Horizontal Circular Pipe Research Articles

Enhancement of turbulent heat transfer by using CuO nano-particle and twisted tape

AbstractA computational model is developed to investigate the convective heat transfer properties and the fluid flow characteristics of cupric oxide - water nano-fluid in a horizontal circular pipe aiming to provide insights into optimizing heat transfer in such systems. A twisted tape with varied twist ratios is inserted. This quantitative investigation used five Reynolds number from 4,000 to 12,000 under a uniform heat flux scenario of 25,000 W m−2. All experiments were performed as a single-phase fluid with cupric oxide values of 0, 0.4, 1, and 2% by volume. By reducing the twist ratio and increasing volume concentration, the average heat transfer coefficient of cupric oxide-water nano-fluid was improved. For a twist ratio of 4D, the maximum heat transfer improvement was 228% greater than the plain pipe. The presence of twisted tape with modest step ratios causes the friction factor to grow.

Experimental Study on Two-Phase Countercurrent Flow Limitation in Horizontal Circular Pipes

The two-phase countercurrent flow limitation (CCFL) in horizontal channels is important in relation to nuclear reactor safety. In this study, we aim to investigate the CCFL characteristics and the flow behaviors in horizontal circular pipes with small diameters. The effects of pipe diameter and the water head in the upper plenum on CCFL characteristics are experimentally studied. An image-processing technique and statistical treatments are implemented to analyze the horizontal countercurrent flow. The results show that the CCFL characteristics for the horizontal circular pipes with small diameters can be well correlated using the dimensionless parameters, which are based on adding fluid viscosity to the Wallis parameters. The CCFL characteristics are significantly affected by the pipe diameter and are slightly affected by the water head above the horizontal pipe. The gas–liquid interface fluctuates with certain periods, and flow pattern transitions happen in the horizontal air–water countercurrent flow. As the air flow rate increases, the occurrence location of the liquid slug appears to shift towards the water entrance. In addition, the further away from the water entrance, the lower the average of liquid holdup.

Experimental investigation of ice slurry viscosity

This work attempted to conduct an experimental study which demonstrates the effect of the initial concentration of solute on the apparent viscosity of ice slurry in a horizontal circular pipe. The study was conducted on ice slurry based on propylene glycol, varying from 5 to 24% with different ice mass fractions varying from 5 to 25%. During the experiments, the initial concentration of the propylene glycol, ice concentration, and flow rate was modified as parameters. The flow tests were performed on laminar flows. The results of the investigation revealed that the ice slurry behaved like a non-Newtonian fluid, while it sometimes behaved like a Newtonian fluid. The rheological behavior of the ice slurry is reflected by its viscosity. For the shear-thickening behavior, the apparent viscosity increases with increasing the shear rate, and for the shear-thinning behavior, the viscosity decreases with increasing the shear rate, while for the Newtonian behavior, the viscosity remains almost constant. Then it was revealed that the viscosity of the mixture became too high for low shear rates at high ice mass fractions by increasing the concentration of the solute. The power law was used to establish a relationship between the apparent viscosity and the indexes of flow and consistency of ice slurry.

Particle deposition and fluid flow characteristics in turbulent corrugated pipe flow using Eulerian-Lagrangian approach

A numerical simulation of aerosol particle deposition in a horizontal circular pipe with a corrugated wall under turbulent flow has been carried out in this research. This paper uses the RNG k-ε turbulence model with Enhanced Wall Treatment to simulate fluid flow. Furthermore, the Lagrangian particle tracking model simulates particle deposition in the corrugated pipe. Air-particle interaction is influenced by Stokes number, surface roughness, flow velocity, particle diameter, and pipe diameter. For the parametric simulation, particle diameter varies from 1 to 30 μm, whereas the Reynolds number ranges from 5000 to 10,000. The effect of corrugation height and pipe diameter on deposition efficiency is also investigated. This study shows that corrugation height significantly increases particle deposition compared to the smooth wall pipe. As the pipe diameter decreases, keeping the corrugation ratio constant, deposition efficiency also increases. Moreover, high flow velocity enhances deposition efficiency for particle diameters lower than 5 μm.

