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Bubbles dispersed in thin liquid layers are ubiquitous and play important roles in the heat and mass transfer in nature and industrial processes including the energy, chemical, and biology engineering; thus, understanding the dynamics of bubbles confined in a liquid layer remains an important topic in multiphase flows. Here, we report the dynamics of bubble formation from a submerged orifice in a thin liquid layer with a thickness comparable to the bubble size. First, four flow regimes, detachment, jetting bursting, non-jetting bursting, and hole-opened bursting, are observed experimentally and their typical features are analyzed. Then, the evolutions of bubble size at different regimes are studied, and a quasi-static force model is proposed to predict the bubble size, which agrees well with the experimental results. We demonstrate the role of the capillary force exerted by the liquid film in the bubble cap and bubble geometry confined in the liquid layer in modulating the bubble size. Finally, a regime map regarding the liquid layer thickness and surface tension is provided and the criteria between different regimes are discussed based on the bubble geometry analysis and energy balance. Our experimental investigation and theoretical analysis provide insights into the formation and bursting dynamics of bubbles confined in a liquid layer. [ABSTRACT FROM AUTHOR]

Highlights • The force balance approach and correlation approach are conducted to predict bubble departure diameter. • A new semi-empirical correlation for bubble departure diameter is proposed in this paper. • The effects of dimensionless parameters on bubble departure diameters are analyzed. Abstract According to the force balance analysis on a bubble, the bubble departure diameter in horizontal subcooled flow boiling is mainly influenced by quasi-steady drag force, surface tension force and bubble growth force while an additional force, buoyancy force, plays an important role in vertical flow boiling. In this paper, the effects of these forces can be concluded by a series of dimensionless parameters including density ratio of vapor and liquid, Prandtl number, Jacob number and bubble Reynolds number. Based on the different forces, two different characteristic lengths are adopted to non-dimensionlize bubble departure diameters in horizontal flow boiling and vertical flow boiling, respectively. Finally, the semi-empirical correlations for bubble departure diameters in both horizontal and vertical subcooled flow boiling are proposed in this paper based on the force balance analysis and available experimental data from literature. The predicted results using the present correlations agree fairly well with the experimentally measured values with a mean relative error of 19.72%. [ABSTRACT FROM AUTHOR]

Subcooled boiling flow is widely used for heat and mass transfer in industries such as nuclear reactor, electronic equipment, and spacecraft, where the bubble dynamics is essential for understanding the gas-liquid flow behavior. Current studies focused on the gas void fraction or bubble size distribution at a global scale, but the dynamics of single bubbles are still obscure, which inhibits the fundamental understanding of gas-liquid flow and the precise prediction of heat transfer. Here, we develop a numerical method that captures the motion and condensation of bubbles in subcooled boiling flow using Euler-Lagrange method, with a proposed model for spatiotemporal lift-off bubble distribution on the heated wall as boundary condition. Our numerical method is validated by the agreement between the calculated gas void fraction distributions with the existing experimental data in vertical subcooled boiling flow. We further investigate the distribution of bubble position and size in the tube and find that the bubble size distribution shows different modes at different radial positions. Analysis of the single bubble dynamics shows that small and large bubbles suffer from centrifugal and centripetal lift forces, and thus tend to accumulate at a radial position near the wall and near the tube center, respectively, which reveals the mechanism of bubble size distribution. Besides, we find that the centripetal wall lubrication force is essential for the path instability of small bubbles near the wall. These findings promote the fundamental understanding of the gas-liquid phase distribution in the subcooled boiling flow and provide a numerical strategy for the precise prediction of mass and heat transfer in subcooled boiling flow. [ABSTRACT FROM AUTHOR]

Though bubbles are abundantly formed during the nucleate boiling in annular flows and affect the industrial performance during nucleation, departure, and bursting, the contribution of bubble dynamics in the heat and mass transfer in annular flows still needs to be quantified. Here, we used the semi-analytical film flow model to simulate the annular flow boiling in a vertical tube. We found the liquid film significantly affects the bubble departure diameter at wide working conditions when its thickness is smaller than the bubble's free departure size. A model for the departure diameter of the bubble considering the confinement of the thin liquid film was proposed, based on which theoretical models for the bubble-induced heat flux due to bubble formation and the bubble-induced droplet entrainment rate due to bubble bursting ejection were proposed. The contributions of the bubble-induced heat flux to the total (wall-to-liquid) heat transfer and the bubble-induced droplet entrainment rate to the total (liquid film-to-vapor core) mass transfer of annular flows can be up to 61% and 38% in the studied parameter range, respectively. The contribution of the bubble-induced heat flux to the total heat transfer increases with decreasing inlet mass flux and increasing tube diameter, wall heat flux, and pressure. The contribution of the bubble-induced droplet entrainment rate to the total mass transfer increases with decreasing inlet mass flux and increasing tube diameter. The proposed models of bubble-induced heat and mass transfer in annular flows may offer the first step to precisely control industrial performance by governing the bubble dynamics. • The contributions of bubble departure and bursting to the heat and mass transfer in annular flows were investigated. • Effects of the operating parameters on the bubble induced heat and mass transfer are quantified. • The contribution of the bubble departure-induced heat flux to the total heat transfer can be up to 61%. • The contribution of the bubble bursting-induced droplet entrainment rate to the total mass transfer can be up to 38%. [ABSTRACT FROM AUTHOR]