Flow of a Biomagnetic Visco-Elastic Fluid in a Channel With Stretching Walls

The flow of a visco-elastic fluid in a channel with stretching walls under the action of an externally applied magnetic field generated by a magnetic dipole was studied in this paper. As per an experimental report, the variation in magnetization M of the fluid with temperature T was approximated as a linear equation of state M=K1T, where K1 is a constant called the pyromagnetic coefficient. In this investigation the model used is that of Walter’s liquid B fluid, which includes the effect of fluid visco-elasticity. By introducing appropriate nondimensional variables, the problem is reduced to solving a coupled nonlinear system of ordinary differential equations subject to a set of boundary conditions. The problem is solved by developing a suitable numerical technique based on finite difference approach. Computational results concerning the variation in the velocity, pressure and temperature fields, skin friction and the rate of heat transfer with magnetic field strength, Prandtl number, and blood visco-elasticity are presented graphically. The results presented reveal that the velocity of blood in the normal physiological state can be lowered by applying a magnetic field of sufficient intensity. The study bears the promise of important applications in controlling the flow of blood during surgery and also during treatment of cancer by therapeutic means when it involves magnetic drug targeting (hyperthemia).

Development of a Magnetocaloric Pump Using a Mn-Zn Ferrite Ferrofluid

Magnetic fluids or ferrofluids are colloidal dispersions of magnetic nanoparticles in a liquid carrier. These nanoparticles have a specific size range in order to remain suspended in the liquid, about 3 to 15 nm. In this range Brownian motion (thermal molecular motion in the liquid) keeps the particles from settling out. Because magnetic particles tend to aggregate, and aggregates sediment faster than single particles, the particles are coated with a stabilizing dispersing agent. The surfactant must be matched to the carrier type and must overcome the attractive Van der Waals and magnetic forces between the particles to prevent agglomeration even when a strong magnetic field is applied to the ferrofluid. A device that can pump a fluid with no moving mechanical parts represents a very encouraging alternative since such device would be practically maintenance free. A magnetocaloric pump achieves this purpose by providing a pressure gradient to a ferrofluid placed inside a magnetic field while experiencing a temperature change. If the temperature change is produced by extracting heat out of an element that needs refrigeration, coupling this heat via a heat pipe with the magnetocaloric pump will result in a completely passive cooling system. For applications near ambient temperature the ferrofluid must have specific characteristics such as low Curie temperature, high pyromagnetic coefficient, high thermal conductivity and low viscosity. This work presents the detailed description of the synthesis of ferrofluids composed of Mn-Zn ferrite nanoparticles and the characterization of its magnetic and thermal properties. Different composition of Mn-Zn ferrites nanoparticles were produce and evaluated. This ferrite ferrofluid was compared with commercially available magnetite ferrofluid in a magnetocaloric pump prototype. Results of saturation magnetization, pyromagnetic coefficient, Curie temperature, particle size, viscosity and pressure increment inside the magnetocaloric pump are presented.

Theory of Lubrication With Ferrofluids: Application to Short Bearings

The momentum equations are written for viscous fluids exhibiting magnetic stresses. The velocity profiles are deduced; then from continuity, a pressure differential equation, equivalent to Reynolds equation is obtained. This equation is discussed with emphasis on the case when magnetic stresses derive from a potential, also when the pyromagnetic coefficient vanishes. The boundary conditions for lubrication problems are then formulated. In particular, short bearings with ferromagnetic lubricants are considered. A numerical example yields the pressure diagrams at low and moderate eccentricity ratios and for different speeds. In conclusion, it is shown that ferromagnetic lubricants may improve substantially the performance of bearings operating under low loads and/or at low speeds. However, a correct variation of the magnetic field, toward the center of the lubricated area, is required. Under such conditions, the extent of the active area of the film is increased and bearing stiffness and stability are improved.