Flow In Annular Duct Research Articles

Experimental investigation of tubing collar's influence on hydrodynamic behavior of annular duct flow

Tubing collars’ influence on hydrodynamic behavior of annular duct flow has been investigated using Particle Image Velocity (PIV) technology. PIV has become an efficient method for complex transient flows visualization. A water flow loop with two replaceable variable cross-sections (VCS), 75–90 mm and 90–110 mm, in a 129 mm inner diameter (ID) pipe was used. The whole field of the variable cross-section annulus (VCSA) was visualized, including forward-facing step (FFS), narrow annulus (NA), and backward-facing step (BFS) flow. The VCSA ratio and Reynolds (Re) number influence on streamline distribution, velocity distribution, and turbulence intensity were discussed. Results showed that the recirculation is easier to form in BFS than FFS flow under the same condition. The VCSA ratio affects the formation of recirculation zones and the location of the reattachment point. Reynolds number mainly affects BFS flow by influencing the main velocity component - axial velocity. The turbulence intensity is relatively high in BFS than FFS flow and is larger at y/h>1.0 than y/h<1.0. Furthermore, the streamwise coherent structures reveal that the first two modes are predominant and represent the main characteristics of the flow by proper orthogonal decomposition (POD) method.

Evaporative heat transfer of R410A flow in an annular duct under oscillatory wall heat flux

In this investigation, the evaporative heat transfer characteristics of R410A flow in a slender annular duct under an oscillatory heat flux are studied experimentally with emphasis on the influences of mean mass flux, heat flux, and oscillating amplitude and period of heat flux. The applied heat flux is varied in ranges of q = 5,000 to 15,000 W m−2 and the mean mass fluxes of 300 and 400 kg.(m−2s−1) are considered, respectively. The results reveal that increasing either oscillating amplitude or period of heat flux enhances the oscillation of surface temperature and evaporation heat transfer coefficient (HTC). The prevailing influence of heat flux oscillations on the evaporation heat transfer causes notable variations in the vapour quality and liquid film thickness. At a high level of vapour quality, the thickness of refrigerant liquid film on the hot surface is decreased, leading to the increase of the evaporation HTC. Furthermore, the oscillation in the wall temperature is slightly stronger as the period of heat flux oscillation boosts in the range of 120 s to 600 s. Based on the present measured data, some correlations are provided for the evaporation HTC of R410A as the function of the heat flux and vapour quality.

Experimental investigation of gas-liquid separation for two-phase flow within annular duct of an ESP skid

Although common in several sectors of the industry, undeveloped two-phase flow in annular ducts has yet to receive attention from researchers. This work investigates experimentally the gas-liquid separation phenomenon in the two-phase flows inside annular ducts. The experimental setup enables flow visualization and analysis through high-speed cameras. This experimental setup's design is based on a non-dimensional and similarity analysis with a real device (Electric Submersible Pump Skid or ESP Skid) in operation at an offshore oilfield in Brazil. The experiments were performed in 5°, 15°, 30° 45° and 60° slopes, horizontally. Flow patterns in the annulus were observed and analyzed. Also, vortices were observed in the intake region. The gas-liquid separation tests enabled the association of the measured separation efficiency with mixture velocities and, consequently, with dimensionless parameters (Froude number) and no-slip void fraction. As observed in the literature, the separation decreases as the mixture velocity increases. The results were qualitatively correlated with literature models, but with high quantitative discrepancies, mainly due to the disregard for radial slip in the models. Also, changes in the trend of separation efficiency were observed and these were caused by flow pattern changes.

