Excess Pressure Loss Research Articles

Solid-Particles Flow Regimes in Air/Water Stratified Flow in a Horizontal Pipeline

Summary The entrainment of solid particles in crude oil occurs during production from reservoirs with low formation strength. The stationary solid-particles bed at the horizontal pipe bottom can cause operational problems such as production decline, excessive pressure loss, equipment failure, erosion, and corrosion. Solid-particles deposition can be managed by operating above the critical solid-particles-deposition velocity, which is the velocity that maintains the continuous movement of particles at the pipe bottom. Here, a comprehensive analysis of solid-particle flow regimes in stratified flow in a horizontal pipeline is presented, which is a novel contribution because it is applied to multiphase flow. The effect of concentration on the solid-particle flow regimes and identification of the critical solid-particles-deposition velocities for various particle concentrations are also investigated. The understanding of solid-particle flow regimes in pipelines for any given set of operational conditions is important for identifying the nature of particle interaction and movement. Experimental studies are conducted in a 4-in. horizontal pipeline for a stratified flow regime that uses air, water, and glass beads at relatively low solid-particles concentrations (<10,000 ppm). The effects of different experimental conditions, such as gas velocity, solid-particles concentration, and particle size, are investigated in this study. Six main solid-particles flow regimes in horizontal air/water flow are identified, and can be distinguished visually: fully dispersed solid flow, dilute solids at wall, concentrated solids at wall, moving dunes, stationary dunes, and stationary bed. Therefore, the critical solid-particles-deposition velocities are determined on the basis of the transition between moving (concentrated solids at wall/moving dunes, as appropriate) and stationary (stationary dunes/bed, as appropriate) solid particles. The experimental data show that with small particle size, the critical solid-particles-deposition velocity is almost independent of concentration, while with larger particle sizes, the critical velocity increases with the concentration.

수평 공기 채널과 수직 물 채널로 구성된 플라스틱 필름/종이 가습 소자의 성능

New materials and shapes for a humidifying element were developed which outperformed the widely used crisscross glass wool Glasdek media design. The new material consists of 50% cellulose and 50% PET . The parallel channel configuration was devised to reduce excessive pressure loss caused by the reduced height (from 7.0 mm to 5.0 mm) of the crisscross configuration. For the same crisscross configuration, the humidification efficiency of the cellulose/PET element was 26% higher than that of the glass wool element. For the same cellulose/PET material, humidification efficiency of the parallel channel configuration was 14% higher than that of the crisscross configuration. As for the pressure drops, the cellulose/PET element was 2–52% higher than those of the glass wool element. For the same cellulose/PET material, the pressure drop of the parallel channel configuration was 14% higher than that of the crisscross configuration. Data were compared against the predictions from existing correlations and those by the proposed model.. † Corresponding Author, knh0001@incheon.ac.kr C 2016 The Korean Society of Mechanical Engineers

Analytic Rayleigh pressure loss model for high-swirl combustion in a rotating combustion chamber

This paper considers the effect of excessive total pressure losses for heat transfer problems in fluid flows with a high circumferential swirl component. At the Institute of Jet Propulsion and Turbomachinery at RWTH Aachen University, a novel gas generator concept is under research. This design avoids some disadvantages of small gas turbines and uses a rotating combustion chamber. During the pre-design of the rotating combustion chamber using CFD tools, unexpected high total pressure losses were detected. To analyze this unknown phenomenon, a gas-dynamic model of the rotating combustion chamber has been developed to explain the unexpected high Rayleigh pressure losses. The derivation of the gas-dynamic model, the physical phenomenon related to the high total pressure losses in high-swirl combustion, the influencing factors, as well as thermodynamic interpretation of the Rayleigh pressure losses, are presented in this paper. The results presented here are of possible interest for a wide range of applications, since these fundamental findings can be transferred to all heat transfer problems in fluid flows with a high circumferential swirl component.

