CHF Enhancement by γ-Fe2O3 Nanofluids with Pool Boiling condition on a Downward Facing Plane

Nanofluids have been widely used in many engineering fields because of their excellent properties, and can be effectively used for cooling electronic equipment and improving energy efficiency. In this study, the heat transfer performance of γ-Fe 2 O 3 nanofluid was investigated. The particle size used in the experiment is about 20 nm, it can be found by X-ray diffraction (XRD) that it is consistent with the characteristic peak and no other impurities. Nanofluids with different concentrations were configured through a two-step method. Since the γ-Fe 2 O 3 nanoparticle are not easily dispersed, the ultrasonic time is relatively long. After a series of experiments and data processing, we can see that nanofluids have the best heat transfer performance at 0.07 g/L. Compared to reverse osmosis (R·O) water case, the enhancement of critical heat flux (CHF) is about 34.09%, and the heat transfer coefficient enhancement is about 49.32%. The movement of bubbles during the experiment is recorded and analyzed. Compared with R·O water case, the bubbles are larger and fewer in the nanofluid case, and what’s more, the bubble movement is relatively intense. The heating surface was characterized after the experiment, and it was found that the wettability of the heating surface was changed, and the roughness of the heating surface decreased. SEM shows that the deposition of nanoparticles on the heating surface is the main cause of CHF enhancement. When the concentration is 0.08 g/L, CHF decreases, mainly because the excessive deposition of nanoparticles increases the thermal resistance of the heating surface and leads to the deterioration of the heat transfer.