Evaporation of a suspended multicomponent droplet under convective conditions (original) (raw)
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Fuel Droplet Heating and Evaporation: Analysis of Liquid and Gas Phase Models
SAE Technical Paper Series, 2007
Recently developed liquid and gas phase models for fuel droplet heating and evaporation, suitable for implementation into computational fluid dynamics (CFD) codes, are reviewed. The analysis is focused on the liquid phase model based on the assumption that the liquid thermal conductivity is infinitely large (infinite thermal conductivity (ITC) model), and the so called effective thermal conductivity (ETC) model. Seven gas phase models are compared. It is pointed out that the gas phase model, taking into account the finite thickness of the thermal boundary layer around the droplet predicts the evaporation time closest to the one based on the approximation of experimental data. In most cases, the droplet evaporation time depends strongly on the choice of the gas phase model. The dependence of this time on the choice of the liquid phase model, however, is weak if the droplet break-up processes are not taken into account. Corrections to Newton's law for droplet transient heating are discussed. For the values of parameters relevant to diesel engines, the values of these corrections were shown to be significant. Recent kinetic models for droplet evaporation into a high pressure background gas are reviewed. It is recommended that the kinetic effects are taken into account when accurate analysis of diesel fuel droplet evaporation is essential. A new dynamic decomposition technique for a system of ordinary differential equations is reviewed.
Numerical investigation of evaporation of a single ethanol/iso-octane droplet
h i g h l i g h t s " Non-uniform vortices inside liquid droplet due to shearing interaction with the gas phase. " Droplet temperature has the most significant effect on evaporation rate. " Droplet composition and predominant evaporating species affects overall droplet temperature. " Droplet composition affects rate of change in droplet diameter.
Multi-component droplet heating and evaporation: Numerical simulation versus experimental data
International Journal of Thermal Sciences, 2011
The earlier reported simplified model for multi-component droplet heating and evaporation is generalised to take into account the coupling between droplets and the ambient gas. The effects of interaction between droplets are also considered. The size of the gas volume, where the interaction between droplets and gas needs to be taken into account, is estimated based on the characteristic thermal and mass diffusion scales. The model is applied to the analysis of the experimentally observed heating and evaporation of monodispersed n-decane/3-pentanone mixture droplets at atmospheric pressure. It is pointed out that the effect of coupling leads to noticeably better agreement between the predictions of the model and the experimentally observed average droplet temperatures. In most cases, the observed droplet temperatures lie between the average and central temperatures, predicted by the coupled solution. For the cases reported in this study, the observed time evolution of droplet radii cannot be used for the validation of the model. It is pointed out that the number of terms in the series in the expressions for droplet temperature and species mass fraction can be reduced to just three, with possible errors less than about 0.5%. In this case, the model can be recommended for the implementation into computational fluid dynamics (CFD) codes and used for various engineering applications, including those in internal combustion engines.
Physics of Fluids, 2015
Droplet evaporation by a localized heat source under microgravity conditions was numerically investigated in an attempt to understand the mechanism of the fuel vapor jet ejection, which was observed experimentally during the flame spread through a droplet array. An Eulerian-Lagrangian method was implemented with a temperaturedependent surface tension model and a local phase change model in order to effectively capture the interfacial dynamics between liquid droplet and surrounding air. It was found that the surface tension gradient caused by the temperature variation within the droplet creates a thermo-capillary effect, known as the Marangoni effect, creating an internal flow circulation and outer shear flow which drives the fuel vapor into a tail jet. A parametric study demonstrated that the Marangoni effect is indeed significant at realistic droplet combustion conditions, resulting in a higher evaporation constant. A modified Marangoni number was derived in order to represent the surface force characteristics. The results at different pressure conditions indicated that the nonmonotonic response of the evaporation rate to pressure may also be attributed to the Marangoni effect.
Numerical analysis of convecting, vaporizing fuel droplet with variable properties
International Journal of Heat and Mass Transfer, 1992
Detailed analysis of a cold fuel droplet suddenly injected into a hot gas stream is examined. The effects of variable thermophysical properties, transient heating and internal circulation of liquid, deceleration of the flow due to the drag of the droplet, boundary-layer blowing, and moving interface are included. Several parametric studies are performed by changing the following quantities : initial droplet temperature, ambient temperature, initial Reynolds number, fuel type, and droplet heating model. The results show that for higher transfer numbers, the vaporization rate is larger and the drag coefficient is significantly reduced mainly due to a large reduction in friction drag. For lower transfer numbers, the boundary-layer blowing effect is weaker and the drag coefficient is dominated by the Reynolds number only. The results also indicate that the constant-property calculation overestimates the drag coefficient.
