Upward Flow Velocity Research Articles

Numerical study on the motion of two parallel spherical particles with different diameters in upward flow

The settling of particles is related to many industrial processes and research fields. However, due to the complex particle–particle and particle–fluid interactions, the settling mechanism of particles in flowing fluids is not fully understood. This article conducts numerical research on the settling process of two particles with different diameters in parallel in upward flow using the immersion boundary method. The numerical method was validated against experimental results including one particle settling, two parallel particles settling, and two series particles settling. The effects of large particle diameter, upward flow velocity, and initial particle spacing on the settling process were explored. The results indicate that the two particles with same diameter will repel each other when settling in upward flow. Moreover, when the diameters differ, the two particles can experience both attractive and repulsive interactions. The larger the diameter of the large particle, the stronger its attractive influence on the small particle. When the diameter of large particle d2 = 3.0d1, large particle only has an attractive effect on small particle. The wake of each particle forms a distinct velocity boundary with the upward fluid. As the upward flow velocity increases, the interactions between the two particles become increasingly intense. With increasing initial spacing between the particles, their mutual interactions gradually weaken.

Investigating condensation from humid air under mixed convection regime

A wide range of industrial applications rely heavily on heat transfer during vapor condensation from a mixture of water vapor and noncondensable gases (NCG). For a vertically-mounted condenser plate, the vapor-diffusion boundary-layer thickness is influenced by the interplay of the thermogravitational and forced flow fields, eliciting classical mixed convection scenario. This thickness in turn dictates the condensation heat and mass transfer rates. While condensation in presence of NCG under free and forced convection scenarios are well-characterized in the literature, its counterpart in the mixed convection regime is relatively uncharted. Herein, condensation from an upward stream of humid air over a vertically mounted mild steel condenser surface is characterized under different flow velocities. The free-stream flow is thus directed opposite to the thermogravitational flow induced next to the plate. We observe that with increasing the magnitude of the upward flow velocity of the free stream, the condensation heat transfer coefficient (CHTC) initially decreases until it reaches a minimum at 0.4 m/s, beyond which the CHTC rises again with the flow velocity. Using the Nusselt analogy for mixed convection for the relevant flow regimes we substantiate our experimental findings and extend the observation for predicting condensation behavior under different experimental ambient conditions.

In situ measurements of dissolved gases in xylem sap as tracers in plant physiology

Abstract Trees transport gases from the ground into the atmosphere through the process of transpiration. Tracing gases transported through this mechanism continuously and under field conditions remains an experimental challenge. Here we measured gases dissolved in the tree sap in situ and in real time, aiming to simultaneously analyse the transport of several gases (He, Ar, Kr, N2, O2 and CO2) from the soil, through the trees, into the atmosphere. We constructed and inserted custom-made semi-permeable membrane probes in the xylem of a fir tree and measured gas abundances at different heights using a portable gas equilibrium membrane-inlet mass spectrometer (‘miniRUEDI’). With this method, we were able to continuously measure the abundances of He, Ar, Kr, N2, O2 and CO2 in sap over several weeks. We observed diurnal variations of CO2 and O2 concentrations that reflected tree physiological activities. As a proof of the concept that trees do uptake dissolved gases in soil water, we irrigated the tree with He-enriched water in a tracer experiment and were able to determine upward sap flow velocity. Measurements of inert gases together with reactive species, such as CO2 and O2, allowed separation of the physical transport and exchange of gases derived from the soil or atmosphere from biological reactions. We discuss the opportunities that our technique provides for continuous in situ measurements of gases in the tree sap.

