Model Of Bubble Evolution Research Articles

Numerical investigation on preparation of expanded polymer beads using supercritical CO2 in a spouted bed

The bead foaming process in a spouted bed is a green way to manufacture expanded beads. A CFD-DEM model has been established to investigate the hydrodynamics behavior in the spouted bed. The simulation results have showed that the establishment of the particle fountain during saturation can effectively disperse the polymer particles and avoid their aggregation. During depressurization, the flow field in the main part of the spouted bed is relatively uniform. Therefore, particles confined within the spouted bed experience similar depressurization profiles, which is beneficial to the uniformity of the expanded beads. Based on the depressurization profiles provided by the CFD-DEM simulation, a bubble evolution model has been built to investigate the effects of operating parameters on the bead foaming results. The simulation results indicate that expanded beads with a narrower cell size distribution can be prepared at a higher saturation pressure rather than a higher pressure release rate.

Experimental and theoretical investigation of the cavity dynamics of underwater launched projectiles

During the underwater launch of a projectile using compressed air, a bubble emerges from the launch tube before the projectile. Upon being pierced by the projectile, this bubble has significant effects on the formation and evolution of the projectile’s shoulder cavity. This paper presents experimental and theoretical analyses of the dynamics of such a projectile’s shoulder cavity launched at low Froude numbers. In the experiments, a dynamic sensor and a camera are used to record the internal pressure and profile of the cavity, respectively. The cavity pressure oscillations explain the cavity ripples observed during the experimental sequence. Accordingly, we establish an independent bubble evolution model to predict the internal cavity pressure based on the assumption of spherical expansion; we also separately construct a shoulder cavity evolution model that treats the cavity as a slender body. The matched asymptotic method is used to solve the shoulder cavity evolution model, and quantitative comparisons between the theoretical and experimental results, including the cavity shape and size, show favourable agreement. Finally, the effects of cavity pressure oscillations and of the nose shape and projectile velocity on the cavity’s behaviour are studied.

Mechanism and numerical model of bubble effect in oil-paper insulation based on microtubule model

In this paper, a numerical model of bubble evolution is established by studying the microstructure of pressboard and the physical process of bubble generation. In the model, the porous structure of fibers is equivalent to microtubules, the gases in the bubbles are classified into two categories, and the ideal gas state equation is used to describe the bubble state. Then the pressure conditions at the bubble boundary and the evaporation rate of water are taken as solution conditions to solve the physical quantities in the state equation. The numerical model provides a new way to calculate the initial temperature of bubble escape (ITBE). And the bubble evolution inside the pressboard is obtained which is hard to be observed in experiment. After that, the influences of moisture content of pressboard and cellulose aging on ITBE in the numerical model are discussed. The model results show that the expansion rate of bubble is not uniform. Bubble growth is slow in the early stage of temperature rise, when the temperature reaches a certain threshold the growth rate of bubble radius increases significantly, which is of great significance to the temperature limit on oil-immersed power transformers.

A mathematical model for predicting bubble growth for low Bond and Jakob number nucleate boiling

In an effort to better understand the physical mechanisms responsible for pool boiling heat transfer, an analytical model is developed that describes the changing shape and size of a growing vapour bubble in a non-uniform temperature field. Indeed, any analysis of thermal transport due to nucleate pool boiling requires bubble frequency predictions which are intimately linked to bubble growth characteristics such as volume and time of detachment from the nucleation site. The model is developed and validated for quasi-static bubble growth due to vaporization within the heat-transfer controlled growth regime. It highlights the need to include the asymmetric nature of growing bubbles when modeling bubble growth and it accounts for the movement of the thermal boundary layer in the bubble׳s vicinity.Analysis of previously published numerical treatments of bubble shape evolution leads to simplifying bubble geometry for low Bond number applications. The geometric model accounts for bubble shape transformation throughout the bubble growth cycle. It is idealized as a segmented sphere atop a cylindrical neck. An analytical model of quasi-static diabatic bubble growth is accordingly developed and is coupled with a geometric detachment relation and a force balance detachment criterion that are dependent on the Bond number.The resultant low Bond number bubble evolution model is validated with images of n-pentane vapour bubble formations issuing from an artificial cavity. In order to solve the mass–energy balance at the vapour bubble interface, a spherical surface area is commonly assumed. This leads to the need for correction factors and provides little insight into the physical mechanism responsible for bubble shape. In this study, the transitioning shape of a vapour bubble is considered in the integral analysis of the interfacial mass–energy balance. The model predicts the following bubble growth and detachment characteristics: profile, volume, center of gravity, bubble height, Aspect Ratio and moment of detachment.

