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The velocity distribution of flow in an eccentric cylindrical annulus is determined in an attempt to investigate the vertical capillary rise in the channel. The critical values of the radii ratio and the eccentricity at which the capillary rise changes from oscillatory to monotone or vice versa are determined. For a particular aspect ratio, the rise becomes monotonic as the eccentricity increases. The oscillations are also dampened as the annulus becomes thinner. These critical values depend on Galileo and Bond numbers as well as the contact angle. The results reduce to the limiting cases of concentric and fully eccentric annuli. The critical values are also calculated for the special arrangements when the radii ratios are 1 and 0. The latter limit is in perfect agreement with the conditions found in the literature for the classical circular channel. [ABSTRACT FROM AUTHOR]

AbstractThis investigation aims to scrutinize the flow and heat transfer characteristics of a hybrid nanofluid composed of Ag-MgO within an eccentric annular space, where the inner circular wall is held at a constant elevated temperature and the outer circular wall is uniformly cooled. Natural convection in such eccentric annular enclosures, with thermal radiation and the effects of heat generation/absorption taken into consideration, plays a vital role in various engineering applications, including solar collectors, nuclear reactors, thermal storage systems, and heat exchangers. The resolution of the fundamental governing equations was executed employing the Gauss-Seidel approach, with the inclusion of a sub-relaxation process, all within the framework of the finite volume method. The impact of the Rayleigh number, radiation number, volume fraction as well as heat generation/absorption coefficient on thermal transfer, flow, and temperature distributions were investigated. It was observed that for low Rayleigh numbers, radiation influences enhance flow stability and improve the conductive heat transfer mode. Conversely, at high Rayleigh numbers, radiation intensifies convective heat exchange. The growth of the Rayleigh number diminishes the impact of heat generation and reinforces the radiation heat transfer process, while heat absorption exhibits the opposite effect. From Nr = 1 onwards, the average Nusselt number values are no longer influenced by an increase in nanoparticle volumetric fraction, and they are solely linked to the radiation number. [ABSTRACT FROM AUTHOR]

This study examines the flow behavior as well as the cuttings transport of non-Newtonian drilling fluid in the geometry of an eccentric annulus, accounting for what impacts drill pipe rotation might have on fluid velocity, as well as annular eccentricity on axial and tangential distributions of velocity. A two-phase Eulerian–Eulerian model was developed by using computational fluid dynamics to simulate drilling fluid flow and cuttings transport. The kinetic theory of granular flow was used to study the dynamics and interactions of cuttings transport. Non-Newtonian fluid properties were modeled using power law and Bingham plastic formulations. The simulation results demonstrated a marked improvement in efficiency, as much as 45%, in transport by increasing the fluid inlet velocity from 0.54 m/s to 2.76 m/s, reducing the amount of particle accumulation and changing axial and tangential velocity profiles dramatically, particularly at narrow annular gaps. At a 300 rpm rotation, the drill pipe brought on a spiral flow pattern, which penetrated tangential velocities in the narrow gap that had increased transport efficiency to almost 30% more. Shear-thinning behavior characterizes fluid of which the viscosity, at nearly 50% that of the central core low-shear regions, was closer to the wall high-shear regions. Fluid velocity and drill pipe rotation play a crucial role in optimizing cuttings transport. Higher fluid velocities with controlled drill pipe rotation enhance cuttings removal and prevent particle build-up, thereby giving very useful guidance on how to clean the wellbore efficiently in drilling operations.

The present study presents a computational investigation into the thermal mixing along with entropy generation throughout the natural convection flow within an arbitrarily eccentric annulus. Salt water is filled inside the eccentric annulus, in which the outer and inner cylinders have T c and T h constant temperatures. The Boussinesq approximation is used to develop the governing equations for the natural convection flow, which are then solved on a structured quadrilateral mesh using the OpenFOAM software package (FOAM-Extend 4.0). The computational simulations are performed for Rayleigh numbers ( R a = 10 3 – 10 5 ), eccentricity ( ϵ = 0 , 0.4 , 0.8 ), angular positions ( φ = 0 ∘ , 45 ∘ , 90 ∘ ), and Prandtl number ( P r = 10 , salt water). The computational results are visualized in terms of streamlines, isotherms, and entropy generation caused by fluid friction and heat transfer. Additionally, a thorough examination of the variations in the average and local Nusselt numbers, circulation intensity with eccentricities, and angular positions is provided. The optimal state of heat transfer is shown to be influenced by the eccentricity, angular positions, uniform temperature sources, and Boussinesq state. Moreover, the rate of thermal mixing and the production of total entropy increase as R a increases. It is found that, compared to a concentric annulus, an eccentric annulus has a higher rate of thermal mixing and entropy generation. The findings show which configurations and types of eccentric annulus are ideal and could be used in any thermal processing activity where a salt fluid ( P r = 10 ) is involved. [ABSTRACT FROM AUTHOR]

The velocity distribution of flow in an eccentric cylindrical annulus is determined in an attempt to investigate the vertical capillary rise in the channel. The critical values of the radii ratio and the eccentricity at which the capillary rise changes from oscillatory to monotone or vice versa are determined. For a particular aspect ratio, the rise becomes monotonic as the eccentricity increases. The oscillations are also dampened as the annulus becomes thinner. These critical values depend on Galileo and Bond numbers as well as the contact angle. The results reduce to the limiting cases of concentric and fully eccentric annuli. The critical values are also calculated for the special arrangements when the radii ratios are 1 and 0. The latter limit is in perfect agreement with the conditions found in the literature for the classical circular channel.

