Pool Boiling Heat Transfer and Critical Heat Flux Enhancement of Copper Nanoparticles Dispersed in Distilled Water

The pool boiling characteristics of copper-distilled water nanofluids are measured employing cylindrical heater surfaces of three different materials, namely, copper, brass and aluminium. Boiling heat transfer coefficient (HCT) enhances for all the three heater surfaces with increasing concentration of copper nanoparticles in the prepared nanofluids. Effects of nanoparticle concentration, heater surface material and heater surface roughness on boiling heat transfer are investigated using copper surfaces of various roughnesses. The increase in surface roughness of both copper and brass heaters after each run with Cu-distilled water nanofluids happens due to the scattered deposition of Cu nanoparticles on the heater surface making it rougher, which in turn increases the number density of the nucleation sites and results in more active boiling. Heater surface material has also significant influence on the HTC of nanofluids. Under identical conditions, the overall HTC enhancement is similar to 45% higher for copper surface compared to that for brass surface. Critical heat flux (CHF), measured using a thin Constantan (TM) wire, increases with increasing Cu nanoparticles loading and displays a maximum enhancement of similar to 60% for nanofluid containing 0.5 wt% Cu. The observed CHF enhancement is attributed to the increased surface roughness of the heating wire due to the formation of peaks and valleys on the wire surface, as revealed in SEM micrographs of the wire after boiling experiments.