An Effective Property, LHF-Type Model for Spray Combustion

2000 ◽  
Vol 122 (2) ◽  
pp. 275-279 ◽  
Author(s):  
Marouan A. A. Nazha ◽  
Hobina Rajakaruna ◽  
Roy J. Crookes
Keyword(s):  
Gas Phase ◽  
Turbulent Mixing ◽  
Energy Transport ◽  
Effective Properties ◽  
Control Volume ◽  
Effective Property ◽  
Type Model ◽  
Two Phase ◽  
Wide Range ◽  
Property Changes

A mathematical model capable of describing the evaporation, mixing and burning characteristics of a confined reacting two-phase flow is presented. The flow field is described by solving the partial differential equations of continuity, momentum, and energy transport, together with the k-ε equations of turbulence. Evaporation is accounted for via a droplet evaporation sub-model which runs in parallel with the gas-phase solver exchanging data with it. Effective properties are calculated in each control volume and the property changes resulting from the evaporation are allowed to propagate according to the turbulent mixing model. Combustion follows the mixing process and is assumed to proceed to equilibrium. The model is validated against experimental results, and its applicability over a wide range of conditions is investigated. [S0742-4795(00)03002-7]

REITERATED HOMOGENIZATION OF INTEGRAL FUNCTIONALS

2000 ◽  
Vol 10 (01) ◽  
pp. 47-71 ◽  
Author(s):  
ANDREA BRAIDES ◽  
DAG LUKKASSEN
Keyword(s):  
Energy Density ◽  
Quadratic Form ◽  
Phase Structure ◽  
Effective Properties ◽  
Effective Property ◽  
Integral Functionals ◽  
Effective Energy ◽  
Two Phase ◽  
Wide Range ◽  
Reiterated Homogenization

We consider the homogenization of sequences of integral functionals defined on media with several length-scales. Our general results connected to the corresponding homogenized functional are used to analyze new types of structures and to illustrate the wide range of effective properties achievable through reiteration. In particular, we consider a two-phase structure which is optimal when the integrand is a quadratic form and point out examples where the macroscopic behavior of this structure underlines an effective energy density which is lower than that of the best possible multirank laminate. We also present some results connected to a reiterated structure where the effective property is extremely sensitive of the growth of the integrand.

A Direct Numerical Simulation of the Unsteady Development of a Deformable Rising Bubble in a Quiescent Liquid

2008 ◽  
Author(s):  
Alpana Agarwal ◽  
C. F. Tai ◽  
J. N. Chung
Keyword(s):  
Weber Number ◽  
Bubble Dynamics ◽  
Stokes Equations ◽  
Control Volume ◽  
Density Ratio ◽  
Simulation Method ◽  
Liquid Pool ◽  
Accurate Information ◽  
Two Phase ◽  
Wide Range

An accurate finite-volume based numerical method for the simulation of an isothermal two-phase flow, consisting of a deformable bubble rising in a quiescent, unbounded liquid, is presented. This direct simulation method is built on a sharp interface concept and developed on an Eulerian, Cartesian fixed grid with a cut-cell scheme and marker points to track the moving interface. The unsteady Navier-Stokes equations in both liquid and gas phases are solved separately. The mass continuity and momentum flux conditions are explicitly matched at the true phase boundary to determine the interface shape and movement of the bubble. The highlights of this method are that it utilizes a combined Eulerian-Lagrangian approach, and is capable of treating the interface as a sharp discontinuity. A fixed underlying grid is used to represent the control volume. The interface, however, is denoted by a separate set of marker particles which move along with the interface. A quadratic curve fitting algorithm with marker points is used to yield smooth and accurate information of the interface curvatures. This numerical scheme can handle a wide range of density and viscosity ratios. The bubble is assumed to be spherical and at rest initially, but deforms as it rises through the liquid pool due to buoyancy. Additionally, the flow is assumed to be axisymmetric and incompressible. The bubble deformation and dynamic motion are characterized by the Reynolds number, the Weber number, the density ratio and the viscosity ratio. The effects of these parameters on the translational bubble dynamics and shape are given and the physical mechanisms are explained and discussed. Results for the shape, velocity profile and various forces acting on the bubble are presented here as a function of time until the bubble reaches terminal velocity. The range of Reynolds numbers investigated is 1 < Re < 100, and that of Weber number is 1 < We < 10.