The capillary-driven flow is an essential portion of liquid behavior under microgravity. Capillary-driven flows in eccentric annuli under microgravity are deeply analyzed in this paper. A second-order differential equation for the climbing height of liquid is derived. It can be solved with the Runge–Kutta method with appropriate initial conditions. The influences of the dynamic angle, the friction force on the annulus wall and the liquid meniscus in the reservoir on liquid behaviors are all considered in this paper. Moreover, effects of eccentricity on flow resistance and flow speed are discussed. This study has been verified by numerical simulation with the volume of fluid method. [ABSTRACT FROM AUTHOR]

The existing calculation models of fluctuating pressure are mainly based on Bingham fluid, power-law fluid and Heba fluid. These rheological models have certain limitations in the scope of application, and it is difficult to accurately describe the actual rheological curves of most drilling fluids. Based on evaluating the calculation model of power-law fluid pressure in eccentric annulus, the constitutive equation of the four-parameter rheological model is extended, and the calculation formula of annular pressure loss is established. In this research, we consider the calculation formula of annular flow under different boundary conditions. The model of fluctuating pressure in the eccentric annulus is obtained using cubic spline interpolation and Gauss integral equation. Compared with the experimental data from concentric annulus and eccentric annulus, the calculated results are in good agreement with the experimental results, compared with the laboratory test data, the error is within the range of ±10%, indicating that the model is sufficiently accurate to meet the requirements of field operations. In addition, the sensitivities of trip rate, drilling fluid flow index and drill string to wellbore size ratio are analyzed. Under the condition of totally eccentric annulus, the gradient of surge pressure decreases to around 50% of that for concentric annulus. The tripping velocity should be strictly limited for operations in the narrow annular space.

Controlled flow boiling conditions enhance the heat transfer rate in various industrial applications such as heat exchangers, fuel rod bundles e t c. In nuclear industry, the presence of mixing vanes, spacers, channel creep deformation e t c. , may lead to the formation of narrow and wide zones around the fuel rods. The asymmetry in the cross-sectional flow area around the fuel rod can be modelled as eccentricity which may cause an irregular coolant flow distribution affecting the heat transfer rate. In the present study, the eccentricity (e) is defined as the ratio of offset (s) to the difference in radii of inner and outer cylinders (R o − R i). The current study introduces a framework that involves calibrating the departure size of vapour bubble (D) in the EMF model framework which enables the accurate prediction of subcooled flow boiling characteristics and CHF power in an annulus (0. 0 ≤ e ≤ 0. 50) at low operating pressure conditions. The developed framework is validated with experimental data and a very good match is noticed. It is observed that eccentricity causes a decrease in coolant peak velocity magnitude by 12.8% in the narrow zone for e = 0. 50. In the subcooled region, the accumulation of vapour bubbles impedes further heat transfer to the liquid coolant, and thus the peak heated wall temperature (≈ 380.88 K) is observed in the narrow zone for e = 0. 50. Eccentricity causes early coolant phase change which in turn results in early occurrence of CHF (q = 522 KWm − 2 ) in the narrow zone of e = 0. 50. A quadratic relationship is also established to predict the CHF power in terms of eccentricity (e) within 5% variation. • Subcooled flow boiling and CHF in an eccentric annulus is investigated. • Modified departure diameter model is used to suit the low pressure conditions. • Eccentricity causes early occurrence of phase change and CHF in the narrow zone. • A CHF correlation is developed based on Re and Ja for an eccentric annulus. [ABSTRACT FROM AUTHOR]

Casing eccentricity is the key factor that determines the evolution of flow rate and flow pattern in the cementing annulus, which restricts the improvement of displacement efficiency. It is an important way to improve displacement efficiency by optimization of slurry column structure, and the related theoretical mechanism has not been reported. Using computational fluid dynamics of Fluent software, 3 D model horizontal annulus with different eccentric casing were developed, and the changes of displacement efficiency in different eccentric casing were discussed. Combined with the poor displacement efficiency with casing eccentricity of 0.4, the best slurry column structure was recommended through analysis of annulus fluid retention volume fraction in different column structure. The results showed that: ① Due to the combined effect of eccentricity and buoyancy, the displacement efficiency of casing eccentricity of 0.1 is better than that of casing concentricity; When the eccentricity is greater than 0.1, the displacement efficiency decreases gradually with the increase of eccentricity under the coupling effect of casing eccentricity and mass diffusion. ② injecting spacer first and then flushing fluid is beneficial to give full play to displacement effect of spacer under positive density difference, and the flushing effect of low density flushing fluid is utilized to improve displacement efficiency. ③ the velocity of wide side is higher than that of narrow side in the casing eccentricity, which causes the cementing slurry to return from the wide side in advance, while the narrow side retains a large amount of drilling fluid. The simulation results provide an important theoretical basis for the structure design and optimization of slurry column under eccentric annulus. [ABSTRACT FROM AUTHOR]

