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Exhaust flow measurements are a significant source of uncertainty for measurements of heat release rate in large‐scale fire experiments. Irregular flow distributions are often present in the exhaust ducts making it difficult to measure flow accurately. Tracer gas dilution (TGD), a measurement method for volume flow, is not sensitive to flow distribution and has been applied to calibrate flow measurement devices at the exhaust ducts of a large‐scale open calorimetry system. The in‐line calibration reduced the bias in the exhaust flow measurement by as much as 6% improving the overall measurement accuracy of the heat release rate. Experimental results provide evidence that the flow calibration is an improvement over the accepted practice of developing a flow correction from the comparison of oxygen consumption calorimetry with the heat output from a gas burner. The flow calibration is valid for a wide range of flow conditions and decouples the oxygen consumption calorimetry measurement from any error in determining the heat release rate from the gas burner. [ABSTRACT FROM AUTHOR]

The results of experimental studies and a comparative analysis of the coolant hydrodynamics in the outlet section of the fuel cartridge behind heads of different designs are presented. The considered fuel assemblies are designed for installation in the core of a RITM-type reactor of a small ground-based nuclear power plant. The aim of the work was to study the distribution of the axial velocity and flow rate of the coolant at the outlet of the fuel bundle, behind the heads of different designs, and in front of the coolant extraction pipe and in the holes of the upper base plate as well as to determine the areas of the fuel bundle from which the coolant flow is most likely to enter the sampling pipe and, accordingly, to the resistance thermometer installed in this pipe. The experiments were carried out on a research aerodynamic stand with an air working medium on a model of the outlet section of the fuel cartridge, which includes a fragment of the outlet part of the fuel bundle with spacer grids, dummies of two types of heads, an upper support plate, and a coolant extraction pipe. When studying the coolant flow rate in the outlet part of the fuel cartridge, the pneumometric method and the method of contrast impurity injection were used. The measurements were carried out over the entire cross section of the model. The hydrodynamic picture of the coolant flow is represented by cartograms of the distribution of axial velocity, coolant flow rate, and contrast impurities in the cross section of the model. The results of the research were used by specialists from the design and calculation departments of Afrikantov OKBM to justify engineering solutions in the design of new cores of RITM reactors. The results of the experiments were compiled into a database and used in the validation of the LOGOS CFD program developed by the employees of RFNC-VNIIEF and ITMP Moscow State University as analogues to foreign programs of the same class, which include ANSYS, Star CCM+, etc. Experimental data are also used to validate one-dimensional thermal-hydraulic codes used in Afrikantov OKBM when substantiating the thermal reliability of the cores of reactor installations; the thermal-hydraulic code KANAL also belongs to this class of programs. [ABSTRACT FROM AUTHOR]

The front velocity in miscible exchange flow along the straight and curved tubes has been investigated. Almost the entire flow lies within the range of inertia dominated regime in the current experimental setup. Available data for straight pipes at different Atwood numbers have been revisited to provide an appropriate ground for better understanding and evaluation of the observations made for the flow in curved tubes. A 19.05 mm diameter and 2.40 m long tube has been formed to follow 55°of an arc in the vertical plane with the radius of curvature of 2.5 meters. The upper and lower parts are separated by a gate valve and filled with heavier and lighter fluids, respectively. The observations and analyses demonstrate how the continuous variations of the flow inclination along the curved path and the change in mixing dynamics associated with it can affect the velocity of downward and upward moving fronts. Most notably it has been detected that the velocity of upward moving front follows a similar trend as in straight pipes due to the continuously increasing mixing. However, the velocity of downward moving heavy front slightly decreases as opposed to the case of straight pipes, signifying the effect of curvature on mixing enhancement. [ABSTRACT FROM AUTHOR]

Combustion instability has arisen as a substantial defect for power generating systems. This is caused by the acoustic sources of the combustor, such as indirect noise, produced by accelerating hot spots, which are less explored due to their complex nature. Understanding the physics of the hot spots, therefore, is of crucial importance to reduce the noise and subsequent instabilities. Further, hot spots are a difficulty in internal combustion engines motivated auto ignition. In this study, hot spot behavior in a combustor of lean-premixed flame of Ethylene, a type of biofuel, influenced by hydrodynamic and thermal conditions, is numerically studied using the flamelet model and large eddy simulation. The impacts of inlet turbulence intensity and preheating unburnt mixture on hot spots are examined in a thermally convective and adiabatic combustor. The results show that although preheating inlet mixture improves combustion efficiency, it aids the hot spot's survival (more than 40 percent improvement in wave's dissipation), and may cause significant instabilities. Similar to increasing the unburnt mixture temperature, decreasing the turbulence intensity and the excitation amplitude diminishes dissipation and dispersion of the wave, which makes the combustor more prone to probable instabilities. Amongst the studied parameters, the turbulence intensity and convective cooling on the walls are the most effective in decreasing the wave's strength by approximately 85 and 95 percent, respectively. It is indicated that a hot spot in real conditions of a combustor is prone to a high level of annihilation. [ABSTRACT FROM AUTHOR]

The effect of jet excitation on turbulence diffusion in order to enhance mass transport at the low Reynolds numbers is investigated experimentally. The instantaneous flow patterns of the excited alternatively pulsating jet is recorded using a high-speed digital camera and applying the laser light-sheet-assisted flow visualization techniques. The spread width of the jet is detected using the binary edge detection techniques and the long-exposure images. The velocity characteristics and turbulent intensities are spotted using the particle image velocimetry PIV. The tracer-gas concentration measurement techniques are used to detect the mixing characteristics of jet flow. At the Reynolds numbers Red < 700, two characteristic flow modes (steady jet dominated and transversely oscillating jet dominated) are identified. At Red < 200, the steady-state jet flow behavior without excitation is detected, and it was named by the steady jet dominated flow mode. At Red is between 200 and 700, a periodically transversely oscillating jet is detected, and it ias named by transversely oscillating jet dominated flow mode. The axial velocities and turbulence intensities at the central axis for transversely oscillating jet dominated flow regime have the maximum values because of the transverse oscillation which is induced by a V-shaped fluidic oscillator. Therefore, the large turbulence intensities induced by the V-shaped fluidic oscillator at low Reynolds numbers significantly enhance the jet mass dispersion at the near-field because of transfer of the axial momentum to the transverse momentum due to alternative pulsating jet and the deflector plate attached at the jet exit. [ABSTRACT FROM AUTHOR]