Characteristics of particle formation in O3-UBAC filter and effects of operational parameter on particles

The ozone oxidation and up-flow biological activated carbon (O3-UBAC) process has been recognized for its ability to extend the operating cycle of biological activated carbon (BAC) filters by expanding the carbon layer and maintaining a dynamic balance of the carbon biofilm. However, the primary focus of O3-UBAC is the removal of organic pollutants, often overlooking the treatment of particles. To address this gap, a pilot-scale study was conducted using sedimentation basin effluent samples from a drinking water treatment plant (DWTP), which were added into BAC columns. The study aimed to investigate the seasonal variation of effluent particles during the UBAC operating cycle, including particle counts, size distribution, and mass composition. Based on particle characteristics and the combined effects of adsorption and biodegradation, the UBAC operation cycle was divided into three periods. Results revealed that hydraulic impacts and biofilm desorption on carbon could increase the proportion of particles >5 μm in effluent. Pre-ozonation demonstrated significant effects on particle counts and Heterotrophic Plate Count (HPC) levels (p < 0.05), with the addition of 1 mg/L O3 resulting in a reduction in particle counts in the effluent. Moreover, particle removal could be achieved by adjusting the upward flow velocity, necessitating comprehensive consideration of pollutants. Furthermore, microbial community analysis under optimal operating conditions unveiled significant changes in the microbial diversity of UBAC-treated water particles. Although the influent and effluent exhibited similarities at different phylum levels, the dominant bacteria differed significantly at various levels.

Experimental evaluation of liquid circulation flow rate induced by an air-injection-type aerator

Despite previous research efforts, there is a lack of experimental data on liquid circulation flow rates, particularly in real-scale facilities. The study aims to fill this gap by proposing a momentum transfer model using a gas–liquid separation flow to estimate inner flow in a real-scale air-injection-type aerator. The liquid circulation flow rate was evaluated using velocity measurements. The air supply pressure and dissolved oxygen (DO) were determined. Experiments were performed at depths of 0.90, 1.30, and 1.75 m. The effect of the inner diffuser was investigated at each depth. The inner diffuser reduced the circulation flow rate but increased the vertical upward flow velocity. For the deepest condition (1.75 m), the inner diffuser reduced the air supply pressure and increased the overall oxygen transfer coefficient. Momentum analysis indicated a suppression effect of the air velocity at the aerator exit owing to the inner diffuser. This indicated that an increase in the gas holdup owing to the deceleration of the air velocity at the aerator exit reduced the air supply pressure owing to the reduction in downstream pressure. This study provides valuable insights into aeration system optimization, considering factors such as energy efficiency and oxygen transfer effectiveness.

Negative-energy Waves in the Vertical Threads of a Solar Prominence

Solar prominences, intricate structures on the Sun’s limb, have been a subject of fascination owing to their threadlike features and dynamic behaviors. Utilizing data from the New Vacuum Solar Telescope, Chinese Hα Solar Explorer, and Solar Dynamics Observatory, this study investigates the transverse swaying motions observed in the vertical threads of a solar prominence during its eruption onset on 2023 May 11. The transverse swaying motions were observed to propagate upward, accompanied by upflowing materials at an inclination of 31° relative to the plane of the sky. These motions displayed small-amplitude oscillations with corrected velocities of around 3–4 km s−1 and periods of 13–17 minutes. Over time, the oscillations of swaying motion exhibited an increasing pattern in displacement amplitudes, oscillatory periods, and projected velocity amplitudes. Their phase velocities are estimated to be about 26–34 km s−1. An important finding is that these oscillations’ phase velocities are comparable to the upward flow velocities, measured to be around 30–34 km s−1. We propose that this phenomenon is associated with negative-energy wave instabilities, which require comparable velocities of the waves and flows, as indicated by our findings. This phenomenon may contribute to the instability and observed disruption of the prominence. By using prominence seismology, the Alfvén speed and magnetic field strength of the vertical threads have been estimated to be approximately 21.5 km s−1 and 1–3G, respectively. This study reveals the dynamics and magnetic properties of solar prominences, contributing to our understanding of their behavior in the solar atmosphere.

