiO2/Al2O3 and SiO2/Al2O3 are considered and pool boiling performances have been investigated in demineralized water. Samples have been prepared using electrophoretic deposition techniques in binary oxide nanofluid of 0.1 wt. % concentration. The coating was performed for a fixed duration of 10 min in a medium of hybrid nanofluids of TiO2/SiO2, TiO2/Al2O3 and SiO2/Al2O3 which are referred to as S1, S2 and S3, respectively, in the text. The surface morphology, wettability and coating layer thickness of the sample are varied with the coating duration. The smooth copper surface is hydrophilic while coated samples are hydrophobic by nature. Experiments were carried out on all surfaces, and the results were compared with the smooth copper surface. The maximum enhancements in BHT coefficient for surfaces S1, S2 and S3 are 38%, 43% and 59%, respectively, corresponding to heat flux of ∼275,∼ 200 and ∼220 kW/m2. The reduction in boiling incipient temperature is 0.7, 3.6 and 4.4°C, respectively.