Influence of Liquid Viscosity and Geometry on Vertical Gas/Liquid Two-Phase Annular-Duct Flow

Summary Two-phase flow in large annular ducts is very common in industrial applications. Nevertheless, many two-phase-flow phenomena in such a geometry have not been fully understood. This article addresses an investigation on the effects of duct geometry and liquid viscosity on vertical upward annular-duct two-phase flows. Compressed air and tap water or mineral oil were the working fluids. Three oil viscosity ranges were tested, from 30 to 400 mPa·s. A 10.0-m-long inclinable experimental setup was designed and built for the experiments conducted in two equivalent geometries. The first is made of a 95-mm-inner-diameter circular pipe (called the reference pipe), and the second is a concentric annular duct with 95-mm hydraulic diameter, the same diameter as the reference pipe. The radial geometries were similar to those observed in oil wells. Flow patterns, total pressure drop, and in-situ volumetric fractions were obtained. According to the results, the standard hydraulic diameter might not be appropriate for the modeling of vertical gas/liquid flow in large annular ducts.

Analysis of Turbulence Characteristics in Two Large Concentric Annular Ducts Through Particle Image Velocimetry

An experimental study is presented on water single-phase flow in two 10.5 m-long annular ducts, with external pipe's internal diameter (De) of 155 mm and two concentric internal pipes of external diameters (Di) of 60 mm and 125 mm, i.e., radius ratio (α = Ri/e) of 0.39 and 0.80, respectively, with the aim of improving the understanding of flows in annular ducts. Particle image velocimetry (PIV) was applied to obtain instantaneous and averaged velocity measurements of the flow field. A charge-coupled device camera (2448 pixel × 2050 pixel, 5 Mpixel, 12-bit ) recorded pairs of images of the seeding particles and a double-pulsed PIV laser (Nd:YAG, frequency doubled to 532 nm), with a measured pulse intensity of 70 to 75 mJ/pulse, provided the illumination. Laminar flows were analyzed for validation purposes, experimental data on turbulent flows were compared with the classical law of the wall of the turbulent boundary-layer model, and the shear stresses derived from PIV data were compared with those calculated from the measured pressure drop. The effects of the Reynolds number and geometry on turbulent velocity profiles and Reynolds stresses are presented. The results suggest that the law of the wall for annular-duct flow is a function of radius ratio. The new experimental results are of great value for the development of computational fluid dynamics models and more refined pressure-drop prediction tools in annular-duct flow.

Phase inversion phenomena in vertical three-phase flow: Experimental study on the influence of fluids viscosity, duct geometry and gas flow rate

Improper sizing of pipelines and production tubings in the petroleum industry is often caused by lack of understanding of three-phase flow, which is characterized by gas flowing together with an immiscible water-oil mixture. There is the presence of a continuous liquid phase and a liquid dispersed phase, as observed in liquid-liquid flows, i.e., one can observe either a dispersion or emulsion of oil in water (o/w) or dispersion or emulsion of water in oil (w/o). The transition from o/w to w/o, or the other way around, is defined as phase-inversion. This phenomenon is characterized by a sharp increase in the pressure gradient, leading to significant pressure loss in the oil production system. The goal is to investigate the effects of oil viscosity, channel geometry (circular pipe or annular duct) and superficial gas velocity on the phenomenon of phase inversion in vertical liquid-liquid-gas flows, using oil with three different viscosities (ranging from 70 mPa s to 280 mPa s), tap water and compressed air as working fluids. The experiments were carried out in three different geometries: (i) glass pipe of 50 mm i.d., (ii) glass pipe of 95 mm i.d. and (iii) concentric annular duct with 95 mm of hydraulic diameter (glass outer pipe and PVC internal pipe). The experiments were performed under equivalent Reynolds number to evaluate the geometry effect. New data as total pressure gradient and volumetric fractions were obtained for all geometries. The results suggest that the extrapolation of results obtained in circular pipes with low viscosity oil and low gas flow rates to annular-duct flow with viscous oils and high gas flow rates can lead to significant errors.

