The overarching aim of this work is to study the freezing process of a single water droplet freezing on a cold surface, which is an interesting and important phenomenon with possible applications in many areas. Understanding the freezing process of a single water droplet is for example an important step when preventing unwanted icing, e.g. in the case of airplane wings and propellers, wind turbine rotor blades, and road surfaces.As a step in understanding the freezing process, the study specifically focuses on the internal flow in the droplet during the freezing process. To do this, the study combines the use of Computational Fluid Dynamics (CFD) to build a model of the freezing process and experimental methods, i.e. Particle Image Velocimetry (PIV) to validate the numerical results. Focus is to start with the heat- and mass transfer inside the droplet using simple geometries with a rigid boundary, not modelling the outside environment as the air and the cooling plate. These components will be incorporated in the model further on.Three papers will be included in the study. In Paper A the CFD model is created and tested on a simple 2D-geometry of a droplet. The numerical result is partially compared to experimental work found in literature. In Paper B the numerical model is developed even further and a more realistic geometry of a real droplet, although with rigid boundaries, is used. The numerical results are as for Paper A validated with experimental results found in literature. In Paper C the internal flow inside the droplet has been investigated experimentally to estimate the velocities in the water, so that in the future the results can be used to validate the numerical work.The results show that is possible to work with a very simple CFD model and still capture the main flow features and freezing characteristics in a freezing water droplet. In line with previous research, this study confirms that the natural convection induced by gravity is significant for the internal flow, as compared to conduction and effects of ice creation. If studying the freezing time the internal flow has little effect. However, when estimating the velocities in the water it is crucial. It can be seen that the gravity effects are most pronounced around the density maximum for water (at T = 4◦C). The experiments show that the method used to study the flow inside the droplet is a working method, and the velocities in the water has been estimated. The next step is to further develop the CFD model and validate the numerical work with the experimental results. An interesting next step is to incorporate a moving interface to capture the volume expansion during the phase change.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:ltu-17930 |
| Date | January 2015 |
| Creators | Karlsson, Linn |
| Publisher | Luleå tekniska universitet, Strömningslära och experimentell mekanik |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Licentiate thesis, comprehensive summary, info:eu-repo/semantics/masterThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | Licentiate thesis / Luleå University of Technology, 1402-1757 |
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