Showing papers on "Volume of fluid method published in 2014"

Maximum magnitude earthquakes induced by fluid injection

Abstract: Analysis of numerous case histories of earthquake sequences induced by fluid injection at depth reveals that the maximum magnitude appears to be limited according to the total volume of fluid injected. Similarly, the maximum seismic moment seems to have an upper bound proportional to the total volume of injected fluid. Activities involving fluid injection include (1) hydraulic fracturing of shale formations or coal seams to extract gas and oil, (2) disposal of wastewater from these gas and oil activities by injection into deep aquifers, and (3) the development of enhanced geothermal systems by injecting water into hot, low-permeability rock. Of these three operations, wastewater disposal is observed to be associated with the largest earthquakes, with maximum magnitudes sometimes exceeding 5. To estimate the maximum earthquake that could be induced by a given fluid injection project, the rock mass is assumed to be fully saturated, brittle, to respond to injection with a sequence of earthquakes localized to the region weakened by the pore pressure increase of the injection operation and to have a Gutenberg-Richter magnitude distribution with a b value of 1. If these assumptions correctly describe the circumstances of the largest earthquake, then the maximum seismic moment is limited to the volume of injected liquid times the modulus of rigidity. Observations from the available case histories of earthquakes induced by fluid injection are consistent with this bound on seismic moment. In view of the uncertainties in this analysis, however, this should not be regarded as an absolute physical limit.

Comparative numerical study of single and two-phase models of nanofluid heat transfer in wavy channel

Abstract: The main purpose of this study is to survey numerically comparison of two-phase and single phase of heat transfer and flow field of copper-water nanofluid in a wavy channel The computational fluid dynamics (CFD) prediction is used for heat transfer and flow prediction of the single phase and three different two-phase models (mixture, volume of fluid (VOF), and Eulerian) The heat transfer coefficient, temperature, and velocity distributions are investigated The results show that the differences between the temperature field in the single phase and two-phase models are greater than those in the hydrodynamic field Also, it is found that the heat transfer coefficient predicted by the single phase model is enhanced by increasing the volume fraction of nanoparticles for all Reynolds numbers; while for the two-phase models, when the Reynolds number is low, increasing the volume fraction of nanoparticles will enhance the heat transfer coefficient in the front and the middle of the wavy channel, but gradually decrease along the wavy channel

Condensation in a Square Minichannel: Application of the VOF Method

Abstract: A number of steady-state numerical simulations of condensation of R134a at mass fluxes of 400 kg m−2 s−1 and 800 kg m−2 s−1 inside a 1-mm square cross section minichannel are proposed here and compared against simulations in a circular cross section channel with the same hydraulic diameter. The volume of fluid (VOF) method is used to track the vapor–liquid interface, and the effects of interfacial shear stress, surface tension, and gravity are taken into account. A uniform wall temperature is fixed as a boundary condition. At both mass velocities the liquid film and the vapor core are treated as turbulent; a low-Re form of the SST k-ω model has been used for the modeling of turbulence through both the liquid and vapor phases. Numerical simulations are validated against experimental data. The influence of the surface tension on the shape of the vapor–liquid interface may provide some heat transfer enhancement in a square cross section minichannel, but this depends on the mass flux and it may be not signifi...

Prediction of effective area and liquid hold-up in structured packings by CFD

Abstract: Interfacial effective area and liquid hold-up in structured packing geometries are investigated using the volume of fluid method. Three-dimensional numerical simulations of gas–liquid flow on inclined plane plate and in a structured packing are performed. The VOF method is used to capture the gas–liquid interface motion. After a first validation case on the wetting phenomena prediction on an inclined plane plate, the effective interfacial area, the liquid hold-up and the degree of wetting of packing are studied as function of liquid flow rate and wall surface characteristic (adherence contact angle). Results show that the liquid flow-rate and the contact angle play a significant role. It is found that the interfacial effective area and the degree of wetting of packing increase as the liquid flow rate increases and as the contact angle decreases. Moreover, under the influence of the contact angle, different liquid film shapes are observed. The simulations results are compared to experimental data available in literature. This work shows that the CFD is a powerful tool to investigate performance characteristics of structured packings. Moreover, this work shows how CFD can be used as an effective tool to provide information on fluid flow behavior and determination of interfacial area, liquid hold-up and minimum flow-rate to ensure complete wetting. These parameters could be further used in process simulation at larger scale for the development and the design of efficient packings.

Comparative numerical study of single-phase and two-phase models for bio-nanofluid transport phenomena

Abstract: A computational fluid dynamics (CFD) simulation of laminar convection of Al2O3–water bio-nanofluids in a circular tube under constant wall temperature conditions was conducted, employing a single-phase model and three different two-phase models (volume of fluid (VOF), mixture and Eulerian). The steady-state, three-dimensional flow conservation equations were discretised using the finite volume method (FVM). Several parameters such as temperature, flow field, skin friction and heat transfer coefficient were computed. The computations showed that CFD predictions with the three different two-phase models are essentially the same. The CFD simulations also demonstrated that single-phase and two-phase models yield the same results for fluid flow but different results for thermal fields. The two-phase models, however, achieved better correlation with experimental measurements. The simulations further showed that heat transfer coefficient distinctly increases with increasing nanofluid particle concentration. The physical properties of the base fluid were considered to be temperature-dependent, while those of the solid particles were constant. Grid independence tests were also included. The simulations have applications in novel biomedical flow processing systems.

