Wide Range Of Fluid Properties Research Articles

A new technology for producing mono-disperse macroemulsions

A new continuous emulsification process has been developed that is capable of generating very uniform droplets in a single stage process. It is based on thread break-up in the lumen of hollow fibre membranes, whose material is selected to be preferentially wetted by the continuous phase of the emulsion to be produced. This phase is pressed from the outside through the fibre wall, while the phase to be dispersed enters the hollow fibre through one of the lumen openings. It is disconnected from the fibre wall by a film of permeating continuous phase inducing instabilities in the inner phase. After break-up, a two-phase train of equally spaced droplets leaves the other lumen end into a product receiver. The emulsion thus generated shows an extremely narrow droplet size distribution and can be produced without emulsifiers. Its mean size is directly correlated with the inner diameter of the fibres, a fact that limits its range to values between 300 and 2000 μ m. The process has the potential of being very cost efficient as it consumes little energy and does not require complex equipment. Four different membranes and a wide range of fluid properties, i.e. viscosity, density and interfacial tension were studied. The purpose of these experiments was an analysis of the droplet diameter and its distribution upon physical properties and operating parameters. The system can be operated very stably within a wide range of fluid and process parameters. Next steps are an investigation of applications and the development of a fluid dynamic model.

Shapes of Single Drops Rising Through Stagnant Liquids

Shapes of single drops rising through infinite stagnant liquids under terminal conditions were measured using a high-speed camera for a wide range of fluid properties. Aspect ratios E and distortion factors γ of drops were evaluated from drop images. Effects of initial shape deformation, surfactants and viscosity ratio κ on E and γ were investigated. As a result, the following conclusions were obtained. (1) Initial shape deformation does not affect E and γ of single drops. (2) Addition of surfactants decreases E and breaks the fore-and-aft symmetry of a drop shape especially in systems of low Morton numbers M. (3) The Tadaki number Ta is the best dimensionless number among the Eotvos number Eo, the Weber number We and Ta for correlating E of drops, and an empirical correlation of E in terms of Ta was proposed for clean drops under the conditions of -11.6 ≤ log M ≤ -0.9, 1.5 × 10-2 ≤ Re ≤ 8.5 × 102, 1.7 × 10-2 ≤ Eo ≤ 9.3, 7.4 × 10-3 ≤ Ta ≤ 3.6 and 0.1 ≤ κ ≤ 100. (4) The viscosity ratio κ does not affect E so much but influences γ. For κ > 1, γ decreases with increasing the drop diameter, that is, the front part of a drop is flatter than the rear part. On the contrary, the rear part is flatter than the front part when κ < 1. The fore-and-aft symmetry always holds for drops with κ ∼ 1.0. (5) Various drop shapes were presented as a database utilized for verification of numerical methods such as an interface tracking method and a boundary element method.

Theoretical analysis of the effect of insoluble surfactant on the dip coating of chemically micropatterned surfaces

Microfluidic flow on chemically heterogeneous surfaces is a useful technique with applications ranging from selective material deposition to the self-assembly of nanostructures. The recent theoretical analysis by Davis [Phys. Fluids 17, 038101 (2005)] of the dip coating of a pure fluid onto vertical, wetting stripes surrounded by nonwetting regions quantified the experimentally observed deviations from the classical Landau-Levich result due to lateral confinement of the fluid by chemical surface patterning. In this present work, the analysis of dip coating of these heterogeneous surfaces is extended to a liquid containing an insoluble surfactant. Using matched asymptotic expansions based on lubrication theory in the limit of a small capillary number, the thickness of the deposited liquid film and the surfactant concentration in the deposited monolayer are predicted for a wide range of fluid properties and process parameters. The increase in the deposited film thickness is shown analytically to be limited by a multiplicative factor of 41∕3 times the result for a pure liquid. Numerical results demonstrate that the thickening due to Marangoni effects is nonmonotonic in the capillary number because of the competition between viscous stresses, Marangoni stresses, and surface diffusion.

A Neural Network Model for Prediction of Liquid Holdup in Two-Phase Horizontal Flow

SummaryAccurately predicting the liquid holdup associated with multiphase flow is a critical element in the design and operation of modern production systems. This prediction is made difficult by complex phase distributions and the wide range of fluid properties encountered in production operations. Consequently, the performance of existing correlations is often inadequate in terms of desired accuracy and application range. This investigation focuses on the development of a neural network model, a relatively new approach that has been applied successfully to a variety of complex engineering problems. Data from five independent studies were used to develop a neural network for predicting liquid holdup in two-phase horizontal flow. A detailed comparison with existing empirical correlations and mechanistic models reveals that for this data set, the neural network model shows an improvement in overall accuracy and performs more consistently across the range of liquid-holdup and flow patterns.