International Journal of Heat and Mass Transfer, 1980
The problem of liquid droplet vaporization in a hot convective gaseous environment is analyzed. A new gas-phase viscous, thermal and species concentration boundary layer analysis is developed using an integral approach. The gas-phase analysis is coupled with a modified form of a previous liquid-phase analysis for the internal motion and heat transfer [S. Prakash and W. A. Sirignano, Inr. J. Heat Mass Transfer 21, 885-895 (1978)]. The coupled problem is solved for three hydrocarbon fuels (n-hexane, n-decane, and nhexadecane). The results show that the droplet vaporization is unsteady, and that the tem~ra~ure distribution within the droplet is nonuniform for a significant part of the droplet lifetime. Some of the results are compared with the already existing correlations after correcting them for the heat flux into the liquid phase.
State of the Art of Fuel Droplet Evaporation
International Journal of Heat and Technology, 2022
The process of fuel droplet evaporating is one of the most important factors that directly affect the efficiency of the combustion process. Therefore, the current study reviews previous studies that focused on the process of evaporation of a drop of fuel. The review is divided into points. The first part is concerned with modeling of the evaporation process under different initial condition and temperature of the droplet. The second part present the experimental studies concerned with measuring the evaporation time of the droplet, as well as the shape of the droplet during the evaporation process. Most of the studies related to this subject can be divided into three categories: The first category is the studies that are concerned with the process of heating the droplet and studying the evaporation time for different types of fuels or by adding nanomaterials to the fuel and studying their effect on the evaporation process. The second category is the studies concerned with the mechanics of droplet evaporation and the study of droplet shape. The third category is the studies that focus on studying the effect of initial conditions, such as temperature and pressure, as well as the concentration of gasses surrounding the drop and their types. There are other studies concerned with projecting the electric field onto the drop during the evaporation process and studying its effect.
Numerical investigation of the evaporation of two-component droplets
2011
A numerical model for the complete thermo-fluid-dynamic and phase-change transport processes of twocomponent hydrocarbon liquid droplets consisting of n-heptane, n-decane and mixture of the two in various compositions is presented and validated against experimental data. The Navier-Stokes equations are solved numerically together with the VOF methodology for tracking the droplet interface, using an adaptive local grid refinement technique. The energy and concentration equations inside the liquid and the gaseous phases for both liquid species and their vapor components are additionally solved, coupled together with a model predicting the local vaporization rate at the cells forming the interface between the liquid and the surrounding gas. The model is validated against experimental data available for droplets suspended on a small diameter pipe in a hot air environment under convective flow conditions; these refer to droplet's surface temperature and size regression with time. An extended investigation of the flow field is presented along with the temperature and concentration fields. The equilibrium position of droplets is estimated together with the deformation process of the droplet. Finally, extensive parametric studies are presented revealing the nature of multi-component droplet evaporation on the details of the flow, the temperature and concentration fields.
Heating and evaporation of a two-component droplet: Hydrodynamic and kinetic models
A previously developed kinetic model for two-component vapour and background gas (air) is applied to the analysis of droplet heating and evaporation in Diesel engine-like conditions. The model used in the analysis is based on the introduction of the kinetic region in the immediate vicinity of the droplets and the hydrodynamic region. The presence of two components in the vapour, finite thermal conductivity and finite species diffusivity in droplets are taken into account. It is pointed out that for parameters which are typical of Diesel engine-like conditions, the heat flux in the kinetic region is a linear function of the temperature at the outer boundary of this region, but is almost independent of the density of the components at this boundary. Mass fluxes of both components in the kinetic region are shown to decrease almost linearly with increasing vapour density at the outer boundary of this region, but are almost independent of the temperature drop in the kinetic region. The model is tested for the analysis of heating and evaporation of a droplet with initial radius and temperature equal to 5 μm and 300 K, respectively, immersed into gas with temperatures 1000 K and 700 K for several mixtures of n-dodecane and p-dipropylbenzene. It is pointed out that an increase in the mass fraction of p-dipropylbenzene and kinetic effects lead to an increase in the predicted droplet evaporation time. The kinetic effects are shown to increase with increasing gas temperature and molar fraction of p-dipropylbenzene.
Iclass 06-184 Experimental Validation of a Droplet Evaporation Model
2006
The pollutant emissions generated by liquid-fuel fired gas turbine engines are strongly influenced by the fuel preparation process that includes atomization, evaporation and mixing. In order to accurately predict the fuel preparation process, sufficiently precise models of the key thermophysical processes are crucial. In the present paper, the performance of fuel droplet evaporation models are considered as applied to a spray produced by a practical gas turbine fuel injector under actual conditions. Of particular interest are numerically efficient models including the “Distillation Curve” (DC) model. The DC model can account for the behavior of multi-component fuels like diesel fuel #2. Fractional boiling is described by the molar weight as a single process variable. This way, the fractional distillation process during evaporation of droplets is taken into account. In addition, the thermophysical properties of the fuel are supplied as a function of the molar weight. Real gas effects...