Eccentric Annulus Research Articles

Numerical Study of Mixed Convection Heat Transfer of a Nanofluid in an Eccentric Annulus

This article deals with a numerical study of mixed convection flow and heat transfer of Al2O3-water nanofluid inside an eccentric horizontal annulus with rotation on the inner cylinder. The inner and outer cylinders are kept at different constant temperatures as Th and T c , respectively. First, the governing dimensional equations in terms of stream function-vorticity formulation in polar coordinate system for eccentric physical domain are transformed in dimensionless form. These equations are then transformed to a rectangular domain in order to get better accuracy of the solution near the boundaries. The resultant equations are further discretized with a finite volume technique based on a second order upwind scheme and then solved by iteration. The effects of the eccentricity ϵ, Reynolds number Re, the nanoparticles volume fraction parameter φ, the Rayleigh number Ra on the mean Nusselt number Nu, and the streamlines and isotherms are investigated. The results are also discussed in detail. It is found that a very good agreement exists between the present results and those from the open literature.

Simulation of cuttings transport with foam in deviated wellbores using computational fluid dynamics

Foam is non-Newtonian pseudo-plastic fluid, which is used for drilling, well intervention, and stimulation. Predicting the cutting transport efficiency of foam in the wellbore annulus is very important to optimize the drilling process. In this paper, the cuttings transport process with foam is numerically simulated using an Eulerian two-phase model in inclined wellbores. A computational fluid dynamics (CFD) software package called FLUENT was used for this goal. The effect of foam quality, foam velocity, drill pipe rotation, and wellbore inclination on cuttings transport phenomena in both concentric and eccentric annulus was investigated. The simulation results are compared to the experimental data from previous studies, with a relative error less than 8 %. This study shows the reliability of the CFD simulation in replicating the actual physical process.

Numerical Study of Three-Dimensional Mixed Convection in an Eccentric Annulus

Mixed convection of air with a Prandtl number of 0.7 in eccentric horizontal annuli is numerically investigated. The inner cylinder is at a higher temperature, while the inner and outer cylinders can be rotated either clockwise or counterclockwise with a constant angular velocity. The effects of various parameters, such as the eccentricity of the annulus and the Rayleigh number, are studied using a three-dimensional model. The Navier–Stokes equations, along with the energy equation, are solved in an orthogonal structured grid of a bipolar coordinate system employing a finite volume method based on the SIMPLE algorithm. Here, both steady and unsteady results are presented in two separate codes. Three-dimensional considerations lead to a complicated flow pattern, whereas Taylor vortices have a major role on heat and flow characteristics. It is shown that the axial component of velocity in some configurations has a considerable value, therefore, flow pattern and heat transfer characteristics change in comparison with a two-dimensional approach. Eccentricity leads to a different flow pattern in the upper and lower parts of the annulus. Mean and local heat transfer results are obtained. The physics of the flow underlying the observed heat transfer behavior is revealed by the velocity vectors and the isotherm plots of the numerical solutions. Results show that flow and heat transfer are strongly influenced by the eccentricity of the inner cylinder and Raleigh number, and that three-dimensionality consideration is inevitable.

The Equation of the Limit Replacement Width of Non-Newton Fluid in Eccentric Annulus

The equation of the limit replacement width of the one-dimension two-phase flow of Bingham fluid replacing Power law fluid in eccentric annulus was established, the numerical solution method of the equation mentioned above was given and taking the 3 wells, such as the He 104-27 well etc for examples, the limit replacement widths of cement slurry displacing mud, whose rheological properties can be described as Bingham and Power law modles respectively, were calculated, by using the equation and the numerical solution method mentioned above, and compared with those of cement slurry displacing mud, whose rheological properties are all described as Binghanm modle.

