Pipe Flow Research Articles

Comparison of Heat Transfer and Friction in Pipes With Various Internal Roughness

Abstract The heat transfer and friction factor of turbulent pipe flows with different internal roughness are experimentally investigated. Three types of roughness in forms of a mesh, hemispherical elements, and a coil are added to the interior of pipes with an inner diameter of 52.5 mm. The working fluid is air, and the Reynolds numbers vary from 20,000 to 90,000 in increments of 10,000. For investigating the heat transfer, the pipe wall is heated to 375 °C while the inlet air remains at the room temperature. The measurements show that the mesh-type roughness results in a maximum Nusselt number, Nu, increase of approximately 6%, the pipes with hemispherical roughness increased the Nu by a maximum amount of 30%, and the coil increased Nu by up to 60% compared with the smooth pipe. The maximum increase of friction factor is 40% for the pipes with mesh-type roughness, 30% for pipes with hemispherical roughness, and 67% for pipes with coil roughness. The experimental results indicate that adding hemispherical and coil roughness to the internal surface of the pipe can lead to a significant improvement in the rate of heat transfer while adding a mesh-type roughness can have marginal improvements and comes with a large frictional loss penalty. The analysis shows that the highest thermohydraulic performance is achieved using the hemispherical roughness elements.

A New Calculation Model for Equivalent Circulating Density Considering Interface Effect between Various Fluids during Cementing Process

Summary Equivalent circulating density (ECD) is an essential parameter in the construction of oil and gas wells, which can be used to control the downhole pressure and prevent serious incidents such as well leakage or blowouts. Different engineering tasks will lead to changes in the ECD calculation model; the classical pipe flow theory can be used to calculate the ECD of circulating drilling fluid, but it is not suitable for the cementing displacement because it does not consider the interface effect between various fluids. In this paper, a new ECD calculation model has been developed that accounts for the changes in fluid interface morphology between displacing fluid and displaced fluid during the cementing process. Moreover, a simulation of the effects of borehole radius, casing eccentricity, displaced fluid density, and flow rate on the ECD were analyzed and quantified by a numerical approach to solve the fluid dynamics equilibrium equations that describe the flow in the eccentric annuli based on the semi-implicit method for pressure-linked equations (SIMPLE) algorithm. The results show that the calculated ECD predicted by the proposed model is larger than the traditional model with the reduction in the borehole radius, and the maximum deviation at the inlet position can reach 0.03 g·cm−3. Variation in the length of the interface transition zone is the main reason for the deviation in ECD prediction accuracy. In the case of constant casing outer diameter, fluid rheology, and displaced fluid density, the ECD decreases with increasing borehole radius. Meanwhile, it increases with higher displaced fluid density, eccentricity, and annular velocity. It is also shown that the length of the mixing zone can reach up to 40% of the pipe length under the conditions of eccentricity and displacement described in the paper. The proposed model predicts the ECD in the annulus by considering the influence of different engineering parameters on the movement of displacement interface, which can effectively ensure the safety of the cementing operation.

Pollen Rupture and Wall Deposition in Turbulent Pipe Flow

Pollen Rupture and Wall Deposition in Turbulent Pipe Flow

Effect of reduced diameter pipeline and impeller position on the performance of reactor coolant pump

In the reactor coolant pump experiments, there are cases where different impellers are replaced on the same volute for experiments, but due to the different diameter of the impeller inlet, there will be a sudden expansion between the inlet pipeline and the impeller inlet, resulting in a decrease in the efficiency of the pump. In order to solve this problem, a scheme of using an inlet pipe with a reduced diameter structure and changing the position of the impeller was proposed, and based on the three-dimensional incompressible Reynolds N-S equation, the reactor coolant pump device was numerically simulated by CFD software. The data simulation results of the reduced diameter structure, straight pipe flow field and changing the position of the impeller were compared with the model experiments, and the reliability of the calculation results was verified. The results show that the inlet pipe with reduced diameter structure and the method of changing the position of the impeller can effectively solve the problem of efficiency decline caused by the sudden expansion of the flow channel.

