Pattamatta, Arvind ; Freystein, Martin ; Dietl, Jochen ; Stephan, Peter (2014)
Numerical Investigation of Taylor-Bubble Characteristics During Flow Boiling in a Square Minichannel.
The 15th International Heat Transfer Conference.
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Kurzbeschreibung (Abstract)

In this paper, a numerical investigation of the hydrodynamic characteristics of Taylor bubbles (T-B) during flow boiling of FC-72 in a square minichannel is carried out. Multiple Taylor bubbles starting from their nucleation, growth and coalescence along with the associated heat transfer mechanisms have been modeled. The simulations are performed using finite volume method within the open source CFD package OpenFOAM by adapting its default VOF model to capture the 3-D interfaces accurately. An explicit evaporation model based on the temperature gradient is used to model the phase change due to boiling. The temporal variation of bubble coalescence pattern is found to exhibit a good agreement with the in-house experimental measurements conducted in microgravity environment. A detailed parametric study is conducted to understand the effects of Reynolds number (Re) and bubble nucleation diameters on the T-B nucleation and coalescence characteristics. The parametric study reveals that the nucleating bubbles tend to grow and coalesce faster at Re = 500 compared to Re = 50 due to higher temperature gradients leading to enhanced evaporation rates. Also it is observed that the bubble coalescence time is reduced nearly by a factor of two for the coalescence of unequal bubble sizes. The heat flux contours in the vicinity of the T-B contact line region predicted by the numerical model is found to exhibit a good qualitative agreement with the experimental measurement.

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