Numerical simulation and experimental study on the whole process of gravel packing in horizontal wells

The gravel packing completion method for horizontal wells has the benefits of long-term high production, wellbore stability, and sand production prevention. The numerical model is critical for gravel packing scheme design and construction guidance in horizontal wells. A lot of work has been done on the numerical model of gravel packing in horizontal wells, but there are still challenges, such as being unable to simulate the entire process, assuming density and viscosity remain constant during horizontal migration, and not integrating formation properties and actual string structures. Therefore, based on the detailed analysis of the whole process of gravel packing flow in horizontal wells, a numerical model, which includes the model of the ground pipes and vertical well sections and an improved three-dimensional numerical model of horizontal sections has been established in this paper. The impact of gravel packing on the horizontal well is then investigated. The accuracy of the pressure calculation model is then evaluated through friction experiments of different types of fluids utilizing a horizontal circular pipe flow device, in which the average error between the measured pressure drop and the calculated pressure drop of the flow friction experiments of water is 1.30%. while as slurry with a proppant concentration of 20% flows, the average error is 6.50%. Many sets of gravel packing experiments are carried out using a full-scale horizontal well gravel packing experimental apparatus to validate the improved three-dimensional numerical model. Finally, numerous well schemes are designed and constructed. After comparing the design parameters and treatment parameters of seven wells, the maximum total time error is 5.78%, the maximum pressure error in the alpha-wave stage (the forward packing stage of gravel from heel to toe in the horizontal wellbore) is 7.3%, and the maximum pressure error in the beta-wave stage (the reverse packing stage of gravel from toe to heel in the horizontal wellbore) is 9.9%, which shows excellent field applicability of the improved model.

The effect of polymeric drag reducing agent on pressure drop reduction in circular pipes: Experimental and statistical investigation

The present work deals with investigating the effect of adding Polyacrylonitrile (PAN) as a drag-reducing agent on the water flow’s hydraulic performance within horizontal smooth circular pipes experimentally and statistically. Several experiments were performed under various operating circumstances such as fluid flow rates at the 6,8,10 l/min for preparing turbulent flow regimes, concentrations of 25,100, 300 ppm of PAN, and inner pipe diameters of 1/2,3/4 in, and temperatures of 30, 40, and 50 °C. The maximum percentage of drag reduction (DR%) was 56 at a concentration of 300 ppm, the flow rate of 6 l/min, temperature of 30 °C and the diameter of 3/4 in. Using the Taguchi method, the results were statistically analyzed. The maximum estimated DR% value was 40.187%, and the error between the predicted and experimental values was about 10%. Moreover, the PAN concentration had a contribution of 96.5% in the polymeric solution DR. Finally, there was a new correlation to predict friction coefficient in terms of the Prandtle-Karman relation with the newly set slope as a linear function of polymer concentration. There was an excellent consistency between this correlation and the experimental data.

Reynolds number and submergence ratio effects on turbulence structures in the shallow wake of a horizontal pipe located on a rough bed

The effects of Reynolds number and submergence ratio on mean velocity, separation length, Reynolds shear stresses (RSS), correlation coefficient, anisotropy, and turbulent kinetic energy (TKE) are evaluated by modifying the free-stream velocity and pipe diameter to understand the fluid–structure interaction in the presence of a rough channel bed. Acoustic Doppler velocimetry is used to acquire three-dimensional velocity data in the experiments. The experimental data demonstrate that the non-dimensional separation length is linearly varying with the Reynolds number up to a critical Reynolds number, and after that, it becomes independent of the Reynolds number. The vertical profiles of the mean velocity, RSS, correlation coefficient, anisotropy, and TKE are not affected by the Reynolds number; however, their profiles are affected by the submergence ratio. The RSS and TKE are found to be larger for the higher submergence ratio below the top level of the pipe throughout the wake region. The reattachment point is found to be the most turbulent as the most pronounced peaks of RSS and TKE are occurring at this point. The quadrant analysis reveals that the RSS contribution of ejection events is higher for a lower submergence ratio, whereas the RSS contribution of the sweep events is higher for a higher submergence ratio. In conclusion, this study provides an in-depth understanding of the turbulent flow characteristics in the wake region of a bed-mounted horizontal circular pipe located on a fixed sand bed, especially the modification of the turbulence properties due to changes in the Reynolds number and submergence ratio.

