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INFLUENCE OF DROPLETS HEATING MANNER TO THE SPRAYED LIQUID THERMAL STATE

DOI: 10.1615/ICHMT.2008.CHT.810
17 pages

Gintautas U. Miliauskas
Department of Thermal and Nuclear Energy, Kaunas University of Technology, Donelaicio 20, LT-44239 Kaunas, Lithuania

Stasys Sinkunas
Department of Thermal and Nuclear Energy, Kaunas University of Technology, Donelaicio 20, LT-44239 Kaunas, Lithuania

Abstract

The change of thermal state and phase transformation intensity of sprayed liquid droplets is modeled according to the iterative method of numerical research under different boundary conditions of heat and mass transfer, when the influence of the Knudsen layer is neglected and warming and evaporation of the droplets has no influence on the state of the carrying air flow. The complex "droplet problem" covers the analysis of combined energy transfer in a semitransparent droplet, also combined heating and evaporation of the droplet. The interaction of unsteady heat and mass transfer processes is examined taking into account spectral absorption of radiation. Temperature of the interphase contact surface is determined, at which the balance of energy fluxes taken to the surface and taken from the surface is reached. The temperature mode of an evaporating droplet depends on the way of droplet heating manner as well. It was defined that heat transfer from a gas to a droplet in different manners, independently on the same primary conditions, the droplet reaches equilibrium evaporation state being in different energetic level. It is determined, that in the case of conductive heating during unsteady evaporation droplets reach a new isothermal state without reference to the initial water temperature and the size of droplets,. In the case of radiant - convective heating a droplet reaches its equilibrium evaporation mode being non-isothermal. The simplest way of energy supply to a liquid droplet is its conductive heating. The research results prove that a peculiar change of the thermal state of sprayed liquid exists in the time scale expressed by Fourier number, irrespective of droplet's dispersivity. The above discussed change can be conveniently defined by the characteristic curves representing the change of a droplet surface, centre, and mean mass temperatures, which are sensibly influenced by temperature of gas mixture and partial pressure of liquid vapour in it.

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