Computational Modeling of Bubble Growth Dynamics in Nucleate Pool Boiling for Pure Water and Aqueous Surfactant Solutions

Computational Modeling of Bubble Growth Dynamics in Nucleate Pool Boiling for Pure Water and Aqueous Surfactant Solutions
Author: Bradley J. Romanchuk
Publisher:
Total Pages: 93
Release: 2014
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ISBN:

A computational model has been developed to simulate growth of an isolated vapor bubble during nucleate pool boiling of pure water and aqueous surfactant solutions at saturated conditions on a surface with a constant temperature. The governing equations of mass, momentum, and energy conservation are solved in the liquid and the vapor phases using a finite volume method. The volume-of-fluid (VOF) method is employed to capture the deforming liquid-vapor interface. The computational domain includes a microlayer near the liquid-solid-vapor contact line and macro region that contains the vapor bubble and the surrounding liquid. Solution of the governing equations in the microlayer provides source terms for the heat transfer and phase change for the macro region. The computational model was validated by comparing with results available in the literature for pure water. Simulations of bubble growth from incipience to departure are conducted for pure water and surfactant solutions of sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), and octylphenol ethoxylate (Triton X-100) at twice the critical micelle concentration (2xCMC). Wall superheats of 4K and 8K are considered and their respective growth cycle characteristics are discussed in detail. The results show that the predicted bubble departing volume and growth rate increases leading to a faster departure time as the wall superheat is increased. The time-dependent surface tension relaxation at the liquid-vapor interface along with increased surface wettability at the liquid-solid interface result in smaller bubbles departing with higher frequency in surfactant solutions compared to boiling in pure water. The dynamic surface tension and surface wettability play an important role in governing bubble growth dynamics in nucleate pool boiling of surfactant solutions.

Computational Study of Adiabatic Bubble Growth Dynamics from Submerged Orifices in Aqueous Solutions of Surfactants

Computational Study of Adiabatic Bubble Growth Dynamics from Submerged Orifices in Aqueous Solutions of Surfactants
Author: Anirudh M. Deodhar
Publisher:
Total Pages: 91
Release: 2012
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ISBN:

The growth dynamics of isolated gas bubbles (inception -> growth -> departure) emanating from a capillary-tube orifice submerged in isothermal pools of aqueous solutions of surfactants is computationally investigated. The Navier-Stokes equations are solved in the liquid and the gas phase. The evolution of the gas-liquid interface is tracked using a Volume-of-Fluid (VOF) method. Surfactant molecules in aqueous solutions have a tendency to diffuse towards the gas-liquid interface and are subsequently adsorbed onto it. This time dependent adsorption process gives rise to the dynamic surface tension behavior of the aqueous surfactant solutions. To computationally model this behavior, the species conservation equation for the surfactant is solved in the bulk fluid and is coupled with the dynamic adsorption-desorption of the surfactant on the interface. A new form of the surfactant transport equation is derived that was necessary to incorporate the interfacial transport in the volume-of-fluid method where the interface is spread over multiple grid cells. Computational results were obtained for bubble growth dynamics from a capillary orifice in a pool of pure water and in an aqueous solution of Sodium Dodecyl Sulphate (SDS). The evolving bubble shape and the flow field in the two phases in the pure liquid and in surfactant solution are compared for a variety of air flow rates (from 4 ml/min to 24 ml/min) in the constant bubble regime. To validate the computational model, the results for the transient shape and size of growing bubbles in pure water were compared with available experimental data and were found to be in excellent agreement. Results show that the dynamic surface tension relaxation gives rise to smaller bubble size at departure in aqueous surfactant solution compared to that in pure water. However, this effect is found to be a function of the air flow rate. At high air flow rates (24 ml/min), the short time for bubble growth allows relatively smaller drop in the surface tension and produces departure diameters similar to bubble diameters in water. At low air flow rates (4 ml/min), the departure time is much larger and allows for complete surface tension relaxation. As such the departure diameters at low air flow rates in aqueous surfactant solution are significantly smaller than those predicted in pure water. Also, the flow patterns around a growing bubble in surfactant solution are altered due to the non-uniform surfactant adsorption along the gas-liquid interface. The computational results elucidate the role of surfactant transport on bubble growth dynamics.