A Preliminary Numerical Study on the Performance of Cyclone Separators in Supercritical CO2 Solar Power Plants

A combined approach of computational fluid dynamics, the discrete phase model, and the wall erosion model was used to numerically investigate the hydrodynamics, separation efficiency, and erosion rate in cyclone separators for s-CO2 solar power plants. Moreover, the results were compared with those for air and CO2 as carrier phases. The experimental data from the literature were used to validate the numerical model, and it was observed that the simulated gas velocities and wall erosion rate accurately aligned with the experimental measurements. The numerical results reveal that s-CO2 had the largest tangential velocity compared to the other two media; its area-weighted axial velocity of upward flow was the lowest in the middle part of the cyclone body, and varied considerably in the bottom region of the conical section. The particles were all collected at the bottom surface of air and CO2, but the separation efficiency of s-CO2 was 81.51%, due to the poor distribution of the vortex and short circuit. Finally, the erosion rate distribution and averaged surface erosion rate were also analyzed for the three carrier phases.

Interaction between Local Shielding Gas Supply and Laser Spot Size on Spatter Formation in Laser Beam Welding of AISI 304

Background. Spatter formation at melt pool swellings at the keyhole rear wall is a major issue for laser deep penetration welding at speeds beyond 8 m/min. A gas nozzle directed towards the keyhole, that supplies shielding gas locally, is advantageous in reducing spatter formation due to its simple utilization. However, the relationship between local gas flow, laser spot size, and the resulting effects on spatter formation at high welding speeds up to 16 m/min are not yet fully understood. Methods. The high-alloy steel AISI 304 (1.4301/X5CrNi18-10) was welded with laser spot sizes of 300 μm and 600 μm while using a specially designed gas nozzle directed to the keyhole. Constant welding depth was ensured by Optical Coherence Tomography (OCT). Spatter formation was evaluated by precision weighing of samples. Subsequent processing of high-speed images was used to evaluate spatter quantity, size, and velocity. The keyhole oscillation was determined by Fast Fourier Transform (FFT) analysis. Tracking the formation of melt pool swellings at the keyhole rear wall provided information on the upward melt flow velocity. Results. The local gas flow enabled a significant reduction in the number of spatters and loss of mass for both laser spot sizes and indicated an effect on surface tension by shielding the processing zone from the ambient atmosphere. The laser spot size affected the upward melt flow velocity and spatter velocity.

Study on the hydraulic classification characteristics of micron‐sized silica particles

AbstractThe present study investigates the motion characteristics of micron‐sized silica particles and how solid–water interaction regulates hydraulic classification. Two methods were evaluated for classifying micron‐sized silica particles. Using the small‐diameter cyclone for hydraulic classification of micron‐sized silica particles resulted in poor separation due to the short residence time of particles in the cyclone. Particle settling in still water showed that settling velocity, drag force, and virtual mass force increased with particle size, providing a basis for size classification. In the particle sedimentation process, drag force and gravity were dominant, with drag force reaching equilibrium with gravity in a fast time. The upward water flow was introduced to classify silica particles, with its superficial velocity between the settling terminal velocities of large and small particles, allowing large and small particles to flow to the overflow and underflow, respectively. The upward flow velocity was higher near the center of the flow field and lower near the wall, leading to a parabolic distribution pattern of the particle group along the radial position. In hydraulic sedimentation classification experiments of silica particles, the average particle size of the overflow sample was lower than that of the feed, and its size range was narrower, indicating the feasibility of hindered sedimentation by upward flow for classifying micron‐sized silica particles.

Three-Dimensional Flow Velocity Estimation of Mountain Glacier Based on SAR Interferometry and Offset-Tracking Technology: A Case of the Urumqi Glacier No.1

Remote sensing estimations of glacier flow velocity could provide effective methods for the long-term monitoring of glacier flow velocity. This paper calculated the velocity in the line-of-sight (LOS) direction by combining DInSAR and offset-tracking technology with ascending and descending Sentinel-1 images of the Urumqi Glacier No.1 from 2016 to 2017. Meanwhile, the velocity in the azimuthal direction was obtained by combining MAI and offset-tracking technology. Then, the eastward, northward, and upward flow velocities were retrieved using the Helmert variance component estimation method. Finally, the standard error of the mean and mean errors of surface velocity in non-glaciated areas of the Urumqi Glacier No.1 were calculated to evaluate the accuracy of the results generated by the proposed method. The results showed: (1) The ascending LOS velocity and the descending LOS velocity were 1.812 m/a and −1.558 m/a from 2016 to 2017. The ascending azimuthal and descending azimuthal velocities were 0.978 m/a and −2.542 m/a, respectively. (2) The glacier flow velocities were 2.571 m/a and 1.801 m/a, respectively, for the eastward and northward directions. In the vertical direction, the velocity was −0.554 m/a. (3) The accuracy of the results generated by the proposed method were 0.028 m/a, 0.085 m/a, and 0.063 m/a in the east, north, and vertical directions. Therefore, it is suitable to use ascending and descending Sentinel-1 images and the study method proposed in this paper to estimate the surface flow velocity of mountain glaciers.