Study on Drag Coefficients for Two Groups of Bubbles

2004 ◽  
Author(s):  
Xiaodong Sun ◽  
Yang Liu ◽  
Basar Ozar ◽  
Mamoru Ishii ◽  
Joseph M. Kelly
Keyword(s):  
Gas Phase ◽  
Fluid Model ◽  
Interfacial Area ◽  
Current Approach ◽  
Two Phase ◽  
Drag Coefficients ◽  
Interfacial Area Transport ◽  
Wide Range ◽  
Two Fluid Model ◽  
Two Fluid

To apply the two-fluid model to a wide range of flow regimes in gas-liquid two-phase flows, the gas phase is categorized into two groups: small spherical/distorted bubbles as Group 1 and large cap/slug/churn-turbulent bubbles as Group 2 in the modeling of interfacial area transport. The interfacial transfer terms of momentum and energy for the gas phase are then divided into two groups accordingly in the implementation of the two-group interfacial area transport equation to the two-fluid model. Thus, the drag coefficients and the interfacial heat transfer for each group bubbles need to be developed. An approach has been sought for evaluating the drag coefficients of each bubble group based on a comprehensive experimental data base obtained in air-water upward flows in various size round pipes. Comparisons have been made with the theory of the drag coefficients and it was found that the agreement is not very satisfactory although the general trends can be predicted by the current approach.

Mechanisms of Convective Heat Transfer of Nanofluids

2008 ◽  
Author(s):  
Dongsheng Wen
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Single Channel ◽  
Effective Properties ◽  
Effective Property ◽  
The Body ◽  
Two Phase ◽  
Continuous Equation

Research on nanofluids has progressed rapidly since its enhanced thermal conductivity was identified about a decade ago. Much evidence shows that the enhancement of convective heat transfer is much higher than that of thermal conductivity only. The mechanism of such enhancement, however, is still unclear. This work reviews the mechanisms of convective heat transfer of nanofluids in a single channel, and identifies two most likely mechanisms: the modification of effective properties and the migration of nanoparticles under flow conditions. A numerical simulation based on a combined Euler and Lagrange method is investigated in this work to illustrate the feature of nanoparticle migration and the drawback of the effective property approach. The motion of discrete nanoparticles is determined by the Lagrangian trajectory method based on the Newton’s second law that includes influence of the body force, various hydrodynamic forces, and the Brownian and thermophoresis forces. The coupling of discrete particles with continuous flow is realized through the modification of the source term of the continuous equation. It concludes that the two-phase flow nature of nanofluids, especially the nanoparticle migration and the resultant non-uniform particle and effective property profile, needs to be considered to properly model the convective heat transfer.

Two-Phase, Two-Component Critical Flow in a Venturi

1972 ◽  
Vol 94 (1) ◽  
pp. 147-151 ◽  
Author(s):  
R. V. Smith
Keyword(s):  
Gas Phase ◽  
Gas Flow ◽  
Critical Flow ◽  
Flow Conditions ◽  
Transfer Coefficients ◽  
Two Phase ◽  
One Dimensional ◽  
Flow Equations ◽  
Heat Transfer Coefficients ◽  
Wide Range

This paper reports the results of an analytical and experimental investigation whose object was to test the hypothesis that the flow of the gas phase controls critical and near critical two-phase flow for cases where the gas flow is essentially in separate streams. The results substantiate the hypothesis. The analytical results also indicate that one dimensional flow equations with reasonably accurate estimates for the droplet size and for the drag and heat transfer coefficients will adequately describe critical and near critical flow over a wide range of flow conditions.

