Characterization and determination of thermal properties of carbonbased nanofluids as heat transfer media

Nanofluid is a new potential fluid for cooling applications. It is a colloidal suspension of nanoparticles such as metals, metal-oxides and carbon-based materials in the conventional base-fluids such as water, ethylene glycol and oils. This new generation of nanofluid possess great thermophysical properties that can be considered for wide range of heat transfer applications. Carbon-based materials is a good candidates to prepare nanofluids due to their high thermal conductivity. However, the inability of carbon particles to disperse homogenously in most fluids imposes a major limitation on an effective application. Therefore, it is crucial to synthesis well dispersed nanoparticles in conventional based fluids. In this research, three type of carbon-based materials were used namely, Multi-walled Carbon Nanotube (MWCNTs), Carbon Nanofibers (CNFs) and graphite flakes. The commercial MWCNTs and CNFs were chemically modified using three different methods of acid treatment, whereas graphite flakes were chemically modified using Hummers method to introduce surface oxygen functional group (SOFG). The presence of SOFG on the carbon materials has been characterized by Fourier Transform Infrared (FTIR) spectroscopy. Morphology, structural and thermal properties were performed using Field Emission Scanning Electron Microscopy (FESEM), Raman spectroscopy and Thermogravimetric analysis (TGA), respectively. Based on the results obtained, modification with acid treatment has significant effect on both the degree of defects and surface group functionality of all samples. Among all, Method B of acid treatment was chosen as the best method to synthesize the commercial. Preparation of nanofluids was followed by using two different parameters: with and without polyvinylpyrrolidone (PVP). The experiment was conducted by setting variable concentration of carbon particle from range 0.1 wt% to 1.0 wt% and the amount of PVP is 10% concentration of carbon particles at different temperature (6 ºC, 25 ºC, 40 ºC). Based on visual method, the dispersion of carbon particles was enhanced by the presence of PVP as the stabilizing agent. Whereas, for thermal conductivity test, graphene oxide without PVP gives the highest thermal conductivity enhancement with 23.28% for concentration of 1.0 wt% at temperature 40 °C with better stability. In overall, we successfully prepared carbon-based nanofluids with better stability and high thermal conductivity.