The substantiation of the choice of design parameters characterizing the mutual orientation of the mixed flows and the ratio of the geometric dimensions of the elements of the flow path of the jet pump that provide an increase in the energy characteristics of borehole ejection systems is given. Depending on the mutual orientation of the mixed flows, three variants of the design of the jet pump are possible, viz. the one with a parallel orientation of the working and ejected flows, the one with the inlet of the ejected flow at a sharp angle, and the one with a perpendicular orientation of the working and ejected flows. The magnitude of the angle between the velocity vectors of the mixed flows directly affects the intensity of vortex formation in the mixing chamber, the amount of energy loss and the efficiency of the jet pump; however, the simplicity of their manufacture remains the determining condition for choosing the design variant of the elements of ejection systems. Based on the use of the laws of conservation of energy, the amount of motion and continuity of the flow, it is determined that the level of energy loss during mixing flows is directly proportional to the magnitude of the angle of entry of the ejected medium. In the course of computer simulation of the jet pump workflow, an asymmetric distribution of hydrodynamic parameters for the non-parallel orientation of the mixed flows has been obtained. In order to reduce energy losses when mixing flows, the value of the angle of entry of the ejected flow must be taken in the range from 0 to 15°. In the case of the implementation of the zero head mode and the maximum ejection coefficient, minimal energy losses during mixing of flows are provided for the main geometric parameter of the jet pump equal to 2.375. In the course of experimental studies, the inverse dependence of the maximum value of the efficiency of a borehole jet pump on the value of its main geometric parameter represented as a power function, has been established. When using ejection systems that implement long-term technological processes (e. g., during oil production), it is necessary to take the minimum possible value of the main geometric parameter of the jet pump for the specified operating conditions.

To support the development of the U.S. Department of Energy (DOE) Versatile Test Reactor (VTR), a new set of experiments has been established at Argonne National Laboratory (ANL). Driven in part by the validation needs for code calculations and simulations of the reference VTR core design, three unique test facilities have been designed, or are in the process of being designed, to allow measurement of the phenomena and behavior prototypic to the full-scale VTR core. The Pressure drop Experimental Loop for Investigations of Core Assemblies in Nuclear reactors (PELICAN) facility, recently constructed and currently operational, is capable of producing full-scale flow rates for measurement of the pressure drop across a prototypic fuel assembly, including axial reflectors, fuel, and plenum components. The REDuced Scale Hydraulic Inlet Plenum (REDSHIP) experiment, beginning construction, will provide measurements of phenomena within the inlet plenum, including flow distributions through the core assembly ducts, pressure losses across the assembly receptacles, and localized velocity flow fields. A separate-effects-test experiment, called Parallel HEated ASsemblies for Advanced Nuclear Tests (PHEASANT), which is in the early stages of design, is being developed to examine the mixing of exiting core assembly jet streams within the upper plenum. As each of the test facilities becomes operational, they will begin generating timely, reliable, and qualified empirical data suitable for verification and validation of computational tools. In collaboration with other efforts across the DOE complex, the ANL experimental programs are well poised to provide continuous support for the advancement of the VTR design. [ABSTRACT FROM AUTHOR]

• Numerical study of floating treatment wetlands (FTWs) spanning the channel width. • Root length and gap distance between FTWs in series affect mass removal. • Longer roots increase pollutant concentration to the FTWs and enhance mass removal. • Longer gap distance increases flow mixing and pollutant concentration to the FTWs. • Longer gap distance decreases the number of FTWs per channel length. Floating treatment wetlands (FTWs) use plants' roots for water quality improvement. The plants are supported by a buoyant structure deployed at the water surface. The roots form a porous zone beneath the structure and remove pollutants carried in suspension through filtering, absorption and uptake. This paper used CFD simulation to model FTWs arranged in series and spanning the channel width and to study the effects of root length and spacing between FTWs on flow distribution and mass removal. The root zone was modelled as a porous media, and removal was computed using first-order decay, for which a range of removal constants was tested. Longer roots increased the reactive volume of the root zone, which increased the fraction of pollutant inflow entering the FTWs. Increasing the distance between FTWs allowed greater mixing between water that went through and beneath the upstream FTW. This increased the concentration entering each FTW, which enhanced mass removal per FTW. However, a larger distance between FTWs reduced the number of FTWs in the channel, reducing the reactive volume. In the tradeoff between mixing and reactive volume, the reactive volume was more important, such that total removal in the channel increased with longer roots and more units of FTW (shorter gap distance). However, removing the gap entirely was detrimental, as FTWs in series removed more mass than a continuous FTW of same volume. This study points to two design recommendations for FTWs in series. First, if resources for building FTWs are not limiting, but the channel length is, it is preferable to prioritize higher reactive volume (shorter gap distance) to achieve maximum removal per channel length. Second, if resources for FTWs are limiting, but channel length is not, it is better to place the FTWs with a longer gap distance, preferably along enough to allow mixing over the full depth between FTWs, as this will achieve maximum removal per FTW. [ABSTRACT FROM AUTHOR]

