Assessment of the magnetic field influence on heat transfer transition of natural convection within a square cavity

Abstract

The present work investigates numerically the natural convection within a square cavity under effects of inclined magnetic field with focus on heat transfer transition. The streamlines and the corresponding isotherms at various magnetic field intensities and angles are evaluated. The results disclose that enhancing the magnetic field intensity causes significant changes of streamlines and isotherms. Both the average Nusselt number (Numean) and maximum streamline function (Smax) decrease with magnetic field and exhibit sinusoidal oscillations with a period of 180°. In the condition of high Hartmann number (Ha), maximum velocity and Nusselt number appear at the left bottommost corner of the cavity subjected to magnetic angle of θ = 45◦, leading to the largest Smax and the best heat transfer performance. Owing to the interaction between the flow field and magnetic field, heat transfer patterns can be characterized by the variation of dimensionless Nusselt number Nu* over the angle of magnetic field, and named Pattern unimodal, Pattern peak-valley, Pattern transition, and Pattern bimodal. At various conditions of Ha and Rayleigh number (Ra), an empirical correlation is proposed to predict the heat transfer transition, which is useful in further understanding of the heat transfer mechanism within the square cavity.