Experimental investigation into laminar forced convective heat transfer of ferrofluids under constant and oscillating magnetic field with different magnetic field arrangements and oscillation modes

•Convective heat transfer increased after using an oscillatory magnetic field. However, it decreased after a constant magnetic field was applied.•The effects of the magnetic field are more intensified in the ferrofluids with higher volume concentration and flows with lower Reynolds number.•The maximum enhancement in the local convective heat transfer coefficient occurs at the last point of application of the magnetic field along the ferrofluid flow.•Decline in the magnetic field strength reduces the enhancement in the convective heat transfer. By increasing the application range of the magnetic field, higher heat transfer coefficients are achievable.•The effect of the oscillation frequency on the local heat transfer coefficient varies in different oscillatory modes of the magnetic field. In this study, the effects of ferrofluids on the forced convective heat transfer in a tube with a round cross section under constant heat flux in the laminar flow regime are investigated experimentally. For this purpose, an experimental setup was designed and built. Furthermore, the effects of an external magnetic field on the forced convective heat transfer were examined for various Reynolds numbers and volume concentrations. The parameters of magnetic field strength, magnetic field arrangement, the constancy or oscillation of the magnetic field and also its oscillatory mode were examined. As a result of the experimental studies, in the absence of a magnetic field enhancement in convective heat transfer was observed after using the ferrofluid compared with distilled water. In addition, convective heat transfer through the circular tube increased after using an oscillatory magnetic field. However, the heat transfer decreased after a constant magnetic field was applied. Based on the results obtained, the effects of the magnetic field are more intensified in the ferrofluids with higher volume concentration and flows with lower Reynolds number. Moreover, the effect of the oscillation frequency on the local heat transfer coefficient varies in different oscillatory modes of the magnetic field. The maximum enhancement of 19.8% was obtained in the local convective heat transfer by using the oscillating magnetic field compared with the case no magnetic field was applied.