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This article deals with the application of the temperature oscillation method (TOIRT method) to the laminar flow of water in a pipe. This dynamic and contactless method was derived for the assumption of homogeneous temperature on the fluid side, but this assumption is violated in the case of laminar flow. Numerical simulations were used to discover the fundamental influence of the amount of incident heat flux, which is modulated by the sine function, on the resulting local values of the heat transfer coefficient. The frequency of the transmitted signal, on the other hand, has no effect. The experimental measurement confirmed the numerical results even with a deviation of 25%, which is still a good result due to the sensitivity of the experimental method in this area. [ABSTRACT FROM AUTHOR]

Amputees often experience high temperatures between the amputated limb and the prosthetic socket, necessitating the use of cooling devices to mitigate this issue. However, challenges arise with the location and size of conventional heat sinks. This research proposes a novel heat sink utilising a phase change material (PCM) to dissipate heat. The leg was chosen as the site for the heat sink, designed in a cylindrical shape. Coolant flow pipes were arranged in a branched configuration inspired by constructal theory, constrained by the dimensions of the artificial leg. The degrees of freedom for the constructal design are branches akin to arterial and venous branching, aiming to minimise pressure drop. Four heat sinks with varying degrees of branching were compared based on temperature reduction, heat dissipation, pressure drop, phase change material melting capacity, and operational efficiency. The cylindrical heat sink measures 50 mm in diameter and 300 mm in length. Ice was employed as the PCM, with water served as the working fluid. The working fluid's temperature and flow rate were maintained at 40 °C and 0.2 L/min, respectively. The experimental work was prepared to validate the theoretical model. The study revealed that the proposed heat sink design, with increased branching, led to a significant temperature reduction, achieving up to 39.62%. Moreover, heat dissipation increased by 236% compared to a single-tube heat sink. The use of branched pipes resulted in a manageable increase in pressure drop, peaking at 39.9 Pa, well within pump specifications, while markedly enhancing heat dissipation. The melting time of the PCM and the melting area increased as the number of branches of the heat sink increased. Ultimately, applying constructal theory in heat sink design for PCM demonstrated its superior performance within spatial constraints, providing a promising solution for prosthetic cooling. [ABSTRACT FROM AUTHOR]

Understanding the flow dynamics of non-Newtonian fluids is crucial in various engineering, industrial, and biomedical applications. However, the existing generalized Reynolds number formulations for non-Newtonian fluids have limited applicability due to their dependencies on their specific viscosity models. In this study, we propose a new viscosity-model-independent generalized Reynolds number formulation for laminar pipe flow. The proposed method is based on the direct adaptation of the measurement principles of rotational viscometers for wall shear rate estimation. We assess the accuracy of this proposed formulation for power-law and Carreau-Yasuda viscosity models through robust friction factor experiments. The experimental results demonstrate the applicability and effectiveness of the proposed viscosity-model-independent Reynolds number, as the measured friction factor data align closely with our Reynolds number predictions. Furthermore, we compare the accuracy of our Reynolds number formulation against established generalized Reynolds formulations for pure shear-thinning (Carreau-Yasuda) and viscoplastic (Herschel-Bulkley-extended) models. The results of the comparative analysis confirm the reliability and robustness of this generalized Reynolds number in characterizing and interpreting flow behavior in systems with visco-inelastic non-Newtonian fluids. This unified generalized Reynolds number formulation presents new and significant opportunities for precise pipe flow characterization and interpretation as it is applicable to any visco-inelastic (time-independent) viscosity model without requiring additional derivations. [ABSTRACT FROM AUTHOR]

This paper designs and builds a stormwater pipe-river/channel experimental system at the first attempt to observe hydraulic dynamics between pipe flow and downstream water levels under different steady state conditions. In addition, a three-dimensional (3D) model is developed to facilitate the understanding of this complex hydraulic interaction, and the reliability of a widely used one-dimensional (1D) model is first investigated. Experiment and simulation results show that (1) a high downstream water level can increase pipe flow capacity at the early stage, and the pipe flow is followed by a slightly downward trend and finally rapidly decreased, (2) pipe flows exhibit complex behaviors during the transition from nonfull to full pipe flow by altering flow area and velocity, and (3) the observed flows are significantly lower than those from the 1D model for the nonfull pipe flow scenario. This study offers insights to the underlying complex hydraulic properties between pipe flows and downstream water levels, and also shows that the 1D model is insufficient to reveal such an interaction process, which may underestimate the urban flooding risk. [ABSTRACT FROM AUTHOR]

High-order accurate Large-eddy simulations (LES) have been carried out for compressible, turbulent flow through two bell-shaped convergent-divergent nozzles- one with a short divergent portion and the other with a longer one. An explicit filtering approach based on approximate deconvolution method is used for the LES. The nozzles have isothermal walls and circular cross-sections. The incoming flow is a turbulent, subsonic fully developed pipe flow at centreline Mach number of around 0.4 and friction Reynolds number 216. An adaptive filter is used to capture the shocks appearing in the divergent portion of the nozzles. The complicated behaviour of the mean flow, Reynolds stresses, production and pressure-strain terms of the axial Reynolds stress budget in the shock train region is shown. The broadband nature of the shock train oscillations having multiple dominant frequencies in these nozzles is observed in the present LES. [ABSTRACT FROM AUTHOR]

The characteristics of uniform momentum zones (UMZs) and UMZ interfaces in turbulent channel flow (TCF) at friction Reynolds number ranging from 600 to 2000 are investigated. The focus is on the Reynolds number effect and the difference among the turbulent channel flow, turbulent pipe flow (TPF), and turbulent boundary layer (TBL). The UMZ is identified using the approach of probability density histograms, a discrete approximation of the probability density function. We find that the average number of UMZs increases with the Reynolds number, similar to the findings in the TBL. The first group of UMZ in the TCF, namely the quiescent core, has a thicker thickness at a higher Reynolds number. Therefore, the UMZ closer to the channel centre significantly influences high Reynolds number wall turbulence by occupying a large portion of the channel. With increasing Reynolds number, the intensity of spanwise vorticity at the UMZ interface increases, while the thickness of the local maximum decreases. The dominance of prograde vorticity at the interface also increases with the Reynolds number. Moreover, the contortion of the UMZ interface is significantly enhanced at high Reynolds numbers than at low Reynolds numbers in both the streamwise and spanwise directions. Furthermore, the number of UMZ for a given snapshot is related to the overall velocity fluctuations in the subregion, increasing with large-scale Q2 events and decreasing with large-scale Q4 events. Comparing the three flow configurations, UMZs show similarities in their trends, along with two notable differences. First, the TPF has more UMZs compared to the TCF and TBL. Second, the innermost group in the TPF is considerably thicker than that of the higher ranks, a pattern absent in the TCF and TBL. The present findings advance the understanding of UMZs in TCF and demonstrate the similarities and differences between the cases of TCF and TBL. [ABSTRACT FROM AUTHOR]

The most common and destructive event of unsteady flow in pipes is water hammer. This phenomenon is caused by a sudden change in boundary conditions in pressurized pipes. Unsteady flow in pipelines can lead to a significant increase or decrease in pressure. This pressure generation may cause cavitation, bursting of pipes, and failure of the whole system. One type of equipment that can control both positive and negative pressure phases is a pressurized tank. Implementing such a pressure tank can impose increased costs. In order to reduce the design costs, the combination of a flywheel with the pressure tank can be used. In this study, a transmission pipeline from Zarineh River to Tabriz city is numerically simulated, and the effect of increasing the inertia of the flywheel on the reduction of the pressurized tank volume is investigated. The results show that increasing the flywheel inertia from 125 to 165 Nm2 can reduce the pressurized tank volume from 90 to 75 m3. [ABSTRACT FROM AUTHOR]