A Critical Review of Condensation Heat Transfer Predicting Models-Effects of Surface-tension Force

Condensation is defined as the transformation of vapor to its liquid state. Gravity and vapor shear are the two forces that drive the flow of the condensate film inside plain tubes. Traditional condensation predicting models generally include the effects of these two forces. For finned tubes, the surface-tension force will also be important. This paper provides a critical review of existed predicting models to correlate condensation heat transfer coefficients. Gravity-force dominated models, vapor-shear dominated models and the effects of surface-tension force are all discussed. Three basic methods have been used to model the vapor-shear dominated annular liquid film. The first model assumed that the vapor core could be replaced with an equivalent liquid flow that would yield the same value for the vapor shear. The second model assumed that the major resistance to heat transfer was offered only by the laminar liquid sublayer. The third model assumed that the velocity in liquid film could be predicted using von Karman universal velocity profile. Yang and Webb (1997) study shows that at low-mass-velocity and high-vapor-quality conditions, the effect of surface tension is comparable to that of vapor shear for condensation heat transfer inside a micro-fin tube with 13 μm fin tip radius. Owing to the manufacturing technology development of integrated circuits, smaller tubes and fin geometries can be made and used for increasing the condensation heat transfer coefficient. Because the surface-tension drainage force is proportional directly to the inverse of fin-tip radius, the importance of the surface-tension effect will increase with the development of micro-fabrication technology. The Yang and Webb (1997) model is the first model that accounts for the effects of vapor and surface-tension forces simultaneously. However, their database did not cover wide range of fluid properties and fin geometries. More work is needed on correlation and theoretically based models.

Drag Coefficients of Single Bubbles under Normal and Micro Gravity Conditions.

Simple but reliable correlations for a drag coefficient, CD, of single bubbles under a wide range of fluid properties, bubble diameter and acceleration of gravity were developed based on a balance of forces acting on a bubble in a stagnant liquid and available empirical correlations of terminal rising velocities of single bubbles. The proposed CD consists of three equations, each of which corresponds to pure, slightly contaminated and contaminated systems. The effect of a frictional pressure gradient due to a liquid flow is also taken into account by introducing a concept of an effective body acceleration. Terminal rising velocities of single bubbles were calculated using the proposed CD, and compared with measured data under the condition of 10-2<Eo<103, 10-14<M<107 and 10-3<Re<105 where Eo, M and Re are Eotvos, Morton and bubble Reynolds numbers, respectively. As a result, it was confirmed that the proposed CD gives better predictions than available drag coefficient models.

Calculation of turbulent boundary layer wall pressure spectra

The suitability of various wave-vector–frequency spectral models for predicting the point wall pressure spectrum due to developed turbulent boundary layer flow over planar, rigid surfaces is investigated. The early Corcos model [G. Corcos, J. Fluid Mech. 18, 353–378 (1964)] along with the incompressible and compressible models developed by Chase [D. Chase, J. Sound Vib. 112, 124–147 (1987)] are given particular attention. The effect of finite-sized measurement transducers is included in the integration of the theoretical wave-vector–frequency spectrum over the in-plane wave numbers in order to arrive at an attenuated point pressure frequency spectrum that can be compared directly to existing experimental data obtained in air, water, and glycerine. The selected experiments cover a wide range of fluid properties and Reynolds numbers. It is found that the Corcos model does not predict the measured data as well as the Chase model. An optimum set of empirical constants needed to exercise the Chase models are presented, but found to depend on the experiment considered. The need to consider viscous effects in future modeling is borne out when dealing with viscous fluids like glycerine.

Computation of turbulent boundary layer wall pressure spectra

The suitability of various wave‐vector–frequency spectral models for predicting the point wall pressure spectrum due to developed turbulent boundary‐layer flow over planar, rigid surfaces is investigated. The incompressible and compressible models developed previously [D. Chase, J. Sound Vib. 112, 125–147 (1987)] are given particular attention. The effect of finite‐sized measurement transducers is included in the integration of the theoretical wave‐vector–frequency spectrum over the in‐plane wave numbers in order to arrive at an attenuated point pressure frequency spectrum that can be compared directly to existing experimental data [G. Schewe, J. Fluid Mech. 134, 311–328 (1983) (air), G. C. Lauchle and M. A. Daniels, Phys. Fluids 30, 3019–3024 (1987) (glycerine), and M. P. Horne and R. A. Handler, Exp. Fluids 12, 136–139 (1991) (water)]. The selected experiments cover a wide range of fluid properties and Reynolds numbers: it is found that the optimum set of empirical constants needed to exercise the Chase...