Numerical investigation of fully developed laminar flow in irregular annular ducts: Triangular–circular combinations

The aim of this study is to reduce the required pumping energy by obtaining accurately the friction factor – Reynolds number product (fRe) of the steady fully developed laminar flow in annular ducts. The study is focused on the annular region between equilateral triangular and circular ducts under all possible combinations. For this purpose, the governing equations are solved using high order finite element method. For regular annuli, it is found that higher values of area ratio lead to monotonic increase in (fRe) value, with (fRe)max=(24, 42.67,96) at the respective values of (Dh)=(0.5,0.75,1) regardless of the particular geometry. For irregular annuli, higher values of area ratio lead to an increase followed by a decrease in (fRe) value, with (fRe)max=(79.631,35.392,19.921) at the respective values of (Dh)=(0.5, 0.75, 1) for the (CT) case, and correspondingly (fRe)max=(91.02,40.45,22.85) for the (TC) case. On the other hand, it is found that (fRe) value inversely proportional with the hydraulic diameter (Dh). For all cases considered in this study, the largest (fRe) at the representative values (AR)=30% is found for the (CC) case with (fRe)max=95.43 whereas the smallest (fRe) is found for the (CT) case with (fRe)min=17.544. More importantly, irregular annuli outperformed the regular annuli and thus are recommended to replace the classical regular annuli currently used in double duct heat exchangers. This in turn will significantly decrease the pumping energy required in such applications in industry.

Convective heat transfer of high temperature molten salt in a vertical annular duct with cooled wall

Convective heat transfer performances of high temperature molten salt in a vertical annular duct with cooled wall were experimentally investigated within the range of Reynolds number 3000–16,000, Prandtl number 4.8–7.6, and fluid temperature 300–400 °C, respectively. The results showed that Nusselt number of molten salt flow in annular duct was remarkably higher than that of circular tube, and it increased with Reynolds number and Prandtl number. Because of variable thermal properties and annular configuration, the heat transfer correlation for fully developed turbulent flow was proposed based on Wiegand correlation and Sieder–Tate correlation, while the heat transfer correlation for transition flow was established by Gnielinski equation and Wiegand equation. Based on the experimental data, the modified heat transfer correlations for molten salt flow in annular duct were developed by least-squares method, and the modified correlations for transition and turbulent flow had good agreement with experimental data.

Heat transfer characteristics of laminar annular duct flow with viscous dissipation

Laminar forced-convection heat transfer in a concentric annular pipe for a Newtonian fluid with constant properties was analysed by taking the viscous dissipation term into account at constant equal and non-equal heat flux boundary conditions. It can be said that viscous dissipation changes the temperature distributions and plays a very important role in heat transfer characteristics of a concentric annular pipe. The flow in this study was considered to be both thermally and hydrodynamically developed. Temperature distributions and Nusselt numbers were obtained for flows having different aspect ratios and Brinkman numbers. Depending on the boundary conditions, there is considerable effect of the viscous dissipation term on the thermal characteristics of the concentric annular flow. Viscous dissipation has higher effect on the heat transfer characteristic for the case where there is constant and equal heat flow from both walls.

DEVELOPMENT OF AN LES METHODOLOGY FOR COMPLEX GEOMETRIES

The present work presents the development of a Large Eddy Simulation (LES) methodology viable for complex geometries and suitable for the simulation of rod-bundles. The use of LES and Direct Numerical Simulation (DNS) allows for a deeper analysis of the flow field and the use of stochastical tools in order to obtain additional insight into rod-bundle hydrodynamics. Moreover, traditional steady-state CFD simulations fail to accurately predict distributions of velocity and temperature in rodbundles when the pitch (P) to diameter (D) ratio P/D is smaller than 1.1 for triangular lattices of cylindrical pins. This deficiency is considered to be due to the failure to predict large-scale coherent structures in the region of the gap. The main features of the code include multi-block capability and the use of the fractional step algorithm. As a Sub-Grid-Scale (SGS) model, a Dynamic Smagorinsky model has been used. The code has been tested on plane channel flow and the flow in annular ducts. The results are in excellent agreement with experiments and previous calculations.

