Oscillatory Flow Conditions Research Articles

Dryout in a Boiling Channel under Oscillatory Flow Condition.

Premature dryout due to flow oscillation is a very important factor in designing boiling systems. The flow oscillation depends, in general, on system size and/or configuration, and therefore the relationship between the premature dryout and the flow oscillation has not been fully understood so far. In this investigation, a CHF experiment in a forced flow boiling channel under the oscillatory flow condition system has been conducted. Numerical simulation has also been conducted based on the lumped-parameter model of the boiling channel. The simulation well represents the transient behavior of the dryout under the oscillatory flow condition.

Rheological behaviour of low-fat and full-fat stirred yoghurt

The rheological properties of a low-fat and a full-fat yoghurt were investigated under continuous and oscillatory flow conditions with a rotational coaxial-cylinder viscometer at different temperatures. In continuous shear flow tests, flow instability phenomena were detected below a critical shear rate value. Flow curves were correlated with the three parameter De Kée-Turcotte model, and the temperature dependence of the relevant parameters was demonstrated. The non-linear viscoelastic properties of both types of yoghurt were described, at first approximation, in terms of the complex modulus G ∗ and phase lag δ. The effects of temperature on weakening of the yoghurt structure was illustrated.

Running Characteristics of a Cross-Flow Water Turbine in Oscillating Flow.

To clarify the effect of the inertia moment on the starting and running characteristics of an axisymmetric cross-flow turbine in oscillating flow, experiments are carried out using turbine test equipment in which wavelike up-and-down oscillating flow conditions are simulated. On the other hand, the dynamic characteristics of this turbine are calculated numerically on the basis of experimental data obtained from experiments in the steady one-way flow condition. The experimental results are compared with the numerical ones and fairly good agreement between them is demonstrated. Furthermore, using the nondimensional equation of motion for the rotating system, the effects of the wave height and the inertia moment of turbine on the running characteristics are investigated.

Sediment transport in oscillatory boundary layers in cases of rippled beds and sheet flow

An experimental study was focused on the process of sediment transport in unsteady flow conditions due to wave action. Wave‐induced oscillatory flow conditions near the seabed were simulated at full scale (1:1) in a new large oscillating water tunnel. Two sets of experiments (series A and B) were carried out. During series A, bed forms and wave‐cycle averaged suspended sediment concentrations were measured under sinusoidal waves. Series B focused on measurement of the wave‐cycle averaged sediment transport rates under regular and random asymmetric oscillatory flows (upper shoreface conditions) and was aimed at the verification of quasi‐steady formulas for the description of cross‐shore sediment transport.Bedform dimensions appeared to decrease considerably under the influence of wave asymmetry and wave randomness. Only the measured ripple dimensions under asymmetric waves (series B) showed good agreement with Nielsen's (1979) relations. For most of the series B experiments the bed was plane (sheet flow), the net sediment transport was directed “onshore” and the measured transport rates showed a strong correlation with the velocity moment < U3 >. An empirical quasi‐steady transport model is proposed which is based on the new tunnel data and other existing data sets. The limitations of the quasi‐steady model approach became clear in the rippled‐bed regime and through the presence of a consistent influence of the wave period in plane‐bed conditions. In rippled‐bed conditions the suspended concentration profiles followed a negative exponential distribution. For most of the experiments the measured concentration decay length showed a linear relation with the ripple height. In plane‐bed/sheet flow conditions the measured suspended concentration profiles followed a negative power function. The power or concentration decay parameter was constant (α ≃ 2.1) for a wide range of velocity conditions. It is suggested that the mobile bed (sheet flow layer) has a strong damping effect on the mixing of suspended sediments (turbulence damping).