Thermocapillary breakdown of falling liquid films at high Reynolds numbers

This paper presents a new correlation in which the heat flux required to break a falling liquid film can be determined from the film Reynolds number. The correlation is based on the balance of local forces in the substrate region for high-Reynolds number films. Validation of the correlation required experimental data for breakdown of wavy liquid films at a significantly higher Reynolds number and heat flux than have been presented in the past. These data are also presented in the paper. The results show that the correlation collapses the experimental data for three liquids with widely varying physical properties at film Reynolds numbers at up to about 10 4. This correlation gives one the ability to predict the thermocapillary breakdown of wavy falling films at high Reynolds number, high heat flux, and over a wide range of fluid properties.

TRANSITION TO ANNULAR FLOW IN TWO-PHASE, TWO-COMPONENT VERTICAL FLOW: EXAMINATION OF CORRELATIONS

The available empirical, semi-empirical and analytical correlations and flow pattern maps for predicting the transition to annular flow in upward, two-phase, gas-liquid flow in a vertical tube were tested against a large set of experimental data. These experimental data were taken on the same rig through an observation section (i.d. = 11.7 mm, L = 30.5 cm), preceded by a heated test section ( L/D≃ 52) and a calming length (L/D = 130), all having the same inside diameter as that of the observation section. The total range of variables covered by these data is: 2≤ReSL≤ 1.3 × 105, 5.6 ≤PrL≤ 7000, 0.01 VSG/VSL ≤ 7900, 2 × 10−4≤ρG/ρLs0.01, and 19.7 × 10−3≤ σ ≤72× 10−3N/m. In total, fifteen correlations and flow-pattern maps were tested with eight liquid-gas combinations covering a very wide range of fluid properties and mass flow rates of both phases. Using the Kutateladze number as the criterion for the transition appears to provide an excellent separation particularly when a lower value than 3.1, as suggeste...

Viscous flow on the outside of a horizontal rotating cylinder—II. Dip coating with a non-newtonian fluid

The flow of a viscous fluid on the outside of a partially submerged, rotating horizontal cylinder is one of the basic fundamental coating flows. The main features of this flow for a Newtonian fluid were described by Campanella and Cerro [ Chem. Engng Sci. 39, 1443 (1984)]. A rapid flow approximation [Cerro and Scriven Ind. Engng Chem. Fundam. 19, 40 (1980)] is used to develop a film profile equation for a power-law type non-Newtonian fluid. The film profile equation allows to compute a unique critical flow regime for each kind of power law fluid characterized by two rheological constants, K and n. Theoretical results are shown to be in very good agreement with experimental results for a wide range of fluid properties.

Correlation of mist‐to‐annular transition during condensation

AbstractA theory is proposed for correlating the mist‐annular transition during condensation based on a balance between destructive and stabilizing forces acting on the liquid film. The resulting correlation is shown to be capable of good agreement with a data base corresponding to a wide range of fluid properties and tube diameters. A fair deal of generality is demonstrated by testing the correlation outside the range from which it was developed.

Laminar, nonisothermal flow of fluids in tubes of circular cross section

AbstractNumerical solutions of the equations of motion and energy are presented in the form of pressure‐loss, flow‐rate relationships for the laminar, nonisothermal flow of Newtonian and non‐Newtonian fluids being heated and cooled in tubes at constant wall temperature. The flow properties are represented by a temperature‐dependent form of the power law equation. The numerical results are shown to be in good agreement with experimental data for a wide range of fluid properties and flow conditions.

Two‐phase concurrent flow in packed beds

AbstractPressure drop and liquid saturation accompanying two‐phase concurrent flow have been studied in a variety of packings and with gas‐liquid systems having a wide range of fluid properties. Two basic flow patterns were observed with nonfoaming systems. Correlations of pressuredrop and liquid‐saturation data were obtained in terms of the single‐phase friction losses for the liquid and the gas when each flows alone in the bed. Deviations from the correlation with foaming systems are discussed and illustrated with sample data.