Inverse Convection Problem for Determining Wall Heat Flux in Annular Duct Flow

An inverse problem for unsteady forced convection in an annular duct is presented. The simulated temperature data taken at the outer wall are used to estimate the time-dependent axially varying surface heat flux distribution at the inner wall of the annular passage. No prior information on the functional form of the unknown wall heat flux is needed in the inverse method. The effects of the functional form of the wall heat flux, the number of the measurement points, and the measurement errors on the accuracy of the estimation are investigated. It is shown that the reconstruction of the timewise and spatial variations of the wall heat flux is satisfactory even if the estimated function is not smooth. [S0022-1481(00)01003-3]

95/06406 Effect of eccentricity and thermal boundary conditions on laminar fully developed flow in annular ducts

95/06406 Effect of eccentricity and thermal boundary conditions on laminar fully developed flow in annular ducts

Effect of eccentricity and thermal boundary conditions on laminar fully developed flow in annular ducts

Numerical solutions for laminar, fully developed, forced convective heat transfer in ecccentric annuli are presented. With an insulated outer surface, two types of thermal boundary conditions have been considered: constant wall temperature (T), and uniform axial heat flux with constant peripheral temperature (H1) on the inner surface of the annulus; these are representative of many practical applications. Isothermal friction factors and Nusselt numbers for concentric annulus are in excellent agreement with previously reported results. Velocity and temperature profiles, and isothermal Re, Nui,T and Nui,1−n values for different eccentric annuli (0 ≤ ϵ∗ ≤ 0.6) with varying aspect ratios (0.25 ≤ r∗ ≤ 0.75) are presented. The eccentricity is found to have a strong influence on the flow and temperature fields. The flow tends to stagnate in the narrow section and has higher peak velocities in the wide section. This flow maldistribution is found to produce greater nonuniformity in the temperature field and a degradation in the average heat transfer. Also, results show that the H1 condition sustains higher heat transfer coefficients relative to the T condition on the inner surface, except for very large eccentricity.

Mixed convection flow in curved annular ducts

Mixed convection flows in concentric curved annular ducts with constant wall temperature boundary condition are studied numerically. The flow is assumed to be fully developed so as to maintain a constant streamwise pressure and temperature gradient. Key parameters for the flow are the radius ratio (ratio of the inner core radius to the outer pipe radius), the Dean number, and the Grashof number. Computations are carried out for flows of various radius ratio with Dean numbers in the range 0–900 and Grashof numbers of 12.5 and 12 500. The secondary flow patterns, the streamwise velocity profiles and the heat transfer coefficients are presented. Effects of the Dean number and the Grashof number on the flow pattern, on the friction ratio (ratio of the friction for a curved annular duct to that for a straight annular duct flow), and on the heat transfer property are discussed based on the computational results. It is found that both the friction ratio and the Nusselt number ratio are strong functions of the radius ratio and the Dean number when Gr = 12.5, while these ratios do not change much with the radius ratio and the Dean number when Gr = 12 500.

The Law of the Wall for Swirling Flow in Annular Ducts

Expressions for the logarithmic portion of the law of the wall are derived for the axial and tangential velocity components of swirling flow in annular ducts. These expressions involve new shear-velocity scales and curvature terms. They are shown to agree well with experiment over a substantial portion of the flow near both walls of an annulus. The resultant velocity data also agree with the law of the wall. The success of the proposed logarithmic expressions implies that the mixing-length model used in deriving them correctly describes flow-velocity behavior. This model indicates that the velocity gradient at any height y in the near-wall region is determined by the wall shear stress, not by the local shear stress. This suggests that the influence of wall shear stress is dominant and that it determines the near-wall wall flow even in flows with curvature and pressure gradient. A physical explanation is suggested for this.

Uniform Asymptotic Approximations for Duct Acoustic Modes in a Thin Boundary-Layer Flow