Experimental and numerical study of forced convictive heat transfer in a horizontal circular pipe with varying angles ribs

Experimental and numerical study of forced convictive heat transfer in a horizontal circular pipe with varying angles ribs

Stratified Two-Phase Turbulent Pipe Flow Simulations

Gas-liquid two-phase flows in pipes are common in various industrial processes requiring fluid transport through pipes and ducts under varying operating conditions. Computational fluid dynamics (CFD) simulations of various conditions of gas-liquid turbulent flow in a horizontal circular pipe are presented in the current paper. The simulations utilize the Level-set Method coupled with the Volume of Fluid (VOF) method to calculate the normal interface for the VOF re-construction step. In the present approach, the flow governing equations are solved numerically first for the mixture, followed by an additional equation for the second phase. A geometric re-construction technique is then used to reconstruct the interface between the two phases. This geometric re-construction technique is based on a piece-wise-linear interface construction approach. For the simulations, a number of eddy viscosity models (EVM) were tested, namely, k-ε, k-ω, and the Re-Normalisation Group (RNG) k-ε in both standard and differential form of turbulence viscosity. Numerical results were validated against detailed measurements and mechanistic models and were found to be in complete agreement. The results were analyzed for the flow physics of the transfer of momentum across the stratified two-phase using the velocity profiles of the gas and liquid phases, liquid hold-up, and different hydrodynamic forces. The paper also highlights the suitability of such a coupled VOF approach for stratified flows via comparisons against measurements and common industrial mechanistic models.

Transient CFD Modelling of Air–Water Two-Phase Annular Flow Characteristics in a Small Horizontal Circular Pipe

The liquid film formed around the inner walls of a small horizontal circular pipe often exhibits non-uniform distributions circumferentially, where the film is thinner at the top surface than the bottom one. Even with this known phenomenon, the problem remains a challenging task for Computational Fluid Dynamics (CFD) to predict the liquid film formation on the pipe walls, mainly due to inaccurate two-phase flow models that can induce an undesirable ‘dry-out’ phenomenon. Therefore, in this study, a user-defined function subroutine (ANNULAR-UDF) is developed and applied for CFD modelling of an 8.8 mm diameter horizontal pipe, in order to capture transient flow behaviour, flow pattern formation and evolving process and other characteristics in validation against experiments. It is found that CFD modelling is able to capture the liquid phase friction pressure drop about maximum of 30% in deviation, consistent to the correlated experimental data by applying an empirical correlation of Chisholm. Due to the gravity effect, the liquid film is generally thicker at the bottom wall than at the top wall and this trend can be further enhanced by increasing the superficial air–water velocity ratios. These findings could be valuable for HVAC industry applications, where some desirable annular flow features are necessary to retain to achieve high efficiency of heat transfer performance.

Numerical investigation of aqueous graphene nanofluid ice slurry passing through a horizontal circular pipe: Heat transfer and fluid flow characteristics

Ice slurry is an attractive phase-change cold storage medium that offers excellent thermal performance, thus rendering it a good prospect for applications in renewable energy storage, power peak-cutting, and valley filling. In this study, a computational fluid dynamic (CFD) numerical framework is employed based on the particle dynamics approach of an Euler-Euler two-fluid model coupling interphase transfer mechanisms. Thermal transport of a water-based graphene nanofluid ice slurry moving in the turbulent regime in a horizontal circular straight pipe is simulated and described. During the flow, the ice crystals tend to cluster on the top of the horizontal pipe, according to the findings, while uniformity of the crystal size distribution improves with an increase of velocity and the ice packing factor (IPF). Under the conditions of inlet IPF of 10% and heat flux q = 8000 (W m−2), the heat transfer coefficient on the heated section wall is increased by around 9% and 15%, respectively, as compared to pure water ice slurry and water. However, since the nanofluids have a higher viscosity than water, the pressure drop of nanofluid ice slurry is about 5% higher than that of pure water ice slurry in the same working environment.

Numerical quasi-three dimensional modeling of stratified oil-water flow in horizontal circular pipe

The stratified oil-water two-phase flow is commonly encountered in offshore oil production systems, and is considered to be among the fundamental flow configuration in two-phase systems. A numerical quasi-three dimensional model for the calculations of the axial pressure gradient, interface height, water holdup, and the flow field in a fully developed oil-water two-phase stratified pipe flow has been developed. The oil-water curved interface configuration is predicted by using minimum energy model. The model solves the governing equations of the steady axial momentum and mass conservation equations together with a low Reynolds number k～ε model of turbulence for the eddy viscosity, performed in the bipolar coordinate system, for convenient describing the curved interface and mapping of the physical domain. The predicted dynamic parameters, such as interface height of close to the pipe wall and in the middle of the pipe cross-section, water holdup, pressure gradient and flow filed are compared with the experiments. At the same time, this model is utilized to study the variation of these dynamic parameters with increasing superficial oil and water velocities. In addition, the numerical model with concave oil-water interface gives more accurate results than a flat interface. It indicates that the interfacial configuration effects are significant.

