Effect of magnetic field on laminar convective heat transfer characteristics of ferrofluid flowing through a circular stainless steel tube

摘要

Ferrofluids have promising potential for heat transfer applications, as they can be easily controlled and manipulated by applied magnetic field produced by either permanent magnets or electromagnets. The present study reports the effect of magnetic field on the convective heat transfer characteristics of ferrofluid flowing through a circular stainless steel (SS) tube (2 mm ID x 2.6 mm OD) under constant heat flux conditions. The convective heat transfer coefficient for various ferrofluid flow rates and applied magnetic field gradients is reported using infrared thermography (IRT) technique. COMSOL simulation has been carried out to calculate the magnetic field and magnetic force distribution inside the SS tube. Bright field visualization of clusters of nanoparticles and aggregation of nanoparticles at the inner wall of the SS tube in the presence of magnetic field have also been carried out in order to explain the possible mechanism for heat transfer enhancement for ferrofluid in the presence of magnetic field. The convective heat transfer coefficient for ferrofluid flow in the presence of magnetic field may increase or decrease depending upon several factors such as, ratio of magnetic force to inertia force acting on the ferrofluid, interaction of ferrofluid flow with the aggregate of nanoparticles formed at the wall of the tube near the vicinity of the magnets, and enhancement in local thermal conductivity of ferrofluid flow resulting from the chain like clusters of nanoparticles within the ferrofluid in the presence of magnetic field. (C) 2016 Elsevier Inc. All rights reserved.