Two-phase flow of ferrofluids

TL;DR

This paper reviews the theoretical understanding of ferrofluids, focusing on their two-phase flow, magnetization behavior, and the application of statistical physics to describe their dynamics.

Contribution

It combines statistical theory and Dirac function methods to develop comprehensive equations for ferrofluid behavior under various conditions.

Findings

Derivation of equations for magnetization relaxation and equilibrium

Application of Langevin equation to ferrofluid magnetization

Complete theoretical framework for ferrofluid dynamics

Abstract

Ferrofluids currently are the only type of magnetic liquid materials with wide practical use. The theory on ferrofluids is an example of success to apply statistics to science. Ferrofluids are two-phase liquids consisting of dispersed nanoscale ferromagnetic particles suspended in a carrier fluid. Due to their tiny size, individual ferromagnetic particles clearly exhibit Brownian motions. Only when a large number of randomly-moving particles are subject to an external magnetic field, can they collectively exhibit magnetization at a macroscale. Using statistical theory, the magnetization of a ferrofluid can be characterized by the celebrated Langevin equation. The monograph combines statistical theory and the method of Dirac function to establish equations for ferrofluids under several conditions, including magnetization relaxation, magnetization equilibrium, and magnetization freezing. It thus provides a quite complete account of the theory of ferrofluid dynamics.