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In the present work, Fe 3 O 4 nanoparticles produced by the ultrasonic precipitation method and characterized by XRD, SEM, and BET methods are used to produce nanofluids using a mixture of water and ethylene glycol (WEG 50:50) as a base fluid and both sodium dodecyl sulfonate and oleic acid as surfactants. The thermal conductivity, dynamic viscosity and surface tension of these Fe 3 O 4 nanofluids are experimentally evaluated for temperatures ranging from 253.15 to 293.15K and different volume concentrations of nanoparticles, 0.01, 0.05 and 0.1% respectively. Experiments indicate that the thermophysical properties of nanofluids are strongly dependant on concentrations of nanoparticles and temperatures, particularly at sub-zero temperatures. Actually, it is shown that the thermal conductivity of nanofluids increases with almost 9.5%, and 14.3%, at 263.15K and 293.15K respectively, with 0.1 vol%. The thermal conductivity enhancement of nanofluids with concentration and temperature is compared to some relevant theoretical models. A good agreement is achieved with a comprehensive model taking into consideration effective medium theory, the nanolayer effect of molecules around the solid particle, Brownian motion of nanoparticles encompassing aggregation and nano-convection. It is also found that the dynamic viscosity of nanofluids decreases with nanoparticle content in particular below Journal Pre-proof J o u r n a l P r e -p r o o f 2 273.15K, up to 40% at 0.1% in volume. Surface tension decreases by adding the surfactant to the base fluid and then increases with Fe 3 O 4 concentration with nearly 38% and 33% with 0.1% in nanoparticle volume fraction at 253.15 and 293.15K, respectively. Finally, these results are promising in view of Fe 3 O 4 nanofluids use in cooling applications.

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