In data assimilation, observations are fused with simulations to obtain an accurate estimate of the state and parameters for a given physical system. Combining data with a model, however, while accurately estimating uncertainty, is computationally expensive and infeasible to run in real-time for complex systems. Here, we present a novel particle filter methodology, the Deep Latent Space Particle filter or D-LSPF, that uses neural network-based surrogate models to overcome this computational challenge. The D-LSPF enables filtering in the low-dimensional latent space obtained using Wasserstein AEs with modified vision transformer layers for dimensionality reduction and transformers for parameterized latent space time stepping. As we demonstrate on three test cases, including leak localization in multi-phase pipe flow and seabed identification for fully nonlinear water waves, the D-LSPF runs orders of magnitude faster than a high-fidelity particle filter and 3-5 times faster than alternative methods while being up to an order of magnitude more accurate. The D-LSPF thus enables real-time data assimilation with uncertainty quantification for the test cases demonstrated in this paper. [ABSTRACT FROM AUTHOR]

The formation of oxygen bubbles in the anodic circuit of a polymer electrolyte membrane (PEM) electrolyser is a major technological problem as it greatly affects heat transfer, process performance and safety. Overall, bubbles evolve in the pipe flow upstream of the gas separator due to oxygen super-saturation created by the chemical reaction at the anode. The accurate prediction of bubble formation in the pipes is important for the correct positioning and design of the gas separator. This paper therefore presents a cell-based one-dimensional numerical model that estimates bubble evolution in a horizontal pipe-flow. For this purpose, the model considers bubble growth at nucleation sites and in the flow, enabling the prediction of the corresponding gas fraction at different locations within the cooling circuit. Furthermore, a sensitivity analysis was conducted based on the derived model to evaluate the impact of various parameters on the degassing rate. It was found that the smaller the pipe diameter, the greater the initial gas content and the greater the number of nucleation sites, the shorter the pipe length required to achieve solubility. • Bubbles evolve in the cooling circuit of PEM-electrolysis due to super-saturation. • A cell-based 1D numerical model predicts the gas fraction at various locations. • A sensitivity analysis shows the impact of various parameters on the degassing. • Degassing is improved by smaller pipe diameters and a higher initial gas fraction. • The higher the number of nucleation sites, the better the degassing. [ABSTRACT FROM AUTHOR]

Wax/paraffin deposition in production wells and oil pipelines is a major challenge for oil production. Extensive research has been conducted to improve understanding of this process. This paper presents a review of experimental work carried out with flow loops. Previous research investigated paraffin deposition process under the influences of temperature, flow rate/velocity, shear stress, water fraction, gas phase, pipe material, asphaltene concentration, and chemical inhibitors. Test results reveal that temperature and shear stress have significant impacts on wax deposition. Limited research has been conducted on wax deposition under multiphase flow. Even though more than 20 years of efforts have been spent on wax deposition studies, unfortunately we have not fully understood this phenomenon. [ABSTRACT FROM AUTHOR]

A three-lobed helical pipe was installed downstream of the bend of a vertical-horizontal pneumatic pipeline. The swirl characteristics under different helical pipe structures were investigated. Results show that: (a) the maximum velocity region rotates quasiperiodically, and the smaller the pitch, the faster the rotation; (b) the 3D morphological changes of the axial velocity distribution in downstream sections are similar: from an arch to a pit and finally to a uniform flat top. The tangential velocity appears as a Rankine vortex near the wall; (c) the swirl decays rapidly along the downstream. The initial swirl intensity, proportional to the helical pipe length, increases first and then decreases with decreasing pitch, whereas the structural parameters have minimal effect on the swirl decay rate; (d) the helical tube remarkably increases the system energy consumption, and the total pressure drop is inversely proportional to the pitch and proportional to the length. [ABSTRACT FROM AUTHOR]

Based on existence results for the Stokes operator and its solution properties in manifolds with cylindrical ends by Große et al. and Kohr et al., the Stokes flow in a three‐dimensional compact domain Ω+$$ {\Omega}^{+} $$ with circular openings Σj(j=1,2)$$ {\Sigma}_j\kern0.1em \left(j=1,2\right) $$ through which the fluid enters and leaves Ω+$$ {\Omega}^{+} $$ through unbounded cylindrical pipes the Stokes flow is modeled as a mixed boundary value problem Ω+$$ {\Omega}^{+} $$ whereas in the cylindrical ends, the velocities and pressures are constant on every straight line in the cylindrical directions with initial values from the openings Σj$$ {\Sigma}_j $$ of Ω+$$ {\Omega}^{+} $$. These values equal the velocities and pressures which are obtained from the mixed boundary values' solution in Ω+$$ {\Omega}^{+} $$ at the openings Σj$$ {\Sigma}_j $$. [ABSTRACT FROM AUTHOR]

Bentonite slurry is readily available, and extensively used in underground construction, where the in-situ infiltration behavior of the slurry is of great interest. As a solid–liquid biphasic fluid, slurry exhibits distinct fluid properties that set it apart from pure water. These unique properties play a significant role in determining its infiltration behavior during construction, making it a critical factor that cannot be overlooked. In this study, slurry shear tests were carried out using a rotational viscometer to characterize its fluid properties, and constant water head infiltration tests were conducted by a self-designed infiltration device to investigate the infiltration behavior of slurry in sand stratum. In addition, theoretical derivation based on the pipe flow was implemented to simulate the slurry flow in the stratum. The results show that, as the slurry infiltration continues, the relationship between the yield stress and initial hydraulic gradient experienced a "nonlinear to linear" process. The nonlinearity at the early stage of slurry infiltration is related to the evolution of the core phase of the slurry, which is the root cause of the nonlinear evolution of the fluid property and infiltration curves. A predicted relation between the fluid parameters of the slurry and its multiphase infiltration behavior was established, which are able to give a better understanding of the slurry behavior in engineering design. [ABSTRACT FROM AUTHOR]

The intermittency characteristics in transitional and turbulent flows can provide critical information on the underlying mechanisms and dynamics. While time–frequency (TF) analysis serves as a valuable tool for assessing intermittency, existing methods suffer from resolution issues and interference artifacts in the TF representation. As a result, no suitable or accepted methods currently exist for assessing intermittency. In this work, we address this gap by presenting a novel TF method—a Fourier-decomposed wavelet-based transform—which yields improved spatial and temporal resolution by leveraging the advantages of both integral transforms and data-driven mode decomposition-based TF methods. Specifically, our method combines a Fourier-windowing component with wavelet-based transforms such as the continuous wavelet transform (CWT) and superlet transform, a super-resolution version of the CWT. Using a peak-detection algorithm, we extract the first, second, and third most dominant instantaneous frequency (IF) components of a signal. We compared the accuracy of our method to traditional TF methods using analytical signals as well as an experimental particle image velocimetry (PIV) dataset capturing transition to turbulence in pulsatile pipe flows. Error analysis with the analytical signals demonstrated that our method maintained superior resolution, accuracy, and, as a result, specificity of the instantaneous frequencies. Additionally, with the pulsatile flow dataset, we demonstrate that IF components of the fluctuating velocities extracted by our method decompose energy cascade components in the flow. Additional investigations into corresponding spatial frequency structures resulted in detailed observations of the inherent scaling mechanisms of transition in pulsatile flows. [ABSTRACT FROM AUTHOR]