Influence of different geometrical dimple configurations on flow behaviour and thermal performance within a 3D circular pipe

Numerical analysis has been performed to evaluate the heat transfer characteristics and per-formance of a circular pipe with geometrical dimple patterns. Using computational fluid dy-namics (CFD) codes, we examine the effects of geometrical configurations on the flow and thermal behavior of circular pipes with concavity (dimple) diameters. Fluid mixing and flow perturbation are facilitated by perforations across the pipe core and wall regions, thereby im-proving thermal efficiency. In addition, a concavity with a diameter of 4 mm enhances heat transfer. Based on the results of the study, the disrupted pipe wall and pipe core region pro-duce swirls and transverse vortices in the flow that provide superior heat transfer compared to conventional (smooth) pipes. In an increasing Reynolds number (Re), mixing, secondary, and separation flows become larger. Performance evaluation factor (PEF) values increased at low Reynolds numbers when dimple diameter was 1mm. As a result of these improved pipes, heat exchanger efficiency may improve in industrial applications, a key factor for energy con-servation.

Experimental investigation of forced convective heat transfer and fluid flow in a mini heat pipe with rectangular micro grooves

In the present study, the convective heat transfer coefficient of water in a laminar flow regime under constant inlet temperature conditions inside a flat mini heat pipe was investigated ex-perimentally. Heat flux ranged from 20-50W and various horizontal heat sink temperatures (operating temperature) ranged from 15-35°C with liquid flow rate (3.563E-8 m3/sec) used during the experiments. The rectangular microchannels performance is evaluated in terms of the temperature profile, heat transfer coefficient, Nusselt number and thermal resistance. The results emphasized that the mini heat pipe temperature gradients are less than the tempera-ture of the copper plate and the heat resistance gradually decreases to its lowest value when the heat flux value reaches its highest value if it does not exceed the capillary limits. The data also demonstrated that the coefficient of heat transfer in the condensation zone is lower than in the evaporation zone at different heat sink temperatures. The augmentation rate for the flat mini heat pipe thermal conductivity reached about 240% at a heat load 30W for the positions of thermosyphon and horizontal, while the rate of increase in the case of the anti-gravity situ-ation at a heat load 30W reaches 210%, then the improvement percentage begins to decrease to 200%. A generalized regression equation is developed for the estimation of the Nusselt number valid for water in a flat mini heat pipe.

Study on the Characteristics of Circumferential and Longitudinal Flow of Vault Concrete during Tunnel Lining Pouring Processes.

With a large number of railroad and highway tunnels opening for operation, the diseases caused by hidden lining defects are increasing. The study of flow characteristics of freshly mixed concrete during tunnel lining casting is the key to revealing the formation mechanism of hidden defects. This paper revealed the location of blank lining formation by investigating the circumferential and longitudinal flow characteristics of concrete in the vault during tunnel pouring to provide suggestions for improving the quality of tunnel lining pouring for the various projects. This paper adopted the method of indoor testing, selected the suitable working conditions and flow parameters, validated the accuracy of the test with a numerical simulation, and simulated the secondary lining pouring process of the tunnel arch from the circumferential direction and longitudinal direction. This revealed the flow characteristics of the freshly mixed concrete in the process of pouring the arch lining. The flow of concrete in the arch lining was basically characterized by two major features which were similar to the flow in the pumping pipe and the layered flow. It also revealed the relationship between the concrete flow rate, flow distance, and the location of the formation of the blank lining risk zone with the slump of the concrete, the pumping pressure, and the radius of the tunnel.

A velocity evaluation method for in-pipe metallic flow through inversion of magnetic field perturbation measured surrounding the pipe

It is important to measure the global and/or local velocity of an in-pipe metallic flow to control its running state in applications such as a Tokamak fusion reactor. The magnetic field outside the pipe wall will be perturbed by the motion induced eddy current when the liquid metal flows across an applied static magnetic field. This phenomenon gives a possibility to evaluate the in-pipe velocity from the measured magnetic field perturbation signals. In this paper, a non-intrusive velocity evaluation method is proposed accordingly for measuring the velocity of liquid metal through measurement and inversion of the magnetic field surrounding the pipe. An efficient forward simulation method to calculate the magnetic field near a metallic flow in a static environmental magnetic field is developed at first. An inversion scheme based on the singular value decomposition and the L-curve method is then proposed to reconstruct the velocity distribution at a pipe cross-section with the linear equations correlating the flow velocity and the magnetic field regulated using the Tikhonov method. The reconstruction results of pipe flows of different velocity modes verified the feasibility and efficiency of the proposed velocity measurement method for in-pipe metallic flows.

