MHD Effect on Nanofluid Heat Transfer, 3-D

Description

This project uses ANSYS Fluent to simulate the flow of a nanofluid through a solid aluminum channel under an applied magnetic field. The flow is steady and modeled as a single-phase flow, with the thermophysical properties of the nanofluid — density, viscosity, specific heat, and thermal conductivity — calculated as functions of the nanoparticle volume fraction. The core of the study is the magnetohydrodynamic (MHD) interaction: the applied magnetic field acts on the electrically conducting nanofluid, altering its flow and heat-transfer behavior through the Lorentz force and Joule heating. The surface-averaged temperature of the nanofluid rises from 293.2 K at the inlet to 304.175 K at the outlet.

Geometry & Mesh

The fluid domain was created in SpaceClaim, and the computational grid was generated in ANSYS Meshing. The mesh is unstructured, with 26,000 elements.

Methodology

Several assumptions underpin the simulation: a pressure-based solver is used, the formulation is steady, and gravitational effects are neglected.

Models — the energy equation is enabled; turbulence uses the standard k-epsilon model with standard wall functions; and the MHD model is applied using the magnetic-induction method, solving the MHD equations with the Lorentz force and Joule heating both included.

Magnetic field — an external field B₀ is imposed by patch, with a 1 T component applied in the relevant directions.

Materials — the working fluid is a water-based nanofluid (density 1312 kg/m³, specific heat 3248 J/kg·K, thermal conductivity 1.09387 W/m·K, viscosity 0.0011 kg/m·s, electrical conductivity 1,000,000 S/m, magnetic permeability 1.257 × 10⁻⁶); the solid channel is modified aluminum (density 2719 kg/m³, specific heat 871 J/kg·K, thermal conductivity 202.4 W/m·K, electrical conductivity 3.541 × 10⁷ S/m). The solid also carries an energy source representing Joule/MHD heating of 1,000,000 W/m³ applied through a UDF.

Boundary conditions — Inlet: velocity inlet at 1 m/s, 5% turbulence intensity, turbulent viscosity ratio 10, and 293.2 K; the outer solid wall is held at 320 K (insulating for the magnetic field), and the fluid-solid interface is a coupled wall.

Methods — SIMPLE pressure-velocity coupling; least-squares cell-based gradients; second-order for pressure, momentum, and energy; and first-order upwind for the turbulence quantities and the magnetic field components. The solution is initialized with a 1 m/s velocity and a temperature of 293.2 K.

Conclusion

Without a magnetic field, the nanofluid's average temperature rises from 293.2 K at the inlet to 304.175 K at the outlet. When the magnetic field is applied, the outlet temperature increases further to 305.14 K. Plots of temperature and velocity along the centerline of the domain are presented for both cases (with and without MHD).

Comparing the outlet temperatures with and without the magnetic field reveals the effectiveness of the MHD effect in this problem: applying the field raises the outlet temperature by about 1 K. This demonstrates how a magnetic field, through the Lorentz force and Joule heating acting on a conductive nanofluid, can be used to enhance heat transfer — the central principle behind MHD-based thermal management.