Effect of the magnetic field on the ferrofluid flow in a curved cylindrical annular duct

Abstract

The laminar fully developed ferrofluid flow of an otherwise magnetic fluid into a curved annular duct of circular cross section, subjected to a transverse external magnetic field, is studied in the present work. The specific geometry is chosen as it is encountered in heat exchangers and mixers where compactness is a priority. Results are obtained for different values of curvature, field strength, and particles’ volumetric concentration. A computational algorithm is used which couples the continuity, Navier Stokes, and magnetization equations using a nonuniform grid. The velocity–pressure coupling is achieved using the so-called continuity-vorticity-pressure variational equation method, adapted to the toroidal-poloidal coordinate system. The results confirm the ability of the method to produce accurate results in curvilinear coordinates and stretched grids, which is important for the standardization of the method’s application to generalized coordinate systems. Concerning the micropolar flow characteristics, the results reveal the effect of the magnetic field on the ferrofluid flow. It is shown that the axial velocity distribution is highly affected by the field strength and the volumetric concentration, that the axial pressure drop depends almost linearly on the field strength, and that a secondary flow is generated due to the combined effect of the external magnetic field and the curvature. The present analysis provides important insight into the effect of the three main parameters, revealing cases where a straight annular pipe might be preferable to a curved one and specific parts of the pipe that could be susceptible to enhanced loads, giving information that is crucial for design optimization.