DNS and RANS for core-annular flow with a turbulent annulus

DNS and RANS simulations were carried out for core-annular flow in a horizontal pipe and results were compared with experiments carried out with water and oil in our lab. In contrast to most existing studies for core-annular flow available in the literature, the flow annulus is not laminar but turbulent. This makes the simulations more challenging. As DNS does not contain any closure correlations, this approach should give the best representation of the flow (provided a sufficiently accurate numerical mesh and numerical method is used). Various flow configurations were considered, such as without gravity (to enforce an on-average concentric oil core) and with gravity (to allow for eccentricity in the oil core location). Both single-phase and two-phase conditions were considered; single-phase flow refers to the water annulus with imposed wavy wall, whereas two-phase flow includes the determination of the wavy interface. Mesh refinement was carried out to assess the numerical accuracy of the simulation results.

Diffusion Enhancement and Taylor Dispersion for Rotationally Symmetric Flows in Discs and Pipes

In this note, we study the long-time dynamics of passive scalars driven by rotationally symmetric flows. We focus on identifying precise conditions on the velocity field in order to prove enhanced dissipation and Taylor dispersion in three-dimensional infinite pipes. As a byproduct of our analysis, we obtain an enhanced decay for circular flows on a disc of arbitrary radius.

Experimental Study on Gas–Liquid Two-Phase Flow Upstream and Downstream of U-Bends

In this study, the influence of U-bends on the flow and pressure propagation characteristics of a gas–liquid two-phase flow in upstream and downstream straight pipes was investigated experimentally. The superficial velocities of the gas and liquid are 0.18–25.11 m/s and 0.20–1.98 m/s, respectively, covering plug flow, slug flow, and annular flow. The experiments were conducted in U-tubes with inner diameters of 9 mm and 12 mm and with a curvature ratio of 8.33. The U-tube was C-shaped. The pressure fluctuations at the axial measurement points of the straight tubes were measured. Flow images of the distal straight tubes and U-bends were obtained. The disturbance from U-bends in the two-phase flow in the vicinity of the bend is very obvious. The perturbation from U-bends in the fluid in the adjacent straight tubes is highly related to the incoming flow pattern. The slug flow has the most significant influence, whereas the effects of the plug and annular flows are small. Fundamentally, it mainly depends on the weight relationship between the gravity, centrifugal force, and inertial force of the gas–liquid two-phase fluid. The pressure fluctuation propagates in the form of a wave with the same dominant frequency in the straight pipes of the U-tube. The pressure pulsation energy in the straight tubes strengthens with decreasing distance from the 180° return bend. In addition, the pressure fluctuation energy downstream of the U-bend is greater than that upstream of the return bend.

Analytical solution for laminar entrance flow in circular pipes

This study introduces an analytical solution for the laminar entrance flow in circular pipes, aiming to confirm the occurrence of velocity overshoot. Velocity overshoot is characterised by the maximum axial velocity appearing near the pipe wall instead of the central axis. Similar to the previous studies, the analytical solution is derived from the parabolised Navier–Stokes equation; however, the specific approach used in linearising the momentum equation has not been attempted before. The accuracy of this analytical solution has been verified through a comprehensive comparison with various published experimental data. The existence of velocity overshoot at a short distance from the inlet, which is evident in numerous numerical calculations based on the full Navier–Stokes equations and corroborated by recent magnetic resonance (MR) velocimetry experiments, is identified analytically for the first time. The parabolised Navier–Stokes equation has inherent self-similarity with respect to the Reynolds number, implying that $Re$ is incorporated into the dimensionless variables rather than serving as an independent flow parameter. According to both MR velocimetry measurements and the present analytical solution, the self-similarity is not valid immediately following the pipe inlet, and this becomes more evident as $Re$ decreases; hence, the analytical solution derived from the parabolised Navier–Stokes equation cannot accurately predict the evolution of the velocity profile within this region near the pipe inlet.