A combined positron emission particle tracking (PEPT) and X-ray computed tomography (CT) technique is presented, and its utility is demonstrated through investigation of flow in a pipe with twisted tape swirl insert with varying flow conditions (diameter-based Reynolds numbers 16,300–63,300). A description of this technique is given, as well as data handling practices used to relate geometric information captured by CT to fluid flow data gathered via PEPT. It is found that the CT component is readily capable of capturing the stainless steel insert geometry in this present system, but the use of combined plastic and metal materials leads to artifacts in imaging of the plastic surface. Nonetheless, CT data are related to PEPT flow measurements, and average velocity fields are calculated via a pseudo-framing and interpolation scheme and used to visualize and interrogate key flow phenomena within the system. Radial velocity profiles of the mean flow characteristics are seen to collapse to a nearly common form across all flow conditions considered. Helical vortices are seen propagating through the flow field, generated by bypass flow around the gap between the insert and pipe wall, with additional coherent secondary flow structures seen in the higher Reynolds number cases. These findings enhance the understanding of the mixing mechanisms in these swirl flows and encourage the continued development of PEPT-CT methodologies for 3D flow measurements in optically inaccessible systems. [ABSTRACT FROM AUTHOR]

Two-phase pipe flow occurs frequently in oil & gas industry, nuclear power plants, and CCUS. Reliable calculations of gas void fraction (or liquid holdup) play a central role in two-phase pipe flow models. In this paper we apply the fractional flow theory to multiphase flow in pipes and present a unified modeling framework for predicting the fluid phase volume fractions over a broad range of pipe flow conditions. Compared to existing methods and correlations, this new framework provides a simple, approximate, and efficient way to estimate the phase volume fraction in two-phase pipe flow without invoking flow patterns. Notably, existing correlations for estimating phase volume fraction can be transformed and expressed under this modeling framework. Different fractional flow models are applicable to different flow conditions, and they demonstrate good agreement against experimental data within 5% errors when compared with an experimental database comprising of 2754 data groups from 14 literature sources, covering various pipe geometries, flow patterns, fluid properties and flow inclinations. The gas void fraction predicted by the framework developed in this work can be used as inputs to reliably model the hydraulic and thermal behaviors of two-phase pipe flows. [ABSTRACT FROM AUTHOR]

Purpose: Permeability is one of the primary concerns in geotechnical engineering research. The permeability coefficient, the most significant parameter defining permeability, has a significant impact on the mechanical and physical properties of the soil by virtue of its value. Because soil is a bulk material and its internal seepage channels are intricate, it is challenging to accurately describe those using straightforward physical parameters. As a result, the models currently in use for calculating the coefficient of permeability of soils are mostly skewed towards empirical statistics and have issues with uneven magnitude and ambiguous physical significance. Thus, one of the key scientific issues in the field of geotechnical engineering is the development of a permeability coefficient estimate model that can characterize the seepage channel. Methods: Based on the idea of hydraulic radius in circular pipe flow, this paper establishes the calculation method of the equivalent hydraulic diameter by analyzing the microstructure of the soil body and proposes the idea of equivalent hydraulic force inside the soil body, taking into account factors such as granular gradation, dry density, and specific gravity of solid particle. Furthermore, a theoretical model based on the equivalent hydraulic diameter has been constructed for the permeability coefficient of the soil body, by introducing the coefficient of fluid dynamic viscous and the water gravity. In order to assess the accuracy and validity of the equivalent hydraulic diameter and the model of soil permeability coefficient estimation, permeability tests were designed and the results of undisturbed loess, single particle size quartz sand, and multi-grain-size quartz sand combinations were obtained. The results of the estimated model, the traditional estimated model, and the permeability coefficient of the tests were compared and analyzed. Results and conclusions: The findings indicate a square relationship between the permeability coefficient and the equivalent hydraulic diameter and a correlation coefficient of more than 97% between the equivalent hydraulic diameter calculation results and the measured permeability coefficient results; the error analysis results demonstrate that the equivalent hydraulic diameter calculation results can meet the permeability test error range. This paper presents an estimation model for the soil permeability coefficient that is universally applicable to a wide range of particle sizes (0.002 to 2 mm). It is compared with experimental test results, Terzaghi formula, Hazen formula, and Amer formula. The results demonstrate that the model developed in this paper has a higher degree of agreement with the experimental results. [ABSTRACT FROM AUTHOR]

Variable air volume air-conditioning system (VAV system) has multiple control loops that interfered with each other, which has serious impacts on its actual operation effect. To solve this problem, the index of global hydraulic stability, which takes the physical quantity of the pipe network pressure and the air flow rate as reference, is proposed based on Graph theory, and a pipe network model for the hydraulic calculation is built. Then, the simulation study based on the actual operation data is carried out in MATLAB. The distribution of the pressure and the air flow in the pipe network is obtained, and the action interferences among adjacent terminal boxes are analyzed based on global hydraulic stability under damper position regulation strategy (DP strategy) and fan frequency regulation strategy (FF strategy). Results indicate that the FF strategy can decrease the total change distance of the damper position compared with the DP strategy, and then the fluctuation of the pressure and the air flow can be reduced. The contribution of this study is to provide an evaluation index of global hydraulic stability, which can also be used in other air-conditioning systems with multiple terminals and multiple control loops. [ABSTRACT FROM AUTHOR]

AbstractGas–liquid swirling pipe flow plays an essential role in phase separators. Bubble motions and flow patterns transitions in the flow are crucial for further investigation of this flow. However, much attention has been paid to these in non-swirl flow instead of swirl flow. In this work, bubble separation generated by a vane-typed swirler in a vertical pipe with an inner diameter of 62 mm was experimentally studied. Superficial air velocities (0.036 − 1.41 m/s) and superficial water velocities (0.02 − 0.95 m/s). The results show that dispersed bubbles gradually transform to gas column flow with increasing superficial water velocities (0.093 − 0.640 m/s) in the swirl flow; gas column flow gradually transforms to swirling intermittent flow with increasing superficial air velocities (0.05 − 0.40 m/s), and one peak increases to two peaks in the probability density function curve of pressure drop; slug flow can transform to swirling intermittent flow. Finally, transition criteria for bubble separation were proposed: when the turbulent fluctuations are strong enough to overcome centrifugal force, then the bubbles move to the pipe center and coalescence with each other, lead to the transition of gas column flow/swirling intermittent flow. [ABSTRACT FROM AUTHOR]

