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Influence of CNFs layer morphology on convective heat transfer behavior


Taha, T.J.; van der Meer, Theo;




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In this work, heat transfer surface modification is made by layers of carbon nanofiber (CNF) on 50µm nickel wire using a chemical vapor deposition process (CVD). Three different CNF layer morphologies are made, at 500˚C, 600˚C and 700˚C, to investigate their influence on heat transfer performance characteristics. Moreover, the influence of the CNFs layer thickness on each batch of morphology is studied. Experimental results shows that samples made at 500˚C creates an insulating layer of CNFs, which is attributed to the dense structure of the layer of fibers, resulting in 25% lower heat transfer compared to the heat transfer performance of the bare wire. However, samples made at 600˚C, exhibit relatively open layer of CNFs and lower thermal conductivity compared to samples made 500˚C, resulting in an enhancement of 24%. This is because the relative open structure leads to relatively better flow permeability which increases the heat transfer surface area. Samples made at 700˚C are partly covered with dense CNFs layer and partly with amorphous layer of carbon. Heat transfer enhancement of 34% is achieved which is attributed to the combined influence of high thermally conductive layer, high effective heat transfer surface area and rougher surface morphology.