FERROFLUID DROPLET HEATING AND VAPORIZATION UNDER HIGH MAGNETIC POWER: A SPHERICAL GEOMETRY MODEL
Régis Zorzo1; Cesar da Cruz Cristaldo1; Fernando Fachini Filho2
1 Universidade Federal do Pampa; 2 Instituto Nacional de Pesquisa Espaciais
doi:10.20906/CPS/COB-2015-2024
Resumo
The models of heating and vaporization of ferrofluid fuel droplet under the influence of external magnetic fields has been recently studied. This process is known as relaxation magnetic heating. The magnetic heating within the droplet together with heat transfer provided from the gaseous environment are responsible to accelerate the ferrofluid fuel droplet. When exposed to an external alternating magnetic field, the nanoparticles dissipate heat through both Brownian and Néel relaxations within the droplet. In the Brownian relaxation the nanoparticle rotate together with its dipole generating heat by friction between nanoparticle and surrounding fluid. In the Néel relaxation the dipole rotate with the nanoparticle fixed, consequently the nanoparticle is heated by "internal friction" due to the movement of the magnetic moment within the nanoparticle. Under a certain frequency of the alternating magnetic field, the droplet core is rapidly heated. Thus the magnetic heating increase the vaporization rate and consequently produce a combustion with less emission of pollutants. The present model is an extension of previous works in which the condition of large magnetic power is considered. A thermal boundary layer is established within the droplet close to the surface. In the present model the solution is obtained in spherical geometry in order to compare with a thermal boundary layer model described by a planar geometry. The results show that there are a small difference between the two model. The thermal boundary layer solution present underestimated results such as vaporization rate, temperature surface of the droplet and heating time is greater than the present model.
Palavras-chave: Ferrofluid; Magneto relaxation heating; Magnetic nanoparticle; Droplet combustion