Droplet vaporization model in the presence of thermal radiation

Calculation of evaporation requires accurate thermophysical properties of the liquid. Such data are well-known for conventional fossil fuels. In contrast, e.g., thermal conductivity or dynamic viscosity of the fuel vapor are rarely available for modern liquid fuels. To overcome this problem, molecular models can be used. Currently, the measurement-based properties of n-heptane and diesel oil are compared with estimated values, using the state-of-the-art molecular models to derive the temperature-dependent material properties. Then their effect on droplet evaporation was evaluated. The critical parameters were liquid density, latent heat of vaporization, boiling temperature, and vapor thermal conductivity where the estimation affected the evaporation time notably. Besides a general sensitivity analysis, evaporation modeling in a practical burner ended up with similar results. By calculating droplet motion, the evaporation number, the evaporation-to-residence time ratio can be derived. An empirical cumulative distribution function is used for the spray of the analyzed burner to evaluate evaporation in the mixing tube. Evaporation number did not exceed 0.4, meaning a full evaporation prior to reaching the burner lip in all cases. As droplet inertia depends upon its size, the residence time has a minimum value due to the phenomenon of overshooting.

show abstract

“…Heat transfer to the droplet was calculated by following the work of Lefebvre and Abramzon and Sazhin [3,29]:…”

Section: Calculation Of Droplet Evaporationmentioning

confidence: 99%

Fuel Evaporation in an Atmospheric Premixed Burner: Sensitivity Analysis and Spray Vaporization

Csemány

Józsa

2017

Processes

View full text Add to dashboard Cite

show abstract

“…In this case, after about 2.5 ms, droplet cooling due to evaporation has a greater effect than droplet heating by the surrounding gas. This effect is not related to maximum droplet temperature during the evaporation due to the contribution of thermal radiation (see [29,30] for details). The model clearly overestimates the measurements in the case of ethanol droplets: the observed deviations between the experimental results and the predictions of the model can reach 4 K and can be attributed to a number of experimental factors, including random motions of the droplets, especially when the distance from the nozzle increases.…”

Section: Droplet Heating and Evaporation In A Hot Air Flowmentioning

confidence: 99%

Monodisperse droplet heating and evaporation: Experimental study and modelling

Maqua

Castanet

Grisch

et al. 2008

International Journal of Heat and Mass Transfer

View full text Add to dashboard Cite

Results of experimental studies and the modelling of heating and evaporation of monodisperse ethanol and acetone droplets in two regimes are presented. Firstly, pure heating and evaporation of droplets in a flow of air of prescribed temperature are considered. Secondly, droplet heating and evaporation in a flame produced by previously injected combusting droplets are studied. The phase Doppler anemometry technique is used for droplet velocity and size measurements. Two-colour laser induced fluorescence thermometry is used to estimate droplet temperatures. The experiments have been performed for various distances between droplets and various initial droplet radii and velocities. The experimental data have been compared with the results of modelling, based on given gas temperatures, measured by coherent anti-stokes Raman spectroscopy, and Nusselt and Sherwood numbers calculated using measured values of droplet relative velocities. When estimating the latter numbers the finite distance between droplets was taken into account. The model is based on the assumption that droplets are spherically symmetrical, but takes into account the radial distribution of temperature inside droplets. It is pointed out that for relatively small droplets (initial radii about 65 lm) the experimentally measured droplet temperatures are close to the predicted average droplet temperatures, while for larger droplets (initial radii about 120 lm) the experimentally measured droplet temperatures are close to the temperatures predicted at the centre of the droplets.

show abstract

“…It was shown to be more effective than approaches based on the numerical solution of the discretised heat conduction equation inside the droplet, and more accurate than solutions based on the parabolic temperature profile model. It was shown that the contribution of thermal radiation to droplet heating and evaporation could be taken it into account using a simplified model, which does not consider the variation of radiation absorption inside droplets [19,20,25].…”

Section: Discussionmentioning

confidence: 99%

Modelling of heating, evaporation and ignition of fuel droplets: combined analytical, asymptotic and numerical analysis

Sazhin

2005

J. Phys.: Conf. Ser.

View full text Add to dashboard Cite

Modelling of heating, evaporation and ignition of fuel droplets: combined analytical, asymptotic and numerical analysis Abstract.The paper discusses recent progress in the development of a combined analytical, asymptotic and numerical approach to modelling of heating and evaporation of fuel droplets and ignition of a fuel vapour/ air mixture. This includes a new approach to combined analytical and numerical modelling of droplet heating and evaporation by convection and radiation from the surrounding hot gas. The relatively small contribution of thermal radiation to droplet heating and evaporation allows us to take it into account using a simplified model, which does not consider the variation of radiation absorption inside droplets. The results of the analysis of the simplified problem of heating and evaporation of fuel droplets and ignition of fuel vapour/ air mixture based on the asymptotic method of integral manifolds are discussed. The semi-transparency of droplets was taken into account in this analysis, and a simplified model for droplet heat-up was used. The results of investigations of the effect of the temperature gradient inside fuel droplets on droplet evaporation, break-up and the ignition of fuel vapour/ air mixture based on a new zero-dimensional code are reviewed. The convection heating of droplets is described in this code based on a combined analytical and numerical approach. A new decomposition technique for a system of ordinary differential equations, based on the geometrical version of the integral manifold method is discussed. This is based on comparing the values of the right hand sides of these equations, leading to the separation of the equations into 'fast' and 'slow' variables. The hierarchy of the decomposition is allowed to vary with time. The application of this technique to analyse the explosion of a polydisperse spray of diesel fuel is presented. It is pointed out that this approach has clear advantages from the point of view of accuracy and CPU efficiency when compared with the conventional approach widely used in CFD codes. IntroductionThe problems of droplet heating, evaporation and ignition of fuel vapour/ air mixture have been widely discussed in the literature [1] - [10]. However, the models used in most practical engineering applications tend to be rather simple. This is due to the fact that droplet heating and evaporation have to be modelled alongside the effects of turbulence, combustion, droplet breakup and related phenomena in realistic 3D enclosures. Hence, finding a compromise between the complexity of the models and their computational efficiency is the essential precondition for successful modelling. In a series of our recent papers [11] -[25] an attempt was made to develop simplified models for droplet heating, evaporation and ignition of fuel vapour/air mixture;

show abstract

Droplet vaporization model in the presence of thermal radiation

Cited by 83 publications

References 14 publications

Fuel Evaporation in an Atmospheric Premixed Burner: Sensitivity Analysis and Spray Vaporization

Fuel Evaporation in an Atmospheric Premixed Burner: Sensitivity Analysis and Spray Vaporization

Monodisperse droplet heating and evaporation: Experimental study and modelling

Modelling of heating, evaporation and ignition of fuel droplets: combined analytical, asymptotic and numerical analysis

Contact Info

Product

Resources

About