Oscillating flow in channels with a sudden change in cross section

In this paper, we have computationally examined oscillating flow (zero mean between) two parallel plates with a sudden change in cross section. The flow was assumed to be laminar incompressible with the inflow velocity uniform over the channel cross section but varying sinusoidally with time. The cases studied cover wide ranges of Re max (from 187.5 to 2000), Va (from 1 to 10.66), the expansion ratio (1:2 and 1:4) and A r (2 and 4). Also, three different geometric cases were discussed: (a) asymmetric expansion/contraction; (b) symmetric expansion/contraction; and (c) symmetric blunt body. For these oscillating flow conditions, the fluid undergoes sudden expansion in one-half of the cycle and sudden contraction in the other. The instantaneous friction factor, for some ranges of Re max and Va, deviated substantially from the steady-state friction factor for the same flow parameters. A region has been identified (see Fig. 3) below which the flow is laminar quasi-steady. A videotape showing computer simulations of the oscillating flow demonstrates the usefulness of the current analyses in providing information on the transient hydraulic phenomena.

Dryout under oscillatory flow condition in vertical and horizontal tubes—experiments at low velocity and pressure conditions

7. Y. M. Yang and J. R. Maa, Dynamic surface etfect on the boiling of mixtures. Clrml. Eqrq Cornn?rm. 25, 47 62 (1984). X. N. Zuber, On the stability ofboiling heat transfer. 7‘rrnts. ,4SME80,71 I 720 (195X). 9. 3. W. Westwater. J. J. Hwalek and M. E. Irving, Suggested standard method for obtaining boiling curves by quenching, I&EC‘ Fn&irtz. 25, 685-692 (19X6). IO. H. S. Lin. Studies on pool boiling heat transfer by quenching with sphere, M.S. Thesis. Chcm. Fngng Dept.. National Chcng Kunp University-. Tainan. Tviwn ( IWO). J. F. C‘hen, Studies 011 pool bwlmp heat transkr c)/’ binary mixtures by quenching with sphere. M.S. Thesis. C’hern. Engng Dept., National Cheng Kung Llnivcrsit!,. Tainan. Taiwan (I9c)2). Y. 1.. Tmn and Y. M. Yang, I’wi hoiling of bmary

Heat/Mass Transfer from a Cylinder in the Strongly Oscillating Flow of a Pulse Combustor Tailpipe

Abstract This paper presents the results of an experimental investigation on the mass transport from a sintered cylinder placed inside the tailpipe of a pulse combustor. Evaporation rates were measured at several different oscillating and mean flow conditions. Also measured were time resolved velocity profiles and high speed laser schlieren video at a single operating condition. Velocity data were taken in front of and behind the cylinder as well as through the cylinder boundary layer, providing quantitative information on the temporal flow behavior. Both the velocity data and schlieren video indicate that the momentum field is non-quasi-steady. Over the range and combination of operating conditions studied, the results show that mass transfer rates are strongly affected by the pressure amplitude, weakly affected by the mean flow Reynolds number and unnoticeably affected by frequency.

Frequency Domain Analysis of In-Line Forces on Circular Cylinders in Random Oscillatory Flow

Experiments were conducted to study random hydrodynamic loading of smooth, rigidly mounted circular cylinders exposed to random oscillatory flow conditions. The experiments were conducted in a water tunnel for statistical Keulegan-Carpenter numbers ranging from KCr = 6.8 to 11.6 and statistical Reynold’s numbers from Rer = 8211 to 20169 under broad and narrow-band flow conditions. A two-input/single-output frequency domain model for the in-line force is used to directly identify frequency-dependent inertia and drag coefficients. This model was also used to show the relative strength of the inertia and drag components in the frequency domain for different random flow conditions parameterized by KCr, Rer and the velocity spectral width, q. This analysis illustrates the effect of statistical flow parameters (KCr, Rer and q) on the nonlinear behavior of the in-line forces. Estimates of the in-line force power spectral density under random flow conditions are determined using the two-input/single-output model and compared to the method for estimating wave forces on a cylindrical structure by Borgman (1967, 1972).

Running Characteristics of a Wave Power Turbine.

