Effect of carbon nanofiber surface morphology on convective heat transfer from cylindrical surface: Synthesis, characterization and heat transfer measurement

• Morphologically different layer of carbon nanofibers are successfully synthesized.
• Scanning electron microscopy and Raman spectroscopy is used to characterize the synthesized layer.
• Heat transfer performance study was conducted for the different layers.

In this work, heat transfer surface modification is made by layers of carbon nanofiber (CNF) on a 50 μm nickel wire using Thermal chemical vapor deposition process (TCVD). Three different CNF layer morphologies are made, at 500 °C, 600 °C and 700 °C, to investigate the influence of morphology on heat transfer performance characteristics. Experimental results show that a CNF layer made at 500 °C behaves like an additional heat resistance, which is attributed to the dense structure of the layer of fibers. This results in 25% lower heat transfer compared to the heat transfer performance of the bare wire. However, samples made at 600 °C, exhibit a relatively porous layer of CNFs with relatively lower thermal conductivity compared to samples made 500 °C, resulting in an enhancement of 24%. This is because the relative porous structure leads to relatively better flow permeability which reduces the thermal resistance of the layer. Samples made at 700 °C are partly covered with a dense CNFs layer and partly with an amorphous layer of carbon. Heat transfer enhancement of 34% is achieved which is attributed to the combined effect of the highly conductive layer, high effective heat transfer surface area and rough surface morphology.