Nucleate boiling heat transfer of R134a on cold sprayed CNT–Cu composite coatings

In this study, the application of mechanical alloying and cold spray process on the fabrication of carbon nanotube–copper (CNT–Cu) composite surface coatings for boiling heat transfer was investigated. Three types of coatings (5, 10, and 15 vol.% CNT) were fabricated. Boiling heat transfer of CNT–Cu composite coatings was investigated under a pool of saturated R134a at 4.8 ± 0.04 °C. Results showed that nucleate boiling can be enhanced by CNT–Cu composite powder coatings fabricated by cold spray. Incipience superheat of the coatings (5–6 K) was considerably lower than that of the plain Cu plate (8 K). At heat fluxes >20 kW/m2, significant differences in the enhancement ratios were observed. The maximum heat transfer coefficient enhancement achieved by the coatings was 1.21–1.74 times that of the plain Cu plate. The one-layer coating with 15 vol.% CNT exhibited the best boiling heat transfer performance in terms of lowering the superheat and enhancing the heat transfer coefficient.