Regulatory gaps and safety concerns induce uncertainty amongst stakeholders, increases investment risk and impedes the deployment of hydrogen refueling stations (HRS). In this study, a risk-informed approach was employed on a potential HRS in Canada, to optimize separation distances, and identify regulatory gaps. This risk assessment improves upon previous ones that assumed uniform hydrogen leak sizes throughout the entire HRS. This analysis considers variable leak sizes based on the varying pipe flow area in different parts of the HRS like the tube-trailer area, hydrogen system area and the dispenser area. For each area, the potential leak sizes of 0.1%, 1%, 10%, and 100% of the pipe flow area were evaluated to cover a range of possible leaks. Leak frequency for 1% and 10% leak sizes were found to be 2.38E-02/year and 2.68E-03/year indicating relatively smaller difference as compared to other leak sizes. Leak frequency and consequence distances were assessed using HyRAM+ (V5.0) and Safeti (V8.9) respectively. Separation distances, which refer to the required spacing measured from the hydrogen process areas beyond which the risks are considered tolerable, were assessed for the tube-trailer area, storage area, and dispenser area at 350 bar and 700 bar dispensing pressures. Results indicated that 700 bar scenario requires substantially larger separation distances up to 39.1 m due to extended harm distances at lower temperatures. This study proposes safety barriers which reduced jet and flash fire frequencies by 100 and 20 events/year, respectively, that enables decreasing separation distances for each area. The comprehensive evaluation of separation distances generates important insights into separation distance criteria and guidelines, addressing the identified gap in existing codes and standards. While the study focuses on a potential HRS in Canada, the methodology, approach, and results presented are broadly applicable and transferable to similar contexts globally. • 10% leak size optimized separation distance for areas in hydrogen refueling station. • 700 bar dispenser required the largest separation distance of 39.1 m • Proposed safety barriers reduced jet fires by 100, flash fires by 20 per year. • Canadian Hydrogen Installation Code lacks guidelines for risk-informed separation. • Regulatory alignment needed with hydrogen requirements in provincial fire code. [ABSTRACT FROM AUTHOR]

Modulated pressure waves propagating in the drilling fluids inside the drill string are a reliable real-time communication technology that transmit data from downhole to the surface during oil and gas drilling. In the analysis of pressure waves' propagation characteristics, the modeling of transient friction in non-Newtonian fluids remains a great challenge. This paper establishes a numerical model for transient pipe flow of power-law non-Newtonian fluids by using the weighted residual collocation method. Then, the Newton–Raphson method is applied to solve the nonlinear equations. The numerical method is validated by using the theoretical solution of Newtonian fluids and is proven to converge reliably with larger time steps. Finally, the influencing factors of the wall shear stress are analyzed using this numerical method. For shear-thinning fluids, the friction loss of periodic flow decreases with the increase in flow rate, which is opposite to the variation law of friction with the flow rate for stable pipe flow. Keeping the amplitude of pressure pulsation unchanged, an increase in frequency leads to a decrease in velocity fluctuations; therefore, the friction loss decreases with the increase in frequency. [ABSTRACT FROM AUTHOR]

In industrial production and water resource management involving fluid flows, two-phase flow measurement in complex environments has always been a research hotspot. In this study, a broadband detection device (40–110 MHz) suitable for two-phase flow in pipes was designed in a laboratory environment, the impedance response of two-phase flow was investigated under different salinity conditions and flow patterns, and a new impedance dispersion model suitable for two-phase flow in pipes was built. The experimental results show that the new model can better describe the rules of impedance dispersion in two-phase flow and is universally applicable, and that the equivalent solution resistance and interfacial polarization frequency have a stable functional relationship with water holdup. Based on the static experimental results, water holdup evaluation models for four flow patterns were established, and the dynamic detection results were predicted. The prediction results show that the new method proposed herein is not affected by changes in salinity and flow pattern when the flow pattern is known, and that its accuracy can meet the production requirements. This study expands the application range of traditional single-frequency conductivity detection techniques and provides a new idea for the development and improvement of systems for online detection of water holdup in two-phase flow. [ABSTRACT FROM AUTHOR]

• A numerical approach for obtaining gas-liquid flow parameters utilizing one-dimensional two-fluid model was proposed. • The two-fluid model was discretized by implicit FEM techniques utilizing the proposed algorithm in this paper. • Four cases utilizing different meshes were utilized to illustrate the gas puffing effect on the momentum exchange process. • The transient numerical trends indicate that the gas puffing manifests in two physical forms between different flow regions. The accumulation of liquid condensate in the wet gas pipelines gives negative effects on the piping efficiency and flow managements. Accurate prediction of the condensate behavior is of crucial importance in the pipeline engineering. In this study, the one-dimensional two-fluid model with the stratified modeling in its source term is used to describe the gas-liquid kinetic motion along the pipe and the flow fields obtained from the newly proposed numerical approach are utilized to analyze the flow characteristics. Firstly, four cases with varying inlet liquid fractions, outlet pressures, and different meshes are utilized to investigate the gas-liquid steady-state variations along the pipe. The numerical results indicate that the outlet pressure influences the working pressure of the inlet gas-liquid, subsequently altering the equilibrium state and momentum exchange direction near the inlet, resulting in different condensate distributions in the pipeline. In the transient analysis with initial empty pipe, the inlet gas-liquid mainly impacts the pressure wave propagations in pressure spread stage, the gas kinetic motion in gas filling stage and the motion of the dividing interface between different regions in liquid filling stage, which is validated by the proposed numerical approach through comparison with the simulation tool OLGA designed by Schlumberger. Furthermore, when the liquid condensates appear in the initial state, the transition zones have two physical forms between different flow regions, which include the sudden dividing interface due to the high liquid amount carried by the inlet gas and the transition region resulted from the liquid accumulations. [ABSTRACT FROM AUTHOR]

Many problems in fluid mechanics require single-shot 3D measurements of fluid flows, but are limited by available techniques. Here, we design and build a novel flexible high-speed two-color scanning volumetric laser-induced fluorescence (H2C-SVLIF) technique. The technique is readily adaptable to a range of temporal and spatial resolutions, rendering it easily applicable to a wide spectrum of experiments. The core equipment consists of a single monochrome high-speed camera and a pair of ND: YAG lasers pulsing at different wavelengths. The use of a single camera for direct 3D imaging eliminates the need for complex volume reconstruction algorithms and easily allows for the correction of distortion defects. Motivated by the large data loads that result from high-speed imaging techniques, we develop a custom, open-source, software package, which allows for real time playback with correction of perspective defects while simultaneously overlaying arbitrary 3D data. The technique is capable of simultaneous measurement of 3D velocity fields and a secondary tracer in the flow. To showcase the flexibility and adaptability of our technique, we present a set of experiments: (1) the flow past a sphere, and (2) vortices embedded in laminar pipe flow. In the first experiment, two channel measurements are taken at a resolution of 512 × 512 × 512 with volume rates of 65.1 Hz. In the second experiment, a single-color SVLIF system is integrated on a moving stage, providing imaging at 1280 × 304 × 256 with volume rates of 34.8 Hz. Although this second experiment is only single channel, it uses identical software and much of the same hardware to demonstrate the extraction of multiple information channels from single channel volumetric images. [ABSTRACT FROM AUTHOR]

In the present work it is presented and tested a promising and innovative procedure, based on inverse problem approach, for the heat transfer performance maximization of pipes fitted with butterfly-shaped inserts. They promote heat transfer enhancement by transferring the fluid from pipe wall and mixing it with bulk fluid from the central flow, maximizing mass and heat transports. However, this kind of inserts might be dangerous in some cases due to the existence of important differences in the fluid temperature and heat flux distributions. It is here proposed the implementation of an inverse method to infrared measurements: it allows to assess the local convective heat flux for forced convection flow in pipes with inserts and, thanks to these results, optimize insert geometry to maximize the heat transfer processes. Three different geometries of butterfly inserts were investigated in terms of local and global thermal behavior to obtain, given a specific application, the most effective one. Although the main objective of the present work is the application of an original approach, the experimental outcomes achieved in this study are already suitable for the design of heat transfer apparatuses for processes where product temperature should be precisely monitored (e.g., food and drug sector). [ABSTRACT FROM AUTHOR]