Advanced Rayleigh Pressure Loss Model for High-Swirl Combustion in a Rotating Combustion Chamber

This paper considers the effect of excessive total pressure losses for heat transfer problems in fluid flows with a high circumferential swirl component. At RWTH Aachen University, a novel gas generator concept is under research. This design avoids some disadvantages of small gas turbines and uses a rotating combustion chamber. During the predesign of the rotating combustion chamber using computational fluid dynamics (CFD) tools, unexpected high total pressure losses were detected. To analyze this unknown phenomenon, a gas–dynamic model of the rotating combustion chamber has been developed to explain the unexpected high Rayleigh pressure losses. The derivation of the gas–dynamic model, the physical phenomenon related to the high total pressure losses in high-swirl combustion, the influencing factors, as well as thermodynamic interpretation of the Rayleigh pressure losses, are presented in this paper. In addition, the CFD results are validated by the gas–dynamic model derived. The results presented here are of possible interest for a wide range of applications, since these fundamental findings can be transferred to all heat transfer problems in fluid flows with a high circumferential swirl component.

A head loss model for slurry transport in the heterogeneous regime

Although sophisticated 2 and 3 layer models exist for slurry flow (here the flow of sand/gravel water mixtures), the main Dutch and Belgium dredging companies still use modified Durand and Condolios (1952) and Fuhrboter (1961) models, while the main companies in the USA use a modified Wilson et al. (1992) model for heterogeneous transport. These older models use one term for the excess pressure losses, the pressure losses resulting from the solids, with an empirical character. A new model has been developed based on energy considerations. The model consists of two terms for the excess pressure losses, one for the potential energy losses and one for the kinetic energy losses. This gives more flexibility matching experimental results. Although the model is derived fundamentally, the slip velocity of the particles is still an unknown in the model. An equation for this slip velocity is derived, based on physical parameters. The resulting model is validated with numerous experimental data from the literature and from the Delft Dredging Laboratory and matches very well. The advantage of this model is, that it requires the parameters known to the dredging industry and is thus easy to use.

Entry flows of polylactides with slip

The entry capillary flow of four different polylactides (previously characterized by Othman et al. (2012)) has been modeled with both a viscous (Cross) and a viscoelastic (K-BKZ) model. The modeling takes into account slip-at-the-wall, which was found to increase with decrease of molecular weight. The flow through different capillary dies and apparent shear rates show the excess pressure losses (ends correction), which are smaller than those for other similar linear polymer melts. The viscous simulations capture well the ends correction, while the viscoelastic simulations improve these predictions, as they also account for the viscoelastic nature of the polymer melts. It is concluded that solely viscous modeling can capture their flow behavior satisfactorily.

Review of cavity-stabilized combustion for scramjet applications

Cavities are widely used as flameholders in supersonic combustors due to their outstanding potential to stabilize combustion without excessive total pressure loss. A review of cavity-stabilized combustion for scramjet applications is provided in this article. The topics cover the fundamental problems and recent advances regarding cavity-organized combustion in high-speed flows, including combustion stabilization modes and mechanisms, flame stability analyses and correlations, combustion oscillations, and other related issues. Remarkable questions such as cavity-coupled fuel injection, flow and combustion coupling, optimal cavity geometry and scale, auto-ignition and flame propagation interactions, and unsteady effects are discussed. Then, an attempt is made to provide some guidelines for the future research of cavity flameholders.

Simulation of Impinging Cooling Performance with Pin Fins and Mist Cooling Adopted in a Simplified Gas Turbine Transition Piece

The gas turbine transition piece was simplified to a one-four cylinder double chamber model with a single row of impinging holes in the outer wall. Heat transfer augmentation in the coolant chamber was achieved through the use of pin fin structure and mist cooling, which could increase the turbulence and heat transfer efficiency. The present research is focused on heat transfer and pressure characteristics of the impinging cooling in the coolant chamber using FLUENT software. With the given diameter of impinging hole, pin fin diameter ratiosD/dhave been numerically studied in ranges from 1 to 2. Three different detachedLwere simulated. The impinging cooling performance in all cases was compared between single-phase and two-phase (imported appropriate mist) flow in the coolant chamber. All the simulation results reveal that the factors ofLandD/dhave significant effects on the convective heat transfer. After the pin fin structure was taken, the resulting temperature decrease of 38.77 K at most compared with the result of structure without pin fins. And with the mist injecting into the cooling chamber, the area weighted average temperature got a lower value without excess pressure loss, which could satisfy the more stringent requirements in engineering.

