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Anh V. Nguyen - One of the best experts on this subject based on the ideXlab platform.
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the gibbs marangoni stress and nondlvo forces are equally important for modeling Bubble Coalescence in salt solutions
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2017Co-Authors: Mahshid Firouzi, Anh V. NguyenAbstract:Some salts can inhibit Bubble Coalescence above a critical concentration. The initial models for prediciting the critical salt concentrations were developed based on the effects of the Gibbs-Marangoni stress and either the London-van der Waals or Casimir-van der Waals attraction on the drainage and rupture of thin liquid films between Bubbles. The later models considered only the Gibbs-Marangoni stress and discarded the van der Waals forces. Here, we present new experimental results of film drainage experiments using halide salts to show that both the Gibbs-Marangoni stress and colloidal forces are equally important. Specifically, our experimental results show that if only the Gibbs-Marangoni stress is considered, the predicted film rupture thickness can differ from the experimental results by as much as 92–156%. The initial models also significantly under-predict the experimental results for the critical salt concentration and film rupture thickness. To examine these deficiencies we use a new mathematical model recently developed to obtain both the salt concentration and rupture thickness of film concurrently, thus removing the inherent ambiguity of the previous models that need the rupture thickness to calculate the salt concentration or vice versa. Indeed, the new modelling approach requires a nonDLVO attractive force together with the Casimir-van der Waals attraction and the Gibbs-Marangoni stress to predict the experimental results for both the salt concentration and rupture thickness of film, which are critical to understanding Bubble Coalescence in salt solutions.
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A microfluidic method for investigating ion-specific Bubble Coalescence in salt solutions
Langmuir : the ACS journal of surfaces and colloids, 2016Co-Authors: Jianlong Wang, Anh V. Nguyen, Say Hwa Tan, Geoffrey M. Evans, Nam-trung NguyenAbstract:This paper reports the direct and precise measurement of Bubble Coalescence in salt solutions using microfluidics. We directly visualized the Bubble Coalescence process in a microchannel using high-speed imaging and evaluated the shortest Coalescence time to determine the transition concentration of sodium halide solutions. We found the transition concentration is ion-specific, and the capacity of sodium halide salts to inhibit Bubble Coalescence follows the order of NaF > NaCl > NaBr > NaI. The microfluidic method overcomes the inherent uncertainties in conventional large-scale devices and methods.
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A quantitative review of the transition salt concentration for inhibiting Bubble Coalescence
Advances in colloid and interface science, 2014Co-Authors: Mahshid Firouzi, Tony Howes, Anh V. NguyenAbstract:Some salts have been proven to inhibit Bubble Coalescence above a certain concentration called the transition concentration. The transition concentration of salts has been investigated and determined by using different techniques. Different mechanisms have also been proposed to explain the stabilizing effect of salts on Bubble Coalescence. However, as yet there is no consensus on a mechanism which can explain the stabilizing effect of all inhibiting salts. This paper critically reviews the experimental techniques and mechanisms for the Coalescence of Bubbles in saline solutions. The transition concentrations of NaCl, as the most popularly used salt, determined by using different techniques such as Bubble swarm, Bubble pairs, and thin liquid film micro-interferometry were analyzed and compared. For a consistent comparison, the concept of TC95 was defined as a salt concentration at which the "percentage Coalescence" of Bubbles reduces by 95% relative to the highest (100% in pure water) and lowest (in high-salt concentration) levels. The results show a linear relationship between the TC95 of NaCl and the reciprocal of the square root of the Bubble radius. This relationship holds despite different experimental techniques, salt purities and Bubble approach speeds, and highlights the importance of the Bubble size in Bubble Coalescence. The available theoretical models for inhibiting effect of salts have also been reviewed. The failure of these models in predicting the salt transition concentration commands further theoretical development for a better understanding of Bubble Coalescence in salt solutions.
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novel methodology for predicting the critical salt concentration of Bubble Coalescence inhibition
Journal of Physical Chemistry C, 2014Co-Authors: Mahshid Firouzi, Anh V. NguyenAbstract:Bubble Coalescence in some salt solutions can be inhibited if the salt concentration reaches a critical concentration Ccr. There are three models available for Ccr in the literature, but they fail to predict Ccr correctly. The first two models employ the van der Waals attraction power laws to establish Ccr from the discriminant of quadratic or cubic polynomials. To improve the two models, the third model uses the same momentum balance equation of the previous models but different intermolecular force generated by water hydration with exponential decaying. The third prediction for Ccr requires the experimental input for film rupture thickness and is incomplete. We show further in this paper that the third model is incorrect. We propose a novel methodology for determining C cr which resolves the mathematical uncertainties in modeling C cr and can explicitly predict it from any relevant intermolecular forces. The methodology is based on the discovery that Ccr occurs at the local maximum of the balance equation for the capillary pressure, disjoining pressure, and pressure of the Gibbs-Marangoni stress. The novel generic approach is successfully validated using nonlinear equations for complicated disjoining pressure.
