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.