ABSTRACT
The problem of stability of flow has been the subject of intensive research due to the difficulty of controlling the flow in potential applications. Therefore, experiments of fundamental character have been done in this area. Berkovsky and Bashtovoi[237] discuss the rupture of drops, layers, and cylinders. Besides, Rothert and Richter[238] and Rothert et al.[239] investigate the rupture of a liquid bridge. Research on surface structures is presented in Refs. [240] and [241]. When a fluid layer is heated from below, natural convection patterns appear whose form depends on the field strength and boundary conditions as shown experimentally by Schwab et al .[242-244] in contrast with a Newtonian fluid, ferrofluids have in natural convection the magnetic Rayleigh number (apart from the usual one) whose influence alone was investigated in microgravity experiments by Odenbach.[245] Another fundamental problem is that of Taylor-Couette flow investigated by Odenbach and Gilly[246] under an azimuthal magnetic field, who used their results to obtain the rotational viscosity as function of the magnetic field strength. Recently, two methods for the measurement of the velocity profile have been proposed. One is the ultrasonic Doppler method by Kikura et al.[247] and the other is the small-angle neutron scattering by Odenbach et al.[248]
Magnetic Susceptibility An important investigation is that related with the experimental calculation of the magnetic susceptibility of a magnetic colloidal suspension.[249] The experiments are made for particular kinds of suspended particles. Experiments have been done for manganese compounds,[250,251] ferrite particles,[252-254] magnetite particles,[255,256] cobalt particles,[257-259] and iron oxide.[251,260] In some experiments the Néel relaxation has been detected.[261-264] It is also of interest to check the dependence of susceptibility on temperature and concentration such as, for example, in the case of magnetite.[265]
The increasing theoretical development of magnetic fluids is due to the potential they have for applications. Berkovsky et al.[266] have proposed the use of magnetic fluid coatings in different hydrodynamic systems to control flow separation, drag, and heat transfer. Applications to loudspeaker drivers, to inspection of internal passages, to instrument damping, and to accelerometers were explained by Bailey.[267] Another use they have is in seals, journal bearings, magnetogravimetric separators, and transducers, as discussed by Anton et al.[268] Charles[269] reviews their uses as magnetic inks and to produce magneto-optic effects in the microwave region, such as birefringence and dichroism. As lubricants they have other applications as supports and dampers.[206]
brakes,[273] actuators,[274] and pressure transducers.[275] In biomedicine, they have been applied to hyperthermia for the treatment of cancer by Jordan et al.[276] and to other related problems by Sincai et al.,[277] Hilger et al.[278] and Hiergeist et al.[279−283] More information on applications is found in Chaps. 4 and 5 of Ref. [207] and in Chaps. 4, 5, and 6 of Ref. [206].
