Penetrative Convection in a Ferrofluid Saturated Porous Layer

Abstract

The magnetic fluid, also known as ferrofluid is a stable colloidal suspension of nanosized magnetic particles in a carrier liquid. The particles are normally magnetite, newlinehematite, or compounds containing iron, with the size of 10 nm or less in diameter. newlineThe carrier liquid is usually an organic solvent, water, or a variety of oil bases, and newlineto prevent the agglomeration of particles, the magnetic particles are coated by the newlinedispersant. Ferrofluids are exceptionally interesting and they consist of three phases, newlineviz. solid phase of magnetic material, carrier liquid, and surfactant. The ferrofluid s newlineperformance obviously depends on the balanced selection of the above phases. Two newlinecommon methods of ferrofluid preparation are wet grinding and chemical precipitation. newlineZahn and Shenton (1980), Charles and Rosensweig (1983) have studied the synthesis of newlineferrofluid by wet grinding of ferrites. This method normally takes a long time, about newline1000 hours and uses micron-sized ferrite particles from ball milling in the presence of newlinesuitable surfactants that act as a grinding aid carrier to produce an average particle newlinesize of about 10 nm. A more efficient method to produce ferrofluid in the laboratory is newlineby the chemical precipitation of particles [see Rosensweig (2013)] newline