Experimental Estimation of Turbulent Flame Velocity in Gasoline Vapor Explosion in Multi-Branch Pipes

The overpressure characteristics of gasoline explosions in multi-branch pipes are caused by various factors, with flame velocity as a particularly significant determinant. Overlooking the impact of turbulent flow in the branch pipes can induce a significant discrepancy in the outcome when using laminar flame velocity to determine the maximum rate of overpressure rise. To quantify the impact of turbulent flame velocity on the rate of overpressure rise in the gasoline explosions within branch pipes, the laminar flame velocity was replaced with its turbulent counterpart. Additionally, modifications to the formula for calculating the maximum overpressure rise rate were implemented. Then, experimental data of peak explosion overpressure and overpressure rise rate under different numbers of branches were obtained. Finally, the empirical data were inputted into the modified formula to determine the maximum rate of overpressure rise, thus enabling the calculation of the turbulent flame velocity across varying numbers of branches. The findings reveal a positive correlation between the number of branches and the turbulent flame velocity during tube explosions. When the number of branch pipes increased from 0 to 4, the turbulent flame velocity was found to range from 8.29 to 13.39 m/s. The increase in the number of branches did not consistently enhance the turbulent flame velocity. As the number of branches increased from zero to three, the turbulent flame velocity rose accordingly. Differently, as the number of branches exceeds three, the turbulent flame velocity exhibits fluctuations and peaks at a level approximately 1.8 times higher. The research method of this paper can provide a reference for estimating the turbulent flame velocity in the combustion process of flammable gas explosions in multi-branch tunnels.

Capturing the edge of chaos as a spectral submanifold in pipe flows

An extended turbulent state can coexist with the stable laminar state in pipe flows. We focus here on short pipes with additional discrete symmetries imposed. In this case, the boundary between the coexisting basins of attraction, often called the edge of chaos, is the stable manifold of an edge state, which is a lower-branch travelling wave solution. We show that a low-dimensional submanifold of the edge of chaos can be constructed from velocity data using the recently developed theory of spectral submanifolds (SSMs). These manifolds are the unique smoothest nonlinear continuations of non-resonant spectral subspaces of the linearized system at stationary states. Using very low-dimensional SSM-based reduced-order models, we predict transitions to turbulence or laminarization for velocity fields near the edge of chaos.

Two-dimensional Numerical Analysis of Waves at Interface of Laminar Core-annular Flow in Vertical Pipe: Detailed Investigation of Influence of Several Physical Parameters

Two-dimensional Numerical Analysis of Waves at Interface of Laminar Core-annular Flow in Vertical Pipe: Detailed Investigation of Influence of Several Physical Parameters

High efficiency integrated urban flood inundation simulation based on the urban hydrologic unit

As the impact of flooding intensifies globally in metropolitan areas, there is an urgent need for high-resolution flood forecasting models to facilitate preparedness and mitigate flood impacts. In response, we have proposed a high efficiency algorithm (HEA) designed to simulate urban flood inundation, leveraging the urban hydrologic unit (UHU) concept from an urban hydrological cycle perspective. The HEA significantly reduces the computational demands associated with high-resolution modeling by using a hydrologic unit derived from the digital elevation model (DEM). This approach effectively shifts the overwhelming burden of computational load to the hydrodynamic algorithm (HDA), which is grounded in the Shallow Water Equations (SWEs), thus enabling efficient flood inundation simulation crucial for time-critical decision making during extreme events. Our research also incorporated the HEA and HDA methods into a self-developed, distributed-framework basin modeling system, named the Taihu Basin Model (TBM). Both the HEA and HDA models were calibrated and validated with observed data on pipe level, flow rate, and inundation depth from our Shuangqiaobang experimental fields. Comparative analysis, focusing on simulated urban flood inundation distribution characteristics, simulation accuracy and timeliness, demonstrated the superior effieicney of the HEA method by three orders of magnitude. The consistency between observed data and the simulated results of both HEA and HDA models underscores the accuracy and reliablility of these models. The HEA model’s simulated urban flood inundation distribution appears more patchy and localized compared to the HDA model, due to the generalization of urban UHUs in the TBM.