Study on Flow Characteristic of Non-Newtonian fluid in Eccentric Annulus

This study studied the flow characteristic of non-newtonian in eccentric annulus of highly-deviated well. On the basis of dimensionless analysis of motion equations and continuity equation, Hele-Shaw model suitable for fluid flow in the annulus was derived. Combined with H-B rheological model, velocity and stream distribution model were founded and calculated by numerical method. Furthermore, two-dimensional flow characteristic in eccentric annulus was got and the influence of different factors (such as yield stress, pressure gradient or eccentricity) on velocity distribution in condition of laminar flow was analyzed. Width of flow core in the annular is proportional to yield stress and inversely proportional to pressure gradient. In eccentric annulus, eccentricity influences the stream distribution remarkably: with the increment of eccentricity, the contour lines of stream function gradually centralize in the widest annular gap, however distribute the most loosely in the narrowest annular gap. Axial velocity is the largest in the widest gap. The larger eccentricity is, the larger contrast of axial velocity between in the widest gap and in the narrowest gap is. There is the largest azimuthal velocity in an annular gap of a certain azimuthal angle, however which equals to zero in the widest and narrowest annular gap separately. The larger eccentricity is, the more homogeneous azimuthal velocity is. The velocity contrast in the entire annulus can be smoothed by increasing pressure gradient, power law index or decreasing yield stress.

Morphological Study of Two Closely Related Marine Planktonic Diatoms:Bellerochea malleusandHelicotheca tamesis

In this paper, we show morphological features of two marine planktonic diatoms that are phylogenetically related, as suggested by molecular studies: Bellerochea malleus and Helicotheca tamesis. In order to study Bellerochea malleus specimens of the species were isolated from samples collected from marginal coral reefs located in the southern portion of Puerto Rico and cultured in the laboratory. Specimens of the species Helicotheca tamesis were isolated from net phytoplankton samples collected from the tropical Mexican Pacific and also cultured in the laboratory. The two species were examined by means of light and scanning electron microscopy. The morphology of Bellerochea malleus agrees well with previous reports: cells arranged in relatively long chains, united by the horn-shaped apical elevations, elliptical valves (not triangular) with depressed valve face bearing an eccentric annulus, from which numerous costae radiate, formation of costate ocelli, and one eccentric or marginal protruded and tubular rimoportula per valve. Helicotheca tamesis also shows the typical morphological features of this species: cells are solitary or form long and distinctly twisted chains, with no apparent apertures between sibling valves, valves are linear to elliptical, weakly silicified and flat. Furthermore, we found one conspicuous and protruded rimoportula per valve, located eccentrically or marginally (not central as previously described), consisting of an elliptic tubular structure. The cingulum is composed of numerous half-bands and segmented copulae. This study compares the morphology of these two species, with a special emphasis on the structure of the rimoportulae.Bellerochea / Diatoms / Helicotheca / Morphology / Phytoplankton / Rimoportulae

Energy conservative dissipative particle dynamics simulation of natural convection in eccentric annulus

In this paper, an efficient numerical approach, the dissipative particle dynamics with energy conservation (eDPD), is used to simulate natural convection in eccentric annulus over a wide range of Rayleigh numbers. A numerical strategy is presented for dealing with irregular geometries in DPD system. The eDPD results are compared to the finite volume solutions and the experimental data, and it is found that the temperature and flow fields for the natural convection in complex geometries are correctly predicted using eDPD. The effect of eccentricity on heat transfer at various locations is examined at Ra=104, and the streamlines and temperature distributions as well as Nusselt number are obtained. The results show that the average Nusselt number increases when the inner cylinder moves downward regardless of the radial position.