The gas lift plunger uses the pressure difference between bottom hole and wellhead to drive the plunger and accumulated liquid to move along the wellbore, which can achieve the purpose of drainage and gas recovery. At present, few studies pay attention to the influence of dynamic eccentricity between the plunger and tubing in the rising course. In this paper, the transient numerical calculation method of gas–liquid two-phase flow was used to study the movement of the plunger under different eccentricities. The results show that the sealing effect of the plunger gradually deteriorates with the increase of the eccentricity. When the plunger axis coincides with the tubing axis, the sealing effect of the turbulence groove can achieve the requirements of plunger lift. When the eccentricity is 1.5 mm, the liquid leakage rate increases by 156.64% compared with concentric state, and the liquid in the upper part of the plunger leaks at a rate of 0.29 kg/s. In addition, the process efficiency of plunger in the eccentric state is significantly reduced based on two aspects that lifting kinetic energy and liquid lifting ability. When the eccentricity is 1.5 mm, pressure difference between the top and bottom of the plunger is reduced by 17.5% compared with the concentric state, and the drainage quality is reduced by 27.8%. [ABSTRACT FROM AUTHOR]

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Copyright of China Sciencepaper is the property of China Sciencepaper and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, we investigate the first Steklov–Dirichlet eigenvalue on eccentric annuli. The main geometric parameter is the distance t between the centers of the inner and outer boundaries of an annulus. We first show the differentiability of the eigenvalue in t and obtain an integral expression for the derivative value in two and higher dimensions. We then derive an upper bound of the eigenvalue for each t, in two dimensions, by the variational formulation. We also obtain a lower bound of the eigenvalue, given a restriction that the two boundaries of the annulus are sufficiently close. The key point of the proof of the lower bound is in analyzing the limit behavior of an infinite series expansion of the first eigenfunction in bipolar coordinates. We also derive a relation between the first eigenvalue and a sequence of eigenvalues obtained by a finite section method. Based on this relation, we also perform numerical experiments that exhibit the monotonicity for two dimensions. [ABSTRACT FROM AUTHOR]

Accurately predicting pressure gradient with inner pipe rotation in concentric or eccentric annuli can provide a theoretical foundation to evaluate equivalent mud weight for avoiding downhole problems caused by overlarge downhole pressure, such as: gas kick, lost circulation, even blowout. Nowadays, many studies were carried out on the basis of theoretical and experimental researches to investigate the laminar helical flow in concentric/eccentric annuli, however, to the best of our knowledge, no simplified model has been reported to predicting pressure gradient (PG) in eccentric annuli with inner pipe rotation for yield-power-law (YPL) fluids. In this paper, a simplified modeling for predicting PG of laminar helical flow in an eccentric annulus with YPL fluids has been established. In addition, the validation of simplified model has been investigated by comparing results with computational fluid dynamic (CFD) simulations, existing experimental measurements and numerical model. Predictions of the simplified model shown good agreement with CFD and experimental results within ±10% error bars for power-law and YPL fluids both in concentric and eccentric annuli. [ABSTRACT FROM AUTHOR]

Eccentric annular regions formed by two impermeable cylinders are considered. Flow of Newtonian fluid in the annular region in the presence of heat transfer is studied. The eccentric annulus is mapped to concentric annular region through conformal mapping. Analytical solution for both temperature and velocity is obtained and graphically depicted. An increase in eccentricity results in an increase in velocity but a decrease in temperature. [ABSTRACT FROM AUTHOR]

In the drilling and production process of the petroleum industry, the research on the flow of nonNewtonian fluids in eccentric annulus is of great significance. At present, drilling fluids are mainly based on Bingham fluids and power law fluids. However, the research on the distribution law of the spiral flow velocity field of eccentric annulus H-B fluid is insufficient. Based on the actual situation of drilling fluid flowing between drill pipe and casing in eccentric annulus, a physical model of eccentric annulus with different eccentricity is established through CREO three-dimensional modeling software, and the eccentric annulus is analyzed. The control equation and solution method of the Herschel-Bulkley (H-B) fluid spiral flow are simulated and analyzed by ANSYS fluid analysis software. Through numerical simulation analysis, it is concluded that due to the eccentricity, the wide gap in the eccentric annular spiral flow field will form a turbulent constant velocity flow area, and there will be a low-speed flow area around the narrow gap. The greater the deviation angle of the spiral flow field, the more uneven the flow field velocity distribution, which is not conducive to the migration of drilling cuttings. The deviation angle of the spiral flow field gradually increases with the increase of drill pipe speed, annulus eccentricity, and drilling fluid fluidity index, and gradually decreases with the increase of annulus flow velocity. The consistency coefficient of drilling fluid and dynamic shear force has no effect on the deviation angle of the spiral flow field. [ABSTRACT FROM AUTHOR]