Active Outer Ring Cooling of High-Loaded and High-Speed Ball Bearings

Bearings for aero engine applications are subjected to a high thermal impact because of the elevated speeds and loads. The high rate of heat generation in the bearing cannot be sustained by the materials used and, in the absence of lubrication, will fail within seconds. For this reason, aero engine bearings have to be lubricated and cooled by a continuous oil stream. The heat that is generated in the bearings through friction is transferred into the oil. Oil itself has limited capabilities and can only remove heat as long as its temperature does not reach critical limits. When the critical limits have been reached or even exceeded, the oil will suffer chemical decomposition (coking) with loss of its properties and subsequently cause a detrimental impact on the rotating machinery. Oil is normally transferred into the bearings through holes in the inner ring, thus taking advantage of the centrifugal forces due to the rotation. On its way through the bearing, the oil continuously removes heat from the inner ring, the rolling elements, and the bearing cage until it reaches the outer ring. Since the oil has already been heated up, its capability to remove heat from the outer ring is considerably reduced. The idea to provide the bearing with an “unlimited” quantity of oil to ensure proper cooling cannot be considered, since an increase in the oil quantity leads to higher parasitic losses (churning) in the bearing chamber and increased requirements on the engine's lubrication system in terms of storage, scavenging, cooling, weight, etc., not mentioning the power needed to accomplish all these. In this sense, the authors have developed a method that would enable active cooling of the outer ring. Similar to fins, which are used for cooling electronic devices, a spiral groove engraved in the outer ring material would function as a fin body with oil instead of air as the cooling medium. The number of “threads” and the size of the groove design characteristics were optimized in a way that enhanced heat transfer is achieved without excessive pressure losses. An experimental setup was created for this reason, and a 167.5-mm pitch circle diameter (PCD) ball bearing was investigated. The bearing was tested with and without the outer ring cooling. A reduction of 50% of the lubricant flow through the inner ring associated with a 30% decrease in heat generation was achieved.

Tube bundle replacement for segmental and helical shell and tube heat exchangers: Performance comparison and fouling investigation on the shell side

Conventional segmental baffles in shell and tube heat exchangers, while having an excellent record of acceptance and functionality, represent some limitations and shortcomings. In particular, shell-side flow path is wasteful which causes excessive pressure loss while recovering less heat transfer. This particular arrangement of baffles also limits maximum thermal effectiveness and encourages dead zones where fouling occurs. This paper describes the results of tube bundle replacement of a segmental shell and tube heat exchanger with a helical heat exchanger, which was conducted in Tabriz Petroleum Company. The aim of the project was to reduce fouling and pressure drop of the critical heat exchanger and; as a result, reduce operation and maintenance costs. Present paper consists of 3 phases. First, tube bundle replacement in industrial field and also the advantages of helical baffles over conventional segmental baffles are going to be discussed. Then, due to limits on the access to the heat exchangers in production lines, comparison of shell-side flow behavior in both cases is going to be presented by CFD means. Finally, computational code is going to be introduced to investigate on heat transfer and pressure drop for both segmental and helical shell and tube heat exchangers.

Effect of Regenerator Entrance Shape on Performance of Compact Pulse Tube Cryocooler

Pulse tube cryocoolers are more attractive than other small cryocoolers because they have no moving parts in the expander and thus have higher reliability. However, Stirling type pulse tube cryocooler needs further improvement on regenerator. The entrance areas at the regenerator ends of the typical pulse tube cryocooler are smaller than the cross-sectional area of the regenerator matrix. So, the working gas flow in the regenerator has non-uniform velocity distribution with the expansion and contraction flow. They cause the excessive pressure loss and reheat loss. In this study, the effect of the regenerator entrance shape on the performance of compact pulse tube cryocooler was examined experimentally. Additionally, the analytical method for losses in the regenerator using experimental data is suggested. Experimentally and analytically, the effect of after-cooler end at the regenrator has been bigger than that of cold-head end.

