Condensation heat transfer on nickel tubes: The role of atomic layer deposition of nickel oxide

• Published in: International journal of heat and mass transfer 2019-04, Vol.133, p.487-493
• Main Authors: Alwazzan, Mohammad, Egab, Karim, Wang, Pengtao, Shang, Zeyu, Liang, Xinhua, khan, Jamil, Li, Chen
• Format: Article
• Language: English
• Subjects: ALD; Atomic layer epitaxy; Carbon; Condensation; Droplet dynamic; Dropwise; Heat flux; Heat transfer; Heat transfer coefficients; Hydrophobic; Metal surfaces; Nickel; Nickel oxides; NiO; Substrates; Thickness; Tubes; Water vapor; Wettability; Wettability contrast
• ISSN: 0017-9310; 1879-2189
• DOI: 10.1016/j.ijheatmasstransfer.2018.12.112

•Experimental study was conducted to systematically investigate the influence of nickel oxide layers formed during a practical application on the condensation heat transfer.•The condensation was significantly enhanced by the coexistence of the hydrophilic nickel oxide and the hydrophobic carbon contents.•The maximum condensation heat transfer performance achieved was on a sample surface containing carbon to nickel oxide contents ratio of 3–1.•Increasing or decreasing the thicknesses of nickel oxide layers other than the optimum case is unfavorable to condensation heat transfer. The search for durable surfaces offering sustainable high rates of condensation is very essential for many applications. Most of the metal surfaces are subject to oxidization when exposed to water vapor and air, as is the case during the condensation under saturation conditions. Due to the relative stability of nickel and nickel oxide (NiO) among other common metals, they were considered herein as the substrates for condensing saturated water vapor under the atmospheric conditions. The main objective of this study was to investigate the influence of NiO layer(s) that would be formed during practical applications on the condensation performance. To mimic such oxide formation, different thicknesses of NiO layers were deposited by atomic layer deposition (ALD) method on the surface of smooth nickel tubes. The influence of the oxide layers on the condensation rate was then experimentally characterized, and the droplet dynamic was analyzed. Due to the presence of the large amount of hydrophobic carbon contents in the deposited NiO-ALD layers, especially at the initial stages of the ALD deposition process, a suitable wettability contrast degree with the corresponding deposited hydrophilic NiO was established. Thus bi-philic wettable surfaces were achieved. The degree of contrast in the wettability was varied by the number of the deposited NiO-ALD layers. It was found that samples with a higher carbon to NiO ratio exhibited a higher condensation heat transfer performance, reaching a maximum heat flux and heat transfer coefficient (HTC) of about 3.9 and 4.2 times that of the filmwise condensation (FWC) at subcooling temperatures of 11.0 °C and 3.5 °C, respectively.