Simulation of condensation flow in a rectangular microchannel

Abstract: The condensation flow of the refrigerant FC-72 in a rectangular microchannel with a 1-mm hydraulic diameter is numerically studied using the volume of fluid (VOF) model. The heat transfer related to the condensation is taken into account by a thermal equilibrium model assuming the interface temperature is at saturation. The numerical method is validated against experiments from the literature and well predicts the flow patterns along the microchannel. The vapor phase in the microchannel forms a continuous column with a decreasing diameter from upstream to downstream. Slugs are periodically generated at the head of the column. Decreasing the wall cooling heat flux or increasing the flow mass flux increases the vapor column length. Waves along the interface cause necks in the column and locally increase the vapor velocity and decrease the pressure, facilitating breakage of the vapor column into slugs. The liquid temperature is close to saturation near the interface and lower downstream and in the thin liquid layer close to the cooling surface. The initial bubble size increases with increasing flow mass flux or decreasing cooling heat flux.

System and method for delivering a target volume of fluid

Abstract: A method for delivering a target volume of fluid to a destination is provided. The method includes delivering a first volume of fluid to the destination in increments each having approximately a first incremental volume, the first volume of fluid being less than the target volume and delivering a second volume of fluid to the destination in increments each having approximately a second incremental volume, the second incremental volume being less than the first incremental volume, such that the sum of the first volume and the second volume is approximately equal to the target volume.

Simple Mechanistically Consistent Formulation for Volume-of-Fluid Based Computations of Condensing Flows

Abstract: Numerous investigations have been conducted to extend adiabatic liquid-gas VOF flow solvers to include condensation phenomena by adding an energy equation and phase-change source terms. Some proposed phase-change models employ empirical rate parameters, or adapt heat transfer correlations, and thus must be tuned for specific applications. Generally applicable models have also been developed that rigorously resolve the phase-change process, but require interface reconstruction, significantly increasing computational cost and software complexity. In the present work, a simplified first-principles-based condensation model is developed, which forces interface-containing mesh cells to the equilibrium state. The operation on cells instead of complex interface surfaces enables the use of fast graph algorithms without reconstruction. The model is validated for horizontal film condensation, and converges to exact solutions with increasing mesh resolution. Agreement with established results is demonstrated for smooth and wavy falling-film condensation.Copyright © 2013 by ASME

A semi‐implicit numerical method for the free‐surface Navier–Stokes equations

Abstract: SUMMARY Semi-implicit methods are known for being the basis of simple, efficient, accurate, and stable numerical algorithms for simulating a large variety of geophysical free-surface flows. Geophysical flows are typically characterized by having a small vertical scale as compared with their horizontal extents. Hence, the hydrostatic approximation often applies, and the free surface can be conveniently represented by a single-valued function of the horizontal coordinates. In the present investigation, semi-implicit methods are extended to complex free-surface flows that are governed by the full incompressible Navier–Stokes equations and are delimited by solid boundaries and arbitrarily shaped free-surfaces. The primary dependent variables are the velocity components and the pressure. Finite difference equations for momentum, and a finite volume discretization for continuity, are derived in such a fashion that, after simple manipulation, the resulting pressure equation yields a well-posed piecewise linear system from which both the pressure and the fluid volume within each computational cell are naturally derived. This system is efficiently solved by a nested Newton type iterative scheme, and the resulting fluid volumes are assured to be nonnegative and bounded from above by the available cell volumes. The time step size is not restricted by stability conditions dictated by surface wave speed, but can be freely chosen just to achieve the desired accuracy. Several examples illustrate the model applicability to a large range of complex free-surface flows and demonstrate the effectiveness of the proposed algorithm. Copyright © 2013 John Wiley & Sons, Ltd.

Experimental and Numerical Study on Velocity Fields and Water Surface Profile in a Strongly-Curved 90° Open Channel Bend

Abstract: The flow pattern changes at open channel bend as the result of the presence of centrifugal force. Parameters such as water surface level, the transverse and depth velocity distribution, secondary flow and separation zones deeply depend on bend angel and radius, while many researchers are interested in flow patterns at bends. This paper presents an experimental and numerical study of the flow patterns in a strongly-curved 90° open channel bend. The numerical modelling was carried out using the finite volume method. In this numerical study, the k – e (RNG) model was used to predict the turbulence, and the volume of fluid (VOF) method was used to simulate the water free surface. The numerical results were verified against data from a program of experiments conducted in this study. A comparison between the experimental data and the results of the numerical model showed that the k – e (RNG) and VOF methods are capable of simulating the flow pattern in the strongly-curved bends. The results showed that ...

Numerical analysis of droplet impact onto liquid film

Abstract: Normal impingement of a single droplet on a thin liquid film is investigated numerically solving the axisymmetric Navier-Stokes equations. Gravity and viscosity are taken into account whereas compressibility effects are neglected. Two phases are tracked by means of volume of fluid method and adaptive mesh refinement is used to increase accuracy of the interface. Numerical results are validated both qualitatively and quantitatively using experimental measurements. Effects of gas density, gas viscosity, and film thickness on the crown behavior are studied. Influence of droplet deviation from spherical shape on the crown behavior is investigated. It is shown that increasing the gas density leads to reduction of crown radius evolution rate, while gas viscosity does not affect the rate of crown radius evolution. Development rate of crown height decreases by increasing the gas density. Reynolds number and splashing regime can change the effect of gas viscosity on the crown height evolution. Deviation of droplet from sphere can change behavior of crown completely as result of change in droplet mass center position. Difference between numerical results and experimental ones is justified using different droplet shapes.