This work is about studying the natural convection of 3-D steady-state non-Newtonian power law fluid numerically. The inner cylinder was put eccentrically into the outer one. The cylinders are held at constant temperatures with the inner one heated isothermally at temperature, Th, and the outer one cooled isothermally at temperature Tc (Th > Tc). The simulations have been taken for the parameters 10³ ≤ Ra ≤ 105, 10 ≤ Pr ≤ 10³, 0.6 ≤ n ≤ 1.4, and 0 ≤ ɛ ≤ 0.9, and an inclination angle, ϕ, from 0° to 90°. The average Nusselt numbers for the previous parameters are obtained and discussed numerically. The results revealed that the average Nusselt number has the highest values when n = 0.6, Ra = 105 at ϕ = 0 which is a signal for the large transfer herein and has the lowest values for n = 1.4, Ra = 10³, at ϕ = 90° which is a signal that the transfer is by conduction more than convection. Furthermore, the increasing of eccentricity causes an increase in the Nusselt number for all the cases. Finally, the best case where we can get the best heat transfer is at ϕ = 0, ɛ = 0.9 among them all. The results have compared with some precedent works and showed good agreement. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Petroleum Research & Studies is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• Conjugate natural convection in a square cavity with a circular cylinder is studied. • An improved LBM that incorporates the effect of heat capacity is adopted. • The wall thickness has a significant effect on the heat transfer. In this paper, an improved lattice Boltzmann model that incorporates the effect of heat capacity is adopted to simulate the conjugate natural convection in a square enclosure with a circular cylinder, and the square cavity considered is bounded by four finite thickness and conductive walls. Influences of Rayleigh number, wall thermophysical properties, and wall thickness on streamlines, isotherms and Nusselt number are analyzed. It is found that the heat transfer rate obtained for different wall thicknesses is usually smaller than that for the zero wall thickness, while this difference is not apparent for a larger thermal conductivity ration. Additionally, the study also shown that the increase of the outer wall thickness tends to decrease the heat transfer rate. The effects of the geometric parameter, including aspect ratio and vertical cylinder location, on heat transfer are also studied. [ABSTRACT FROM AUTHOR]

The two-dimensional time-dependent natural convection heat transfer of non-Newtonian nanofluids is studied numerically between the gap of two horizontal cylinders. The inner and outer cylinders were kept at T i and T o ( T i > T o ), respectively. The finite volume technique was used in the study. The effects of Ra number ( 10 3 ≤ R a ≤ 10 6 ), aspect ratio ( 0.4 ≤ AR ≤ 1.2 ), power law index of the nanofluid ( 0.6 ≤ n ≤ 1.4 ), horizontal eccentricity ( 0.2 ≤ ε H ≤ 0.8 ), vertical eccentricity ( - 0.8 ≤ ε v ≤ + 0.8 ) and rotation of the inner cylinder ( 0 ≤ ω ≤ 500 ) on the flow field and heat transfer were investigated. It was found that a very good agreement exists with the present numerical results and the results of the open literature. The results indicate that with increasing the Ra number from 10 3 to 10 6 the heat transfer increases by about 80%. The increase in aspect ratio also increases the heat transfer. The results showed that with increasing the power law index from 0.6 to 1.4, the heat transfer decreases by a rate of about 78%. In addition, the time to reach steady-state conditions increases with increasing power law index. Simulations were performed for a power law index of 0.8 to investigate the effect of eccentricity of the inner cylinder, and it was observed that the heat transfer is higher for negative vertical eccentricities, and the time to reach steady conditions shortens with the effect of negative vertical eccentricity and power law index. [ABSTRACT FROM AUTHOR]

Highlights • Oscillatory flow of electro-thermo-convection in eccentric annulus is studied for the first time. • A unified lattice Boltzmann model is adopted to solve the whole set of governing equations. • Results are presented for different control parameters and radius ratio. • The flow undergoes steady state, periodic oscillation and chaotic state as electric Rayleigh number increase. • The formation of oscillating flows is strongly related to the value of radius ratio. Abstract A detailed numerical investigation for oscillatory electro-thermo-convection of dielectric liquids in horizontal eccentric annulus is carried out based on a unified lattice Boltzmann method (LBM). The liquid is under the simultaneous action of a strong unipolar charge injection and a thermal gradient. The self-oscillatory behaviors and heat transfer characteristics for different Rayleigh number Ra , electric Rayleigh number T , Prandtl number Pr , mobility parameter M and radii ratio are studied systematically. The results show that the values of Ra within the range from 103 to 104 have little effect on the periodic oscillatory convection, while the flow develops from steady to periodic oscillatory and finally evolves into chaotic as T increases, and the fundamental frequency and the fluctuation amplitude as well as the heat transfer rate increase with T. Moreover, it is found that the fluid properties have significant impact on the oscillatory convection, and the formation of oscillating flows is strongly related to the value of radius ratio. [ABSTRACT FROM AUTHOR]