A study of various factors affecting Newtonian extrudate swell

Finite-element simulations have been undertaken for the benchmark problem of extrudate swell present in extrusion. Both cases of planar and axisymmetric domains were considered under laminar, isothermal, steady-state conditions for Newtonian fluids. The effects of inertia, gravity, compressibility, pressure-dependence of the viscosity, slip at the wall, and surface tension are all considered individually in parametric studies covering a wide range of the relevant parameters. The present results extend previous ones regarding the shape of the extrudate and in particular the swelling ratio. In addition, the excess pressure losses in the system (exit correction) were computed. The effect of the domain length is also studied and is found to be of importance in all cases, except for slip and surface tension effects. The effect of the extrudate length is particularly important for inertia and gravity flows. Inertia reduces the swelling down to the asymptotic theoretical values at infinite Reynolds numbers. Gravity acting in the direction of flow also reduces exponentially the swelling. When the flow is creeping and gravity is zero, surface tension, slip at the wall, and pressure-dependence of viscosity, all decrease the swelling monotonically, while compressibility increases it after a small initial reduction. The exit correction decreases monotonically with inertia, gravity, and slip, increases monotonically with compressibility and pressure-dependence of the viscosity, and is not affected by surface tension.

3D Numerical Simulation of the Fluidized Bed’s Cold Distributor

Because of excessive pressure loss when the gas went through distributor in fluidized bed (FB), based on the principle and method of computational fluid dynamics (CFD), using the software, FLUENT, the inner flow field in the fluidized bed with distributor was simulated. This article analyzed the three-dimensional velocity field distribution, pressure field distribution under the different arrangement of hole form. and the good advice was given on the structural optimization of the cold distributor.

Experimental Studies on the Effect of Mechanical Cleaning Devices on Annular-Cuttings Concentration

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 134269, ’Experimental Studies on the Effect of Mechanical Cleaning Devices on Annular Cuttings Concentration and Applications for Optimizing ERD Systems,’ by Ramadan Ahmed, SPE (currently with the University of Oklahoma), Munawar Sagheer, SPE, Nicholas Takach, SPE, Reza Majidi, SPE, Mengjiao Yu, SPE, and Stefan Miska, SPE, University of Tulsa, and, Christophe Rohart, SPE, and Jean Boulet, SPE, VAM Drilling, originally prepared for the 2010 SPE Annual Technical Conference and Exhibition, Florence, Italy, 19-22 September. The paper has not been peer reviewed. In horizontal and highly deviated portions of an extended-reach-drilling (ERD) well, cuttings beds form on the low side of the annulus. The cuttings bed partially blocks the annulus, resulting in excessive pressure loss and a higher equivalent circulating density (ECD). Recently, the use of downhole mechanical cleaning devices (MCDs) has been introduced to mitigate the problem without inducing excessive ECD. The full-length paper presents results of an experimental study that was conducted to evaluate cuttings-removal efficiency of MCDs. Results indicate that the tools significantly reduce the amount of cuttings in the annulus. Introduction Efficient cuttings transport is an important issue in drilling highly deviated and horizontal wells. In directional wells, drilled cuttings tend to accumulate on the low side of the annulus and form a thick cuttings bed when the flow velocity becomes insufficient to suspend the cuttings-bed particles. Particularly in high-angle and horizontal boreholes, the formation of a thick cuttings bed can give rise to numerous difficulties such as lost circulation, differential sticking, and high torque and drag. Recently, hydromechanical hole-cleaning devices (HHCDs) have been developed to enhance cuttings-transport efficiency in directional wells. These tools are introduced in the drillstring with different spacing arrangements. These tools have helical grooves or blades on their surface to assist cuttings-bed removal. A negative angle also is designed on each blade to improve the scooping effect on the cuttings bed. While rotating the drillpipe, the blades scoop the cuttings bed and help to bring the cuttings into suspension. At the same time, the circulation of the drilling fluid allows the suspended cuttings particles to be carried away, thus leading to better hole cleaning. Because of hydrodynamic and hydromechanical effects, the tools help to reduce the cuttings accumulation in highly deviated and horizontal sections of the wellbore where the buildup of a cuttings bed cannot be avoided. Thus, several of these tools are used in a typical drilling application to reduce the in-situ cuttings concentration and, hence, reduce the occurrence of hole-cleaning-related problems. HHCDs improve hole cleaning by creating more turbulence, bringing cuttings into suspension, and scooping the cuttings bed. The interaction between the tools and the slurry that contains cuttings particles and drilling fluid is a complex fluid-mechanics problem for which an analytical solution would be difficult to develop. Therefore, an experimental approach is the best option to provide practical solutions, perform sensitivity analysis, and obtain a better understanding of the use of these tools.