Flow-induced vibrations of a rigid prism with an open semicircular cross section, supported elastically, were experimentally studied in a free-surface water channel. The objective of the study was to explore the prism's potential to promote flow mixing in its wake and simultaneously harvest mechanical energy from the incoming flow. The mechanical dimensionless parameters, namely the mass ratio and damping, were kept constant, focusing primarily on the influence of flow speed (or reduced velocity U ∗) on mixing efficiency and energy extraction. The following findings were obtained: (i) a clear correlation exists between the efficiency of mixing and the efficiency of energy extraction, (ii) mixing efficiency is higher in the near wake and gradually decreases downstream, and (iii) mixing efficiency scales with A ∗ (f ∗ / U ∗) 2 , where A ∗ and f ∗ represent the dimensionless amplitude and frequency of the prism's oscillation, respectively. This indicates that flow mixing is directly influenced by the transverse acceleration of the prism and the unperturbed flow speed. Then, maximum mixing efficiency is expected to be achieved when high oscillation amplitudes occur at low reduced velocities which suggest that synchronization of vortex shedding contributes to enhance flow mixing. • Experiment on water channel have been carried out to explore the potential to promote flow mixing and harvest energy. • A correlation exists between the efficiency of mixing and the efficiency of energy harvesting has been found. • Flow mixing is more dependent on the mean oscillating accelerations than on the mean velocity oscillation. • Flow Mixing is higher under vortex shedding synchronization. [ABSTRACT FROM AUTHOR]

muddy flows are gravitational flows, which are the difference in density or difference in weight of unit volume between two fluids due to suspended sediments. Due to the abundance of these streams in nature knowing and studying the characteristics and factors affective it is imperative and unavoidable. The creation of obstacle in the flow path can affect on the muddy flow character such as flow mixing rate and flow density. In this paper by the Flow 3D software the effect of trapezoidal obstacle in the characteristics of the muddy flow especially its mixing rate has been studied. : In order to Verification, results of the this numerical model Were compared with the results of laboratory work Naji Abhari et al. The results showed that the presence of the obstacle caused the kinetic energy of turbulence to increase by almost 1000% more than Without obstacle. the depth-density variation diagram for two channels showed that the current density in channel With obstacle was less than obstacle-free type. also by increasing 1% the height of obstacle, an average of 2% would be added to the turbulence energy and one-percent increase in the angle of entrance prevented an increase of 1.366 % of the energy of turbulence. Simulation for obstacle with different velocities indicates that with increasing the velocity of the pure water, the amount of maximum energy of turbulence and as a result of flow mixing increases.

EGR cylinder-to-cylinder dispersion poses an important issue for piston engines, since it increases NOx and particulate matter (PM) emissions. In this work, the EGR distribution on a 6-cylinder intake manifold is analyzed by means of experiments, 0D/1D engine modeling and 3D CFD simulations at three different working points. Using a comprehensive set of measurements, statistical regressions for NOx and PM emissions are developed and employed to quantify the sensitivity of numerical configuration to EGR dispersion and subsequent increase of pollutants. CFD mesh and time-step size independence studies are conducted, taking into account their interrelation through the Courant number. The obtained numerical configuration is validated against experimental measurements, considering different unsteady RANS turbulence submodels (k − ε and SSTk − ω) as well as the inviscid case. The agreement of the different approaches is quite sensitive to the operating conditions, obtaining root mean square errors for the average cylinder-to-cylinder EGR distribution between 1% and 17% and for the transient C O 2 traces between 8% and 29%. However, for the worst-case scenario, the error in NOx and PM emissions prediction is below 2%. The regressions are employed to find a greater EGR distribution impact on pollutants when EGR rate or dispersion are increased. Flow investigation reveals the underlying reasons for the discrepancies and similarities between the predictions of the different turbulence submodels. A statistical analysis shows the significant errors that average C O 2 probes make when assessing EGR cylinder-to-cylinder distribution, which is explain by the flow heterogeneity at some operating conditions. [ABSTRACT FROM AUTHOR]

The present study examines the use of a two-stage electrohydrodynamic (EHD) gas pump with its electrodes assembly anchored at one corner of a square channel to modify the characteristics of flow inside the channel. Specifically, the proposed EHD pump is examined for its effectiveness in enhancing flow mixing as well as reducing the power requirement. The present study is also aimed at confirming one of the important conclusions drawn from the authors' earlier works that, given the same number of emitting electrodes, the performance of an EHD pump can be specifically tailored by rearranging the location and orientation of the electrodes so that the modified characteristics of flow can achieve the desired effect. To evaluate the effectiveness of the proposed electrode configuration, the performance of the pump is compared with that of a previous study in which a two-stage gas pump utilizes an electrode assembly mounted on the two parallel walls. For both pumps, the emitting electrodes are flush mounted on the channel walls so that the air flow produced is similar to that of a wall jet. Through the performance assessment, the results obtained from the present study can provide useful information for practical applications of EHD gas pumps. • An EHD gas pump with electrodesanchored at one corner of a square channel is evaluated for its improved performance. • The results are compared with those from the previous study with aligned electrodes. • The results show that the proposed pump can promote flow mixing which is good for applications in electronics cooling. • Most importantly, a desired flow characteristic can be attained through the arrangement of electrode configuration. [ABSTRACT FROM AUTHOR]

This work is an experimental study into the hydrodynamics of the coolant flow in the in-vessel pressure duct of a pressurized water reactor. In the article, an experimental testbench and a nuclear reactor model under investigation are described, the measurement methods are set forth, and the operating variables at which the study was conducted and the obtained results are provided. In the experiments, the mixing of the loop coolant flows inside the model of the nuclear reactor downcomer was simulated. The study was conducted on the high-pressure aerodynamic testbench of Alekseev State Technical University in Nizhny Novgorod. The scale model of the nuclear reactor had the structural components characteristic of loop-type reactor units, such as the annular downcomer and the bottom pressure vessel. The experiments were conducted at Reynolds numbers within the 20 000–50 000 range measured in the annular gap of the downcomer of the model. The axial velocity field at the inlet to the reactor core simulator was investigated using a pneumometric probe. The temperature field was recorded in the experiment by the impurity diffusion method, i.e., by introducing of a contrast tracer into one of the loops of the model. The degree of mixing the flows was estimated by the admixture (tracer) concentration at the inlet to the core simulator. Propane was used as the contrast admixture. The study has yielded the spatial distribution of the tracer in the coolant flow in the annular downcomer and in the bottom pressure vessel. The data on the distribution of the contrast admixture are presented in the form of charts. The swirling of the coolant flow in the in-vessel pressure duct has been analyzed. It has been shown that the mixing intensity in the bottom pressure vessel is affected by the central vortex with the central axis. The parameters of mixing the admixture in the model of the in-vessel pressure duct have been estimated. [ABSTRACT FROM AUTHOR]