Abstract In the process of drilling, the tubing-casing annulus are easily to be eccentric. Heat transport phenomenon occurring in such tubes and annulus can be complex, and this paper investigates forced convection in a vertical eccentric annulus with different radius ratios and eccentricity (normalized by the radius difference). Physical experiments and numerical simulation have been conducted with constant inner tube inlet temperature and flow rate of hot water. Results show that with the increase of radius ratios, the convection heat transport coefficient increases. For a radius ratio of 1.875, the heat transport coefficient increases as the eccentricity increases when the Re > 2000 and it decreases when the Re < 2000. For a radius ratio of 2.25 and Re < 1500, the influence of eccentricity is trivial, but for Re > 1500, the increase of eccentricity strengthens the heat convection. For a radius ratio of 3.06, the heat transport coefficient increases as the eccentricity increases. An empirical correlation for Nusselt number is derived as a function of Reynolds number, Prandtl number and eccentricity. Highlights • For D o / D i = 1.875, the effect of eccentricity is identified into two zones. • For D o / D i = 3.06, the increase of eccentricity enhances the convective heat transport. • The increase of radius ratio strengthens the heat transport of annular channels. • With low eccentricity and low Reynolds number, the increase of radius ratio can hardly improve the heat exchange efficiency. • Three kind of empirical correlations are regressed through parametric analysis. [ABSTRACT FROM AUTHOR]

In this paper we study the flow an elasto-visco-plastic fluid whose deviatoric stress is made up by a "seemingly" visco-plastic part (regularized Bingham fluid) and a viscoelastic part (Rivlin–Ericksen fluid) in a "slightly" eccentric annulus. The flow is driven by an applied horizontal pressure gradient and by the motion of the inner cylinder. Using the eccentricity as perturbation parameter we show that secondary flows appear at the first order approximation. We investigate the various flow patterns depending on the different non-dimensional groups appearing in the governing equations. In particular we observe the occurrence of rotating and counter-rotating vortices depending on the material and geometrical parameters of the system. • We study the flow of an elasto-visco-plastic fluid in a "slightly" eccentric annulus. • The flow is of Couette–Poiseuille type. • We perform an asymptotic expansion around the eccentricity parameter. • We solve the zero and first order problem numerically via Spectral methods. • We show that secondary flows appear at the first order. [ABSTRACT FROM AUTHOR]

In the present study, Lattice Boltzmann method is employed to investigate a two dimensional mixed convection heat transfer of Al2O3-water nanofluid in a horizontal annulus between a cold outer cylinder and the hot, rotating inner cylinder. To do so, the double lattice Boltzmann equation is utilized for the base fluid and the nanoparticles to describe the dynamic as well as the thermal behavior of nanofluid. Moreover, different forces such as Brownian, drag and gravity acting on the nanoparticles are taken into consideration. Calculations have been performed for Rayleigh number ranging from 103 to 2×104, Reynolds number from 5 to 120, vertical and horizontal eccentricity from -0.75 to 0.75 with volume fraction of nanoparticles from 0 to 0.1. The current computational results reveal that by adding nanoparticles, the mean Nusselt number for Ra 104, it decreases. Also, with Re>80, the mean Nusselt number increases with increasing Reynolds number; although for low Reynolds number this rising trend is not observed. Besides, when the inner cylinder moves vertically upward from the center, the addition of nanoparticles increases Nusselt number relative to the base fluid.

The formation of a cutting bed in an annulus involves safety problems in drilling especially in the horizontal well and the directional well. In this work, three axial laminar velocity field calculation models for the power-law fluid in an annulus are modified by considering the effect of the cutting bed. The proposed models are employed to numerically simulate the annulus flow with the cutting bed. Verified by the experimental data in literature, all of them can be applied to the situation of the annulus flow with the cutting bed. The modified concentric annulus model enjoys the best performance, while the flat channel flow model has the worst performance. [ABSTRACT FROM AUTHOR]

The paper presents the results of numerical simulations of natural convective heat transfer processes occurring in concentric and eccentric annular cylindrical buffer layer filled with the nanofluid. The considered buffer layer is used in the special type of coil heat exchanger to prevent the possible leakage of the refrigerant - working medium in the coil. Eccentricity of the layer may affect the heat transfer and thus thermal characteristics of the heat exchanger. The obtained results are presented in the form of dependences effective thermal conductivities vs. Rayleigh numbers. A significant effect of the eccentricity and the nanoparticle concentration on heat transfer process is observed. [ABSTRACT FROM AUTHOR]

Rotating casing is helpful to improve cementing quality. In the case of casing rotation and non-rotation, the influence of density difference and casing eccentricity on displacement efficiency and displacing interface in highly deviated wells have been numerically simulated based on Herschel-Bulkley model. The simulation results indicate that the displacement efficiency increases first and then decreases as the density difference or casing eccentricity increases. Under the same displacement conditions, rotating casing can improve displacement efficiency. In order to visually observe the casing rotation change the fluid flow state, the displacement process and displacing interface are experimentally simulated by using substitute drilling fluid and cement slurry. To select reasonable casing rotation speed while cementing, the impact of casing rotation speed on displacement efficiency is analyzed by combining experiments and simulations. Considering cementing requirements and operating risks, the casing rotary speed is recommended at 20–30 r/min in highly deviated wells. [ABSTRACT FROM AUTHOR]

