(378o) The Effect of Micro and Nano Material on Critical Heat Flux (CHF) Enhancement

An experimental investigation was conducted to study the behaviors of nano and micro materials on critical heat flux (CHF). Pool boiling experiments were implemented on several concentrations of nano and micro particles on an electrically heated Ni-Cr wire of 0.4 mm diameter at atmospheric pressure. Zinc oxide (ZnO) and silica (SiO₂) were used as a nano and micro fluids with concentration [0.01, 0.05,0.1,0.3,0.5,1]g/l. The experimental data showed a marked increase in critical heat flux for both nano and micro fluids for different concentrations compared to distilled water. When using nanomaterial, the reason behind this enhancement is the deposition of nano particles or porous layers that will increase the wettability of the heater surface hence, will increase the CHF, this nano particles deposition formed during nano fluid boiling. As vapor bubbles grow, the evaporating liquid in the micro layer leaves behind nanoparticles which then concentrate at the base of the bubble to form this pours layer. This layer significantly improves the surface wettability by reducing the static contact angle on the nano fluid-boiled surfaces compared with the pure-water-boiled surfaces. Nano particles found to be bond to the hot heater in a form of a thin layer which leads to a change of heater wire surface morphology between the start and the end of the boiling experiments. The enhancement in CHF when the nano fluid used was found to be higher than that of micro fluid.