An active vortex generator is proposed for heat transfer enhancement in heat sinks and heat exchangers and removal of highly concentrated heat fluxes. It is based on applying a uniform magnetic field of permanent magnets to a magnetic fluid (ferrofluid) flowing in a heated channel. Numerical simulations are carried out for a 2 Vol% ferrofluid at different Reynolds numbers (150‐210) and magnetic field intensities (0‐1400 G) to investigate the possibility of simultaneous heat transfer enhancement and pressure drop reduction by the proposed method. Comparisons are also made with the other conventional vortex generators. Results indicate that the external magnetic field acts as a vortex generator that changes the velocity distribution, improves the flow mixing, and thereby increases the convective heat transfer. Surprisingly, the heat transfer enhancement is accompanied by a decrease of the friction coefficient due to the flow separation and decrease of the flow contact with the surface. It is also concluded that increasing the magnetic field intensity, decreasing the flow rate, and adding a second identical magnetic vortex generator have favorable effects on both pressure drop and heat transfer. A maximum of 37.8% enhancement of heat transfer with a 29.18% reduction of pressure drop has been achieved at the optimum condition. [ABSTRACT FROM AUTHOR]

Flow-mixing is common in technological processes, and both ejectors and turbofans can produce an interaction between flows with different energy potentials. Ejectors have been extensively used, and their analytical models have been widely presented. To the best of the authors' knowledge, there is a lack of studies exploring the efficiencies of turbofans. The goal of this paper is to compare thermodynamic processes in these devices. Their efficiencies are compared in terms of compression and entrainment ratios. A comprehensive one-dimensional subsonic thermodynamic models of the ejector and turbofan are presented. The quantitative indices are obtained for the same initial conditions expressed as the ratio of differences in enthalpies for ideal compression and ideal expansion. When initial conditions are equal to the numeric value of the combination of the isentropic efficiency of the evaluated components (numerical case 0.16), both devices have the same efficiencies; at lower initial conditions (numerical case 0.10), a turbofan's entrainment ratio is 1.5 times and compression efficiency 1.25 times higher; at higher values of initial conditions (numerical case 0.28), the ejector is more efficient. Such distinctive characteristics of turbofans and the nature of their variation may correspond to the specific application areas of technological equipment that require certain flow-mixing parameters. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental study of mixing fluid flows of different temperatures in a T-junction. The experiments were performed with liquids having substantially different physical properties. The distribution fields of the average and fluctuation temperatures on the surface of the wall of the T-junction, and the structure of the temperature field in the mixing region of cold and hot fluid flows were obtained. [ABSTRACT FROM AUTHOR]

• Delayed detached eddy simulation (DDES) is used to investigate an annular swirling jet in a non-premixed burner. • Stereo-PIV measurements are done to perform a database of comparison for the DDES. • The simulated flow exhibits four instability modes including the Kelvin–Helmholtz and swirling instabilities • Spectra analysis was also performed to obtain the oscillation frequency of the swirling jet. Delayed detached eddy simulation (DDES) is accompanied with Stereo-PIV measurements to study the non-reacting flow field of a non-premixed swirl burner in this paper. Comparisons of experimental and numerical data show that the DDES results are capable of predicting the mean swirling flow features adequately. The instantaneous flow field is found to be strongly affected by the Kelvin–Helmholtz instability. The flow near the injector involves a complex behavior including a recirculation zone. The 3D flow structure at the burner exit, visualized by the iso-surface of Q-criterion, displays four instability types. The dominant instabilities are vortex ring structures induced by the Kelvin–Helmholtz instability, and finger structures induced by the swirling instability. Pressure fluctuation signal recorded in the swirling jet region show that the computational flow passes through transition instants from RANS to DDES equations. After that, the swirling jet becomes fully developed with an oscillation frequency of 222 Hz. [ABSTRACT FROM AUTHOR]

Highlights • Two adjacent karst springs exhibited different flow path mixing behaviors. • REE concentrations at the springs increased in response to storm flow. • Negative Ce anomalies during pre-storm flow were neutralized in response to storms. • REEs, isotopes, Mg/Ca and Ca/Zr proved useful complementary source mixing tracers. Abstract Karst aquifers are dynamic hydrologic systems which can be sensitive to short-term recharge events (storms) and heterogeneous recharge characteristics (point recharge at sinks, irregular soil thicknesses). In this study, two adjacent karst springs, Tippery Spring and Near Tippery Spring, were monitored to better understand flow and source mixing characteristics in response to two storms in May and June 2017. Monitoring techniques included high-resolution discharge and temperature logging and collection of spring water using automatic samplers to analyze chemical parameters such as stable water isotopes and Mg/Ca ratios along with Ca/Zr ratios and rare earth elements (REEs) which have had limited testing in karst systems. The two springs exhibited behaviors which were both unique to each spring and shared depending on which parameter is considered. Spring-specific behaviors included discharge and isotopic response, with Tippery Spring having a flashier and faster conduit flow behavior relative to Near Tippery Spring's delayed storm response. Absolute Mg/Ca values were spring-specific, owing to the relative fraction of limestone and dolostone in their respective recharge areas, although both springs showed similar Mg/Ca ratio shifts after storms. While Ca/Zr ratios changed in timing and intensity with storm intensity, both springs exhibited a decline in Ca/Zr ratios as calcium-rich carbonate matrix water was displaced by zirconium-rich storm recharge water from sinking streams off the clastic upland ridges. Flushing of recharged storm water resulted in an increase in total REE concentrations at both springs (from <0.15 ppb to >1.0 ppb), with the timing and magnitude of concentration increases determined by the degree of surface connectivity intrinsic to each spring and the intensity of the recharge event. REEs and Ca/Zr ratios provided additional and complementary tracer techniques to better understand transient recharge and flow behaviors in karst springs. [ABSTRACT FROM AUTHOR]

A mixing process is simulated and a calculation technique for determining the mixing ratio is created based on experimental studies. Influence of some factors on this ratio is determined in the recirculation mixing zone in the swirling flow behind the flame tube head. [ABSTRACT FROM AUTHOR]

