You are invited to the seminar of a student Nitzan Dahan – MSc - Rapid Nucleate Boiling at Elevated Pressures: Alcohols vs Synthesized Liquids

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SCHOOL OF MECHANICAL ENGINEERING SEMINAR
Wednesday, March 3, 2021 at 14:00

 Rapid Nucleate Boiling at Elevated Pressures: Alcohols vs Synthesized Liquids
Nitzan Dahan
MSc Under the supervision of Dr. Herman Haustein

Boiling is a very effective process for extracting and transporting heat, it can be applied in many technologies and industries ranging from large power plants to micro-electronics cooling. On the other hand, it is also a very complex, multi-scale and somewhat chaotic phenomenon. Although having been a subject of research for several decades, consistent prediction of boiling heat transfer is still challenging, due to its sensitivity to local conditions and the complexity of the many coupled mechanisms involved. Since boiling heat transfer is strongly related to bubble dynamics (i.e., bubble nucleation, growth and departure) as well as global factors such nucleation site density, coalescence and overall vapor evacuation, it is crucial to understand each mechanism in the boiling phenomena. Even for a single bubble, recent work has identified at least four inherently different growth regimes: slow growth, low- or high-pressure rapid growth and the explosive mode. This study examines both rapid regimes, as many processes operate under elevated pressures – e.g., the cooling in nuclear power plants.
Here, a new nucleate boiling system has been constructed and successfully operated at pressures of several atmospheres – implemented at TAU for the first time. The test-section allows optical and thermal visualization of the bubbles and heater surface, by video microscopy and IR thermography, on a specially designed transparent heater with a laser-drilled micro-bore as an imposed nucleation site. Nucleate boiling experiments of two liquid families (organic liquids, Hydrofluorocarbon liquids) were performed in a fully controlled environment, with high resolution and high-speed visualization of the bubble growth: from nucleation until departure from the surface. Methanol at atmospheric conditions was used as a “test case” to validate the new experimental system, which compared well to the literature. Experiments were extended to Methanol and HFE7100 also at elevated pressures, where results were compared to existing theory and models.
As the literature contains almost no boiling data of HFE7100, the present study extends its knowledge base. In addition, this one of the few studies that gives detailed bubble growth curves within the high-pressure boiling regime. These new results indicate that previous models are very limited in this regime, and more modeling is still required.
  
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