Assessment of Fe3O4–water nanofluid for enhancing laminar convective heat transfer in a car radiator

Increasing the heat transfer rate in car radiators by using nanofluids leads to better control of engine temperature at hard working conditions and reduces the required radiator dimensions. However, due to the possibility of disposal of radiator coolants in the environment, use of an eco-friendly nanofluid coolant is of particular importance. Therefore, in the current research, Fe3O4–water nanofluids with the nominal particle diameter of 28 nm were synthesized. The experiments were performed at vol% ranging from zero to 0.9, three radiator input temperatures (72, 80 and 88 °C) and four radiator fan speeds (1000, 1500, 2000 and 2500 rpm). Although the fluid flow rate was constant in this study, Re number varied in a narrow range (30–100) according to the change in the nanofluid concentration. It is interesting to say that the best working condition of the radiator obtained at 0.1 vol% and more increase in the nanoparticle concentration deteriorated the heat transfer. At 0.1 vol%, the heat exchanging performance of the radiator is improved by an average of 21% in comparison with the pure water. At this concentration, maximum Re number was also obtained according to the measured density and viscosity of the nanofluids. It can be concluded that at higher nanofluid concentrations (> 0.1 vol%), not only the particle agglomeration but also Re number reduction may lead to heat transfer deterioration. Moreover, at 0.1 vol% of nanoparticles, the outlet coolant temperature from the radiator decreased with increasing the radiator fan speed from 1000 to 2500 rpm. However, for temperatures more than 80 °C, the difference between the output fluid temperature at the fan speeds of 2000 and 2500 rpm was not significant. Therefore, as an overall conclusion, the concentration of 0.1 vol% and fan speed of 2000 rpm could be recommended in the car radiator with inlet temperatures at the range of 80–88 °C.