Analytical approximations for the acoustic modes in a duct carrying a uniform core flow with a thin shear layer at the walls are developed using the method of matched asymptotic expansions. Both two-dimensional and cylindrical duct propagation are considered. Numerical results for eigenvalues calculated using the theory are presented for the two-dimensional problem and compared with results from earlier analyses. It is found that the new approximations yield a significant increase in accuracy. HE problem of sound transmission through a duct carrying a uniform core flow with a thin boundary layer at the walls has been of interest for some time. Such a flow has practical applications in modeling a fully developed real flow profile. Perhaps the strongest motivation for studying the problem, however, is the possibility of obtaining analytical results using asymptotic analyses which can yield physical understanding of shear flow propagation phenomena in more realistic flows which must be treated numerically. Analytical studies based on the assumption of small boundary-layer thickness have been carried out by several researchers during the past decade. Eversman and Beckemeyer1 developed an inner expansion for acoustic pressure in the layer from which they were able to derive an approximate equivalent boundary condition applicable at the outer edge of the layer. Using this condition they showed that the formulation of the shear layer problem reduces to that of the associated uniform flow problem with the well-known particle displacement continuity boundary condition as the layer thickness vanishes. In a later paper, Eversman2 employed the equivalent boundary condition to formulate the eigenvalue problem for acoustic modes in an annular duct flow. Using the known uniform flow solutions in the core flow, an approximate eigenvalue equation is developed. Numerical solution of this single equation yields the acoustic wave numbers and circumvents the task of numerically integrating the differential equation and iterating for the shear flow eigenfunctions. The procedure is equally applicable to rectangular duct geometries, for which it leads to an eigenvalue equation equivalent to one later derived less formally by Tester. 3 A slightly different analysis by Swinbanks,4 also for rectangular ducts, yields similar approximate results. Other studies less directly related to the present work are discussed in Sec. IV.B ofRef. 5. The work reported in the present paper arose in the course of some research on shear flow propagation in which it was desirable to obtain analytical representations of the acoustic

Prediction of turbulent flow in annular ducts with differential transport model of turbulence

In general, flow in an annulus will be strongly asymmetric because of unequal curvatures and, possibly, dissimilar texture of the two boundaries. As a result, the turbulent flow structure in such geometries possesses a number of features which can not satisfactorily be accounted for with a simple model of turbulence. The present paper provides predictions based on a more elaborate model, developed by the author, in which differential transport equations are solved for the turbulent shear stress, the turbulent kinetic energy and the rate of the turbulence energy dissipation, simultaneously with the mean momentum equation. The complete model thus consists of a closed set of four coupled non-linear partial differential equations. Predictions of flow in annuli with both smooth and rough cores with various radius ratios display in all cases very good agreement with experimental results of various authors.

Mass transfer at the solid‐liquid interface for climbing film flow in an annular duct

AbstractA method utilizing a diffusion controlled electrochemical reaction was used to measure average and instantaneous mass transfer coefficients at the solid‐liquid interface in upward gasliquid climbing film flow in a vertical annular duct. These measurements give some indication of the mechanics of flow of the film, the extent of turbulence at the inner wall, and the effect of film thickness and wave motion on the mass transfer process at the inner wall. Predictions of incipient downflow of the film, shear stress at the inner wall, and interfacial shear stress were obtained from these measurements. Fluctuations in the velocity gradient at the inner wall were also studied. Results of this study are in good agreement with previous work and with theoretical predictions based on simplified momentum balance concepts.

Non-Newtonian flow in annular ducts

Non-Newtonian flow in annular ducts

Momentum transfer in climbing film flow in annular duct

AbstractThe characteristics of upward gas–liquid flow in a vertical annular duct were investigated. The flow regime studied was the climbing film regime in which water flowed as a film up the inner core of the annulus while air flowed in the annular space, the outer wall of the annulus remaining dry. Friction losses, air velocity distributions, and film characteristics were studied, the latter by photographing the climbing film through the transparent outer tube. Friction loss and film thickness were correlated with Lockhart–Martinelli parameters, X, Φ, and RL. The presence of the climbing film caused the point of maximum velocity of the air profile to move toward the outer tube, indicating that the film created a rough wall condition. The inner portion of the velocity profile was correlated by Nikuradse's rough tube equation, while the outer portion was correlated by a logarithmic equation which previous workers have reported for single‐phase flow. Kapitza's theory of wave formation was applied to the climbing film and was found to predict reasonable values for the mean film thickness. However, it failed to predict reliable values for the wavelength of surface waves.