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INFLUENCE OF INTERNAL NATURAL CONVECTION ON WATER DROPLETS FREEZING ON COLD SURFACES

DOI: 10.1615/ICHMT.2014.IntSympConvHeatMassTransf.110
pages 169-176

Linn Karlsson
Division of Fluid Mechanics Luleå University of Technology, SE-971 87 Luleå, Sweden

Anna-Lena Ljung
Division of Fluid Mechanics, Luleå University of Technology, SE- 971 87, Luleå, Sweden

Staffan Lundstrom
Luleå university of technology

Аннотация

The freezing of water droplets is a relevant and topical subject with application to ice accretion in-connection to wind turbines, aircrafts and cold roads, for instance. The freezing of liquid water has been studied both experimentally and using different CFD-models, but for a single water droplet there are only a couple of studies made using CFD. An interesting approach is therefore to compare CFD-simulations to already existing experimental results. This study aims to examine the freezing process of a water droplet placed on a chilled surface using ANSYS CFX. A simple geometrical model of a droplet is created and a mesh analysis is performed to find the most suitable mesh for the set-up. By the use of a source term the velocity in the solid zone is set to zero and buoyancy is added to the model to account for internal natural convection. The droplet is assumed not to change form during the simulations and the model do not account for a subcooled liquid. Results show that the water droplet freezes from bottom to top and the freezing front evolution depends on the internal temperature and velocity field, which is in agreement with existing experiments. A comparison between the two cases where buoyancy is present and where it is not is performed. The result shows that there is a great difference in average velocity as well as velocity and pressure distribution between the two cases. Three bottom surface temperatures are investigated, and results show that both the volume of the remaining liquid part as well as the average velocity decreases as the bottom temperature increases. The overall temperature in the droplet instead increases as the bottom temperature increases.

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