Evaluation of heat transfer transition for nanofluids within an enclosure based on magnetic field angles

Abstract

The present simulation deals with Magnetohydrodynamics (MHD) with focus on heat transfer attributes with the addition of nanoparticle volume concentration (NVC). Influences of the governing parameters, including natural convection strength of Rayleigh number (Ra), magnetic field intensity of Hartmann number (Ha), and magnetic directions with a complete period of γ = 0°–180° are studied. The results disclose that MHD heat transfer patterns can be divided into three groups, i.e., Type-1 (Increase), Type-2 (Transition), and Type-3 (Optimum). With the increasing Ha, the heat convection is suppressed, resulting in Type-1. Enhancing Ra improves the thermal convection and thus leads to the occurrence of Type-3. In between, a critical Ha (Hacr) at a specific Ra exists for heat transfer transition (Type-2). The flow structure and heat transfer patterns vary with γ stemming from the Lorentz force component. The maximum stream function and best heat transfer rate are found at γ = 45°, corresponding to a higher Hacr for Type-2. For a wide range of Ra values, the combination of Ha2/Ra is adopted to describe the relationship between the Hacr and γ for the heat transfer transition with an empirical equation as Ra ≥ 5 × 104.

Keywords

• Heat transfer transition
• Nanofluids
• Natural convection
• Magnetic field angles
• Magnetohydrodynamics
• Nanoparticle volume concentration