Numerical Study of Single Bubble Nucleate Boiling Heat Transfer in Engine Cooling System

In the pursuit of extracting the most performance, engines are being continuously down sized and their power density continuously increased. This significantly increases the heat load on the engine for which the traditional cooling systems may not be sufficient. In the view of this fact; it is worth to explore controlled nucleate boiling to optimize engine cooling system designs. In order to utilize nucleate boiling in cooling systems, a detailed understanding of single bubble dynamics and its associated heat transfer is essential. In this work, a contact line evaporation model is developed which is then coupled to a conjugate surface to understand the individual contribution of micro layer and other sub processes towards overall heat transfer mechanism. The models use volume of fluid (VOF) interface capturing method and incorporates physics like contact line evaporation, transient conduction and bubble growth. For the assessment of the model, two fluids, water and a refrigerant (HFE7100) are studied and results are validated. The results indicate that micro layer heat transfer is significant to the overall heat flow. The contribution of this layer in overall heat transfer is ~30% for both HFE7100 and water. In the second stage, a coupled flow boiling model is studied for a single engine operating condition. The bubble dynamics, i. e. bubble inception, growth, departure and its associated heat transfer is discussed. Overall, present simulation results show good match with test data and the importance of contact line heat transfer is clearly indicated.