One of the most significant benefits of directional drilling is the increase in well productivity using multiple wells from a single vertical wellbore. During directional drilling, the drill pipe rests on the low-side of the annulus because of gravity. Moreover, cuttings beds form on the low-side of the annulus. Cuttings beds are undesirable because they increase hydraulic resistance of the annulus and consequently, the bottom hole pressure and Equivalent Circulating Density (ECD). Beside this, the annular flow becomes complicated. As a result, predicting relevant hydraulic characteristics of the annulus (friction pressure gradient and wall shear stresses acting on the bed and wellbore) becomes challenging due to lack of accurate hydraulic models that account for bed formation in eccentric annulus. In this study, a numerical simulation-based investigation has been performed in order to analyze the effect of cuttings bed formation on annular flow of power law fluid in a partially blocked eccentric (90%) annulus under laminar flow condition. The investigation is conducted using Computational Fluid Dynamics (CFD) software (ANSYS Fluent). The effects of fluid rheological properties (fluid behavior index and consistency index) and flow geometry (diameter ratio, and cuttings bed height) on velocity profile, frictional pressure loss and bed/wall shear stress are investigated. CFD simulation results are validated with available experimental measurements and they have shown reasonable agreement. Subsequently, the results are systematically analyzed using dimensionless hydraulic parameters ( fRe and Π bed ) and geometric constants ( a and b ) to develop approximate models for frictional pressure loss and average bed shear stress. When compared with CFD simulation results, the new models have demonstrated better accuracy than the existing ones. [ABSTRACT FROM AUTHOR]

In this paper, the steady state and laminar mixed convection of nanofluid in horizontal eccentric annulus with rotating inner cylinder has been investigated numerically. The inner and outer cylinders are considered at constant temperature T i and T o respectively, where T i > T o . The annular space is filled with Alumina-water nanofluid. The nonlinear governing equations and the associated boundary conditions in the polar coordinate are solved numerically using the finite volume method and SIMPLER algorithm. In order to perform the numerical simulations, a code has been written to model the problem using bipolar orthogonal co-ordinates as well as non-orthogonal co-ordinates grid types. It is worth mentioning that in non-orthogonal co-ordinates grid types the code is able to model the problem with or without the effects of non-orthogonality. Due to the inconsiderable non-orthogonality of the grid, difference between the results of three schemes is < 3%. Considering the computational cost, the code developed for non-orthogonal co-ordinates grid types without effects of non-orthogonality has been used for this study. The effects of the eccentricity and the nanoparticle volume fraction on the heat transfer inside the annuli have been investigated. According to the results, the average Nusselt number increases by increasing the downward eccentricity of the inner cylinder. Furthermore, the maximum average Nusselt number occurs for an optimal nanoparticle volume fraction. [ABSTRACT FROM AUTHOR]

A numerical study of mixed convection flow and heat transfer of copper-water nanofluid inside an eccentric horizontal annulus is presented. The inner and outer cylinders are kept at constant temperatures as Th and Tc, respectively. The inner cylinder rotates to generate the forced convection effect. The numerical work was carried out using an in-house CFD code written in FORTRAN. Different scenarios were explored to explain the effects of different parameters on the studied problem. These parameters are Richardson number, eccentricity ratio, and solid volume fraction. The range of the Richardson number, solid volume fraction of the nanoparticles, and the eccentricity ratio, are 0.01 ≤ Ri ≤ 100 (natural convection), 0 ≤ ζ ≤ 0.05, 0 ≤ ε ≤ 0.9, respectively. All results were performed with thermal Grashof number, and radius ratio Rr, equaled to 104 and 2, respectively. The effects of eccentricity, nanoparticles volume fraction, and Richardson number on the average Nusselt number, streamlines and isotherms were investigated. Results were discussed, and were found to be in good agreement with previous works. It was also found that, the eccentricity has a positive remarkable effect on the average Nusselt number, while the effect of nanoparticles concentration was more pronounced at mixed convection region (Ri = 1). [ABSTRACT FROM AUTHOR]

In the present study, Lattice Boltzmann method is employed to investigate a two dimensional mixed convection heat transfer of Al2O3-water nanofluid in a horizontal annulus between a cold outer cylinder and the hot, rotating inner cylinder. To do so, the double lattice Boltzmann equation is utilized for the base fluid and the nanoparticles to describe the dynamic as well as the thermal behavior of nanofluid. Moreover, different forces such as Brownian, drag and gravity acting on the nanoparticles are taken into consideration. Calculations have been performed for Rayleigh number ranging from 10³ to 2×104, Reynolds number from 5 to 120, vertical and horizontal eccentricity from -0.75 to 0.75 with volume fraction of nanoparticles from 0 to 0.1. The current computational results reveal that by adding nanoparticles, the mean Nusselt number for Ra <104 increases as Rayleigh number increases while in the case of Ra >104, it decreases. Also, with Re>80, the mean Nusselt number increases with increasing Reynolds number; although for low Reynolds number this rising trend is not observed. Besides, when the inner cylinder moves vertically upward from the center, the addition of nanoparticles increases Nusselt number relative to the base fluid. [ABSTRACT FROM AUTHOR]