To clarify the running characteristics in oscillating flow of a cross-flow turbine with two axisymmetric nozzles, experiments are carried out using a turbine test equipment in which wavelike up-and-down oscillating flow conditions are simulated. On the other hand, the dynamic characteristics of this turbine are calculated numerically on the basis of experimental data obtained from experiments in steady one-way flow conditions. The experimental results are compared with the numerical results and good agreement between them is demonstrated. Furthermore, the effects of load control and period of oscillating flow on the running characteristics are investigated.

Platelet Aggregation on Extracellular Matrix: Effect of a Recombinant GPIb-Binding Fragment of von Willebrand Factor

Platelets in whole blood incubated on extracellular matrix (ECM) produced by bovine corneal endothelial cells under oscillatory flow conditions demonstrate extensive aggregate formation. Since both platelet-subendothelium and platelet-platelet interactions are mediated by von Willebrand factor (vWF), we used this system to examine the effect of a recombinant GPIb-binding fragment of vWF (designated RG12986), comprising residues 445-733 of the native vWF subunit, on platelet reactivity with ECM. The seven cysteines present in the RG12986 fragment were reduced and alkylated in order to achieve a monomeric conformation. The recombinant vWF fragment binds to unstimulated platelets in the absence of exogenous modulators. When added to platelet-rich plasma, it inhibits ristocetin-induced platelet agglutination. Binding of 51Cr-labeled platelets in reconstituted whole blood to ECM was inhibited by RG12986 in a dose dependent and saturable manner, with IC50 of 4 microM and maximal inhibition (about 70%) at 6 microM. Scanning electron microscope (SEM) analysis showed that addition of RG12986 to whole blood significantly inhibited platelet aggregation on ECM. The extent of inhibition observed with RG12986 at a final concentration of 4 microM was similar to that obtained with the cell adhesion peptide RGDS at the concentration of 0.1 mM. The ability of the RG12986 fragment to inhibit platelet aggregation on ECM is in agreement with the concept that blockade of vWF-GPIb interaction may inhibit further events leading to activation of the glycoprotein IIb/IIIa (GPIIb/IIIa) complex and subsequent thrombus formation.

Laminar/turbulent oscillating flow in circular pipes

A two-dimensional oscillating flow analysis was conducted simulating the gas flow inside Stirling engine heat exchangers. Both laminar and turbulent oscillating pipe flow were investigated numerically for Re max = 1,920 (Va = 80), 10,800 (Va = 272), 19,300 (Va = 272), and 60,800 (Va = 126). The results are here compared with experimental results of previous investigators. Predictions of the flow regime on present oscillating flow conditions are also checked by comparing velocity amplitudes and phase difference with those from laminar theory and quasi-steady profile. A high Reynolds number k- ϵ turbulence model was used for turbulent oscillating pipe flow. Finally, the performance of the k- ϵ model was evaluated to explore the applicability of quasi-steady turbulent models to unsteady oscillating flow analysis.

Continuous and oscillatory flow properties of concentrated coal/water suspensions

AbstractA Theological characterization of coal/water suspensions has been carried out under continuous and oscillatory flow conditions. Shear stress ‐ shear rate data were correlated with the Shangraw‐Grim‐Mattocks (SGM) equation. The analysis of the SGM parameters indicated that a limiting concentration ϕ0 exists above which the suspensions exhibit plastic behavior and suggested that a strong particle aggregation still occurs at high rates of shear. Oscillatory flow tests revealed marked non‐linear viscoelastic properties and analogies were found between the continuous and oscillatory flow behaviors of the coal/water suspensions, particularly under limiting flow conditions.

Effect of Hematocrit on Wall Shear Rate in Oscillatory Flow: Do the Elastic Properties of Blood Play a Role?

