Studies of influences of liquid-phase species diffusion on spherically symmetric combustion of miscible binary droplets

✍ Scribed by B.D. Shaw

• Publisher: Elsevier Science
• Year: 1990
• Tongue: English
• Weight: 919 KB
• Volume: 81
• Category: Article
• ISSN: 0010-2180
• DOI: 10.1016/0010-2180(90)90025-m

✦ Synopsis

Spherically symmetric combustion of binary miscible droplets is studied for the case where liquid-phase species transport is slow relative to droplet surface regression rates. Attention is focused upon later periods of combustion, following decay of initial transients, when droplet species profiles change slowly relative to droplet size changes, and d 2 law combustion (the square of the droplet diameter decreases linearly with time) closely holds. The gas phase is assumed to remain quasi-steady. It is demonstrated that when droplet species profiles change slowly relative to droplet size changes, the mass-flux fraction of a given species off the droplet surface is approximately equal to the volume-averaged mass fraction of that species within the droplet. The ratio of the liquid-phase species diffusion coefficient to the burning-rate constant is treated as a small parameter, and asymptotic solutions for droplet species profiles are developed in terms of this parameter. A concentration boundary layer, where species profiles change sharply in the radial coordinate, is shown to be present at the droplet surface. It is shown that accounting for the boundary-layer structure may be important when predictions of droplet combustion characteristics are made. Sample solutions for heptane-dodecane mixtures and water-methanol mixtures indicate that the variables most affected by accounting for the concentration boundary-layer structure are droplet temperatures and surface compositions.