Flow instability or transition from laminar to turbulent for the various fluids is a subject of research for the fluid dynamics. Various approaches have been devised to look into the various aspects of the transition from laminar to turbulent flow. The present investigation deals with the application of Energy gradient method to study the effect of the eccentricity and presence of the secondary solid phases in the flow instability for the fully developed annular flow. For the annulus of different radius ratio, the different eccentricity ratio has been considered for the Newtonian fluid. Also for the concentric case, the effect of the solid secondary phase has been studied with the possibility of the solid deposition at the bottom of the annulus. These cases have practical relevance with the annular flow in the well bore in case of horizontal drilling. The derivations have been carried out for all these cases for flow instability analysis. [ABSTRACT FROM AUTHOR]

This paper deals with numerical study of filter cake formation and fluid loss on the borehole walls during an over-balanced drilling operation. Filter cake formation is a result of three interlinked phenomena; free flow of drilling fluid in the annulus, porous flow of filtrate through the formation and mud solids deposition on the well's wall. A numerical approach is developed for modeling and simulation of the cake growth, in which, initially, a three-dimensional non-Newtonian flow field of power law drilling mud is computed using finite difference method, and then, radial permeation of the filtrate and the rate of cake growth is accomplished by an explicit Runge-Kutta method. Extensive computer runs was carried out to investigate the effect of free flow parameters on the cake thickness profile and the simulation results indicated that, unexpectedly, increasing drill string rotation in a concentric case (within the conventional range of parameters for drilling operation) has almost no effects on cake thickness and permeate velocity. By increasing eccentricity, the effect of drill string rotation increases and a maximum and minimum cake thickness occurs in widening and narrowing gap, respectively. However, this impact can be neglected in high rotation rate. The effect of drill string and particle radius was studied as well. [ABSTRACT FROM AUTHOR]

When cementing horizontal wells, it is essential to keep the displacement interface steady, in order to achieve good cementing quality, especially in eccentric annuli. Considering the displacement behavior between shear-thinning fluids in a horizontal eccentric annulus, the Lattice-Boltzmann method (LBM) was used to investigate the displacement interface shape. The classical Hele-Shaw approach was used to simplify the model from 3D flow into a 2D model. In the simulations, the effects of eccentricity and density ratio on the displacement interface shape and on the interface length versus time were analyzed in detail, resulting in an understanding of the fingering mechanism. Comparison of LBM with the FLUENT solutions showed that the results with LBM are essentially in agreement. In general, a greater density ratio and a lower eccentricity will result in a shorter displacement interface i.e. better displacement in a horizontal eccentric annulus. For a given density ratio, there is an optimum eccentricity to achieve a steady interface. The study provides guidance to the design of wellbore cement jobs and demonstrates that LBM is a promising tool for modeling of the fluid displacement process. [ABSTRACT FROM AUTHOR]

Numerical investigation of mixed convection flow and heat transfer with different nanofluids inside an eccentric horizontal annulus is presented. The nanofluids include Cu, TiO 2 and Al 2 O 3 nanoparticles with water as a base fluid. The inner and outer cylinders are kept at different constant temperatures with the inner at a higher magnitude than the outer. Moreover, the inner cylinder rotates to create the forced convection effect. Different scenarios are explored to clarify the effects of Richardson number, eccentricity ratio, and solid volume fraction with ranges of 0.01 (forced convection) ≤ Ri ≤ 100 (natural convection), 0 ≤ ε ≤ 0.9, and 0.01 ≤ λ ≤ 0.05, respectively. Results are accomplished with Grashof number, and radius ratio, equal to 10 4 and 2, respectively. The generated results include the average Nusselt number, streamlines, and isotherms. The numerical work is carried out using an in-house CFD code written in FORTRAN. Results are discussed and are found to be in good approval with preceding works. It is found that the effect of nanoparticles on the heat transfer enhancement is more pronounced at mixed convection (Ri = 1) and natural convection regions (Ri >1), however at forced convection region (Ri ≤ 0.1) the nanoparticles addition has an opposite effect. [ABSTRACT FROM AUTHOR]

Of all of the rheological parameter models for drilling fluids, the yield-power-law (YPL) model is the best one for performing actual calculations. However, no exact general analytical solution has been found for YPL fluids in both concentric and eccentric annuli because currently, all of the published methods for predicting the surge and swab pressures for YPL fluids apply the narrow-slot approximation technique. To analyze the actual flow characteristics of YPL fluids in an eccentric annulus, this paper introduces an exact model for predicting the surge and swab pressures based on fluid mechanics and the properties of YPL fluids. This model fully analyzes the effects of the rheological parameters of drilling fluids, of the geometric parameters of the annulus and of the pipe velocity on the surge and swab pressures. The results show that the maximum velocity weakens with an increased clearance ( θ ) when the main flow path is in the range of θ = 0 ∼ 120 deg, that the surge and swab pressures decrease with an increase in the eccentricity of the annulus but increase rapidly with an increase in the diameter ratio, and that the surge and swab pressures are most sensitive to changes in the fluid behavior index (n) when 0.7 < n < 1. When the results of this model are also used to evaluate the validity of the narrow-slot model, it is found that the accuracy of the narrow-slot model, which is slightly affected by the rheological parameters (τ 0 , K and n), is high when the diameter ratio is larger than 0.8 (i.e., the accuracy is within 2% error). However, when the diameter ratio is less than 0.6, the accuracy is influenced by only a few factors, among which Bingham plastic fluids (n = 1) has the most effect, followed by power-laws fluid (τ 0 = 0). [ABSTRACT FROM AUTHOR]

