Heat Transfer in Multiphase and Melting Flows
Pim Waasdorp is a PhD student in the department Physics of Fluids. (Co)Promotors are prof.dr. D. Lohse and dr. S.G. Huisman from the faculty of Science and Technology.
In this work we study the heat transfer in a variety of topics. We begin with studying the heat transfer and its energy spectrum in turbulent bubbly flow. When adding bubbles to a turbulent flow, the classical -5/3 scaling in the turbulent kinetic energy spectrum changes to a bubble induced -3 scaling. We investigate the thermal energy spectrum and find that a similar transition happens here. The frequency where this transition starts is dependent on the size and amount of bubbles present. Furthermore, we provide evidence that the presence of bubbles enhances mixing, and adding salt and changing the bubble size, or adding more bubbles, enhances mixing further. We then move on to study melting in quiescent conditions. First, we study the melting of olive oil, by making a vertical wall, cylinder, and sphere, and placing the object in a tank with quiescent water. We hold the object in place and study the melting process. For all three geometries we derive a theoretical model that described the melt-rates fairly well, and gives an agreement for the right order of magnitude of the melt-rate. Finally, we study the melting of (water) ice balls in similar quiescent surroundings, as a function of the ambient salt concentration. The flows that appear when ice is melting in water are driven by density difference. If there is no salt in the ambient water, the cold melt water is heavier than the room-temperature ambient water. When adding salt, this situation changes, and the resulting flows lead to local instabilities and different morphology during the melting process of the ice balls. We find a scaling behavior for the Nusselt number as a function of the Rayleigh number. For low salt concentration the driving is strong enough to have a scaling similar to natural convection, which is expected, whereas for high salt concentration, the scaling relates to forced convection.