PARTICULATE SUSPENSION FLOW INDUCED BY SINUSOIDAL PERISTALTIC WAVES THROUGH ECCENTRIC CYLINDERS: THREAD ANNULAR

This paper describes a new model for obtaining analytical solutions of peristaltic flow through eccentric annuli. A mathematical model of peristaltic pumping of a fluid mixture (as blood model) in a circular eccentric cylinders is presented and it is motivated due to the fact that thread injection is a promising method for placing medical implants within the human body with minimum surgical trauma. For the eccentric annuli, the inner cylinder is rigid and moving with a constant velocity V, and the outer one is hollow flexible cylinder that has a sinusoidal wave traveling down its wall. The coupled differential equations for both the fluid and the particle phases have been solved by using two methods and the expressions for the velocity distribution of fluid and particle phase, flow rate, pressure drop, friction forces at the inner and outer cylinders have been derived. The results obtained are discussed in brief. The significance of the particle concentration and the eccentricity parameter as well as the nature of the basic flow has been well explained.

Flow Resistance Experiments in HTS Cable Form

High-temperature superconducting cables have application in the Navy for power cables as well as degaussing cables. The current interest is in using a gaseous cryogen circulated by means of a cryogenic fan as the cooling media for the HTS conductor. Flow through this style of cable is through an eccentrically situated corrugated annular region. Correlations do not currently exist for this arrangement since it is not a simple configuration. Experiments were carried out to measure pressure drop with varied flow rate of air and nitrogen through 10-m sections of tubing. A variety of tubing configurations was used including smooth tube, eccentric smooth annulus, and eccentric corrugated annulus with HTS wire bundle forming the inner filling material. A method was developed for comparing the relative flow resistance of tubing configuration, which included determining an effective hydraulic diameter based on observed data set fit to the Darcy-Weisbach equation and the Colebrook equation. The effective hydraulic diameter allowed for easy comparison of flow impedance for all configurations regardless of specific flow conditions.

Exact solution and CFD simulation of magnetorheological fluid purely tangential flow within an eccentric annulus

In this paper, hydrodynamic characteristics of Magnetorheological (MR) fluid flow within an eccentric annulus have been investigated analytically and numerically. The MR fluid obeys the Herschel–Bulkley constitutive relation with a magnetic field dependent on yield stress. While the eccentric ratio or the gap between two cylinders is very small, local flow can be assumed between two parallel plates. With this simplification of motion equation, the effects of the magnetic field, eccentricity ratio and power-law exponent (n=0.25, 0.5 and 1) on the tangential velocity, torque and pressure gradient are analyzed analytically. Then, the results were compared with two-dimensional (2D) simulations for a system of two eccentric cylinders filled with a MR fluid. The Computational Fluid Dynamics (CFD) simulation results show good agreement with analytical solution. A wider range of the various parameters has been studied by the 2-D simulations. The influences of MR effects on flow field are significant and not negligible. The viscosity increases by increasing the magnetic field and eccentricity ratio, consequently providing an enhancement in the yield stresses and total torque required to rotate the inner cylinder.

An Experimental and Numerical Study of Two-phase Flow in Horizontal Eccentric Annuli

The aerated fluids have a potential to increase rate of penetration, minimize formation damage, minimize lost circulation, reduce drill pipe sticking, and, therefore, assist in improving the productivity. The technology of drilling using aerated fluids in the area of offshore drilling is very common. The use of compressible drilling fluids in offshore technology has found applications in old depleted reservoirs and in the new fields with special drilling problems. However, the drilling performed with gas-liquid mixture, calculating the pressure losses and the performance of cutting transportation is more difficult than single-phase fluid due to the characteristics of multi-phase fluid flow. In case configured drilling is directional or horizontal, these types of calculations are becoming more difficult depending on the slope of the wells. Both hydraulic behavior and mechanism of cutting transportation of the drilling fluids formed by gas-liquid mixture are not fully understood yet, especially there is a large uncertainty in selection of most appropriate flow regarding two phases. In this study, gas-liquid flow inside horizontal eccentric annulus is simulated using an Eulerian-Eulerian computational fluid dynamics model for two-phase flow patterns in an annulus, i.e., dispersed bubble, dispersed annular, plug, slug, wavy annular. A flow loop was constructed in order to conduct experiments using air-water mixtures for various in-situ air and water flow velocities. A digital high speed camera is used for recording each test dynamically for identification of the liquid holdup and flow patterns.

