Thermomagnetic cooling of current carrying micro-wire in ferrofluid: Two-phase approach

Thermomagnetic convection is a controlling phenomenon for heat-transfer in ferrofluids. It depends upon the magnetic field gradients, variation in magnetic susceptibility, particle concentration and temperature gradients. This article presents the effect of these parameters on cooling of a current carrying micro-wire in ferrofluid with a focus on magnetophoresis effects. A two-phase Euler-Euler model is developed. The predictions of this model are compared with experimental results and predictions from a single-phase ferrofluid model. For ferrofluid with volume fraction of φ = 0.02, the predicted average wire temperature from the Euler-Euler two-phase model is approximately 1 K lower than the measured wire temperature,while the single phase model is 5 K higher. Under identical magnetic field and heat flux conditions, variations in the particle concentration are found to have a non-negligible effect on thermomagnetic convective cooling. The maximum temperature of the wire for φ = 0.01 ferrofluid is significantly increased by 10 K and greater enhancement to cooling is observed in the case of φ = 0.04, where the inception of thermomagnetic cooling is advanced. Correspondingly, significantly different thermal and velocity fields are observed for different volume fractions. The simulations show different regimes of heat transfer. During the first few hundred milliseconds after applying electrical current, a thin boundary layer develops near the wire surface and the colder region is thermally stratified. At larger time, dispersion of ferro-particles between colder and hotter regions produces concentration gradients which affect the thermal and velocity fields. Eddies generated by thermomagnetic convection are found to form at the bottom of the vertical wire and retain their structure as they are convected upwards by natural convection. The particle concentration at the wire surface (φws) varies from 0.0188 to 0.0260 for an initial volume fraction (φ) of 0.02. This variation disturbs the thermal boundary layer and generates thermal vortices around the heated wire that differ from single-phase model predictions. •Validation of Two-Phase and Single-phase thermomagnetic model with experiment.•Variation in local concentration of ferroparticles around heated Cu-wire.•Plume-like flow structures for the higher concentration ferrofluid.•Continuous rising of thermal cells adjacent to the vertical wire.