Dynamics of vapor bubbles and associated heat transfer in various regimes of boiling

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A direct numerical study is performed to analyze the bubble growth during different regimes of boiling using Combined Level-Set and Volume of Fluid (CLSVOF) based approach. The effects of substrate superheat and applied electric field have been elaborately studied and parametric studies concerning the changes in interface morphology during bubble growth have been performed. A significant enhancement in heat transfer rate and reduction in critical wavelength is observed only above a threshold limit of applied electric field.The combined influence of surface superheat, buoyancy, surface tension and applied electric field governs the instabilities at the liquid-vapor interface. These instabilities leading to the bubble growth, is dominated by the applied electric field at low-gravity conditions. Depending on the surface superheat, a sufficiently high intensity of electric field leads to the liquid-solid contact, favoring the transition from film to nucleate boiling. The wettability instigated transition from film to nucleate boiling has been studied. Transition of boiling mode leading to liquid-solid contacts has been observed in high wettability surface conditions while the same phenomenon has been observed in low wettability conditions too with the application of sufficient intensity of electric field.The growth and departure of a single bubble during nucleate boiling is simulated with a microlayer model to include the contribution of microlayer evaporation into the bubble growth. The effect of surface superheat and liquid subcooling has also been analyzed. The dynamics of bubble after departure from the surface has been studied at various subcooled conditions of liquid.
Supervisor: Gautam Biswas and Amaresh Dalal