The controlling mechanisms of horizontal flame spread over thick rods in upward cross flow

This work studies the flame spread over horizontal thick PMMA (polymethyl methacrylate) rods with three radii under different oxygen concentrations and upward cross flow velocities. The flame spread rate and the limit oxygen concentration are measured. Far away from the extinction limit, the flame spread rate increases with the flow velocity but decreases with radius. Near the extinction limit, the flame spread rate is insensitive to the flow velocity and radius. The flame spread rate can be correlated by the stretch rate, and it is found that the flame spread rates for different radii are close at the same stretch rate. A scaling analysis shows that the flame spread rates are approximately square-root dependent on the stretch rate. Prior to the extinction, the flame has entered the regressive burning regime where the flame leading edge will not spread forwardly but continuously retreat. The flame extinction is dependent on the local stretch rate and in-depth heat conduction. For a given radius, the limit oxygen concentration increases with the stretch rate. For a given stretch rate, the smaller cylinder can sustain at lower oxygen concentration due to the less solid-phase heat loss.

Clarification of Biologically Treated Wastewater in a Clarifier with Suspended Sludge Layer

The article presents the results of an experimental study on the clarification of biologically treated wastewater in a clarifier with a suspended sludge layer. The pilot plant was receiving effluent from trickling filters treating municipal wastewater. An experimental clarifier worked under steady-state conditions considering the influent characteristics and variable operating parameters in terms of flow velocities and height of the suspended layer. From the experimental dependences between different technological parameters it was found that the optimum range of the upward flow velocities providing a dynamic equilibrium of the suspended layer was 0.6–1.4 mm/s. Upward flow velocities below 0.5 mm/s can lead to sludge compaction at the bottom of the unit, while values greater than 1.8 mm/s may cause sludge washout. It was also found that higher suspended layer height values favor higher efficiency of the clarifier and can achieve suspended solids in the discharge of less than 5.0 mg/L; this height should be greater than 0.6 m Technological efficiency of the experimental clarifier was significantly higher than the conventional unit and was comparable with tertiary treatment technologies.

Studying Disturbance Wave Velocity and Wall Shear Stress of Vertical Upward Annular Flow in Narrow Rectangular Channel

As two important parameters, the velocity of disturbance wave and the wall shear stress in annular flow are very important to solve the closed equations of the mechanical model for annular flow. In this study, the disturbance wave velocity and wall shear stress of annular flow in a vertical narrow rectangular channel with a cross section of 70 mm × 2 mm were studied. According to the experimental results, it is found that the wave velocity and wall shear stress of disturbance wave increase with increasing gas phase velocity and liquid phase velocity. Also, existing correlations for predicting the velocity of disturbance wave were summarized and evaluated using the current experimental data. A new correlation for wall shear stress based on the disturbance wave velocity has been proposed. Compared with the existing correlation for predicting wall shear stress, this new correlation can well predict the current experimental data and MAPE is only 7.32%.

