A COMPUTATIONAL STUDY OF THE EFFECT OF MAGNETIC FIELD ON HEAT TRANSFER IN FERROFLUID FLOW IN A CIRCULAR TUBERahul Nath DOI: 10.1615/TFEC2017.mnp.017669 摘要This paper presents a homogeneous flow model based computational study of the heat transfer enhancement under magnetic field of DI-water-magnetite (Fe_{3}O_{4}) ferrofluid flow in a circular tube (of 0.005 m in diameter and 5 m in length) subjected to constant heat flux. At the inlet the velocity and temperature are uniform (300 K). The flow is steady, laminar, incompressible, two-dimensional and axisymmetric. Stream function-Vorticity method and finite-difference discretization have been used. A limiting case validation of the numerical results has been carried out. A thin steel pipe of relative permeability of 100 and permanent NdFeB magnets of coercivity = 912,000 A/m have been used. The parameters studied are: ferroparticle volume fraction (0.5%, 0.86%, 1%, 2%, 3%), flow Reynolds number (1000, 1250, 1500, 1750), wall heat flux (0.1 kW/m^{2}, 1 kW/m^{2}, 10 kW/m^{2}), relative magnetic permeability of ferrofluid, number of magnets and the gap between the magnets. The results reveal that the magnitude of the local peaks in Nusselt number (in the vicinity of the magnets) increases with the relative permeability of the ferrofluid, and with the volume fraction of ferroparticles. However, the aforesaid magnitude of local increase in Nusselt number is higher for lower Reynolds number flow. The local rise in Nusselt number is not much affected by changes in the wall heat flux, number of magnets and the gap between the magnets. The maximum heat transfer coefficient is about 3.5% higher than that for the case of no magnetic field. |
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