Ferrofluid droplet vaporization under very large magnetic power: Effects of pressure and effective thermal conductivity of liquid

The aim of current analysis is to quantify the influence of the effective thermodynamic and transport coefficients and of the transient process of mass and energy accumulation in the gas phase (pressure effect) on the heating and vaporization of a single ferrofluid droplet. Ferrofluids under external alternating magnetic field heat up themselves due to the magnetic Brownian relaxation mechanism. Under the condition of very large magnetic power compared to the thermal power provided by heat transfer from the gas phase, the magnetic heat source together with the heat transfer from the gas phase impose a thermal boundary layer adjacent to the droplet surface in the liquid side and the temperature presents a maximum inside the droplet, not at the surface. Since the transport coefficient increases significantly with a dispersion of a small quantity of nanoparticles, the heat transfer from the thermal boundary layer to the droplet core increases. Then the temperature of that region increases faster comparing to the case without nanoparticle dispersion. The temperature inside the thermal boundary layer increases slower because of the heat transfer to the droplet core as well as to the droplet surface. Therefore, the boiling condition which is found inside the thermal boundary layer is reached later when considering effective thermal conductivity. The droplet vaporization rate is augmented by the heat transfer from the thermal boundary layer to the droplet surface. In addiction, the strong dependence of the magnetic relaxation mechanism on temperature imposes a dependence of the vaporization rate on the initial condition of the problem.