The influence of the coefficient of restitution on flow regimes within horizontal particle-laden pipe flows

Numerical simulations of the particle-laden gas–solid flow in horizontal circular pipes have been used to identify the role of particle collision coefficients in flow regimes within it. A four-way coupling Euler–Lagrangian approach was employed, using direct numerical simulations of the gas phase and Lagrangian particle tracking to account for the drag, gravitational and lift forces, together with particle–wall and inter-particle interactions. The influences on the flow of the mass loading ratio (Φm) and of the coefficients of restitution for collisions both between particles and the wall (ep−w) and between particles (ep−p) are assessed by examining the fluid and particle velocities, particle concentration distribution, turbulence kinetic energy, static pressure, inter-phase transferred momentum, and the secondary flow motions of both the fluid and particle phases. Three dominant flow regimes that include three sub-regimes based on their secondary flow patterns are identified, the transition between which depends on the combination of Φm, ep−w, and ep−p. Additionally, the quantitative dependence of these transitions on these three parameters is also reported for a series of Stokes and Froude numbers.

English

Explosions due to gas leaks from accidents and human errors are major concerns faced in natural gas and related industries. Understanding its formation and dissociation mechanisms at field conditions is keys to its successful prevention and management. In the present study, two different meshes with different sized flow channels were proposed to prevent and control methane combustion in a circular gas pipeline. The perforated metal steel of 6 mm aperture and woven wire steel mesh with 1.31 mm aperture, 0.28 mm wire diameter installed in between the flange positioned 2000 mm in a 6300 mm horizontal circular pipe were used. The effects of propagated flame flow temperature variation and equivalence ratio on wire gauze combustion have been investigated and analyzed experimentally. Methane-air mixture at variable concentrations within the lower and upper flammability ranges of 6 and 9% were used in creating an explosive mixture through the pipe length. The parameters investigated were measured and recorded. The results indicated that the inflated period for methane-air concentrations and mesh sizes varied significantly with time. The wall temperature decreased with a decrease in mesh size. The woven wire and perforated plate on flame propagation showed greatly the mitigating capability of the meshes, with a flame temperature declining tremendously. Therefore, woven wire and perforated sheets installed in gas pipelines can reduce explosion risks efficiently and effectively. However, woven wire mesh is preferable because it declines the flame temperature compared to the perforated metal mesh. Key words: Explosion, combustion, flame propagation, temperature, steel meshes (Woven wire and perforated plate).

Flow regimes within horizontal particle-laden pipe flows

This study presents numerical simulations for particle-laden gas–solid flows in horizontal circular pipes to identify the key flow regimes as a function of the main dimensionless parameters. A Euler–Lagrangian approach is employed, using direct numerical simulations (DNS) coupled with a Lagrangian particle tracking (LPT) method, to consider the drag, gravitational and lift forces on particles, as well as the effect of inter-particle collisions. The influence of the Stokes number (Sk), mass loading ratio (Φm) and Froude number (Fr) on critical flow regimes is assessed to identify conditions under which gravity bias becomes either negligible or dominant with regard to fluid characteristics and particle statistics. Three different regimes of the flow behaviour are identified, depending on the combination of these dimensionless parameters. These flow regimes are described and their dependence on these three parameters (Sk, Φm and Fr) is reported, including the significance of gravity in generating a bias on distributions of the flow statistics.

Torricelli's curtain: Morphology of horizontal laminar jets under gravity

Viscous fluid exiting a long horizontal circular pipe develops a complex structure comprising a primary jet above and a smaller secondary jet below with a thin fluid curtain connecting them. We present here a combined experimental, theoretical, and numerical study of this “Torricelli's curtain” phenomenon, focusing on the factors that control its morphology. The dimensional parameters that define the problem are the pipe radius a; the mean exit velocity U of the fluid; the gravitational acceleration g; and the fluid's density ρ, kinematic viscosity ν, and coefficient of surface tension γ. Rescaling of experimentally measured trajectories of the primary and secondary jets using a for the vertical coordinate and LD=U(a/g)1/2 for the horizontal coordinate x collapses the data onto universal curves for x<10LD. We propose a theoretical model for the curtain in which particle trajectories result from the composition of two motions: a horizontal component corresponding to the evolving axial velocity profile of an axisymmetric viscous jet and a vertical component due to free fall under gravity. The model predicts well the trajectory of the primary jet, but somewhat less well that of the secondary jet. We suggest that the remaining discrepancy may be explained by surface tension-driven (Taylor–Culick) retraction of the secondary jet. Finally, direct numerical simulation reveals recirculating “Dean” vortices in vertical sections of the primary jet, placing Torricelli's curtain firmly within the context of flow in curved pipes.

