Syntheses of ferrofluids using polyethylene glycol (PEG) coated magnetite (Fe3O4), citric acid, and water as the working liquid in a cylindrical heat pipe

Abstract

Ferrofluids were synthesized from magnetite (Fe3O4) nanoparticles coated with three different base fluids: polyethylene glycol (PEG), citric acid (CA), and water. Each of the fluids act as the working liquid in a cylindrical heat pipe. The ferrofluids were synthesized using a two-step method with varied concentrations; 0.04 g/ml and 0.06 g/ml for PEG, and 5, 10, 15, 20 % weight for CA, respectively. Ferrofluid with the most optimal condition was used as the working liquid in a cylindrical heat pipe. Heat inputs of 5, 10, and 15 W were then applied to test its performance. From the x-Ray diffraction (XRD) analysis, the formation of Fe3O4 phase has been confirmed. Fourier transform infrared (FTIR) spectroscopy was able to identify the occurrence of a new absorption at a wavenumber of 1029.70 cm−1. This result gives a clear indication of the existence of PEG molecules on the surface of Fe3O4 nanoparticles. The magnetic properties measured by vibrating sample magnetometer (VSM) suggest that with the PEG addition, the value of saturation magnetization is reduced from 55.36 emu/g Fe3O4/PEG-a to 53.24 emu/g Fe3O4/PEG-b. Thermal conductivity and specific heat analyses revealed that the values are within specified ranges of 0.58–0.6​ W/m.K and 4055–4085 J/kg.K. The investigation of the heat pipe filled with ferrofluid demonstrates that the optimal thermal resistance is 3.2 °C/W at heat input of 15 W.