Analysis of Heat Transfer and Flow Behaviors of Magnetic Fluid in Twisted Square Tubes with Alternating Electromagnetic Fields

Abstract

This work investigated the thermal and flow behaviors of magnetic fluid flowing in the twisted square tubes with various twisted pitches, both with and without an electromagnetic field (EF) influence. The Reynolds number ranged from 4500 to 10500, with a pitch spacing of 100-200 mm, power input of 180-220 V, electromagnetic flux of 0.25-6.5 µT, frequency of 0.25-1.25 Hz, and nanofluid concentration of 0.02% by vol. Without EF, the twisted square tube has a more significant Nusselt number and flow resistance than the straight square tube, and the magnetic fluid increases by 10.5% and 5.35%, respectively. The electromagnetic field causes particles to migrate toward the square tube wall, which significantly influences boundary layer disturbance. Increased electromagnetic flux and frequency increase the intensity of nanoparticle turbulence and the coolant thermal conductivity. The EF flux effect increases the Nusselt number by 10.71% and the friction factor by 5.78%. In addition to the EF frequency effect, the Nusselt number increases by 13.45%. Furthermore, the predicted results are generally compatible with the observed data, with a maximum error of 7.92%.