Evaporation of Nearly Monosized Droplets of Hexane, Heptane, Decane and Their Mixtures in Hot Air and an Air/Steam Mixture

• Main Authors: S. Horender, M. Sommerfeld
• Format: Article
• Language: English
• Published: SAGE Publishing 2012-06-01
• Series: International Journal of Spray and Combustion Dynamics
• Online Access: https://doi.org/10.1260/1756-8277.4.2.123

This paper describes experiments on evaporating initially nearly monosized droplet chains with diameter 230 ± 15 μm under atmospheric conditions in a grid generated upward turbulent flow with initial liquid temperatures in the range 320 to 350 K and air temperatures in the range 365 to 455 K. The mean air velocity was 5 m/s and the initial droplet velocities were 17 m/s, resulting in a Reynolds number for the flow around the droplets of 100. The turbulent Stokes number was around 10. The liquids used were n-hexane, n-heptane, n-decane and mixtures thereof. A single chain and, for a reduced data set, a spray of 5 parallel chains, to study the influence of increased mass loading, have been investigated. Additionally, the influence of steam with mass fraction 15% on the evaporation rates has been investigated. The size of the droplets was measured by back light illumination and recording by a digital camera with macro optics. Digital image processing was applied to deduce the size of the droplets and their positions. Laser Doppler measurements delivered the droplet velocities. Besides the generation of a data set for validation of evaporation models the main findings were that turbulence of the surrounding air could increase evaporation for decane and that mixtures evaporated preferentially, indicating mixing inside the droplets being larger than pure diffusion limited. For heptane as evaporating liquid it was found that for elevated droplet loading at air temperature below the boiling point the evaporation rate decreased, while at higher temperatures the droplet loading hardly showed any influence on the evaporation rates. Adding steam led to increased evaporation rates for all liquids, most likely due to condensation on the droplets surfaces.