Abrupt section changes are a classic problem in the study of flow in cylindrical ducts or pipes. For its analysis, there are a wide set of exiting data from previous studies, among which some authors stand out and will be mentioned. Those previous works have been used to obtain reliable results for the resolution of section changes along a pipe, either due to cross area increases or reductions on a 1D basis. It is also known that a numerical 2D axisymmetric simulation (CFD) could find a consistent result compared to experimental data in almost all fluid flow fields. The main novelty of the present study is the development of a simple numerical approach used to solve the minor loss calculation. Firstly, a theoretical analysis is developed, and then the results of the numerical simulations carried out on the behavior that affects the water and air flow rate in an abrupt section change, for both contraction and expansion problems, are presented. In both cases, the results are analyzed with different meshes (discretizations) and turbulence models. Finally, the obtained numerical results are compared with those in the technical literature. Also, a theoretical approach is shown in order to show a whole frame of the discussion. The core results are the loss coefficient evolution as a function of the section change both for the sudden contraction and the expansion of a pipe flow. As the results follow the existing experimental values, it is concluded that the developed model provides a feasible and quick design tool to analyze possible geometrical changes without the need for further experiments. [ABSTRACT FROM AUTHOR]

In the modern aerospace industry, the importance of a lubrication system is self-evident for aero-engines, and the aero-engine bearing chamber return line is an even more challenging environment, as it involves a complex two-phase flow. The designer of the scavenge pipe needs to have an accurate understanding of the flow conditions in the scavenge pipe. This paper establishes a visual scavenge pipe test system. The flow direction was vertical flow, the test temperature was 370 k, and a high-speed camera was used to take high-definition flow photographs, which can observe the three main flow types: bubble flow, slug flow, and annular flow. Code program was created to analyze many pictures taken to obtain the apparent flow rate and perimeter of bubbles in the pipe under different flow conditions and to explore the gas–liquid two-phase flow in the scavenge pipe. A support vector machine (SVM) was used for data regression prediction, and the converted velocities of the gas–oil phases were inputted as eigenvalues to obtain the predicted values of bubble-flow velocity. The bubble-flow analysis prediction model established in this paper has a good prediction effect with root mean square error RMSE = 0.0172, which can more objectively and accurately describe the bubble-flow characteristics in the scavenge pipe. [ABSTRACT FROM AUTHOR]

It is important to control turbulence in industrial processes. Past experimental and numerical researches have shown that a turbulent puff in pipe flow can be removed or delayed by flattening the profile of the upstream velocity because a flattened velocity profile causes the point of inflection on it to collapse. The energy gradient theory has been developed to study turbulent transition, and the relevant studies have shown that turbulence arises due to the generation of singularities in the flow field. In pressure-driven flows like the pipe flow, the point of inflection on the velocity profile leads to the appearance of a singular point in the unsteady Navier–Stokes equation. In this study, the energy gradient theory is used to demonstrate why the point of inflection on the profile of velocity of pipe flow is the critical point for generating turbulence. Then, it is shown how flattening the velocity profile leads to the elimination of the point of inflection on the velocity profile of pipe flows to delay turbulent transition. It is also clarified why this technique is not effective at higher Reynolds number because the flattened velocity profile violates the criterion for flow stability relating to transition to turbulence.

Controlling pressure impact of water hammer is an important guarantee for safe and stable running of pipeline systems. Previously, we proposed a spring self-adaptive auxiliary control (SAC) system to improve the pressure control ability of a surge tank. However, the working efficiency of the SAC system is affected by various parameters. A reasonable designing strategy becomes an urgent need to properly determine the parameters of the SAC controller. In this study, based on our calibrated numerical model, various transient responses of a SAC system with different parameters were further investigated. The latency response threshold and the spring orifice coefficient were identified to be the two most sensitive parameters that determine the controller working efficiency. Based on the objectives of reducing the in-pipe extreme pressure and in-tank water level fluctuation, an analytical dual-objective optimizing Method was proposed for application. The results demonstrated that the pressure control capability of SAC controller can be optimized by the proposed method. [ABSTRACT FROM AUTHOR]

The mass transfer from a stagnant CO2 gas pocket to the flowing water in a horizontal pipe was investigated experimentally, considering the application of pH adjustment by injecting gaseous CO2 for raw water in water treatment industries. In the experiments, the variation of the CO2 gas pocket volume and the corresponding pH values of the pipe flow with time under different conditions were recorded. The mass transfer coefficient of the CO2 gas pocket in the pipe flow was then calculated. The results showed that the injection of gaseous CO2 into the pipe flow could effectively adjust the pH. The volume of the CO2 gas pocket decreased exponentially. Different from most studies on bubble mass transfer, it was found that the ambient CO2 concentration could not be neglected in this study due to the large volume of the gas pocket and the restricted space in the pipe. The mass transfer coefficient increased with the increasing ratio of the CO2 injection rate to the water flow rate and exhibited a sharp reduction as the volume of the CO2 gas pocket decreased by about 80%. The outcomes of this paper can contribute to a better understanding of gas bubble mass transfer in pipe flows. HIGHLIGHTS The mass transfer of a large CO2 gas pocket in the horizontal pipe flow was investigated, which has been hardly reported before.; During mass transfer processes, the pH variation of the pipe flow could be divided into three regimes, and the volume of the gas pocket was reduced exponentially.; The CO2 concentration in the pipe flow is important to mass transfer due to the large volume of the gas pocket and the restricted space in the pipe.;

AbstractThe effective reconstruction of osteochondral biomimetic structures is a key factor in guiding the regeneration of full-thickness osteochondral defects. Due to the avascular nature of hyaline cartilage, the greatest challenge in constructing this scaffold lies in both utilizing the biomimetic structure to promote vascular differentiation for nutrient delivery to hyaline cartilage, thereby enhancing the efficiency of osteochondral reconstruction, and effectively blocking vascular ingrowth into the cartilage layer to prevent cartilage mineralization. However, the intrinsic relationship between the planning of the microporous pipe network and the flow resistance in the biomimetic structure, and the mechanism of promoting cell adhesion to achieve vascular differentiation and inhibiting cell adhesion to block the growth of blood vessels are still unclear. Inspired by the structure of tree trunks, this study designed a biomimetic tree-like tubular network structure for osteochondral scaffolds based on Murray’s law. Utilizing computational fluid dynamics, the study investigated the influence of the branching angle of micro-pores on the flow velocity, pressure distribution, and scaffold permeability within the scaffold. The results indicate that when the differentiation angle exceeds 50 degrees, the highest flow velocity occurs at the confluence of tributaries at the ninth fractal position, forming a barrier layer. This structure effectively guides vascular growth, enhances nutrient transport capacity, increases flow velocity to promote cell adhesion, and inhibits cell infiltration into the cartilage layer. [ABSTRACT FROM AUTHOR]