The effect of polyacrylamide drag reducing agent on friction factor and heat transfer coefficient in laminar, transition and turbulent flow regimes in circular pipes with different diameters

In the present study, the effect of polyacrylamide (PAM) addition as a drag-reducing agent on the hydraulic and heat transfer performance of water flow inside horizontal smooth circular pipes was investigated at different heat fluxes. One of the limitations of using solutions containing drag reducing agents (DRAs) is heat transfer reduction (HTR) properties of these substances. The effect of different hydraulic and thermal factors on this phenomenon has been less systematically investigated. In this study, a large number of experiments were conducted under different operating conditions including concentrations of 50, 100, 150 ppm of PAM, inner pipe diameters of 12.7, 19.05, 25.4 mm, applied heat fluxes to pipes including 11, 15, 19 kW/m2, and fluid flowrates at the range of 0.5–20 l/min to prepare laminar, transition, and turbulent flow regimes. The maximum percentage of drag reduction (%DR) obtained at the diameter of 12.7 mm, flowrate 20 l/min, concentration 150 ppm, and at zero-wall heat flux (adiabatic condition) by 50%. By applying heat flux, the%DR decreased. Results showed that the addition of the drag reducing polymer reduces the heat transfer but applying constant heat flux to the pipe decreases the effect of polymer on the percentage of heat transfer reduction (%HTR). The maximum%HTR of 44.5% was achieved at the flowrate of 0.5 l/min and the concentration of 150 ppm and the heat flux of 11 kW/m2. Increasing pipe diameter at all the heat fluxes and polymer concentrations, decreased%DR and%HTR.

Experimental study on the effect of diameter on gas–liquid CCFL characteristics of horizontal circular pipes

The gas–liquid two-phase countercurrent flow in horizontal pipes is closely related to the safe operation of marine diesel engines with underwater exhausts, and nuclear power plants with pressurized water reactors. A visualization experiment on the effect of the diameter size on the counter current flow limitation (CCFL) characteristics of horizontal pipes was performed in the diameter range of 20–130 mm using air and water as the two phases. The results indicate that with a certain gas flow rate, the flow rate of the backflow liquid significantly increases with increasing diameter. Wallis models and those using the Froude–Ohnesorge numbers can correlate the effect of the change in diameter size when the diameters are greater than 100 mm, whereas they lose normalization capability with diameters less than 100 mm. From an analysis of the physical mechanism of formation of this diameter effect, a novel correlation model based on a new dimensionless group for each phase, consisting of the dimensionless inertia and dimensionless viscous force, was proposed for predicting the CCFL characteristics of small diameter pipes. Meanwhile, another correlation based on the Wallis model was also advanced for predicting the CCFL characteristics of large diameter pipes.

Numerical Simulation of the Force Analysis of Gas-Solid Two-Phase Sepiolite Particles in a Horizontal Pipe

In order to study the force that sepiolite particles exert in a horizontal pipe, a method for analysing the simulation of the two-way coupling of gas-solid two-phase flow of sepiolite particles has been proposed in this paper. A three-dimensional model of the gas-solid two-phase flow of sepiolite particles was constructed, based on the Discrete Element Method (EDM). In this model, the force and motion of the sepiolite particles were established according to Newton’s second law, turbulent flow was simulated using the k-ε model, and the two-way coupling correlation between the sepiolite particles and the turbulent flow was established according to Newton’s third law. Through numerical simulation of the gas-solid two-phase flow of sepiolite particles in a horizontal pipe, the distribution of both the velocity and pressure were obtained. In addition, the properties of the gas-solid two-phase flow of sepiolite particles were obtained. The results of the simulation demonstrated that the main forces acting on the sepiolite particles in a horizontal circular pipe in a turbulent state were drag, lift, gravity and the buoyancy of the particles. It was found that the Basset force, the Magnus force, the additional mass force and the pressure gradient force had a negligible influence on the movement of the sepiolite particles.

Investigation of boiling hydrogen two phase flow characteristics in a horizontal circular pipe

Investigation of boiling hydrogen two phase flow characteristics in a horizontal circular pipe