Evaluating the effectiveness of CFD-DEM and SPH-DEM for complex pipe flow simulations with and without particles

We investigate the effectiveness of two computational fluid dynamics (CFD) approaches: mesh-based CFD and meshfree particle-based smoothed particle hydrodynamics (SPH) for simulating pipe flows of varying complexity. The study covers laminar and turbulent flows, different fluid rheologies (Newtonian, power-law, Bingham plastic, Herschel-Bulkley), and different particle-laden scenarios, validated using experimental Lagrangian measurements obtained by positron emission particle tracking or available theoretical solutions, as appropriate. We assess these methods based on their ability to predict radial profiles of local phase velocity and concentration, as well as computational cost. In single-phase flows, CFD aligns well with experimental data and theoretical models. SPH exhibits boundary discrepancies due to no-slip condition approximations and limitations in turbulent flow simulation which need further development. Integrating the discrete element method (DEM) significantly enhances both techniques for particle-liquid flows. Mesh-based CFD is computationally efficient, while particle-based SPH can offer more insights into Lagrangian fluid dynamics.

Gasoline Engine Inlet Structure Design and Performance Analysis

By creating a three-dimensional model of the intake pipeline, using AVL software to mesh and virtual simulation experiments, using the control variable method, changing the temperature conditions and pressure conditions one by one to observe the flow of the air pipe and the cylinder, and observing the numerical changes of the flow direction coefficient and tumbling flow ratio, the best solution was found. Through the virtual simulation experiment of the 3D model, the influence of external factors such as temperature and pressure on the air flow in the cylinder is obtained. The relationship between the characteristic parameters of the air intake tract was found through AVL numerical simulation, and the established three-dimensional model could accurately obtain the data after testing, which provided theoretical proof for the subsequent optimization scheme. The experimental results show that the tumbling flow ratio is increased as much as possible without changing the flow coefficient and the fuel economy of the engine is improved. But it also affects the flow coefficient, making it go down. Temperature has little effect on the flow in the cylinder. The flow velocity in the cylinder changes significantly under different pressures, and the area of the vortex area increases.

An Experimental Study of Heating Heavy Fuel Oil by Hot Air using Helical Fins in a Double-Pipe Heat Exchanger

In present work, the effect of helical fins with height 20 mm and pitch 100 mm on the performance of the double pipe heat exchange investigated experimentally. The heat exchanger had been chosen as a heat recovery device in bricks factory to recover heat from exhaust gases to preheat the heavy fuel oil. Air had been chosen as a hot gas instead of furnace exhaust gases because of the similar thermal properties and it flows in the inner pipe with different velocity (20, 27, and 34) m/s and inlet temperature (200, 225) °C while, heavy fuel oil enters shell side with counter flow at mass flow rates (0.06, 0.08, and 0.1) kg/s and constant inlet temperature of 40 °C. Both of pipes and helical fins are made from stainless steel. The experimental results show that increasing Reynolds number from 139139 to 333934 led to increase heat transfer rate, oil outlet temperature, overall heat transfer coefficient and effectiveness of heat exchanger with (8%, 4%, 5% and 5%) respectively while, increasing oil mass flow rate from (0.06 to 0.1) kg/s cause decreasing oil outlet temperature and effectiveness of with (10% ,14%) respectively. The results shown the double pipe heat exchanger with helical fins produce heat transfer rate and oil outlet temperature higher than smooth double pipe heat with average 15% and 8.6%, as well as increasing Nusselt number, Overall heat transfer coefficient and effectiveness of heat exchanger with average 26%,15% and 13% respectively. The results clear that, for 225°C exhaust air and velocity 27 m/s, the application of double pipe with helical fins by preheat heavy fuel oil could reduce the viscosity and reduce electric power required and save 1.69 MW annually for one factory.

Quantitative description of polymer drag reduction: Effect of polyacrylamide molecular weight distributions

The effect of molecular weight distribution of polyacrylamide (PAAm) on drag reduction was studied in two flow geometries. Commercial PAAm with different weight averaged molecular weights (Mw = 5 × 105 to 1.8 × 107 g/mol) were investigated in turbulent pipe and rotational flows. Comparison of PAAm with different molecular weight distributions showed that drag reduction is not only a function of the averaged molecular weight. Broader polymer molecular weight distributions provided increased drag reduction over polymers of same average molecular weight but with a more narrow distribution. The role of distribution widths is of significance as polymer degradation in turbulent flows causes narrowing of the molecular weight distributions. Multiple linear regression was employed to connect weight fractions of polyacrylamide with drag reduction. Multiple linear regression was successfully applied to describe drag reduction in turbulent pipe and rotational flows indicating that drag reduction can be quantitatively derived from the molecular weight distribution of PAAm.