We study the behaviour of the streamwise velocity variance in turbulent wall-bounded flows using a direct numerical simulation (DNS) database of pipe flow up to friction Reynolds number ${{Re}}_{\tau } \approx 12000$. The analysis of the spanwise spectra in the viscous near-wall region strongly hints to the presence of an overlap layer between the inner- and the outer-scaled spectral ranges, featuring a $k_{\theta }^{-1+\alpha }$ decay (with $k_{\theta }$ the wavenumber in the azimuthal direction, and $\alpha \approx 0.18$), hence shallower than suggested by the classical formulation of the attached-eddy model. The key implication is that the contribution to the streamwise velocity variance $(\langle{u}^2\rangle)$ from the largest scales of motion (superstructures) slowly declines as ${{Re}}_{\tau }^{-\alpha }$ , and the integrated inner-scaled variance follows a defect power law of the type $\langle u^2 \rangle ^+ = A - B \, {{Re}}_{\tau }^{-\alpha }$ , with constants $A$ and $B$ depending on $y^+$. The DNS data very well support this behaviour, which implies that strict wall scaling is restored in the infinite-Reynolds-number limit. The extrapolated limit distribution of the streamwise velocity variance features a buffer-layer peak value of $\langle u^2 \rangle ^+ \approx 12.1$ , and an additional outer peak with larger magnitude. The analysis of the velocity spectra also suggests a similar behaviour of the dissipation rate of the streamwise velocity variance at the wall, which is expected to attain a limiting value of approximately $0.28$ , hence slightly exceeding the value $0.25$ which was assumed in previous analyses (Chen & Sreenivasan, J. Fluid Mech. , vol. 908, 2021, R3). We have found evidence suggesting that the reduced near-wall influence of wall-attached eddies is likely linked to the formation of underlying turbulent Stokes layers. [ABSTRACT FROM AUTHOR]

AbstractWith the growing challenges of heat transfer in marine vehicles and underwater power stations, the demand for an effective tube heat exchanger has surged. Numerical simulations were conducted on the constant, laminar flow of an incompressible viscous fluid inside a wavy tube while keeping the wall temperature consistent. The laminar flow was modeled in two dimensions using ANSYS FLUENT 19.2. For the water fluid model, an integrated algorithm was used to link the pressure and velocity fields. Primarily examined were circular tube banks organized in a staggered arrangement. The primary equations were approached via a finite volume method based on a combined technique. This study aimed to evaluate and contrast the heat exchange and flow traits of four distinct tube designs: asteroid (ASTB), hypotrochoid (HTB), Wavy edge circle (WCTB), and mixed bundle (MBT). The influence of tube design on a heat exchanger’s thermal-flow efficiency was measured across Reynolds numbers ranging from 100 to 400. The results indicated an improved Colburn factor and a decrease in both the friction factor and tube performance for all scenarios examined. Three key metrics determined the optimal tube design: the performance evaluation criterion (PEC), the global performance criterion (GPC), and the average Nusselt number (Nu). Regardless of the Reynolds number, the conventional HC had the least efficient PEC, while the STB registered the peak PEC value. The highest GPC was attained with the STB. Nu values remained relatively consistent for ASTB, HTB, WCTB, and MBT. In evaluating the average Nusselt number, the ASTB outperformed the STB (92–106% higher), HTB (36–48% higher), WCTB (21–32% higher), and MBT (57–64% higher). [ABSTRACT FROM AUTHOR]

Gas–oil–water three-phase slug flows in pipes commonly exist in the oil and gas industry as oil fields are becoming mature and water production is becoming inevitable. Although studies on multiphase flows in pipes have been ongoing for decades, most previous research has focused on gas–liquid or oil–water two-phase flows, with limited studies on gas–liquid–liquid flows. This leads to limited modeling studies on gas–liquid–liquid flows. One factor contributing to the complexity of the gas–liquid–liquid flow is the mixing between the oil and water phases, which have closer fluid properties and low interfacial tension. Restrictions or piping components play a crucial role in altering phase mixing. Unfortunately, modeling studies that consider the effects of these restrictions are limited due to the scarcity of experimental research. To address this gap, we conducted experimental studies on a gas–liquid–liquid flow downstream of a restriction and developed a new mechanistic modeling approach to predict the pressure gradient. Our model focuses on the flow pattern where the oil and water phases are partially mixed. This work emphasizes the modeling approach. The model evaluation results show that the model outperforms other existing models, with an average absolute relative error of 6.71%. Additionally, the parametric study shows that the new modeling approach effectively captures the effects of restriction size, water cut, and gas and liquid flow rates on the three-phase slug flow pressure gradient in horizontal pipes. Most previous slug flow modeling work assumes either a stratified flow or fully dispersed flow between the oil and water phases. This work provides a novel perspective in modeling a three-phase slug flow in which the oil and water phases are partially mixed. In addition, this novel approach to modeling the restriction effects on the pressure gradient paves the way for future modeling for different types of piping components or restrictions. [ABSTRACT FROM AUTHOR]

From an engineering point of view pulsatile pipe flows, which include the hydrodynamic and acoustic fluctuations, can cause many problems such as vibration, noise and structural fatigue etc. Knowledge of the characteristics of hydrodynamic fluctuations (pseudo sound) and acoustic waves inside pipes particularly those with bends make is crucial to pipeline vibration and noise reduction. Numerical simulation of the pulsatile pipe flows shows challenges especially in curved pipes with different flow modes compounded, and predicting the acoustic fluctuations is even tougher. In this work, the unsteady flows of a straight and curved pipe with a 90° elbow induced by a pulsatile pressure inlet were calculated by Detached Eddy Simulations (DES). The pipe acoustic fields are solved through an acoustic perturbation equation, which takes the time derivative of hydrodynamic pressure as the aeroacoustic source. The characteristics of the flow and sound fields are discussed detailly, and special attention is paid to the influence of the 90° elbow on the curved pipe flow. The results show that the amplitude of hydrodynamic pressure fluctuations decrease almost linearly along the straight pipe, and the 90° elbow has obvious local influence on the flow pressure and velocity especially in the downstream side. The acoustic field is of 1-D standing wave pattern because of the fundamental pulsation frequency lower than the pipe cutoff frequency, and the 90° elbow has only negligible effect on the acoustic field in the flow frequency range. [ABSTRACT FROM AUTHOR]

This study focused on using swirling flow as a method to stabilize the detonation behavior and shorten the deflagration-to-detonation transition (DDT) distance of pulse detonation engines; additionaly, the study investigates the effect of swirling flow on flame propagation behavior and DDT distance. A swirling flow in which the circumferential velocity in the radial direction gradually increased from the center toward the wall and decreased near the wall was confirmed. Laser doppler velocimetry (LDV) confirmed that the swirl number is smaller in the axial velocity distribution when the number of swirling injector couplings is small. The DDT shortening ratio obtained using ten swirling injector couplings is larger than that obtained using five couplings. These results indicate that injector-induced swirling flow can increase the burning velocity and is an effective method to shorten the DDT distance. • Swirling flow used to stabilize detonation behavior and shorten DDT distance. • Circumferential velocity distribution across pipe section measured using a particle image velocimetry. • Swirl number of pipe swirling flow measured using a laser Doppler velocimeter. • The swirling flow increased the flame propagation velocity and reduced the DDT distance. [ABSTRACT FROM AUTHOR]