Electromagnetic-thermal coupling behaviors and thermal convection during two-phase zone continuous casting high strength aluminum alloy tube

In this paper, the two-phase zone continuous casting (TZCC) technique was used to prepare 2D12 aluminum alloy tubes and a 3D model of TZCC was established to investigate the electromagnetic-thermal coupling as well as fluid flow behaviors under different mold temperatures. The calculated temperature in the induction heated mold agrees well with the measurement. It was found that the heat flux from the mold to the melt leads to a convex isoliquid fraction line of dendrite coherency point and circular thermal convection in front of the mushy zone. The velocity of the transverse flow increases remarkably with increasing mold temperature while the upward flow velocities at the outer wall are nearly constant. Experimental results indicate that the surface exudations with segregated solute appear at the surface of tubes when the mold temperature is higher than 883 K, and their size and quantity increase with increasing mold temperature. The serious solute redistribution and the thermal convection lead to solute segregation at the surface of tubes. Further, the residual liquid with segregated solutes flows to the surface of the tube and forms the surface exudation due to its lower freezing point than the Al matrix.

RMB experimental program on the hydrodynamical behavior of fuel assemblies

The Brazilian Multipurpose Reactor - RMB is a 30 MW pool type research reactor, that uses Materials Testing Reactor - MTR type fuel assemblies. It has a 5x5 square array core with 23 fuel assemblies and two in-core irradiation positions, operating with upward flow and average velocities nearly 10 m/s in the fuel plates channels. The IEA-R1 is a 5 MW pool type research reactor, which also has a 5x5 square array core with 19 standard fuel assemblies, four control fuel assemblies and a central beryllium irradiation device. It operates with downward flow nearly 1.8 m/s in the channels. In order to verify and provide data and information about the dynamical behavior of fuel assemblies under nominal and critical conditions, the experimental circuit ORQUÍDEA is being designed. This circuit will permit upward and downward flow and dynamical behavior of the fuel assemblies and its parts will be tested and verified. Flow rate, temperature, pressure and differential pressure transducers are the instruments of the circuit. Endurance and critical flow velocity tests will be performed. The COLIBRI experimental circuit is being designed to make tests that allow the studies of the fluid-structure phenomenology of fuel plates similar to those of the RMB fuel assemblies when subjected to high flow velocities, which can induce pressure differences between the channels formed by the fuel plates. This work presents a preliminary design for the ORQUÍDEA and COLIBRI experimental circuits to be built at the Instituto de Pesquisas Energéticas e Nucleares - IPEN of the Comissão Nacional de Energia Nuclear - CNEN.

Investigating the feasibility of artificial convective cloud creation

In this paper, we study the physical justification and experimental possibility of stimulating convection in the atmosphere to create artificial convective clouds and precipitation. A prerequisite for creation of artificial convective clouds is the presence of water vapor in the atmosphere; this is an encouraging factor as water vapor is present even in regions with an arid climate. Furthermore, numerous cases of convective cloud development under the influence of powerful heat sources are known, even for days lacking conditions for natural cloud development. In this paper, we analyze the results and failure causes of worldwide experiments with meteotrons, which are stationary installations designed to initiate powerful updrafts. To enhance meteotron jet buoyancy, a combined method based on use of a turbojet engine is proposed; the jet output by the engine creates an aerosol cloud that absorbs shortwave solar radiation. An overview of mathematical models of convective jets is given and the assumptions made during mathematical formulation of the problem are analyzed. Theoretical and laboratory results are compared. A mathematical model of a convective jet is proposed and an analytical solution is obtained in cylindrical coordinates. It is shown that the upward flow velocity decreases to a minimum at an altitude where the jet and environment temperatures are aligned. In contrast, the jet radius increases and, at the temperature equalization height, the jet adopts an umbrella form. We conclude that, for an artificially created stream to contribute to development of cloud convection, the temperature equalization height should be equal to or greater than the condensation level. The results obtained in this study can be used in the trials on creation of artificial updrafts and clouds.

Use of 1-D subsurface thermal profiles to characterize the groundwater flow in the Central Nile Delta region

