1,721,135 research outputs found
Oscillating droplet evaporation modelling for spray combustion simulation
Full text linkThe vapour and gas phase conservation equations are analytically solved in a spheroidal coordinate systems, yielding the drop surface vapour flux under steady-state conditions, for oblate and prolate drops. The drop evaporation rate can be defined as function of drop spheroid shape and drop surface. The solution is easily implementable to the case of prolate/oblate oscillating drops, under quasi-steady assumption, which is found to be valid under the range of operating conditions typical of spray combustion applications
Effect of temperature dependence of gas thermo-physical properties on analytical modelling of drop heating and evaporation
No full textNumerical and Analytical Study of Large Amplitude Shape Oscillations of Viscous Droplets
Full text linkNew approaches to modelling heat/mass transfer processes in spherical and non-spherical mono-component droplets
Full text linkHeat and mass transfer modelling of sub-micrometer droplets under atmospheric pressure conditions
No full textThe mathematical modeling of heat and mass transfers of submicrometer droplets vaporizing in gaseous surroundings at atmospheric pressure is investigated, including the effect of equilibrium/nonequilibrium assumption at the liquid/gas interface and of surface curvature on the droplet evaporation behavior. The numerical limitations of some of the most frequently used models for academic and industrial research activities on sprays have been enlightened. Emphasis is given to the verification of the validity of the assumptions imposed when they are extrapolated outside the range of operating conditions within which they have been derived, for instance, when they are used to predict the heat and mass transport phenomena occurring in submicrometer aerosol particles
An analytical approach to model heating and evaporation of multicomponent ellipsoidal drops
No full textAn analytical model for heating and evaporation of non-spherical multicomponent drops is reported, based on the solution of
energy and species conservation equations in orthogonal curvilinear coordinates, accounting also for the effect of convective
conditions according to the film theory approach. The instantaneous heat and evaporation rates of multicomponent drops
is calculated as function of increased surface area due to drop deformation. The model is applied to predict evaporation
characteristics of spheroidal drops under quasi-steady and transient conditions, analysing the effect of drop size, composition
and velocity on the temperature evolution, for a range of drop and gas temperature condition
Modeling the effect of shape deformation induced by gravity on the evaporation of pendant and sessile drops
No full textPendant and sessile drops form a spherical cap only in the absence of gravity. The effect of gravity on drop shape is often neglected on the basis of the assumption that the drop size is smaller than the capillary length [L c =( sigma / g rho )1 / 2], although the deformation may not be fully negligible even in those cases. This paper focuses on evaluation of the effect that deformation due to gravity has on the evaporation characteristics of pendant and sessile drops. The drop shape is described by the Bashforth-Adams equation, a non-linear second order ordinary differential equation, which is solved numerically using a Runge-Kutta method with variable time steps. Under quasi-steady approximation, the species and energy conservation equations in the gas phase have analytical solutions, even for temperature-dependent gas thermophysical properties, once the solution of a basic Laplace problem is known. The Laplace equation is solved in axial symmetric geometry by using COMSOL Multiphysics((R)), for a wide range of drop sizes and contact angles, yielding vapor distribution, vapor fluxes, and evaporation rates. Comparison with the results from drops of same size in microgravity (i.e., having a spherical cap shape) shows that the effect is also perceptible for drops with a size smaller than the capillary length and that it can become quite important for those with larger sizes. Complementary results are found for sessile and pendant drops with respect to wall wettability, suggesting that the phenomenon can be analyzed using a unitary approach
Analytical model of small- and large-amplitude drop oscillation dynamics
No full textThe mechanical energy balance over a bulk of fluid that oscillates between prolate and oblate shapes in another immiscible fluid is solved using a general spheroidal coordinate system. The drop shape is described by a unique parameter that may continuously vary over the time, making the implementation of the model rather simple. Potential flow is assumed, and inertial and viscous effects are accounted for in both the inner and outer flow fields. The characteristics of drop oscillation for small and large amplitudes are studied, and the results are compared with theoretical, experimental, and numerical data from the open literature. The rather satisfactory validation of the model over a large variety of operating conditions allows its extension to include other physical phenomenon, like evaporation and its effect on drop oscillation
Moving boundary and time-dependent effects on mass transfer from a spherical droplet evaporating in gaseous environment
Full text linkAnalytic modelling of drop evaporation is often approached under quasi-steady approximation, disregarding the inherent unsteadiness of such phenomenon and the fact that drop radius shrinking due to evaporation settles a moving boundary problem.
Such assumption yields simple and very useful analytical solutions of the species conservation equations. However it is known that, after the sudden immersion of a drop in a gaseous environment, a relaxation time is needed to reach quasi-steadiness and the evaporation rate during this period is expected to be much higher than that under steady conditions. The present work is aimed to define the analytical problem of evaporation in a gaseous environment relaxing the above mentioned approximation. The spherically
symmetric, time-dependent species conservation equation for vapour transport in a gaseous environment is derived in nondimensional form accounting for moving boundaries. Numerical solution allows to evaluate the relaxation time as a function of the Spalding mass transfer number and to quantify the evaporated mass during this time lapse
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