Microlayer dynamics during the growth process of a single vapour bubble under subcooled flow boiling conditions

The phenomena of microlayer formation and its dynamic characteristics during the nucleate pool boiling regime have been widely investigated in the past. However, experimental works on real-time microlayer dynamics during nucleate flow boiling conditions are highly scarce. The present work is an attempt to address this lacuna and is concerned with developing a fundamental understanding of microlayer dynamics during the growth process of a single vapour bubble under nucleate flow boiling conditions. Boiling experiments have been conducted under subcooled conditions in a vertical rectangular channel with water as the working fluid. Thin-film interferometry combined with high-speed cinematography have been adopted to simultaneously capture the dynamic behaviour of the microlayer along with the bubble growth process. Transients associated with the microlayer have been recorded in the form of interferometric fringe patterns, which clearly reveal the evolution of the microlayer beneath the growing vapour bubble, the movement of the triple contact line and the growth of the dryspot region during the bubble growth process. While symmetric growth of the microlayer was confirmed in the early growth phase, the bulk flow-induced bubble deformation rendered asymmetry to its profile during the later stages of the bubble growth process. The recorded fringe patterns have been quantitatively analysed to obtain microlayer thickness profiles at different stages of the bubble growth process. For Re = 3600, the maximum thickness of the almost wedge-shaped microlayer was obtained as δ ~ 3.5 μm for a vapour bubble of diameter 1.6 mm. Similarly, for Re = 6000, a maximum microlayer thickness of δ ~ 2.5 μm was obtained for a bubble of diameter 1.1 mm.

Three-Dimensional Simulation of Vapour Bubble Growth in Superheated Water Due to the Convective Action by an Interface Tracking Method

In this paper, the growth of a rising vapour bubble in superheated water was numerically studied using an advanced interface tracking method, called the InterSection Marker (ISM) method. The ISM method is a hybrid Lagrangian-Eulerian Front Tracking algorithm that can model an arbitrary Three-Dimensional (3D) surface within an array of cubic control-volumes. The ISM method has cell-by-cell remeshing capability that is volume conservative, maintains surface continuity and is suited for tracking interface deformation in multiphase flow simulations. This method was previously used in adiabatic bubble rise simulation with no heat and mass transfers to or from the bubble were considered. This present work will extend the ISM method's application to simulate vapour bubble growth in superheated water with the inclusion of additional physics, such as the convective heat transfer mechanism and the phase change. Coupled with an in-house variable-density and variable-viscosity single-fluid flow solver, the method was used to simulate vapour bubble growth due to the convective action. The forces such as the surface tension and the buoyancy were included in the momentum equation. The source terms for the mass transfer were also modelled in the CFD governing equations to simulate the growth. Bubble properties such as size, shape, velocity, drag coefficient, and convective heat transfer coefficient were predicted. Effects of surface tension and temperature on the bubble characteristic were also discussed. Obtained numerical results were compared against the analytical and past works and found to be in good agreement.

A myriad of melt inclusions: a synchrotron microtomography study of melt inclusions and vapour bubbles from Colli Albani (Italy)

<p>Melt inclusions provide a window into the inner workings of magmatic systems. Both mineral chemistry and volatile distributions within melt inclusions can provide valuable information about the processes modulating magma ascent and preceding volcanic eruptions. Many melt inclusions host vapour bubbles which can be rich in CO<sub>2</sub> and H<sub>2</sub>O and must be taken into consideration when assessing the volatile budget of magmatic reservoirs. These vapour bubbles can be the product of differential volumetric contraction between the melt inclusion and host phase during an eruption or indicate an excess fluid phase in the magma reservoir. Thus, determining the distribution of volatiles between melt and vapour bubbles is integral to our fundamental understanding of melt inclusions, and by extension the evolution of volatiles within magmatic systems.</p><p>A large dataset of 79 high-resolution tomographic scans of clinopyroxene and leucite phenocrysts from the Colli Albani Caldera Complex (Italy) was recently acquired at the German Electron Synchrotron (DESY). These tomograms allow us to quantify the volume of melt inclusions and associated vapour bubble both glassy and microcrystalline melt inclusions. Notably, in the glassy melt inclusions the vapour bubbles exist either as a single large vapour bubble in the middle of the melt inclusion or as several smaller vapour bubbles distributed around the edge of the melt inclusion. These two types of melt inclusions can coexist within a single crystal. We suggest that the occurrence of these rim- bubbles is caused by one of two exsolution pathways, either pre-entrapment and bubble migration or post entrapment with preferential exsolution at the rims. By combining the analysis of hundreds of melt inclusions with the chemistry of the host phase we aim to unveil magma ascent rates and distribution of excess fluids within the magmatic system of Colli Albani, which produced several mafic-alkaline large volume ignimbrites.</p>

Numerical Investigation of Rising Vapour Bubble in Convective Boiling Using an Advanced 3D Hybrid Numerical Method

This chapter introduces an advanced and new type of Three-Dimensional (3D) numerical method called the InterSection Marker (ISM) method. The ISM method - a hybrid Lagrangian–Eulerian 3D front-tracking algorithm specifically crafted for multi-phase flow simulation. The method was used to simulate rising vapour bubble behaviour in Convective boiling conditions. Two applications: bubble growth and bubble condensation due to the convective action, were investigated. Numerically obtained bubble properties, such as size, shape and velocity, are compared well against the past works, and the ISM method proved to be an efficient numerical tool for the interface tracking of multi-phase flow CFD simulations involving heat and mass transfer.

Modeling for Fluid Flow and Heat Transfer in Closed Loop Pulsating Heat Pipe

Numerical modelling of multi turn Closed Loop Pulsating Heat Pipe (CLPHP) is presented in this paper for ethanol as working fluid. Modelling is carried out for 1mm and 2mm ID PHP for different number of turns, different orientations and at constant wall temperature boundary conditions. Momentum and heat transfer variations with time are investigated numerically solving the one dimensional governing equations for vapor bubble and liquid plugs. Evaporation and condensation takes place by heat transfer through liquid film present around the vapour bubble. The code takes into account the realistic phenomena such as vapour bubble generation, liquid plug merging and super heating of vapor bubbles above its saturation temperature. During merging of liquid plugs, a time step adaptive scheme is implemented and this minimum time step was found to be 10−7 s. Nature of flow is investigated by momentum variation plot. Model results are compared with the experimental results from literature for nine different cases. Maximum variation in heat transfer for all these cases is found to be below ±34%. Keywords: Closed Loop Pulsating Heat Pipe, Liquid Plug, Plug momentum, Vapor Bubble, Heat Transfer, Thin Film Evaporation and Condensation