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Different Effects of Monovalent Anions and Cations on the Bubble Coalescence and Lifetime of Aqueous Films between Air Bubbles
2013Co-Authors: Mahshid Firouzi, Anh V. NguyenAbstract:Ions of inorganic salts are known to affect Bubble Coalescence via the surface charge density as described by the classical DLVO theory of colloid stability. Our experimental results obtained for monovalent salts of different concentrations show different effects of monovalent anions (F-, Cl-, Br- and I-) and cations (Li+, Na+, K+ and Cs+) on the lifetime of liquid films between two Bubble surfaces. These results highlight the significant effects of ion radius and polarizability on the interaction of salt ions with water molecules in saline liquid films and at the air-water interface. They also show the important role of approach speed between the Bubble surfaces. For each salt, there is a critical concentration beyond which the film lifetime rapidly increases and Bubble Coalescence is inhibited. These results are relevant to a number of chemical engineering processes taking place in saline water, including mineral separation by flotation using air Bubbles in bore water.
Yixiang Liao - One of the best experts on this subject based on the ideXlab platform.
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update to the musig model in ansys cfx for reliable modelling of Bubble Coalescence and breakup
Applied Mathematical Modelling, 2020Co-Authors: Yixiang LiaoAbstract:Abstract The MUSIG (Multiple Size Group) model in the commercial CFD code ANSYS CFX is a population balance approach for describing binary Bubble Coalescence and breakup events. It is widely used in the simulation of poly-dispersed bubbly flows. The purpose of this work is to identify the internal inconsistencies in the discrete method that is applied for the solution of the population balance equation in MUSIG, and to propose an internally consistent one for discretising the source and sink terms that result from Bubble Coalescence and breakup. The new formulation is superior to the existing ones in preserving both mass and number density of Bubbles, allowing arbitrary discretisation schemes and is free of costly numerical integrations. The numerical results on the evolution of Bubble size distributions in bubbly flows reveal that the inconsistency in the original MUSIG regarding Bubble breakup is non-negligible for both academic and practical cases. The discussion on the effect of internal inconsistency as well as updates to the model presented in this work are necessary and important for calibration of Bubble Coalescence and breakup models using the MUSIG approach.
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baseline closure model for dispersed bubbly flow Bubble Coalescence and breakup
Chemical Engineering Science, 2015Co-Authors: Yixiang Liao, Roland Rzehak, Dirk Lucas, Eckhard KrepperAbstract:Abstract A set of closures for two-fluid modelling of adiabatic bubbly flows has been defined as baseline model, which provides a common basis for further improvement and development. It includes closures for Bubble forces, Bubble-induced turbulence as well as Bubble Coalescence and breakup. In this work, the baseline model is implemented in the commercial code ANSYS CFX 14.5 and applied to the case of adiabatic upward vertical pipe flows. Special attention is paid to the performance of the newly proposed Coalescence and breakup model. The comparison with measurements shows that the baseline model is able to capture the evolution of Bubble size distribution, gas volume fraction and velocity profiles along the pipe over a wide range of flow conditions.
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application of new closure models for Bubble Coalescence and breakup to steam water vertical pipe flow
Nuclear Engineering and Design, 2014Co-Authors: Yixiang Liao, Dirk Lucas, Eckhard KrepperAbstract:Abstract New closure models for Bubble Coalescence and breakup proposed in Liao et al. (2011) , Nucl. Eng. Des. 241, 1024, are assessed for the case of condensing steam–water pipe flows. Steady-state CFD calculations are performed employing the commercial CFD solver ANSYS CFX. Predicted evolution of cross-section averaged Bubble size and gas volume fraction distribution along the pipe is compared with the measurements provided by the TOPFLOW facility ( Lucas et al., 2010 . CFD4NRS-3, Int. Workshop on Experimental Validation and Application of CFD and CMFD Codes to Nuclear Reactor Safety Issues, Paper 13.1, 14.16.09, Washington D.C., USA.). It is shown that for cases with small initial Bubble size and low gas volume fraction, Bubble Coalescence and breakup can be taken to be nearly negligible and the change of Bubble size is primarily due to condensation. Nevertheless, with the increase of initial Bubble size or gas volume fraction, Bubble Coalescence and breakup become more prevalent. Performance of new and standard closure models of Bubble Coalescence and breakup is investigated It is shown that both models overestimated the breakup rate; in particular, the standard model. The numerical results are also found to be dependent on the inlet liquid temperatures and inter-phase heat transfer models have a significant impact on the results.