Magnetothermodynamic Peristaltic Flow of Bingham Non-Newtonian Fluid in Eccentric Annuli with Slip Velocity and Temperature Jump Conditions

AbstractIn this paper, we studied the peristaltic flow and heat transfer of an incompressible, electrically conducting Bingham Non-Newtonian fluid in an eccentric uniform annulus in the presence of external uniform magnetic field with slip velocity and temperature jump at the wall conditions. The viscous and Joule dissipations are taken into account. The inner tube is rigid and moving with a constant axial velocity, while the outer tube has a sinusoidal wave traveling down its wall. Under zero Reynolds number condition with the long wavelength approximation, the axial velocity and the stream function are obtained analytically. A numerical solution for the governing partial differential equation of energy is performed in order to analyze the temperature distribution. The effects of all parameters of the problem are numerically discussed and graphically explained.

Exact solution of the heat conduction equation in eccentric spherical annuli

In this study, an analytical solution to the heat conduction equation in an annulus between eccentric spheres with isothermal boundaries and with heat generation is obtained using Green's function method. Deriving Green's function in bispherical coordinates for eccentric spherical annuli, an exact solution of heat equation for eccentric spheres with constant surface temperatures is expressed in terms of Green's function and source distribution. The solution is general and can easily be applicable to any space dependent heat source. Results are presented as temperature distributions and local Nusselt numbers for sources having practical and theoretical importance: uniform source, impulse source, shell source. Analytical results are compared with the results of the Computational Fluids Dynamics (CFD) solver Fluent and perfect agreement is observed.

Natural convection flow and heat transfer in an eccentric annulus filled by Copper nanofluid

A numerical study of natural convection flow and heat transfer of Copper (Cu)–water nanofluid inside an eccentric horizontal annulus is presented. The inner and outer cylinders are kept at constant temperatures as Th and Tc, respectively. First the governing equations in terms of stream function-vorticity formulation in polar coordinate system for eccentric physical domain are derived and then transformed to a rectangular domain in order to get better accuracy of the solution near the boundaries. The resultant governing equations are discretized with a finite volume technique based on second order upwind scheme and then solved by iteration. The effects of the eccentricity ε, radii ratio (RR), the nanoparticles volume fraction parameter ϕ, the Rayleigh number Ra and the Prandtl number Pr on the mean Nusselt number Nu, streamlines and isotherms are investigated. The results are also discussed in detail. It is found that a very good agreement exist between the present results and those from the open literature.

Natural convection of power-law fluid between two-square eccentric duct annuli

The present paper numerically studies two-dimensional steady-state natural convection of non-Newtonian power-law fluid between two eccentric horizontal square ducts with constant temperature. The inner and outer ducts are assumed to be held at hot and cold temperatures, respectively. The conservation equations of mass, momentum and energy are dicretized using finite volume technique based on second order upwind and finally SIMPLE algorithm is utilized to solve the resultant system of equations. The effects of power-law index (0.6⩽n⩽1.4), Rayleigh number (103⩽Ra⩽106), aspect ratio (0.25⩽AR⩽0.75), eccentricity (-0.2⩽e⩽+0.2) and Prandtl number (10⩽Pr⩽103) on heat and fluid flows are investigated. Also the Nusselt number for various values of governing parameters is obtained and discussed. The results indicate that with increasing the power-law index n from 0.6 to 1.4 the mean Nusselt number that indicates heat transfer rate decreases. It is shown that there is a minimum situation for the Nusselt number versus the eccentricity dependent on the other parameters. Also it is found that varying the Prandtl number almost does not affect heat transfer characteristics except for some cases.