As part of the Consortium for Advanced Simulation of Light Water Reactors, the subchannel code CTF is being used for single-phase and two-phase flow analysis under light water reactor operating conditions. Accurate determination of flow distribution, pressure drop, and void content is crucial for predicting margins to thermal crisis and ensuring more efficient plant performance. In preparation for the intended applications, CTF has been validated against data from experimental facilities comprising the General Electric (GE) 3 × 3 bundle, the boiling water reactor full-size fine-mesh bundle tests (BFBTs), the Risø tube, and the pressurized water reactor subchannel and bundle tests (PSBTs). Meanwhile, the licensed, well-recognized subchannel code VIPRE-01 was used to generate a baseline set of simulations for the targeted tests and solution parameters were compared to the CTF results. The flow split verification problem and single-phase GE 3 × 3 results are essentially in perfect agreement between the two codes. For the two-phase GE 3 × 3 cases, flow and quality discrepancies arise in the annular-mist flow regime, yet significant improvement is observed in CTF when void drift and two-phase turbulent mixing enhancement are considered. The BFBT pressure drop benchmark shows close agreement between predicted and measured results in general, although considerable overprediction by CTF is observed at relatively high void locations of the facility. This overestimation tendency is confirmed by the Risø cases. While overall statistics are satisfactory, both BFBT and PSBT bubbly-to-churn flow void contents are markedly overpredicted by CTF. The issues with two-phase closures such as turbulent mixing, interfacial and wall friction, and subcooled boiling heat transfer need to be addressed. Preliminary sensitivity studies are presented herein, but more advanced models and code stability analysis require further investigation. [ABSTRACT FROM AUTHOR]

Blind tees are commonly used in offshore production systems for the flow mixing and measurement of oil and gas products. Since subsea pipelines usually consist of multiple bends, the blind-tee effects on bend combinations should be thoroughly investigated. In this paper, numerical simulations have been conducted to investigate the effects of blind tees on the flow physics in double-bend combinations. First, three-dimensional flow characteristics are analyzed to illustrate the blind-tee effects on double-bend pipes. Then, the absolute helicity density is introduced to quantitively evaluate the mixing capacity along the bend pipes with and without blind tees. Significant differences in flow behaviours and mixing qualities are observed in different bend configurations. If a blind tee is arranged in the first bend, strong vortices are generated, and the mixing conditions are significantly improved. However, when the blind tee is in the second bend, its internal flow is negatively influenced by the upstream elbow, resulting in a poor mixing condition. Besides, the effects of the structural parameters of double-bend combinations on the flow behaviours and mixing conditions have been systematically investigated. The analysis and results of this study can provide guidance for the application of blind tees in complex piping systems. • Structural effects of bend combinations are reported. • Mixing conditions in combined bends with blind tees are quantified. • Influence of upstream structure on downstream bend flow are revealed. • Optimal design schemes for different bend combinations are recommended. [ABSTRACT FROM AUTHOR]

The second law and entropy generation characteristics of a new hybrid nanofluid containing graphene nanoplatelets decorated with platinum nanoparticles are evaluated in a chaotic twisted channel. Although several investigations have been carried out on flows inside chaotic channels in the relevant literature, very few studies have employed nanofluids as working fluids in such configurations. The geometrical perturbations cause formation of counter rotating Dean roll-cells which intensify mixing in the flow and disturb the boundary layer. The intensity of perturbations considerably enhances at higher Dean numbers. The maximum velocity is shifted toward the outer wall due to the centrifugal force, and the maximum frictional entropy generation occurs there. Because the roll-cells lead to more uniform temperature distribution, thermal entropy generation reduces with increase of distance from the inlet of each bend. Moreover, by increasing concentration and Dean number, thermal entropy generation and Bejan number decrease while frictional entropy generation intensifies, however, due to dominance of thermal entropy generation, overall irreversibility of the nanofluid flow reduces. Besides, the temperature gradients become greater at higher wall heat fluxes which lead to the more intense thermal entropy generation. In addition, the difference between the Bejan numbers related to different wall heat fluxes is more noticeable at higher concentrations. [ABSTRACT FROM AUTHOR]

This study aims to investigate entropy generation for flow of three different nanofluids in a chaotic minichannel. Fluid particles in this channel move in chaotic trajectories, which can intensify the flow mixing. The results show that the contribution of heat transfer to entropy generation is greater than that of friction. With increasing the concentration, thermal entropy generation decreases for the alumina–water and Cu–water nanofluids, while intensifies for the magnetite–water nanofluid. With increase in Reynolds number for all nanofluids, thermal entropy generation decreases while frictional entropy generation increases. With the concentration increment, frictional entropy generation rate has an ascending trend for the alumina–water and magnetite–water nanofluids, while has a descending trend for the Cu–water nanofluid. Moreover, as Reynolds number increases from 50 to 200 at concentration of 1%, total entropy generation reduces 66.25%, 65.9% and 68.9% for the magnetite, alumina and Cu nanofluids, respectively. Based on the second law of thermodynamics, the Cu–water nanofluid is a more appropriate coolant owing to smaller total entropy generation. Moreover, use of the Cu–water and alumina–water nanofluids is more suitable at greater concentrations, while employing the magnetite–water nanofluid is only recommended at low concentrations. [ABSTRACT FROM AUTHOR]

Accurate measurements of volume or mass flow in large conduits can be difficult to achieve due to non-ideal flow characteristics such as asymmetry of the velocity profile and off-axis flow components due to swirl. The tracer gas dilution method is independent of these and other non-ideal flow characteristics, but relies on the conservation and uniform mixing of the tracer. This study demonstrates the application of the tracer gas dilution method to measure the volume flow in a large-scale exhaust duct used for flue gas venting. The estimated measurement uncertainty was less than ± 3.5% and considered contributions from instrumentation, degree of mixing, and repeatability of the method. This level of uncertainty demonstrates that the method can be applied as an independent comparison or quality check for other flow measurement methods in large exhaust ducts or flow conduits. [ABSTRACT FROM AUTHOR]