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Application of new closure models for Bubble Coalescence and breakup to steam–water vertical pipe flow
Nuclear Engineering and Design, 2014Co-Authors: Yixiang Liao, Dirk Lucas, Eckhard KrepperAbstract:Abstract New closure models for Bubble Coalescence and breakup proposed in Liao et al. (2011) , Nucl. Eng. Des. 241, 1024, are assessed for the case of condensing steam–water pipe flows. Steady-state CFD calculations are performed employing the commercial CFD solver ANSYS CFX. Predicted evolution of cross-section averaged Bubble size and gas volume fraction distribution along the pipe is compared with the measurements provided by the TOPFLOW facility ( Lucas et al., 2010 . CFD4NRS-3, Int. Workshop on Experimental Validation and Application of CFD and CMFD Codes to Nuclear Reactor Safety Issues, Paper 13.1, 14.16.09, Washington D.C., USA.). It is shown that for cases with small initial Bubble size and low gas volume fraction, Bubble Coalescence and breakup can be taken to be nearly negligible and the change of Bubble size is primarily due to condensation. Nevertheless, with the increase of initial Bubble size or gas volume fraction, Bubble Coalescence and breakup become more prevalent. Performance of new and standard closure models of Bubble Coalescence and breakup is investigated It is shown that both models overestimated the breakup rate; in particular, the standard model. The numerical results are also found to be dependent on the inlet liquid temperatures and inter-phase heat transfer models have a significant impact on the results.
Eckhard Krepper - One of the best experts on this subject based on the ideXlab platform.
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baseline closure model for dispersed bubbly flow Bubble Coalescence and breakup
Chemical Engineering Science, 2015Co-Authors: Yixiang Liao, Roland Rzehak, Dirk Lucas, Eckhard KrepperAbstract:Abstract A set of closures for two-fluid modelling of adiabatic bubbly flows has been defined as baseline model, which provides a common basis for further improvement and development. It includes closures for Bubble forces, Bubble-induced turbulence as well as Bubble Coalescence and breakup. In this work, the baseline model is implemented in the commercial code ANSYS CFX 14.5 and applied to the case of adiabatic upward vertical pipe flows. Special attention is paid to the performance of the newly proposed Coalescence and breakup model. The comparison with measurements shows that the baseline model is able to capture the evolution of Bubble size distribution, gas volume fraction and velocity profiles along the pipe over a wide range of flow conditions.
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application of new closure models for Bubble Coalescence and breakup to steam water vertical pipe flow
Nuclear Engineering and Design, 2014Co-Authors: Yixiang Liao, Dirk Lucas, Eckhard KrepperAbstract:Abstract New closure models for Bubble Coalescence and breakup proposed in Liao et al. (2011) , Nucl. Eng. Des. 241, 1024, are assessed for the case of condensing steam–water pipe flows. Steady-state CFD calculations are performed employing the commercial CFD solver ANSYS CFX. Predicted evolution of cross-section averaged Bubble size and gas volume fraction distribution along the pipe is compared with the measurements provided by the TOPFLOW facility ( Lucas et al., 2010 . CFD4NRS-3, Int. Workshop on Experimental Validation and Application of CFD and CMFD Codes to Nuclear Reactor Safety Issues, Paper 13.1, 14.16.09, Washington D.C., USA.). It is shown that for cases with small initial Bubble size and low gas volume fraction, Bubble Coalescence and breakup can be taken to be nearly negligible and the change of Bubble size is primarily due to condensation. Nevertheless, with the increase of initial Bubble size or gas volume fraction, Bubble Coalescence and breakup become more prevalent. Performance of new and standard closure models of Bubble Coalescence and breakup is investigated It is shown that both models overestimated the breakup rate; in particular, the standard model. The numerical results are also found to be dependent on the inlet liquid temperatures and inter-phase heat transfer models have a significant impact on the results.
