The induced non-uniformity of magnetic field enables to enhance heat transfer through the annular gap in a uniform magnetic field three – five times

Abstract

We have investigated the influence of the induced non-uniformity on thermomagnetic convection when the inner cylinder of an annular gap has high magnetic permeability and a special wave-like shape. The outer uniform magnetic field induces a non-uniformity, which causes thermomagnetic convection. The problem is analyzed numerically. The in-house code uses the finite volume method with exponential interpolation functions for vorticity and temperature and linear functions for the stream function and magnetic field potential. It was found that increasing the periodicity and amplitude of the wave-like structure enhances heat transfer by 30–50 % compared to a circular annular gap filled with magnetic fluid, and 3–5 times compared to an annular gap filled with ordinary fluid. Such a way of creating induced non-uniformity of magnetic field and convection enhancement is especially effective for microfluidics, as the gravitational Rayleigh number is low in this case, and it is a hard technical problem to create a non-uniform magnetic field in small channels by directly using permanent magnets.