Nucleate Pool Boiling Heat Transfer in Aqueous Surfactant Solutions

Nucleate Pool Boiling Heat Transfer in Aqueous Surfactant Solutions
Author:
Publisher:
Total Pages:
Release: 2001
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ISBN:

Saturated, nucleate pool boiling in aqueous surfactant solutions is investigated experimentally. Also, the role of Marangoni convection, driven both by temperature and surfactant concentration gradients at the vapor-liquid interface of a nucleating bubble is computationally explored. Boiling of surfactant solutions is important in many key industrial applications such as hygiene and personal care, pharmaceutical, and food processing, among others. Moreover, surfactants in trace amounts are present in boilers of conventional power plants and have also been shown as promising agents to augment the nucleate boiling performance of water. Their efficient use, however, requires precise knowledge of their solutions' boiling behavior. This need is addressed here through systematic experimentation and quantification of boiling performance with respect to surfactant's ionic nature and molecular weight. In addition, the computational modeling attempts to quantify the extent of Marangoni convection during initial bubble growth transients. An exhaustive literature review demonstrates significant property (primarily surface tension and to some degree steady-state shear viscosity) variations and altered boiling behavior of water in the presence of surfactants. A generalized quantification of boiling behavior is not available however, though the available results and analyses suggest the possibility of dynamic surface tension being a primary correlating parameter for the boiling heat transfer. Experimental measurements of dynamic and equilibrium surface tension using the maximum bubble pressure method indicate dynamic surface tension to be higher than the corresponding equilibrium value, both at room and elevated temperatures.

Bubble Nucleation and Dynamics

Bubble Nucleation and Dynamics
Author: Ho-young Kwak
Publisher:
Total Pages: 372
Release: 2020-04-21
Genre:
ISBN: 9781536169973

For phenomena involving bubble nucleation, the molecular cluster model is used to predict the tensile strength and superheat limit of liquids and the amount of decompression for gaseous bubble nucleation in supersaturated solutions. The book investigates various gaseous bubble nucleation events including the bubble formation in gas-water solutions, CO bubble formation in iron melts, the formation of microcellular foams in polymers, the nucleation of nano-sized H2O bubbles in rhyolite melts, and bubble nucleation in shear flow fields. The book also investigates vaporous bubble nucleation events such as bubble formation on a cavity-free surface and inside a solid nanopore in 3M NaCl solution, superheat limit of liquids, and bubble nucleation near the absolute zero temperature by quantum tunnelling in liquid helium. For bubble dynamics phenomena, a set of homologous solutions of the Navier-Stokes equations for evolving spherical bubbles are used to treat gaseous bubble growth in organic solutions, polymer solutions, and in viscous rhyolitic melts. The growth and collapse of laser-induced vapor bubbles in liquid, and on solid particles is discussed as an example of homologous motion of the spherical object. Sonoluminescence phenomena in water and in sulfuric acid solutions, the pressure and shock wave propagation in bubbly mixtures, the gravitational collapse of Newtonian stars, and the core collapse of supernovas are also treated using these homologous solutions. The motion of a fire-ball generated by a TNT explosion underwater is obtained using a zero gravitational constant in the equation of motion for Newtonian stars.

A Contribution Towards the Numerical Study of Bubble Dynamics in Nucleate Boiling at Local Scale Using a Conservative Level Set Method

A Contribution Towards the Numerical Study of Bubble Dynamics in Nucleate Boiling at Local Scale Using a Conservative Level Set Method
Author: Muhammad Sajid
Publisher:
Total Pages: 153
Release: 2010
Genre:
ISBN:

Nucleate boiling is an efficient means of heat transfer that has been the subject of many studies which have lead to more empirical results than knowledge on the physical mechanisms that govern the phenomena. In this work, a conservative level set method (LSM) was applied to the study of bubble dynamics during nucleate pool boiling which reduces the computational cost of reinitialization techniques traditionally used with LSM to limit phase loss. Also a force-balance approach to modelling dynamic apparent contact angle (CA) was proposed in this study based on the physics of the moving contact line (CL). It was tested against the traditional CL velocity approach and validated in comparison to available experimental data. In comparison to the CL velocity model our approach reduces the non-physical stick/slip behaviour of the CL and allows a smoother transition from the minimum receding to the maximum advancing CA, which is more akin to the physical phenomena. It was also demonstrated that the heat transfer during bubble growth is proportional to the apparent CA.