Porcine blood was used to examine the relationship between hematocrit levels and wall shear rate patterns in straight and curved artery models under fixed oscillatory flow conditions characteristic of larger arteries. It is demonstrated that porcine blood models both the viscous and elastic components of the 2 Hz complex viscosity of human blood quite accurately over a broad range of shear rates (1-1000 s-1) and hematocrits (20%-80%). For a fixed oscillatory flow waveform (Poiseuille peak shear rate = 168 s-1; mean shear rate 84 s-1), increases in hematocrit produced a decrease in the peak wall shear rate in both the straight and curved artery models and a corresponding decrease in wall shear rate reversal on the inside wall of the curved artery model. The same trends were also observed for oscillatory flows of aqueous glycerin solutions of increasing viscosity in the range of viscosity of the blood samples tested. Aqueous glycerin solutions produced wall shear rate waveforms of the same magnitude and shape as the porcine blood. This indicates that variations in the shear rate, and therefore the shear stress, were caused primarily by changes in the viscous and not the elastic properties of blood. The results suggest that simple Newtonian fluids may be sufficient for in vitro determination of the first order effects to be expected of human blood flow in large vessels having complex geometries and shear rates in or above the range of the present study.

Examination of the roles of glycoprotein Ib and glycoprotein IIb/IIIa in platelet deposition on an artificial surface using clinical antiplatelet agents and monoclonal antibody blockade

The mechanism of platelet thrombus growth on an artificial surface is incompletely understood. While glycoprotein (GP)Ib and GPIIb/IIIa are required for normal attachment and thrombus formation on subendothelium, their roles in platelet deposition to artificial surfaces remain unclear. Using selected platelet inhibitors (aspirin [ASA], low molecular weight dextran, monoclonal antibodies 10E5 [v GPIIb/IIIa], and 6D1 [GPIb]) we examined the mechanism of platelet deposition to polyethylene (PE) surfaces under steady laminar and oscillatory flow conditions. Polyethylene-100 (PE-100) tubes (0.86 mm internal diameter) were perfused under steady laminar flow with citrated human whole blood reconstituted with 111indium-labeled platelets at 312 seconds-1 shear rate in the presence and absence of platelet inhibitors. The effect of oscillatory flow on platelet deposition was examined in a microwell system using 3/16-inch diameter discs of National Heart, Lung, and Blood Institute primary reference PE as the test surface. ASA and dextran did not significantly (P greater than .05) inhibit platelet deposition in laminar flow (not tested in oscillatory). Antibody 10E5 was a potent inhibitor (laminar less than 1%, P less than .0001, oscillatory less than 1.6%, P less than .01) of platelet deposition in both systems, and in this case, true adhesion (first attached layer) was blocked. Antibody 6D1 unexpectedly inhibited 70% of platelet deposition (P less than .01) in steady laminar flow and 56.5% in oscillatory flow (P less than .01). Scanning electron microscopy demonstrated platelets atop platelets in the controls, rare platelets in the 10E5 group, and a patchy monolayer of platelets in the 6D1 group. Transmission electron microscopy of cross-sections confirmed these observations. We conclude that the adhesion of the first platelet layer to an artificial surface requires GPIIb/IIIa. The data also suggest that GPIb is required for the development of the second layer in vertical platelet thrombus growth.

Examination of the Roles of Glycoprotein lb and Glycoprotein Ilb/IIIa in Platelet Deposition on an Artificial Surface Using Clinical Antiplatelet Agents and Monoclonal Antibody Blockade