The effect of geometric parameters on mixed convection in an inclined eccentric annulus

Laminar mixed convection in an inclined eccentric straight annulus is studied numerically in this article. The coupled Navier–Stokes and energy equations are solved using finite difference method. The projection algorithm is employed for solution and to cope with the problem geometry, the cylindrical bipolar coordinate is used. To model natural convection, Boussinesq approximation is used for the body force term in the equations of motion. Developing hydrodynamic and thermal conditions are assumed for simulation. The inner wall is subjected to a fixed heat flux and the outer one is insulated. The effect of different parameters such as eccentricity, radius ratio and inclination on flow field and thermal characteristics is studied. It has been found that the Nusselt number has a local maximum value about 55° from vertical by laying down the annuli.

The Effects of Density Difference on Displacement Interface in Eccentric Annulus During Horizontal Well Cementing

It is known that the interface of slurry displacement during cementing reflects the extent of two-phase fluid in- termixing. A longer interface means that more displacing fluid becomes contaminated. When the interface becomes too long, it can occur that the trailing edge of the interface fails to reach a designed cementing segment at the end of opera- tion, which reduces displacement effectiveness and adversely affects cementing quality and well integrity. In this paper, a 3D numerical model was developed and employed to analyze the effects of slurry density difference on the displacement interface in the eccentric annulus of horizontal wells. The simulation results showed that smaller density difference can create shorter interface and lead to better displacement efficiency when casing is centrally placed in a horizontal borehole. When the casing is eccentric, slurry tends to advance in the annular upper side under smaller density difference; other- wise, the opposite result will be obtained under greater density difference. Therefore, there exists an optimal density dif- ference under which a minimum interface length can be achieved for a given casing eccentricity. In addition, the optimal density difference increases as the shear thinning index, consistency index and yield point of a cement slurry increase. In order to minimize the intermixing extent of two-phase fluids and slurry fingering effects in cementing operations, it is necessary to take into consideration the comprehensive influence of casing eccentricity, slurry density, and rheological parameters to design slurry parameters properly, which will achieve higher displacement efficiency and better cementing quality.

Lattice Boltzmann simulation of melting phenomenon with natural convection from an eccentric annulus

In the present study, a double-population thermal lattice Boltzmann was applied to solve phase change problem with natural convection in an eccentric annulus. The simulation of melting process from a concentrically and eccentrically placed inner hot cylinder inside an outer cold cylinder with Prandtl number of 6.2, Stefan number of 1 and Rayleigh number of 105 was carried out quantitatively. It was found that the position of the inner cylinder inside the outer cylinder significantly influence the flow patterns including the size and shape of two formed vortexes. It is also observed that the maximum of liquid fractions occurs where the inner cylinder is mounted at the bottom of outer cylinder.

Peristaltic Transport through Eccentric Cylinders: Mathematical Model

This paper discusses the effect of peristaltic transport on the fluid flow in the gap between two eccentric tubes (eccentric-annulus flows). The inner tube is uniform, rigid, while the outer tube has a sinusoidal wave traveling down its wall. The flow analysis has been developed for low Reynolds number and long wave length approximation. The velocity and the pressure gradient have been obtained in terms of the dimensionless flow rateQ¯, timet, azimuthal coordinate θ and eccentricity parameter ϵ (the parameter that controls of the eccentricity of the inner tube position). The results show that there is a significant deference between eccentric and concentric annulus flows.

Peristaltic Transport through Eccentric Cylinders: Mathematical Model

This paper discusses the effect of peristaltic transport on the fluid flow in the gap between two eccentric tubes eccentric-annulus flows. The inner tube is uniform, rigid, while the outer tube has a sinusoidal wave traveling down its wall. The flow analysis has been developed for low Reynolds number and long wave length approximation. The velocity and the pressure gradient have been obtained in terms of the dimensionless flow rate $\overline{Q}$, time t, azimuthal coordinate θ and eccentricity parameter e the parameter that controls of the eccentricity of the inner tube position. The results show that there is a significant deference between eccentric and concentric annulus flows.