Entry Flow of Polyethylene Melts in Tapered Dies

Abstract The excess pressure losses due to end effects (mainly entrance) in the capillary flow of several types of polyethylenes were studied both experimentally and numerically under slip and no-slip conditions. These losses were first measured as a function of the contraction angle ranging from 15° to 90°. It was found that the excess pressure loss attains a local minimum at a contraction angle of about 30° for all types of polyethylenes examined. This was found to be independent of the apparent shear rate. This minimum becomes more dominant under slip conditions that were imposed by adding a significant amount of fluoropolymer into the polymer. Numerical simulations using a multimode K-BKZ viscoelastic model have shown that the entrance pressure drops can be predicted fairly well for all cases either under slip or no-slip boundary conditions. The clear experimental minimum at about 30° can only slightly be seen in numerical simulations, and at this point its origin is unknown. Further simulations with a viscous (Cross) model have shown that they severely under-predict the entrance pressure by an order of magnitude for the more elastic melts. Thus, the viscoelastic spectrum together with the extensional viscosity play a significant role in predicting the pressure drop in contraction flows, as no viscous model could. The larger the average relaxation time and the extensional viscosity are, the higher the differences in the predictions between the K-KBZ and Cross models are.

Extrudate swell of Boger fluids

Boger fluids are dilute polymer solutions exhibiting high elasticity at low apparent shear rates, which leads to high extrudate swell. Numerical simulations have been undertaken for the flow of three Boger fluids (including benchmark Fluid M1), obeying an integral constitutive equation of the K-BKZ type, capable of describing the behavior of dilute polymer solutions. Their rheology is well captured by the integral model. The flow simulations are performed for planar and axisymmetric geometries without or with gravity. The results provide the extrudate swell and the excess pressure losses (exit correction), as well as the shape and extent of the free surface. All these quantities increase rapidly and monotonically with increasing elasticity level measured by the stress ratio, S R . It was found that the main reason for the high extrudate swelling is high normal stresses exhibited in shear flow (namely, the first normal-stress difference, N 1). Surprisingly, the elongational parameter of the model or a second normal-stress difference N 2 do not affect the results appreciably. Gravity serves to lower the swelling considerably, and makes the simulations easier and in overall agreement with previous experiments.

Fountain flow revisited: The effect of various fluid mechanics parameters

AbstractNumerical simulations have been undertaken for the benchmark problem of fountain flow present in injection‐mold filling. The finite element method (FEM) is used to provide numerical results for both cases of planar and axisymmetric domains under laminar, isothermal, steady‐state conditions for Newtonian fluids. The effects of inertia, gravity, surface tension, compressibility, slip at the wall, and pressure dependence of the viscosity are all considered individually in parametric studies covering a wide range of the relevant parameters. These results extend previous ones regarding the shape of the front, and in particular the centerline front position, as a function of the dimensionless parameters. The pressures from the simulations have been used to compute the excess pressure losses in the system (front pressure correction or exit correction). Inertia leads to highly extended front positions relative to the inertialess Newtonian values, which are 0.895 for the planar case and 0.835 for the axisymmetric one. Gravity acting in the direction of flow shows the same effect, while gravity opposing the flow gives a reduced bulge of the fountain. Surface tension, slip at the wall, and compressibility, all decrease the shape of the front. Pressure‐dependence of the viscosity leads to increased front position as a corresponding dimensionless parameter goes from zero (no effect) to higher values of the pressure‐shift factor. The exit correction increases monotonically with inertia, compressibility, and gravity, while it decreases monotonically with slip and pressure‐dependence of the viscosity. Contour plots of the primary variables (velocity‐pressure) show interesting trends compared with the base case (zero values of the dimensionless parameters and of surface tension). © 2009 American Institute of Chemical Engineers AIChE J, 2010