Single-mode bubble evolution simulations of Rayleigh Taylor instability with spectral element method and a viscous model

Based on the single-mode potential model of Jacobs and Rikanati, Firstly, a viscous single-mode bubble evolution model of Rayleigh Taylor instability (RTI) is developed in this study. Viscous effects of RTI’s early stage growth for low Atwood number have been explained. In addition, direct numerical simulations of single mode RTI are studied with Navier–Stokes equations and a transport-diffusive equation for miscible fluids, in which these equations are discritized with discontinuous Galerkin (DG) spectral element method. The turbulent mixing of RTI has kinetic energy dissipation, and the dissipation rate is determined by the inertial and viscous effects. Therefore, the numerical techniques must include a dissipation mechanism for kinetic energy. For this reason, the high accurate spectral element method is employed in this study. Agreement between the theoretical model and the numerical results shows that simulations of RTI is feasible using the mathematical miscible fluid model. The results also suggest that a high order numerical method may provide the capability of simulating small scale fluctuations in turbulent flows with RTI.

A viscous vortex single-mode bubble evolution model of Rayleigh Taylor instability and its numerical study

This paper has developed a viscous single-mode bubble evolution model of Rayleigh Taylor Instabilities (RTIs), which is an extension of the single-mode potential models of Jacobs and Rikanati. The viscous vortex model explained the viscous effects of its early stage of RTI development for low Atwood number flow. Furthermore, direct numerical simulations of RTI are studied with Navier-Stokes equations and a transport-diffusive equation. Agreement between the theoretical model and the numerical results shows that simulations of these instabilities are feasible using the mathematical miscible fluid model simulating RTI.

A viscous vortex single-mode bubble evolution model of Rayleigh-Taylor instability and its numerical study

A viscous vortex single-mode bubble evolution model of Rayleigh-Taylor instability and its numerical study

A methane bubble curtain in meromictic Sakinaw Lake, British Columbia

Hydroacoustic surveys in meromictic Sakinaw Lake found an approximate 20‐m‐wide dual‐column bubble curtain originating from a depth of 42–60 m all around the main basin at the interface between the chemocline and the sediments. With the exception of the small upper basin, Sakinaw Lake is oligotrophic and permanently salt stratified, with a 30‐m mixolimnion overlying an anoxic monimolimnion containing high concentrations of sodium chloride and dissolved sulfide. Nitrogen is the major factor limiting the lake's phytoplankton productivity. The mainly methane bubbles in the curtain have a fairly narrow range of sizes, with most of the bubbles (75%) having radii between 600 and 850 µm with a peak at 735 µm, which is close to a third of the size of bubbles reported for Kinneret Lake in Israel. We hypothesize that different bubble generation mechanisms cause this difference. A simple bubble evolution model that includes gas dissolution and buoyancy is in good agreement with the acoustically observed bubble characteristics and is used to infer bubble densities and gas flux rates. Few of the bubbles reach the surface with any methane left in them. The bubble flux of methane into the upper part of the lake is 3 mg m−2 yr−1. The dual‐column nature of the bubble plume and the extensive and persistent nature of the bubble curtain around the lake suggest that there may be unique physical and biological conditions in Sakinaw Lake affecting methane generation and bubble ebullition.

A model of extravascular bubble evolution: effect of changes in breathing gas composition.

Observations of bubble evolution in rats after decompression from air dives (O. Hyldegaard and J. Madsen. Undersea Biomed. Res. 16: 185-193, 1989; O. Hyldegaard and J. Madsen. Undersea Hyperbaric Med. 21: 413-424, 1994; O. Hyldegaard, M. Moller, and J. Madsen. Undersea Biomed. Res. 18: 361-371, 1991) suggest that bubbles may resolve more safely when the breathing gas is a heliox mixture than when it is pure O(2). This is due to a transient period of bubble growth seen during switches to O(2) breathing. In an attempt to understand these experimental results, we have developed a multigas-multipressure mathematical model of bubble evolution, which consists of a bubble in a well-stirred liquid. The liquid exchanges gas with the bubble via diffusion, and the exchange between liquid and blood is described by a single-exponential time constant for each inert gas. The model indicates that bubbles resolve most rapidly in spinal tissue, in adipose tissue, and in aqueous tissues when the breathing gas is switched to O(2) after surfacing. In addition, the model suggests that switching to heliox breathing may prolong the existence of the bubble relative to breathing air for bubbles in spinal and adipose tissues. Some possible explanations for the discrepancy between model and experiment are discussed.