Free convection in an open-ended horizontal eccentric annulus between two eccentric horizontal square ducts with different eccentricities has been experimentally studied with several heat fluxes. Constant heat flux for outer duct and insulated inner square rod boundary conditions were used. The wall temperature of the outer duct was measured along the length for different eccentricities. The eccentricity ratio was changed ( E = −1, −0.5, 0, 0.5, 1) in both upper (negative eccentricity) and lower direction (positive eccentricity). Results indicate that with the increase of eccentricity in both directions, the convection heat transfer coefficient decreases. Also, the lower heat transfer rate is found to be at the middle section between both ends led to maximum surface temperature. The generated Rayleigh number due to the heat flux was changed from 4 × 10 5 to 2.9 × 10 6 . Empirical relations are derived from the average Nusselt number as a function of the Rayleigh number and the eccentricity ratio. [ABSTRACT FROM AUTHOR]

The drilling fluid that is retained in the annulus may become the channeling path for oil, gas and water in the formation. Therefore, ensuring drilling fluid non-retention during cementing is an effective method to improve the annular sealing quality. In order to solve the problem that precious researches can't obtain the conditions of drilling fluid non-retention on the casing and well walls in eccentric annulus, this paper establishes a non-retention condition model through mechanism analysis of displacing fluid elements. Furthermore, several rules are obtained on the basis of the calculation results: for the retention range of drilling fluid, it becomes decreasing gradually on the casing and well walls as casing eccentricity increases, and the retention degree in the annular narrow gap will be more severe. Moreover, for the drilling fluid in the annular wide gap, the critical yield stress of drilling fluid non-retention and the difference of critical yield stress between casing and well walls a re increasing. But the opposite results will obtain in the annular narrow gap. So, we can conclude that a better cementing effect can be obtained with the adjustment of displacing fluid properties and construction parameters on the basis of drilling fluid non-retention in the annular narrow gap. [ABSTRACT FROM AUTHOR]

Within the annular heat pipe heat exchangers, heat transfer capacity and assembly eccentricity are two crucial issues for the overall thermal performance (such as heat transfer capacity, flow friction, and temperature distribution). This study aimed to investigate: 1) the heat transfer and fluid flow characteristics of two annular heat exchangers for the purpose of configuration optimization; and 2) the influence of an assembly clearance and the resulting eccentricity on heat transfer characteristic and temperature distribution. Two types of densely longitudinal fins with different heights were designed to enhance heat transfer. Three eccentricities were compared under uniform heat flux and uniform temperature conditions, and two mediums of air and helium were considered to fill the assembly clearance. The results indicated that due to the larger heat transfer area, the average heat transfer coefficient and friction factor produced by the high fins equipped annular heat exchanger were about 20% and 28% higher than the ones with short fins within Re = 2000–15000. The thermal resistance of the clearance varied with the assembly eccentricity. The larger the eccentricity, the smaller the average thermal resistance. Significant temperature gradients appeared in assembly clearance under uniform heat flux conditions. Under uniform temperature conditions, the temperature gradients are outstanding in the annular heat exchanger. A filling medium with greater thermal conductivity is suggested since it can effectively improve the circumferential temperature nonuniformity. This study provides a design guideline as well as heat transfer performance optimization for the heat pipe heat exchangers. • Heat transfer characteristic of dense fins equipped annular heat exchanger. • Assembly eccentricity effect investigation of annular heat pipe heat exchanger. • Combined method of experimental test and numerical simulation. • Heat transfer enhancement can achieve by increasing the fins height. • Eccentricity significantly affect thermal resistance and heat transfer distribution. [ABSTRACT FROM AUTHOR]

The enhancement of the thermal performance of heat exchanging equipment transport energy at low financial cost by various techniques is presented in this review. Various annular passage configurations have been used in the reviewed studies, namely circular, ellipse, rectangular, square, triangular, and rhombic annular channels with different fluid and boundary conditions. The effect of eccentricity in both horizontal and vertical directions on heat transfer rate in most numerical and experimental investigations for horizontal and vertical annular passages is studied. The effects of heater length, as well as the Darcy, Prandtl, Reynolds, Grashof and Rayleigh numbers on heat transfer in concentric and eccentric annular passages are also investigated. In case of rotating the inner, outer or both cylinders of the annular cylinder arrangement, the generated secondary flow influences the heat transfer to fluid flow in an annular passage. The effect of nanofluid on the increased enhancement of heat transfer in an annular channel is presented. Related studies on curved, covered annular channels showed augmented heat transfer rate in comparison with straight annular channels. In this review, a good agreement is evident between experimental and numerical data, which could help researchers design thermal systems supported by annular passages with the goal of retarding energy consumption by equipment and machineries in applications that could ultimately contribute to appeasing the global energy crisis. [ABSTRACT FROM AUTHOR]