Intrinsic Stacking Interactions of Natural and Artificial Nucleobases

2019 ◽  
Author(s):  
Drew P. Harding ◽  
Laura J. Kingsley ◽  
Glen Spraggon ◽  
Steven Wheeler
Keyword(s):  
Gas Phase ◽  
Electrostatic Interactions ◽  
Density Functional ◽  
Molecular Descriptors ◽  
Stacking Interactions ◽  
Interaction Energies ◽  
Functional Theory ◽  
Binding Partner ◽  
Heavy Atoms ◽  
Wide Range

The intrinsic (gas-phase) stacking energies of natural and artificial nucleobases were explored using density functional theory (DFT) and correlated ab initio methods. Ranking the stacking strength of natural nucleobase dimers revealed a preference in binding partner similar to that seen from experiments, namely G > C > A > T > U. Decomposition of these interaction energies using symmetry-adapted perturbation theory (SAPT) showed that these dispersion dominated interactions are modulated by electrostatics. Artificial nucleobases showed a similar stacking preference for natural nucleobases and were also modulated by electrostatic interactions. A robust predictive multivariate model was developed that quantitively predicts the maximum stacking interaction between natural and a wide range of artificial nucleobases using molecular descriptors based on computed electrostatic potentials (ESPs) and the number of heavy atoms. This model should find utility in designing artificial nucleobase analogs that exhibit stacking interactions comparable to those of natural nucleobases. Further analysis of the descriptors in this model unveil the origin of superior stacking abilities of certain nucleobases, including cytosine and guanine.

Numerical modeling of the influence of bubbles on flow and heat transfer in the descending gas-liquid flow in a pipe

2012 ◽  
Vol 9 (1) ◽  
pp. 131-135
Author(s):  
M.A. Pakhomov
Keyword(s):  
Heat Transfer ◽  
Gas Phase ◽  
Liquid Flow ◽  
Bubble Diameter ◽  
Gas Content ◽  
Two Phase ◽  
Eulerian Description ◽  
Flow And Heat Transfer ◽  
Gas Liquid Flow ◽  
The Mathematical Model

The paper presents the results of modeling the dynamics of flow, friction and heat transfer in a descending gas-liquid flow in the pipe. The mathematical model is based on the use of the Eulerian description for both phases. The effect of a change in the degree of dispersion of the gas phase at the input, flow rate, initial liquid temperature and its friction and heat transfer rate in a two-phase flow. Addition of the gas phase causes an increase in heat transfer and friction on the wall, and these effects become more noticeable with increasing gas content and bubble diameter.

scholarly journals A multi-site, year-round turbulence microstructure atlas for the deep perialpine Lake Garda

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Sebastiano Piccolroaz ◽  
Bieito Fernández-Castro ◽  
Marco Toffolon ◽  
Henk A. Dijkstra
Keyword(s):  
Turbulent Mixing ◽  
Meteorological Data ◽  
Time Of Day ◽  
Monthly Basis ◽  
Lake Garda ◽  
Standardized Protocol ◽  
Wide Range ◽  
Buoyancy Driven Convection ◽  
Monitoring Activity ◽  
Additional Monitoring

AbstractA multi-site, year-round dataset comprising a total of 606 high-resolution turbulence microstructure profiles of shear and temperature gradient in the upper 100 m depth is made available for Lake Garda (Italy). Concurrent meteorological data were measured from the fieldwork boat at the location of the turbulence measurements. During the fieldwork campaign (March 2017-June 2018), four different sites were sampled on a monthly basis, following a standardized protocol in terms of time-of-day and locations of the measurements. Additional monitoring activity included a 24-h campaign and sampling at other sites. Turbulence quantities were estimated, quality-checked, and merged with water quality and meteorological data to produce a unique turbulence atlas for a lake. The dataset is open to a wide range of possible applications, including research on the variability of turbulent mixing across seasons and sites (demersal vs pelagic zones) and driven by different factors (lake-valley breezes vs buoyancy-driven convection), validation of hydrodynamic lake models, as well as technical studies on the use of shear and temperature microstructure sensors.

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