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Droplet supercooling in marine icing tests
Abstract Droplet supercooling in marine icing tests is studied theoretically using established correlations for convection and evaporation. The effect of freestream turbulence on heat and mass transfer is included through an empirical modification to the Nusselt and Sherwood numbers. Droplets are shown to cool following a modified exponential decay, with the trajectory length and shape determined by a thermal mixing length and a cooling exponent. The space needed for supercooling is shown to increase with (droplet diameter)1.8, and also depend on wind speed, injection speed and ambient temperature. Turbulence at realistic offshore levels shortens cooling distances by up to 50%. A reanalysis shows that previous marine icing tests have typically reached supercooling higher than 80% of cooling potential for small droplets up to 100–200 μm, and possibly up to 300–400 μm in long setups at low wind speeds if boosted by turbulence or a contracting tunnel; larger droplets have been significantly undercooled compared to field conditions.
Highlights Droplet thermal trajectories follow exponential decays with front-loading. Trajectories can be expressed using a thermal mixing length and a cooling exponent. Moderate turbulence may shorten droplet cooling distances by up to 50%. Marine icing tests have typically reached almost full supercooling for droplets up to 100–200 μm.
Droplet supercooling in marine icing tests
Abstract Droplet supercooling in marine icing tests is studied theoretically using established correlations for convection and evaporation. The effect of freestream turbulence on heat and mass transfer is included through an empirical modification to the Nusselt and Sherwood numbers. Droplets are shown to cool following a modified exponential decay, with the trajectory length and shape determined by a thermal mixing length and a cooling exponent. The space needed for supercooling is shown to increase with (droplet diameter)1.8, and also depend on wind speed, injection speed and ambient temperature. Turbulence at realistic offshore levels shortens cooling distances by up to 50%. A reanalysis shows that previous marine icing tests have typically reached supercooling higher than 80% of cooling potential for small droplets up to 100–200 μm, and possibly up to 300–400 μm in long setups at low wind speeds if boosted by turbulence or a contracting tunnel; larger droplets have been significantly undercooled compared to field conditions.
Highlights Droplet thermal trajectories follow exponential decays with front-loading. Trajectories can be expressed using a thermal mixing length and a cooling exponent. Moderate turbulence may shorten droplet cooling distances by up to 50%. Marine icing tests have typically reached almost full supercooling for droplets up to 100–200 μm.
Droplet supercooling in marine icing tests
Puolakka, O. (author)
2024-01-04
Article (Journal)
Electronic Resource
English
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