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Application of new closure models for Bubble Coalescence and breakup to steam–water vertical pipe flow
Nuclear Engineering and Design, 2014Co-Authors: Yixiang Liao, Dirk Lucas, Eckhard KrepperAbstract:Abstract New closure models for Bubble Coalescence and breakup proposed in Liao et al. (2011) , Nucl. Eng. Des. 241, 1024, are assessed for the case of condensing steam–water pipe flows. Steady-state CFD calculations are performed employing the commercial CFD solver ANSYS CFX. Predicted evolution of cross-section averaged Bubble size and gas volume fraction distribution along the pipe is compared with the measurements provided by the TOPFLOW facility ( Lucas et al., 2010 . CFD4NRS-3, Int. Workshop on Experimental Validation and Application of CFD and CMFD Codes to Nuclear Reactor Safety Issues, Paper 13.1, 14.16.09, Washington D.C., USA.). It is shown that for cases with small initial Bubble size and low gas volume fraction, Bubble Coalescence and breakup can be taken to be nearly negligible and the change of Bubble size is primarily due to condensation. Nevertheless, with the increase of initial Bubble size or gas volume fraction, Bubble Coalescence and breakup become more prevalent. Performance of new and standard closure models of Bubble Coalescence and breakup is investigated It is shown that both models overestimated the breakup rate; in particular, the standard model. The numerical results are also found to be dependent on the inlet liquid temperatures and inter-phase heat transfer models have a significant impact on the results.
Yong Jin - One of the best experts on this subject based on the ideXlab platform.
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Population balance model for gas - Liquid flows: Influence of Bubble Coalescence and breakup models
Industrial and Engineering Chemistry Research, 2005Co-Authors: Tiefeng Wang, Jinfu Wang, Yong JinAbstract:In dispersed gas-liquid flows, the Bubble size distribution plays an important role in the phase structure and the interphase forces, which, in turn, determine the multiphase hydrodynamic behaviors, including the spatial profiles of the gas fraction, gas and liquid velocities, and mixing and mass-transfer behaviors. The population balance model (PBM) is an effective method to simulate the Bubble size distribution. The Bubble Coalescence and breakup models have a distinct influence on the prediction ability of the PBM. This work compares several typical Bubble Coalescence and breakup models. The results show that the Bubble size distributions predicted by the PBM are quite different when different Bubble Coalescence and breakup models are used. By using proper Bubble Coalescence and breakup models, the Bubble size distribution and regime transition can be reasonably predicted. The results also show that it is necessary to take into account Bubble Coalescence and breakup due to different mechanisms.
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Population Balance Model for Gas−Liquid Flows: Influence of Bubble Coalescence and Breakup Models
Industrial & Engineering Chemistry Research, 2005Co-Authors: Tiefeng Wang, Jinfu Wang, Yong JinAbstract:In dispersed gas−liquid flows, the Bubble size distribution plays an important role in the phase structure and the interphase forces, which, in turn, determine the multiphase hydrodynamic behaviors, including the spatial profiles of the gas fraction, gas and liquid velocities, and mixing and mass-transfer behaviors. The population balance model (PBM) is an effective method to simulate the Bubble size distribution. The Bubble Coalescence and breakup models have a distinct influence on the prediction ability of the PBM. This work compares several typical Bubble Coalescence and breakup models. The results show that the Bubble size distributions predicted by the PBM are quite different when different Bubble Coalescence and breakup models are used. By using proper Bubble Coalescence and breakup models, the Bubble size distribution and regime transition can be reasonably predicted. The results also show that it is necessary to take into account Bubble Coalescence and breakup due to different mechanisms.
Mahshid Firouzi - One of the best experts on this subject based on the ideXlab platform.