• A new classification criterion of flow pattern in the T-junction under steady condition is proposed. • The rolling motion causes the branch jet to sweep up and down in the T-junction. • The influence map on the sweeping phenomenon under rolling motion condition is proposed. Flow mixing experiments are performed on the Ocean Conditions Simulation Platform (OCSP) test facility to investigate the flow pattern evolution mechanisms in a T-junction with branch jet under steady and rolling motion conditions. Plane Laser-Induced Fluorescence (PLIF) technology is used to display and test the instantaneous flow pattern in the T-junction. The effects of the main fluid Reynolds number, inflow rate ratio and rolling Reynolds number on the flow pattern characteristics are discussed at a range of 2110–15850, 1–20 and 0–3520, respectively. Based on the experimental results, new classification criteria of flow pattern in the T-junction under steady condition are proposed from the perspective of the evolution of vortex structure. The flow patterns are classified into the single shear vortex, co-rotating vortex pair, transition region and counter-rotating vortex pair according to the fluid Reynolds number and inflow rate ratio. Under rolling motion condition, the branch jet periodically sweeps up and down in the T-junction due to the effect of additional inertial force. The sweeping phenomenon of the branch jet caused by rolling motion enhances the flow instability in the T-junction that can be inhibited by increasing the fluid Reynolds number or decreasing the inflow rate ratio and rolling Reynolds number. In addition, the influence mechanisms of fluid Reynolds number, inflow rate ratio and rolling Reynolds number on the flow pattern in the T-junction are investigated. These results can inform the analysis, design, safe operation and performance improvement of equipment in various industrial applications involving flow mixing in a T-junction. [ABSTRACT FROM AUTHOR]

The effect of side injection on mixing of the two axial flows i.e flow through the ware and flow through the gap between ware and walls in the preheating nzone of tunnel kiln is investigated. The 3D temperature field in the cross section between two cars is calculated using the CFD tool (ANSYS Fluent). The mixing quality is evaluated using the contours of temperature, the frequency of temperature distribution and the maximum temperature difference. The influence of injection flow rate, injection velocity, position of nozzels and nozzle number on the mixing behaviour are analyzed. The results show that use of two side injection nozzles is more effective than one side injection nozzle to achieve mixing. Moreover, a relatively better mixing is achieved when the nozzles are installed at the opposite side walls at higher vertical distance (larger distance apart). The mixing quality increases strongly until an impulse flow rate of about 4 N. For higher values of impulse, the influence becomes relatively low. [ABSTRACT FROM AUTHOR]

Hot air from the cooling zone of a continuous kiln is available at the end of the corresponding firing zone. It can be used again with the application of special injectors. 3D simulations in a domain containing injector nozzles are carried out to evaluate the temperature distribution inside the continuous kiln in case of using the hot air which comes from the cooling zone. The roller hearth kiln is taken as a computational domain in this study. Parameters referring to the direction of the burner streamline, the quantity of the air sucked and the effect of the cone length are studied. The temperature distribution at the outlet is determined in case of fixing the burner against or along the direction of the main flow. It is shown that the maximum air velocity at the outlet of the burner cone is about 90m/s. The upstream model temperature distribution is found better than the downstream one. It is also suggested that a burner with longer outlet duct can protect the product from direct exposure to the flame. [ABSTRACT FROM AUTHOR]

• Effects of rolling motion with momentum ratio (M R) of 0.95 are investigated. • Effects of inflow rates under rolling motion condition are studied. • Synergistic effect exists between velocity and temperature. • Additional frequency peaks occur under rolling motion condition. The present study numerically investigates the flow mixing characteristics in the T-junction with momentum ratio (M R) of 0.95 under rolling motion condition. The effects of different inflow rates of 0.47–1.9 kg·s−1 and the synergistic effects between velocity and temperature are discussed. The results show that the rolling motion significantly changes the upstream instantaneous velocity field, especially that near the wall, which induces the variations of the instantaneous M R and the mixing length of the temperature field. The rolling motion increases the range of the velocity fluctuation while decreasing that of the temperature fluctuation. Under rolling motion condition, increasing the inflow rates decreases the range of the velocity fluctuations and inhibits the variation of M R. This weakens the flow mixing of main and branch fluids thereby increasing the range of the temperature fluctuations. In addition, it is found that the synergistic effects between velocity and temperature occur at the junction of the main and branch fluids, where the power spectrum densities (PSDs) of y velocity component fluctuation and temperature fluctuation exhibit the same frequency peaks of 0.2 Hz, 5.8 Hz, 14.7 Hz, and 31.2 Hz. By comparing the PSDs along with the y -axis, it is revealed that the high temperature fluctuation area of y / D = 0–0.33 has a faster energy cascade with a larger slope of −5/3 in the low-frequency area (0.1–10 Hz) and −13/2 slope in the high-frequency area (>10 Hz). [ABSTRACT FROM AUTHOR]

Normal pressure hydrocephalus (NPH) is an intracranial disease characterized by an abnormal accumulation of cerebrospinal fluid (CSF) in brain ventricles within the normal range of intracranial pressure. Most NPH in aged patients is idiopathic (iNPH) and without any prior history of intracranial diseases. Although an abnormal increase of CSF stroke volume (hyper-dynamic CSF flow) in the aqueduct between the third and fourth ventricles has received much attention as a clinical evaluation index in iNPH patients, the biomechanical effects of this flow on iNPH pathophysiology are poorly understood. This study aimed to clarify the potential biomechanical effects of hyper-dynamic CSF flow through the aqueduct of iNPH patients using magnetic resonance imaging-based computational simulations. Ventricular geometries and CSF flow rates through aqueducts of 10 iNPH patients and 10 healthy control subjects were obtained from multimodal magnetic resonance images, and these CSF flow fields were simulated using computational fluid dynamics. As biomechanical factors, we evaluated wall shear stress on the ventricular wall and the extent of flow mixing, which potentially disturbs the CSF composition in each ventricle. The results showed that the relatively high CSF flow rate and large and irregular shapes of the aqueduct in iNPH resulted in large wall shear stresses localized in relatively narrow regions. Furthermore, the resulting CSF flow showed a stable cyclic motion in control subjects, whereas strong mixing during transport through the aqueduct was found in patients with iNPH. These findings provide further insights into the clinical and biomechanical correlates of NPH pathophysiology., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Numerical experiments of wave-current interaction have been performed to investigate the evolution and dissipation of horizontal large-scale vortical structures generated by differential wave breaking and current shearing at river mouths. Specific focus is on the role played by turbulence of scales smaller than the water depth and by seabed friction on the dissipation of the mentioned macrovortices. The analysis reveals two regions of turbulence generation: at the river mouth, and along the curved seaward boundary of the shoal. In the latter zone, macrovortices are formed due to differential wave breaking induced by the sudden variation in water depth and enhanced by opposing currents which favour wave steepening. Such vortices are then advected towards the shore. Among the dissipative mechanisms, dissipation induced by seabed friction is deemed dominant, in particular in the most shallow waters of the shoal. Sub-grid turbulence dissipation, conversely, is more efficient offshore, although exerting some effect also over the shoal when supported by the continuous action of waves.

