Polydisperse spray flames in vortex flows

[EN] A new mathematical analysis of the dynamics of laminar spray diffusion flames in the vicinity of a vortex flow field is presented. The governing equations for a spray evaporating in an unsteady vortex are studied. New similarity solutions are found for the dynamics of the spray and the flame it supports. Analytical solutions for the spray flames are derived using Schvab-Zeldovich parameters, through which the radial evolution of the flames is found. The results based on the solution reveal the significant influence the droplets size has on the diffusion flame dynamics in the vicinity of vortical flows.Dagan, Y.; Katoshevski, D.; Greenberg, BJ. (2017). Polydisperse spray flames in vortex flows. En Ilass Europe. 28th european conference on Liquid Atomization and Spray Systems. Editorial Universitat Politècnica de València. 702-708. https://doi.org/10.4995/ILASS2017.2017.4716OCS70270

Influence of a Standing Wave Flow-Field on the Dynamics of a Spray Diffusion Flame

A theoretical investigation of the influence of a standing wave flow-field on the dynamics of a laminar two-dimensional spray diffusion flame is presented for the first time. The mathematical analysis permits mild slip between the droplets and their host surroundings. For the liquid phase, the use of a small Stokes number as the perturbation parameater enables a solution of the governing equations to be developed. Influence of the standing wave flow-field on droplet grouping is described by a specially constructed modification of the vaporization Damkohler number. Instantaneous flame front shapes are found via a solution for the usual Schwab–Zeldovitch parameter. Numerical results obtained from the analytical solution uncover the strong bearing that droplet grouping, induced by the standing wave flow-field, can have on flame height, shape, and type (over- or under-ventilated) and on the existence of multiple flame fronts

Comparison between analytical, numerical, and experimental results of grouping effects in droplet streams

[EN] Grouping of droplets was studied in monodisperse droplet streams. This very controllable system allows to study basic effects. In experiments droplet streams with monodisperse droplets were generated, however, with initially two different inter droplet spacing. A larger inter droplet spacing is followed by a little bit smaller one, which is followed by a larger one and so on. Due to this initial boundary condition groups of two droplets form, which approach each other and finally coagulate. It was found, that the velocity of the droplet approach is linearly dependent on the spacing between the droplets. This process was simulated by direct numerical simulation using the in-house code FS3D. The results of the simulations show the same linear behaviour. For larger computational domains the numerical results approach the experimental results.Roth, N.; Gomaa, H.; Livne, A.; Katoshevski, D.; Weigand, B. (2017). Theoretical and Experimental Study of Grouping Effects on Droplet Streams. En Ilass Europe. 28th european conference on Liquid Atomization and Spray Systems. Editorial Universitat Politècnica de València. 395-402. https://doi.org/10.4995/ILASS2017.2017.4685OCS39540

Droplets Expelled during Human Expiratory Activities and their Origin.

This paper presents the findings of the most comprehensive program of study to date aimed at quantifying the number, size distribution and evaporation of droplets produced during virtually any expiratory activity. This international research program included teams of investigators from a number of universities, with each group contributing to essential aspects of the research. This research revealed many previously unknown aspects of expiratory aerosol dynamics and characteristics. This paper will focus on the findings that the time taken for expiratory droplets to achieve short term equilibrium is comparable to that for pure water droplets and that the droplet size distributions have distinct features reflecting specific production mechanisms whose intensity varies with the nature of the activity