Characterization of bubble population morphology in direct contact heat transfer process under different flow regimes and its influence on heat transfer performance

In this study, the effect of bubble population morphological characteristics and heat transfer performance in the direct contact boiling heat transfer process under two different flow modes are comparatively investigated. Based on the visualization method and homogeneity theory, the relationships between the bubble population morphological characteristics, distribution homogeneity, specific interface area, and volumetric heat transfer coefficient were investigated. The obtained results show that the bubble morphology tends to flatten with the increase of the dispersed phase flow rate in both flow modes. The more uniform the distribution of the bubble population, the better the specific interface area, and the trend is more obvious in the two-phase reverse flow mode. In addition, it was found that the specific interface area was positively correlated with the volumetric heat transfer coefficient. The synergistic relationship between the uniformity of bubble population distribution and the improvement of heat transfer is explained from the perspective of a specific interface area. It is concluded that different flow patterns affect the morphological characteristics of the bubble population and its distribution, which in turn affects the specific interface area of the two-phase contact heat transfer and ultimately the heat transfer performance. The morphology of the bubble population and its uneven distribution has a strong correlation with the flow pattern. This thesis provides a new idea to study the influence of bubble cluster morphology characteristics and heat transfer performance in direct contact boiling heat transfer process under different flow patterns and provides a new way for heat exchanger design.