Effect of Viscoelasticity in Fountain Flow of Polyethylene Melts

Abstract Fountain flow is the phenomenon of deceleration and outward motion of fluid particles as they approach a slower moving interface. Numerical simulations have been undertaken for the flow of viscoelastic fluids, obeying an integral constitutive equation of the K-BKZ type, capable of describing the behavior of polymer melts. Two polyethylene melts are considered, a branched LDPE and a linear HDPE. Their rheology is well captured by the integral model. The flow simulations are performed for planar and axisymmetric geometries and show the shape and extent of the free surface, as well as the stresses and pressures in the system. The semicircle is a good rough approximation for the free surface of fountain flow, but detailed computations show the effect of elasticity on the free surface, which is non-monotonic for the LDPE as the elasticity level (or apparent shear rate) increases. The less elastic HDPE shows a monotonic decrease in the extent of the flow front as elasticity increases. In all cases, the excess pressure losses (front pressure correction) increase with increasing flow rate. The effect of a nonzero second normal stress difference is to extend the flow front and increase the pressure losses.

Fountain flow of pseudoplastic and viscoplastic fluids

Numerical simulations have been undertaken for the benchmark problem of fountain flow present in injection-mold filling. The Finite Element Method (FEM) is used to provide numerical results for both cases of planar and axisymmetric domains under steady-state conditions. The Herschel–Bulkley model of viscoplasticity is used, which reduces with appropriate modifications to the Bingham, power-law and Newtonian models. The present results extend previous ones regarding the shape of the front, which is essential in correctly capturing the flow field. In particular the centreline front position is found as a function of the dimensionless power-law index (in the case of pseudoplasticity) and the dimensionless yield stress (in the case of viscoplasticity). The pressures from the simulations have been used to compute the excess pressure losses in the system (front pressure correction or exit correction). Both shear-thinning and shear-thickening lead to more extended front positions relative to the Newtonian values, which are 0.895 for the planar case and 0.835 for the axisymmetric one. Viscoplasticity leads also to more extended front positions as the dimensionless yield stress goes from zero (Newtonian behaviour) to higher values of the yield stress. In both cases of non-Newtonian behaviour, the front tends to follow the development of the fully developed Poiseuille velocity profile, which tends towards a plug-like profile at the extreme cases of non-Newtonianness. The front pressure (exit) correction increases monotonically with the decrease in the power-law index and the increase in the dimensionless yield stress.

Correlations To Predict Frictional Pressure Loss of Hydraulic-Fracturing Slurry in Coiled Tubing

Summary Compared with conventional-tubing fracturing, coiled-tubing (CT) fracturing has several advantages. CT fracturing has become an effective stimulation technique for multizone oil and gas wells. It is also an attractive production-enhancement method for multi-seam coalbed-methane wells, and wells with bypassed zones. The excessive frictional pressure loss through CT has been a concern in fracturing. The small diameter of the string limits the cross-sectional area open to flow. Furthermore, the tubing curvature causes secondary flow and results in extra flow resistance. This increased frictional pressure loss results in high surface pumping pressure. The maximum possible pump rate and sand concentration, therefore, have to be reduced. To design a CT fracturing job properly, it is essential to predict the frictional pressure loss through the tubing accurately. This paper presents correlations for the prediction of frictional pressure loss of fracturing slurries in straight tubing and CT. They are developed on the basis of full-scale slurry-flow tests with 1½-in. CT and slurries prepared with 35 lbm/1,000 gal of guar gel. The extensive experiments were conducted at the full-scale CT-flow test facility. The proposed correlations have been verified with the experimental data and actual field CT-fracturing data. Case studies of wells recently fractured are provided to demonstrate the application of the correlations. The correlations will be useful to the CT engineers in their hydraulics design calculations.