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the gibbs marangoni stress and nondlvo forces are equally important for modeling Bubble Coalescence in salt solutions
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2017Co-Authors: Mahshid Firouzi, Anh V. NguyenAbstract:Some salts can inhibit Bubble Coalescence above a critical concentration. The initial models for prediciting the critical salt concentrations were developed based on the effects of the Gibbs-Marangoni stress and either the London-van der Waals or Casimir-van der Waals attraction on the drainage and rupture of thin liquid films between Bubbles. The later models considered only the Gibbs-Marangoni stress and discarded the van der Waals forces. Here, we present new experimental results of film drainage experiments using halide salts to show that both the Gibbs-Marangoni stress and colloidal forces are equally important. Specifically, our experimental results show that if only the Gibbs-Marangoni stress is considered, the predicted film rupture thickness can differ from the experimental results by as much as 92–156%. The initial models also significantly under-predict the experimental results for the critical salt concentration and film rupture thickness. To examine these deficiencies we use a new mathematical model recently developed to obtain both the salt concentration and rupture thickness of film concurrently, thus removing the inherent ambiguity of the previous models that need the rupture thickness to calculate the salt concentration or vice versa. Indeed, the new modelling approach requires a nonDLVO attractive force together with the Casimir-van der Waals attraction and the Gibbs-Marangoni stress to predict the experimental results for both the salt concentration and rupture thickness of film, which are critical to understanding Bubble Coalescence in salt solutions.
-
A quantitative review of the transition salt concentration for inhibiting Bubble Coalescence
Advances in colloid and interface science, 2014Co-Authors: Mahshid Firouzi, Tony Howes, Anh V. NguyenAbstract:Some salts have been proven to inhibit Bubble Coalescence above a certain concentration called the transition concentration. The transition concentration of salts has been investigated and determined by using different techniques. Different mechanisms have also been proposed to explain the stabilizing effect of salts on Bubble Coalescence. However, as yet there is no consensus on a mechanism which can explain the stabilizing effect of all inhibiting salts. This paper critically reviews the experimental techniques and mechanisms for the Coalescence of Bubbles in saline solutions. The transition concentrations of NaCl, as the most popularly used salt, determined by using different techniques such as Bubble swarm, Bubble pairs, and thin liquid film micro-interferometry were analyzed and compared. For a consistent comparison, the concept of TC95 was defined as a salt concentration at which the "percentage Coalescence" of Bubbles reduces by 95% relative to the highest (100% in pure water) and lowest (in high-salt concentration) levels. The results show a linear relationship between the TC95 of NaCl and the reciprocal of the square root of the Bubble radius. This relationship holds despite different experimental techniques, salt purities and Bubble approach speeds, and highlights the importance of the Bubble size in Bubble Coalescence. The available theoretical models for inhibiting effect of salts have also been reviewed. The failure of these models in predicting the salt transition concentration commands further theoretical development for a better understanding of Bubble Coalescence in salt solutions.
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novel methodology for predicting the critical salt concentration of Bubble Coalescence inhibition
Journal of Physical Chemistry C, 2014Co-Authors: Mahshid Firouzi, Anh V. NguyenAbstract:Bubble Coalescence in some salt solutions can be inhibited if the salt concentration reaches a critical concentration Ccr. There are three models available for Ccr in the literature, but they fail to predict Ccr correctly. The first two models employ the van der Waals attraction power laws to establish Ccr from the discriminant of quadratic or cubic polynomials. To improve the two models, the third model uses the same momentum balance equation of the previous models but different intermolecular force generated by water hydration with exponential decaying. The third prediction for Ccr requires the experimental input for film rupture thickness and is incomplete. We show further in this paper that the third model is incorrect. We propose a novel methodology for determining C cr which resolves the mathematical uncertainties in modeling C cr and can explicitly predict it from any relevant intermolecular forces. The methodology is based on the discovery that Ccr occurs at the local maximum of the balance equation for the capillary pressure, disjoining pressure, and pressure of the Gibbs-Marangoni stress. The novel generic approach is successfully validated using nonlinear equations for complicated disjoining pressure.
-
Different Effects of Monovalent Anions and Cations on the Bubble Coalescence and Lifetime of Aqueous Films between Air Bubbles
2013Co-Authors: Mahshid Firouzi, Anh V. NguyenAbstract:Ions of inorganic salts are known to affect Bubble Coalescence via the surface charge density as described by the classical DLVO theory of colloid stability. Our experimental results obtained for monovalent salts of different concentrations show different effects of monovalent anions (F-, Cl-, Br- and I-) and cations (Li+, Na+, K+ and Cs+) on the lifetime of liquid films between two Bubble surfaces. These results highlight the significant effects of ion radius and polarizability on the interaction of salt ions with water molecules in saline liquid films and at the air-water interface. They also show the important role of approach speed between the Bubble surfaces. For each salt, there is a critical concentration beyond which the film lifetime rapidly increases and Bubble Coalescence is inhibited. These results are relevant to a number of chemical engineering processes taking place in saline water, including mineral separation by flotation using air Bubbles in bore water.
