Enhanced nucleate pool boiling heat transfer on CNTs-Cu nanoparticles-coated surfaces: Effects of sintering temperature and CNTs composition on pool boiling behavior

The present study involves the experimental investigation of pool boiling heat transfer characteristics on CNTs-Cu nanoparticles-coated heating surfaces. The advantages of coating the mixture of infinitesimal CNTs with Cu particles on the copper surface are to generate the active nucleation site density by porous structures and enhance the thermal conductivity of the heating surfaces. To explore the effects of sintering temperatures and CNTs composition on pool boiling behavior, we fabricated the boiling test sections under the sintering temperatures of 700, 750, and 800 °C for four different CNTs compositions of 0.0CNTs-100Cu, 0.2CNTs-99.8Cu, 0.3CNTs-99.7Cu, and 0.5CNTs-99.5Cu in wt.%. We first analyzed the surface morphologies, that is, the average pore size, porosity, and pore density, to characterize each tested sample. Pool boiling experiments were later conducted under atmospheric pressure using water to obtain the pool boiling curves and bubble dynamics for different sintering temperatures and CNTs composition. Based on the experimental analysis, nucleate boiling heat transfer enhancement was interpreted in relation to the sintering temperature with surface morphologies and CNTs composition in relation to improved pore density. Compared to the bare copper surface, the achieved maximum enhancement for boiling heat transfer coefficient and critical heat flux were 3.86 and 1.49, respectively, when a 0.5CNTs-Cu-coated surface sintered at 800 °C was applied.