Although the roll-streak (R-S) is fundamentally involved in the dynamics of wall turbulence, the physical mechanism responsible for its formation and maintenance remains controversial. In this work we investigate the dynamics maintaining the R-S in turbulent Poiseuille flow at R = 1650. Spanwise collocation is used to remove spanwise displacement of the streaks and associated flow components, which isolates the streamwise-mean flow R-S component and the second-order statistics of the streamwise-varying fluctuations that are collocated with the R-S. This partition of the dynamics into streamwise-mean and fluctuation components facilitates exploiting insights gained from the analytic characterization of turbulence in the second-order statistical state dynamics (SSD), referred to as S3T, and its closely associated restricted nonlinear dynamics (RNL) approximation. Symmetry of the statistics about the streak centreline permits separation of the fluctuations into sinuous and varicose components. The Reynolds stress forcing induced by the sinuous and varicose fluctuations acting on the R-S is shown to reinforce low- and high-speed streaks, respectively. This targeted reinforcement of streaks by the Reynolds stresses occurs continuously as the fluctuation field is strained by the streamwise-mean streak and not intermittently as would be associated with streak-breakdown events. The Reynolds stresses maintaining the streamwise-mean roll arise primarily from the dominant proper orthogonal decomposition (POD) modes of the fluctuations, which can be identified with the time average structure of optimal perturbations growing on the streak. These results are consistent with a universal process of R-S growth and maintenance in turbulent shear flow arising from roll forcing generated by straining turbulent fluctuations, which was identified using the S3T SSD. [ABSTRACT FROM AUTHOR]

We present data from direct numerical simulation (DNS) of the fully turbulent flow through nominally two-dimensional channels containing longitudinal, surface-mounted, rectangular ribs whose widths (W) are either one third of or equal to the gap (S - W) between consecutive ribs across the domain, where S is the span (centre-to-centre spacing) of the ribs. A range of the ratio of channel half-height (H) to span (S) is considered, covering 0.25 = H/S = 2.5. In each case, a fixed rib height (h) of 0.1H was used, but a number of cases with much smaller heights, h/H = 0.025 or 0.05, were also studied. The secondary flows resulting from the presence of the ribs are examined, along with their sources in terms of the axial vorticity transport equation, which highlights the effects of spanwise inhomogeneity in the Reynolds stresses. We show that the strength of the secondary flows depends strongly on H/S (and, correspondingly, on W/S) and that the major sources of axial vorticity arise near the top corners of the ribs, with convection of that vorticity dominating its spread. We also show that for smaller ribs, the secondary flow strengths are similar to those predicted by Zampino et al. (J. Fluid Mech., vol. 944, 2022, A4) using a linearised model of the Reynolds-averaged equations, which does not include the vorticity convection process; the behaviour of secondary flow topology and strength with varying W/H is thus noticeably different. [ABSTRACT FROM AUTHOR]

Nowadays, the studied flowing molten salt heated methane/steam reforming membrane reactors are of roughly the same structure and vastly different sizes, which needs to be further explored with the consideration of reactor design optimization and system economy. This research investigates the effect of catalyst bed thickness, membrane tube configuration and reactor length on reactor performance under a series of operation conditions. The impact of concentrated solar thermal cost and methane cost on the levelized cost of hydrogen are focused to provide reference for the reactor design from an economic perspective. The results show that the catalyst bed thickness of 10 mm and the membrane diameter of 20 mm are appropriate for reactor design. Long membrane tube with big flow rate is more economical than the short one and its advantages in economy will be further reflected with the decreasing CST cost. [Display omitted] • A model of molten salt heated membrane reformer is developed. • The catalyst bed thickness of 10 mm is appropriate for reactor design. • Increasing the membrane diameter beyond 20 mm is not sensible. • Membrane reactors with long pipe and high flow rate are more economical. [ABSTRACT FROM AUTHOR]

The node pressure and flow rate along the shale gas flow process are analyzed according to the characteristics of the shale gas flow pipe network, and the non-leaking and leaking processes of the shale gas flow pipe network are modeled separately. The changes in pressure over time along each pipe segment in the network provide new ideas for identifying leaking pipe sections. This paper uses the logarithmic value of pressure as the basis for judging whether the flow pipe network is leaking or not, according to the process of varying flow parameters resulting in the regularity of leakage. A graph of the change in pressure of the pipe section after the leak compared to the pressure of the non-leaking section of pipe over time can be plotted, accurately identifying the specific section of pipe with the leak. The accuracy of this novel method is verified by the leakage section and statistical data of the shale gas pipeline network in situ used in this paper. [ABSTRACT FROM AUTHOR]

This document discusses a research paper on the topic of flow through gated circular culverts. The authors propose a classification of flow types and introduce a power relationship between discharge and head. They argue that a more robust flow equation should consider the dynamic nature of the gate opening. Another study by Zeng et al. provides dimensionless flow rating equations for different flow types. The document provides valuable information for researchers studying flow through culverts, focusing on the computation of flow in gated culverts. The authors analyze experimental data and suggest a simplified flow type categorization that yields accurate flow estimates. They also discuss the challenges of defining flow type separation criteria and emphasize the importance of balancing simplicity and accuracy in hydraulic engineering practice. [Extracted from the article]

Simulations of the processes contributing to the deposition of trace gases and small particles from the air to natural surfaces routinely describe the consequences of changing molecular diffusivity in terms of the Schmidt number, Sc ≡ ν/D, where ν is kinematic viscosity and D the molecular diffusivity of the constituent in question. Using well-verified results of pipe flow experiments, early workers proposed that the relevant property entering dry deposition and other models of similar kind should be Sc−2/3 rather than Sc−1 as would be expected from historic flat plate experiments. Upon reconsideration, it is now proposed that no universal power-law dependence on Sc can be expected; the corresponding role of molecular diffusivity is likely to be site-specific. Relevant experimental evidence remains elusive. [ABSTRACT FROM AUTHOR]

Compared to helically coiled tube exchangers (HCTs), longitudinally curved tube exchangers (LCTs) have received little attention from scientists over the past decade, leading to a lack of correlations estimating the Nusselt number and friction factor. In view of recent studies promoting the use of LCTs (waved, C-shaped or sinusoidal) in linear solar concentrating systems, this study examines whether or not correlations of and developed explicitly for HCTs could be applied to LCTs. A (SST) turbulent model has been run on HCTs and validated by experimental correlations from the literature. With an amplitude ratio equal to unity (waviness amplitude to the curvature radius ratio) and the same curvature ratio (tube radius to the curvature radius ratio), LCTs and HCTs are geometrically similar. For these similar configurations, the numerical results of over the Reynolds number range overlap almost perfectly, which is not for. Over the LTC amplitude ratio range, no significant change in the mean was reported, with a max relative error of 3.98%, whereas was highly dependent on it. One key finding: with a similar curvature ratio, correlations of the mean developed previously for HCTs could be used for LCTs, which is not valid for the mean. [ABSTRACT FROM AUTHOR]

The aim of this study is to utilize waste thermal energy from industries into useful heat for water and air heating. In this paper, the thermal modeling and performance of three fluid heat exchangers (TFHE) have been experimentally investigated. The TFHE considered here is an enhanced version of the double‐pipe heat exchanger. A novel TFHE having fin (1 mm thin copper wire of 10 mm pitch) acts as a roughness element, which is wrapped on the helical coil's outer surface for increasing heat transfer (HT) rate and the turbulence effect for normal water, and this outer surface finned helical coil is inserted between two concentric straight tubes. The innermost tube carries atmospheric air, the finned helical coil tube carries waste hot fluid while normal water flows in the inner annulus of the outermost tube. The coiled‐side Reynolds number is varied in the range of 7000–30,000, while the curvature ratio of 0.1315, pitch‐to‐inside diameter ratio of 2.88 and wire‐to‐tube diameter e/d=0.182 $e/d=0.182$ of the helical tube is kept constant. A counterflow arrangement has been made for experimentation. Nusselt number is calculated using the traditional Wilson plot method that is compared and validated with results available in the literature. The overall HT coefficient is found to increase by increasing the volume flow rate of fluids, while effectiveness decreases or increases depending on residence time and capacity ratio. The percentage increment in the Nusselt number, maximum friction factor, overall HT coefficient between waste hot fluid to normal water, effectiveness is found to be 21.10%–23.88%, 90.91%, 3.40%–29.45%, 3.40%–25.33%, respectively, for the coil side. TFHE is thus proposed for heating water and space simultaneously. [ABSTRACT FROM AUTHOR]

