Preparation and Flow Boiling Heat Transfer Performance of Concave Cr Coating on Stainless Steel Surface.

To improve the heat transfer performance (HTP) of stainless steel, the micro-nano concave chromium (Cr) coating was fabricated on the surface of 304 stainless steel by the combination technology of electrodeposition and anodic oxidation. The effects of electroplating and anodizing time on the morphology, contact angle (CA) and heat transfer coefficient (HTC) of the coating were studied. The results show that the samples with large surface area and good wettability have higher HTC. Besides, the Cr coating obtained after 2 h electroplating has silver white appearance, smooth surface and a thickness of about 37 μm. The 2-h electroplated Cr coating after anodizing for 30 min presents a concave pore structure with a pore diameter of 7.4 μm and the best wettability (a CA of 41.8°), which is 20° lower than that of the stainless steel substrate. The two-phase heat transfer efficiency of the sample with the concave Cr coating was increased by 22.84 % when the fluid mass flux is 33.3 kg m−2 s−1 and the inlet temperature is 40 °C and the fluctuations of pressure drop in the micro-channel was effectively reduced. The enhanced HTP of concave Cr coating is owing to the larger specific surface area and better wettability caused by the unique rough concave structure. [ABSTRACT FROM AUTHOR]