Problem Of Bubble Growth Research Articles

Simulation of subcooled flow boiling in manifold microchannel heat sink

The manifold microchannel (MMC) heat sink has become the most popular one among emerging technologies for high heat flux thermal management because of its high surface-to-volume ratio. Even though numerous numerical studies have been performed for the single-phase flow in the MMC heat sink, researches on two-phase flow boiling/condensation in this type of microchannel is seldomly reported because of its issues with flow pattern prediction. In the present work, a numerical approach involving two-phase interface capturing, phase change and solid heat conduction is conducted for the simplified MMC unit cell model. Heat and mass transfers of Lee model and interfacial heat resistance model for phase change are validated by the single bubble growth problem. Besides, both phase-change models are shown to provide good predictions against the experimental temperature database, with all of the data points falling within −5% to +20% and −5% to +10% error bands for Lee model and interfacial resistance model, respectively. Furthermore, a liquid-vapor interface region with thin thickness and accurate interface temperature can be obtained by the interfacial resistance model coupled with a homogeneous nucleation-site model.

Extension of a Standard Flow Solver for Simulating Phase Change in Cryogenic Tanks

Cryogenic-liquid-propelled rockets are equipped with tanks containing subcooled liquid propellants such as hydrogen and methane. The pressure evolution in such tanks is governed by the heat exchange of the vapor with the tank walls and liquid surface and the phase change at the liquid vapor interface. Because phase change is a major driver for the pressure evolution, the accurate prediction of the phase change rate is of crucial importance for the design of cryogenic liquid tanks and their pressurization systems. Therefore, in this study the commercial multiphase flow solver FLOW-3D® is extended with a customized phase change model based on the temperature gradients at the phase boundaries. The clear advantage of the temperature gradient model over, for example, kinetics-based models is that it contains no model constants. To validate the customized phase change model, liquid evaporation at a heated wall, liquid evaporation at a superheated liquid body at a wall, the bubble growth problem in superheated liquid, and meniscus evaporation in a heat pipe are considered. The numerical solutions of all computations show a good agreement with reference solutions. Furthermore, the phase change model is applied to the microgravity tank flow problem SOURCE-2, where HFE-7000 evaporates at a superheated wall. With the new phase change model, FLOW-3D is able to predict the pressure evolution with a maximum deviation of 0–20% compared with measurements.

A model of cavitation for the treatment of a moving liquid metal volume

A homogeneous cavitation model, derived from the Keller–Miksis equation, is developed and applied to the two-phase problem of bubble growth, break-up and propagation in the melt. Numerical simulations of the ultrasonic field emanating from an immersed sonotrode are performed, and the calculated acoustic pressure is applied to the source term of the bubble transport equation to predict the generation, propagation and collapse of cavitation bubbles in the melt. The use of baffles to modify the flow pattern and amplify sound waves in a launder conduit is examined to determine the optimum configuration that maximizes the residence time of the liquid in high cavitation activity regions. The simulation results demonstrate that dimensions that match integer wavelengths, and are therefore in resonance with the travelling waves, are desirable since they lead to an increase in the concentration of nucleating bubbles in the liquid compared with other dimensions.

A lattice Boltzmann method for simulation of liquid–vapor phase-change heat transfer

A lattice Boltzmann model for the liquid–vapor phase change heat transfer is proposed in this paper. Two particle distribution functions, namely the density distribution function and the temperature distribution function, are used in this model. A new form of the source term in the energy equation is derived and the modified pseudo-potential model is used in the proposed model to improve its numerical stability. The commonly used Peng–Robinson equation of state is incorporated into the proposed model. The problem of bubble growth and departure from a horizontal surface is solved numerically based on the proposed model.

BUBBLE CONTRACTION IN HELE-SHAW CELLS

Although the problem of bubble growth in Hele-Shaw cells has been extensively studied, little attention has been paid to bubble contraction. In this paper, the asymptotic characteristics of the contraction are studied. A method is developed to predict whether the bubble will remain connected or split into several parts. A simple procedure for determining the contraction points at which the last traces of the bubble finally disappear is described.

Numerical Solution for the Spherical Bubble Growth Problem in a Uniformly Ultraheated Liquid

A multi-point, implicit-type, finite-difference method for solving the bubble growth (or collapse) problem in an ultraheated liquid is proposed. The method is applicable to both inertia-controlled growth and heat-diffusion-controlled growth. The results are compared with several asymptotic solutions, involving Plesset-Zwick and Mikic-Rohsenow-Griffith solutions. Present results strongly support the Mikic-Rohsenow-Griffith solution for the wide range of bubble growth conditions, e.g. given fluids, pressure, liquid ultraheat, etc.

An approximate solution to a bubble growth problem

An approximate solution to a bubble growth problem

First Paper: Temperature Effects on Cavitation in a Centrifugal Pump: Theory and Experiment

A theoretical model is proposed to explain the development of cavitation in a centrifugal pump. A basic assumption is that the pump always behaves as a head generating-volume flow device, hence the density of the cavitating fluid becomes important, and this is estimated assuming that cavitation is a bubble growth problem. Essentially the model applies to best efficiency flowrate and complete breakdown, and is semi-empirical since test data at ambient conditions are required. From these data predictions are made of the variation of breakdown and inception points with temperature and speed. Experimental results are then presented and these show excellent agreement with the predicted results over a wide range of temperature, and hence thermodynamic properties, at constant speed. However, the agreement between the predicted speed effect and the experimental results indicates that the scaling used could be in error.