Numerical Simulation Of Bubble Behaviors During Nucleate Pool Boiling On Microscale Heated Wire

Energy problems have become one of the primary problems of social development nowadays with the development of the science and technology. It is of great importance to realize heat transfer process with smaller temperature difference and high efficiency, on a basis of reasonable utilization of available energy and development of new energy. Nucleate pool boiling is widely used in many fields for its small temperature and pressure differences and high heat transfer efficiency at different boiling regimes. The research on nucleate pool boiling is also of significance for many industrial fields, such as thermal energy and power engineering, nuclear engineering, cryogenic engineering, chemical engineering, space technologies, etc. Nucleate boiling heat transfer is usually accompanied with the growth and detachment process of bubble, the mechanism and behaviors of which are the basis for boiling heat transfer enhancement. Therefore the research on bubble dynamics in nucleate boiling, especially on microscale heated surface, is of most significance and is promising in many practical applications.Bubble behaviors are controlled by many factors, due to the complexity of boiling process. When scales down, the heat transfer equations for normal sizes cannot be employed anymore. Though there are many researches focus on the overall heat transfer performance at microscale, it is few investigating the local and detailed transport processes that are influenced by many factors. In this thesis, a numerical model was developed for describing bubble movements by analyzing subcooled boiling process on a heating Platinum wire with diameter of60mm and length of65mm. The dominant factors that influence bubble motion, collision, coalescence and circling were further analyzed by comparison of the experimental observation and the simulation. The analytical results show that bubbles coalescence is mainly affected by surface tension while the Marangoni effect could be neglected. The main reason for bubble jet flows and acceleration is duo to the Marangoni effect. Bubble sweeping phenomenon is the result of multiple factors, including surface tension and Marangoni effect. The simulation is in good agreement with the experimental investigation. The thermocapillarity effect, rather than fluid viscosity, is critical factor for lateral acceleration of bubbles. For bubble circling phenomenon, small bubbles can be driven along the interface to the top of a larger bubble by thermocapillary force before they depart, when the effective viscosity of fluid is negligible.