In this study, the heat transfer performance of γ-Fe2O3 nanofluid is investigated. The particle size used in the experiment was about 20 nm. It was found by X-ray diffraction that it was consistent with the characteristic peak and no other impurities. Nanofluids with different concentrations were configured through a two-step method. Since the γ-Fe2O3 nanoparticles are not easily dispersed, the ultrasonic time was relatively long. After a series of experiments and data processing, we could see that nanofluids have the best heat transfer performance at 0.07 g/L.

Compared to a reverse-osmosis (R·O) water case, the enhancement of critical heat flux (CHF) was about 34.09%, and the heat transfer coefficient enhancement was about 49.32%. The movement of bubbles during the experiment was recorded and analyzed. Compared with the R·O water case, the bubbles were larger and fewer in the nanofluid case, and what is more, the bubble movement was 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. Scanning electron microscopy showed that the deposition of the nanoparticles on the heating surface was the main cause of CHF enhancement. When the concentration was 0.08 g/L, CHF decreased, mainly because the excessive deposition of the nanoparticles increased the thermal resistance of the heating surface and led to the deterioration of heat transfer.