The mechanism of platelet thrombus growth on an artificial surface is incompletely understood. While glycoprotein (GP)Ib and GPIIb/IIIa are required for normal attachment and thrombus formation on subendothelium, their roles in platelet deposition to artificial surfaces remain unclear. Using selected platelet inhibitors (aspirin [ASA], low molecular weight dextran, monoclonal antibodies 10E5 [v GPIIb/IIIa], and 6D1 [GPIb]) we examined the mechanism of platelet deposition to polyethylene (PE) surfaces under steady laminar and oscillatory flow conditions. Polyethylene-100 (PE-100) tubes (0.86 mm internal diameter) were perfused under steady laminar flow with citrated human whole blood reconstituted with 111indium-labeled platelets at 312 seconds-1 shear rate in the presence and absence of platelet inhibitors. The effect of oscillatory flow on platelet deposition was examined in a microwell system using 3/16-inch diameter discs of National Heart, Lung, and Blood Institute primary reference PE as the test surface. ASA and dextran did not significantly (P greater than .05) inhibit platelet deposition in laminar flow (not tested in oscillatory). Antibody 10E5 was a potent inhibitor (laminar less than 1%, P less than .0001, oscillatory less than 1.6%, P less than .01) of platelet deposition in both systems, and in this case, true adhesion (first attached layer) was blocked. Antibody 6D1 unexpectedly inhibited 70% of platelet deposition (P less than .01) in steady laminar flow and 56.5% in oscillatory flow (P less than .01). Scanning electron microscopy demonstrated platelets atop platelets in the controls, rare platelets in the 10E5 group, and a patchy monolayer of platelets in the 6D1 group. Transmission electron microscopy of cross-sections confirmed these observations. We conclude that the adhesion of the first platelet layer to an artificial surface requires GPIIb/IIIa. The data also suggest that GPIb is required for the development of the second layer in vertical platelet thrombus growth.

Rheology of hydroxyethyl guar gum derivatives

The rheological properties of aqueous solutions of hydroxyethyl guar gum, a synthetic derivative of guar gum, have been studied under continuous and oscillatory shear flow conditions. Data obtained from both experimental techniques were satisfactorily fitted according to Cross-type models. The effect of polymer concentration, molecular weight and temperature on the rheological behavior of hydroxyethyl guar gum systems have been investigated and discussed in terms of rheological parameters like the zero-shear viscosity η 0 and the characteristic times λ and λ′.

Potential Applications of Pulsed Flow for Minimizing Concentration Polarization in Ultrafiltration

Abstract Various methods have been proposed to control or minimize concentration polarization and membrane fouling. A brief review of these alternatives is presented in this paper. Flow pulsation as a means of improving transmembrane flux has been studied experimentally by a few investigators. A mathematical model is developed to evaluate the performance of a tubular membrane module under oscillatory flow conditions. Besides the effect of osmotic pressure and axial pressure variation, the model considers the convective-diffusive mass transport without decoupling the momentum equation from the solute continuity equation. Model equations are solved by a finite difference method as part of an iterative solution. Model predictions of transmembrane flux with experimental data are found to be in good agreement. By flow pulsing, it is possible to improve the transmembrane flux by more than 68% at pulsing frequency of 60 cycles · min−1. An analysis of extra power requirement for flow oscillation shows that the ga...

Novel rheological model for the gelation kinetics of ionic polysaccharides

AbstractHomogeneous networks of an ionic polysaccharide (namely pectate) in the presence of divalent ions were prepared in situ by proper procedure and the kinetics of the gel formation was studied by means of a coaxial cylinder rheometer in oscillatory flow conditions. The stress response was expanded in a Fourier series and the variation of the components of the fundamental harmonic with time during the gelation process were examined. A model is proposed for the correlation between kinetic parameters such as the concentration of the species active during the gel formation and the rheological parameters that can be experimentally determined, like G′ and G′′. Considerations are developed concerning the mechanism that governs the gelation process under dynamic conditions.

A Chaotic Attractor in a Periodically Forced Two-Phase Flow System

Motivated by the enhancement of heat transfer under oscillating flow conditions in single-phase heated channels and by stability problems in two-phase systems such as those in boiling water reactor...

Rheological properties of polysaccharide solutions and derived printing pastes in continuous and oscillatory flow conditions

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTRheological properties of polysaccharide solutions and derived printing pastes in continuous and oscillatory flow conditionsRomano Lapasin, Sabrina Pricl, Marco Graziosi, and Giuseppe MolteniCite this: Ind. Eng. Chem. Res. 1988, 27, 10, 1802–1806Publication Date (Print):October 1, 1988Publication History Published online1 May 2002Published inissue 1 October 1988https://doi.org/10.1021/ie00082a012RIGHTS & PERMISSIONSArticle Views118Altmetric-Citations11LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (569 KB) Get e-Alerts Get e-Alerts