Enhanced pool boiling heat transfer of multilayer copper-nanoparticle-packed beds by copper mesh coating

Abstract

Pool boiling heat transfer has drawn a wide interest in dissipating high density heat flux produced by electronic products etc. In this work, the advantages of the copper mesh and the multilayer nanoparticle-packed beds in improving pool-boiling heat transfer was combined to give a good performance. The copper-nanoparticle-packed beds were firstly prepared, and then the effects of the layer thickness and porosity in the bed on the pool boiling heat transfer were explored. After obtaining the optimal thickness and porosity of the multilayer beds, the copper mesh was further coated on the multilayer beds to further enhance the pool-boiling heat transfer. Results turn out that: The increased thickness of the beds has a negative effect on enhancing heat transfer coefficient (HTC) because of the increased bubble-escape resistance, however, this effect will be set-off by the positive effect of the increased wetted area when the thickness was increase to be larger than 3 mm in this work. The onset of nucleate boiling of the optimal 4-layer beds without coating is about 1.7 °C which is much lower than most reported values, and the HTC is about 9 × 104 W/(m2·k) which is 9 times higher than that of the smooth surface. With the optimal bed further coated with copper mesh, the HTC can be further increased to 9.8 × 104 W/(m2·k). This enhancement arrives from the fact that the copper mesh prevents the continuous merging of bubbles, thus reducing the bubble detachment diameter by 30% and increasing detachment frequency of bubbles by 0.5 times.