Algal blooms are increasingly frequently reported in reservoirs, posing a serious threat to the water environment and operation status. The phytoplankton that causes blooms is affected by environmental conditions including light-heat, water quality and hydrodynamics. Exploring the environmental coupling effects (including hydrodynamic effects) of phytoplankton is critical for reservoir management, but such studies are still scarce. This study monitored the phytoplankton and environmental factor data of Zipingpu Reservoir for 29 months and constructed a novel partial least squares structural equation modeling to quantify the impacts of environmental conditions on the phytoplankton in the canyon-shaped reservoir. There were significant spatial differences in the biomass of phytoplankton in the reservoir, and the biomass reached its peak in May to July every year. The model explained 51.4% of the spatiotemporal variation in phytoplankton and revealed that the coupling effect of flow and nutrition affected the transparency (with a coefficient of −0.427, p < 0.01) and then influence the biomass of phytoplankton. The coupling effect of flow and meteorology indirectly modified phytoplankton biomass by changing physicochemical properties (with a coefficient of 0.261, p < 0.01). Meteorology indirectly affected stratification by changing the physicochemical properties of the water and promoted temporal variation in phytoplankton biomass. The contribution rates of hydrodynamic conditions, including operation, flow and stratification variables, to phytoplankton dynamics were extremely high, reaching 34.9%. The flow change caused by reservoir operation will significantly affect phytoplankton (with a coefficient of 0.352, p < 0.01), especially when the temperature is appropriate, and a hydrodynamic operation strategy aiming to avoid rapid increases in the water level (more than 0.8 m d−1) in the reservoir may be effective in restraining blooms. This study not only further clarifies the coupling effects of environmental conditions on phytoplankton, but also provided important information to support sustainable blooms prevention and control decisions by reservoir managers. [Display omitted] • The proposed structure equation model explained 51.4% of phytoplankton variation. • Coupling effect of hydrodynamic conditions has the highest explanation rate of 34.9%. • Water level rapid rise during the suitable temperature period promoted algal blooms. • Flow-depended nutrients and transparency features dominated to the spatial variation. • Temperature-driven thermal stratification results in the temporal variation pattern. [ABSTRACT FROM AUTHOR]

A carbonating tank is continuously operated and filled with water supplied by an immersed flow injecting nozzle. At the same time, CO 2 gas is introduced from the gas tank. CO 2 gas can be dissolved in water and can form carbonated water with minimum production of gas bubbles depending on various process conditions. Therefore, the flow mixing phenomenon of CO 2 and water can be affected by the placement of the injecting nozzle and the flow rate in consideration of the interfacial surface. In this study, the gas–liquid flow mixing with the mass transport inside the carbonation process tank is numerically predicted. The Euler–Euler methodology is used to observe the effects of the design of the injecting nozzle, the gas bubble size, as well as the velocities of liquid and gas on the gas volume fraction, liquid velocity, gas concentration, interfacial area, and mass transfer coefficient. [ABSTRACT FROM AUTHOR]

Flow mixing characteristics inside a wire-wrapped 37-pin bundle were measured using a wire-mesh sensing system. The subchannel flow mixing within a sodium-cooled fast reactor (SFR) core subassembly is an important phenomenon to predict temperature distributions for the core thermal design and safety analysis. To identify the mixing characteristics experimentally, a dedicated test facility including the wire-mesh sensor system and tracing liquid injection system was developed. The conductivity fields at the end of a 37-pin bundle were visualized in several different flow conditions which are corresponding to 20–115% flow of the prototype reactor nominal flow based on the Reynolds number. A CFD preliminary analysis under pre-determined boundary conditions was also performed to verify the design parameters and range of various operating values of the current mixing test. The experimentally identified mixing characteristics were compared with the CFD results, which show reasonable agreements with each other. The current experimental work includes the uncertainty evaluation by performing the separated test for the elementary parameters. [ABSTRACT FROM AUTHOR]

• A newly designed fractal flow mixer was proposed. • Mixer was successfully manufactured using two additive manufacturing techniques. • Simulations were conducted to characterise the hydrodynamics and mixing. • Majority of the flow was uniformly mixed with a distribution index close to unity. The uniform distribution and mixing of fluids is a common functional requirement in a range of process intensified fluid handling applications. Traditional manufacturing processes have limited the design and performance of flow distributors and mixers. However, the maturing of additive manufacturing (AM) has increased the range of manufacturable geometries, enabling the construction of novel high-performance flow distribution devices. An additively manufactured fractal flow mixer was designed using the concept of self-similar bifurcating channels that symmetrically bifurcates a flow into multiple channels, achieving flow uniformity through a series of sequential stages. After four stages of bifurcation, a y-junction on each channel was introduced before the outlet, mixing the flow from two modules. Computational fluid dynamics (CFD) simulations were carried out to characterise the hydrodynamics and mixing performance of the newly designed mixer over a range of operating conditions and for mixing two gases. Effect of inlet Reynolds numbers (Re) and flow ratio was studied, the maximum relative standard deviation (RSD) was found to be ∼8%, and majority of the flow was uniformly mixed with a distribution index close to unity. The fractal flow mixer was successfully manufactured using vat photopolymerisation (VP) and laser powder bed fusion (L-PBF) techniques without any supports. [Display omitted] [ABSTRACT FROM AUTHOR]