The aim of this paper is to propose an efficient numerical scheme to deal with heat transfer problems in pipe flow with a large length/diameter ratio. The generalized finite difference method (GFDM) is combined with a space stepping algorithm (SSA) for the solution. The SSA divides the solution domain into a number of overlapping sections in the length direction of the pipe. Due to the large Peclet number, the heat transport process is dominated by advection, which allows an approximate boundary condition to be applied at the downstream cross section. The problem is then solved section by section. Using the uniform distributed points, the solution matrix for each section does not change, and only the right hand side needs to be refreshed for the changing boundary conditions. This leads to a highly efficient scheme for problems with a large pipe length. To show the accuracy of the numerical scheme, a problem with available analytical solution is studied. Then the method is applied to problems of single pipe with different pipe wall temperature and flow Reynolds number, and concentric annular pipe. Numerical results confirm the stability and efficiency of the GFDM-SSA. The method can be applied to many real world transient heat transfer problems in which the pipe is heated or cooled along its length with arbitrary wall temperature for heat exchange and other purposes. [ABSTRACT FROM AUTHOR]

In various systems, such as rocket engines, efficiency is improved by increasing the pressure so that these systems operate at extremely high supercritical pressures. At this pressure, pseudo-boiling occurs, and heat transfer deteriorates, suddenly decreasing when certain temperature limits are exceeded. This study numerically solved the Navier-Stokes equations for a circular cooling channel. In addition, supercritical hydrogen was used as a coolant. The thermophysical and transport properties were defined as a user-defined function in ANSYS FLUENT. The results showed that increasing the operating pressure significantly reduced the heat transfer deterioration, improved the cooling capabilities, and minimized pressure drops. Increasing the mass flow rate enhances the heat transfer but increases the pressure losses. The influence of the operating pressure and the mass flow rate on the deterioration of the heat transfer was investigated in detail. [ABSTRACT FROM AUTHOR]

We derive a class of exact solutions to the incompressible unsteady Navier–Stokes equations. These solutions are generated by the eigenfunctions of the Stokes operator and can be applied to studying boundary value problems for the Navier–Stokes equations related to pipe and channel flows. We explore the relation between the spectrum of the Stokes operator, generalized Beltrami flows, and exact solutions of the Navier–Stokes equations. Relevant properties of the Stokes eigenfunctions are also discussed in some detail. [ABSTRACT FROM AUTHOR]

Turbulence is a common phenomenon characterized by its chaotic nature in time and coherent structures in space. A recent study was able to solve the temporal component of turbulent velocity and produce a temporal correlation function analytically by the hypothesis of isentropic motion or superfluid in a viscous fluid [W. Chen, "On Taylor correlation functions in isotropic turbulent flows," Sci. Rep. 13, 3859 (2023)]. However, the spatial distribution of the turbulent velocity is still unknown. In this study, the spatial topology of a turbulent pipe flow [Jackel et al., "Coherent organizational states in turbulent pipe flow at moderate Reynolds numbers," Phys. Fluids 35, 045127 (2023)] was investigated with the theory of nondissipative dynamics or superfluid. Ten elementary excitation modes on the boundary of the second law have been identified. The temporal, radial, azimuthal and longitudinal components of the longitudinal velocity have been solved and specified. The spatial topology on the cross section is described by the employment of orthogonal correlation functions. This theory satisfactorily agrees with the experimental data at the azimuthal wavenumber from 2 to 7. In the spatial topology, each azimuthal wavenumber corresponds to one pair of positive and negative velocity torsos along the mean longitudinal flow. Many other spatial topology examples involve the combinations of three basic structures of resonant superfluids, i.e., nodes, antinodes, and saddles. The essential differences between the flow fields of a regular fluid and superfluid are summarized. This work provides spatial solutions and methods to complement the temporal solutions in earlier studies [W. Chen, "On Taylor correlation functions in isotropic turbulent flows," Sci. Rep. 13, 3859 (2023); W. Chen, "An asymmetric probability density function," Phys. Fluids 35, 095117 (2023)]. The method and results should advance the understanding of turbulence and coherent states. [ABSTRACT FROM AUTHOR]

The mechanisms driving the transition to turbulence in pulsatile flows are not well understood. Prior studies in this domain have noted the dynamics of this flow regime to depend on the mean Reynolds number, pulsation frequency (i.e., Womersley number), and inflow pulsatile waveform shape. Conflicting findings, particularly regarding the role of the Womersley number on the critical Reynolds number and the development of turbulence, have been reported. The discord has primarily been observed for flows, with Womersley numbers ranging from 4 to 12. Hence, in this work, we use particle image velocimetry to explore the effects of the Womersley number within this 4–12 range on the dynamics of the pulsatile transition. Eighteen test cases were captured using six mean Reynolds numbers (range 800–4200) and five Womersley numbers. Turbulent kinetic energy, turbulence intensity (TI), and phase lag were computed. Our results indicated that the critical Reynolds number was roughly independent of the Womersley number. At high Womersley numbers, the TI trend maintained lower pulsatility, and the flow was observed to mimic a steady transitional flow regime. A plateau of the TI-velocity and TI-acceleration phase lag was observed at a Womersley number of 8, highlighting that this may be the critical value where further increases to the Womersley number do not alter the transition dynamics. Furthermore, this suggests that the phase lag may provide a universal indicator of the specific influence of the Womersley number on transition for a given flow. Overall, these findings elucidate critical details regarding the role of the Womersley number in the transition to turbulence. [ABSTRACT FROM AUTHOR]

To understand the variations in pressure drop and heat transfer characteristics within the scavenge pipe of aero-engines, studying and attempting to discriminate the flow patterns of two-phase flow inside the scavenge pipe is of great significance. To achieve this, this paper establishes a flow pattern identification model. High-speed photography was utilized to capture images of four distinct flow patterns inside the scavenge pipe under typical operating conditions. Through image preprocessing, feature extraction, and Relief-F feature selection, the primary texture and shape features are obtained as inputs for the identification model. Four machine learning methods, namely unsupervised learning K-means, supervised learning backpropagation neural network (BP), radial basis function neural network (RBF), and support vector machine (SVM), are selected for flow pattern identification. For the optimization of hyperparameters in supervised learning methods, this paper utilizes the particle swarm optimization (PSO) algorithm. Consequently, PSO-BP, PSO-RBF, and PSO-SVM models are further established. After inputting the two types of features, texture and shape, into the mentioned models, a comparison of the classification accuracy and generalization ability of the four models is conducted. The results indicate that, for the flow pattern identification problem of oil–air two-phase flow inside the scavenge pipe studied in this paper, the most suitable identification model is the PSO-SVM model. [ABSTRACT FROM AUTHOR]