Mixing is a precondition for efficient chemical and biochemical reactions, especially in limited time and space, such as in a laboratory on a chip system under various flow conditions. In this work, a novel method of preparing a total glass chip mixer with a streamline herringbone structure is presented. The main mixing channel and the embedded herringbone pattern were simultaneously generated by one-step photolithographic exposure and one-step wet etching of glass substrate. The mixing performance under typical pressure flow as well as high DC voltage-activated migration conditions, thanks to the charged and stable surface nature of the glass substrate, was investigated experimentally by microscope fluorescent imaging using charged and neutral fluorescence molecular probes, respectively. The passive chip mixer was effective for both hydrodynamic and electrodynamics migration conditions, and over 90 % mixing was achieve in 20 mm in the mixing channel of only 300 nL. The applicability of the chip was demonstrated by a chemiluminescence reaction with enhanced signal and detection power. The chemical resistive surface, integrity, transparency, and high mixing efficiency of this passive chip mixer are advantageous for microanalytical systems of various flow conditions, especially miniaturized chromatography or electrophoresis systems. [ABSTRACT FROM AUTHOR]

Ethylene jet diffusion flames under the influence of acoustic modulation from a loudspeaker at the natural flickering frequency ( f = 10 Hz) and the acoustic resonant frequency ( f = 66 Hz) are experimentally and numerically studied. Experimental measurements (using hot-wire anemometry), numerical simulation results, and theoretical analysis results are consistent at the burner exit for cold jet flow without acoustic modulation. For cold jet flow with acoustic modulation, the maximum value of axial velocity measured at the axisymmetric axis, which occurs at a phase angle of ϕ = 90 ° , is compared to that obtained using numerical simulation. The axial velocities at the burner exit predicted by the numerical simulation for f = 10 and 66 Hz show similar characteristics, where the maximum and minimum values occur at ϕ = 90 ° and ϕ = 270 ° , respectively. Additionally, the maximum and minimum values are several times the steady state value (0.4 m/s). For f = 10 Hz, the shape of the Schiliren contours surrounding the flame changes from cap-like, to semicircle-like, to shuttle-like. The shape of the Schiliren contours inside the flame is mushroom-like for 45 ° ⩽ ϕ ⩽ 225 ° . For f = 66 Hz, different from the case of f = 10 Hz, the Schiliren contours keep a separation distance surrounding the flame because the resonant coupling effect mainly governs the fuel line. The Schiliren structure inside the flame is found only in the luminous root for 180 ° ⩽ ϕ ⩽ 225 ° due to the small difference in the refractive index for the other phase angles. The streamlines, iso-contours of axial velocity, or iso-contours of ethylene concentration can be used to quantitatively determine the puff flame at both 10 and 66 Hz. For the flow field at f = 10 Hz, there is strong flow interaction between the gas flow and ambient surroundings. At 66 Hz, however, interaction between the sound wave and the fuel line occurs, i.e., acoustic resonance. [ABSTRACT FROM AUTHOR]

Effects of ionic concentration gradient on electroosmotic flow (EOF) mixing of one stream of a high concentration electrolyte solution with a stream of a low concentration electrolyte solution in a microchannel are investigated numerically. The concentration field, flow field and electric field are strongly coupled via concentration dependent zeta potential, dielectric constant and electric conductivity. The results show that the electric field and the flow velocity are non-uniform when the concentration dependence of these parameters is taken into consideration. It is also found that when the ionic concentration of the electrolyte solution is higher than 1 M, the electrolyte solution essentially cannot enter the channel due to the extremely low electroosmotic flow mobility. The effects of the concentration dependence of zeta potential, dielectric constant and electric conductivity on electroosmotic flow mixing are studied. [ABSTRACT FROM AUTHOR]

Spectroscopic measurements of flames are amongst the most important analytical diagnostic techniques that allow one to improve thermal and energy efficiency of industrial furnaces. A chemical seeding laser-induced plasma spectroscopy (CS-LIPS) was successfully developed and applied for mixing analysis of a methane-air diffusion flame. The results obtained showed that sensitivity of this system was much improved using silica rod as the target material in place of the tungsten material used in our previous studies. Profiling of Mg spectral emission and mixing in the flame was made more clearly with the introduction of magnesium aerosols as a tracer into the combustion airflow. [ABSTRACT FROM AUTHOR]

T-100 is a multipurpose small power unit developed by Sundstrand Power Systems (USA). An extensive research programme was launched for the detailed tests of the rig components including inlet protection system, Compressor stage, Combustor and the Turbine stage. Turbomachinery Group at Cranfield was involved in the study of the Turbine unit used in this programme. From the design point of view, detailed aerodynamics in these small units are of great interest especially where high velocities and narrow passages are involved. Experimental study was carried out to investigate the flow in the region between the nozzle guide vanes and the turbine rotor entry. The main concern was to find out how the nozzle guide vane flow was modified by the rotor and how the rotor flow was affected by the nozzle guide vanes. Laser measurements were taken at these positions for various flow conditions. An other area which needs considerable attention is downstream of the turbine rotor where the turning of flow and mixing process make the situation very complicated. Laser studies were undertaken in that region and to gain more confidence on laser results, a Cobra pressure probe was traversed at these stations. This paper describes various steps undertaken to obtain laser results within the machine. At the end typical laser results have been presented and discussed.

Abstract: A novel flow field for algae raceways has been proposed, which is fundamentally different from traditional paddlewheel-driven raceways. To reduce freezing and heat loss in the raceway during cold time, the water is drained to a deep storage canal. The ground bed of the new raceway has a low slope so that water, lifted by propeller pump, can flow down in laterally-laid serpentine channels, relying on gravitational force. The flow rate of water is controlled so that it can overflow the lateral channel walls and mix with the main flow in the next lower channel, which thus creates a better mixing. In order to optimize the design parameters of the new flow field, methods including flow visualization, local point velocity measurement, and CFD analysis were employed to investigate the flow mixing features. Different combinations of channel geometries and water velocities were evaluated. An optimized flow field design and details of flow mixing are presented. The study offers an innovative design for large scale algae growth raceways which is of significance to the algae and biofuel industry. [Copyright &y& Elsevier]

The paper presents the review of researches of the ignition and combustion stabilization of the water-coal fuel. Working models of plants are described, the results of their tests in laboratory and industrial conditions are given. Two schemes of the water-coal fuel ignition are presented -one with burners with hydrocarbon (solar) fuel, and the other with the system of plasma ignition. Advantages of these two systems are described. The promising future of the systems of plasma ignition application in industrial conditions is demonstrated. [ABSTRACT FROM AUTHOR]