Borehole temperature logs of twelve wells were analyzed to clarify the connection among groundwater and the subsurface thermal conditions in the central part of the Nile Delta as an irrigated land in an arid area. The annual average surface air temperature amid the interval from 1997 to 2017 was 22.74 °C, and the annual increment is 0.0629 °C year−1. This surface warming influenced the subsurface thermal system. Thermal gradient of the conducted temperature–depth (T–D) profiles varies from − 0.009 °C m−1 (well 4) to 0.0098 °C m−1 (well 12). The vertical change in the thermal gradient values lower than zero was detected in wells 1, 3, 4, 5, 6, 7, 9, and 11 while wells that have gradient higher than zero were wells 2, 8, 10, and 12. The T–D logs were numerically examined and the outcomes compared with standard curves to predict the vertical groundwater stream direction and speeds. The logged wells could be divided into three groups. Wells were characterized by downward groundwater flow as wells 1, 4, 7, 8, and 10. Wells were of upward groundwater flow as in wells 2, 3, 5, 9, 11, and 12. Wells were characterized with upward and downward groundwater flows as well 6. Vertical downward groundwater flow velocities in the study area ranged from 11.53 cm year−1 in well 10 at a depth of 200–236 m to 69.20 cm year−1 in well 1 at a depth of 32 m. The upward groundwater flow velocities varied from 498.26 cm year−1 in well 11 at a depth below 60 m to 10.65 cm year−1 in well 12 at a depth below 115 m. Seawater intrusion effect was estimated from the upward groundwater movement in the northern part (well 11), and the downward movement of the freshwater was reflected from well 10 in the southern part of the study area. Downward flow noticed in wells 7 and 6 reflects the recharge effect of Damietta and Rosetta Nile branches, respectively. The groundwater flow velocity and flow direction change with depth could be related to the aquifer heterogeneity, groundwater pumping, and surface water–groundwater interaction.

Exact Solution for PTT Fluid on a Vertical Moving Belt for Lift with Slip Condition

Objectives: This attempt is made to investigate the problem of a study of thin film flow for lift while considering a steady, incompressible, non-isothermal, Phan-Thien Tanner fluid on a vertical belt with slip condition. Method/Comparative analysis: The nonlinear differential equation has been derived from the continuity and momentum equations. Exact solution has been obtained, which gives us velocity-profile of fluid, flow rate, temperature, average velocity of fluid and net upward flow. The special cases such as the linear PTT (LPTT), quadratic PTT (QPTT), cubic PTT (CPTT), exponential PTT (EPTT) and upper convected Maxwell (UCM) models are considered, from the same model of PTT fluid. The behavior the velocity and depth is discussed, in effect of various parameters. The velocity and temperature are compared for those special cases. Findings: The analogy of the EPTT, CPTT, QPTT, LPTT and UCM fluid models for the velocity profile and temperature distribution reveals that the velocity profile of the UCM fluid model increases quickly as compared to the velocity of the EPTT fluid. The temperature distribution for EPTT fluid is higher than the temperature for its special case: UCM fluid model. The velocity of PTT fluid is observed to be increased with incorporation of slip condition on vertical belt. Improvements: None of the previous work has been done using no-slip boundary conditions, however slip conditions are used in piece of work. Also, a thorough discussion on cases is novelty in this work. Keywords: Exact Solution, Heat Transfer, Lift Problem, Phan-Thien Tanner, Thin Film Flow

Numerical study of a fire-driven flow in a narrow cavity

Air cavities and gaps between material layers are common in construction systems, e.g. ventilated façades. Air cavity may provide a pathway for smoke and flame spread in case of fire. Performing physical testing to investigate different systems and fire scenarios is resource demanding. Fire Dynamics Simulator (FDS version 6.7.0) was used to simulate fire driven flow between two parallel vertical walls. Flame heights, thermal impact to the interior wall surface and upward flow velocities were predicted with FDS and compared with experimental results. The fire source was a propane burner with 8 × 391 mm2 gas outlet area. Heat release rates were 6.6 kW and 12.4 kW and the distance between the parallel walls was 40 mm. Two different convective heat transfer coefficient sub grid scale models available in FDS were investigated. In this study the cavity width to mesh cell size ratio was equal or above 10, resulting in good predictions of flame heights, upward flow velocities and wall temperatures. 2 mm grid resulted in 25% lower HRR in locations near the burner gas inlet, compared to 4 mm grid, indicating the importance of well resolved gas outlet boundary.

Experimental study on improving the separation performance of liquid-solid fluidized bed using flotation reagent and newly designed aeration unit

ABSTRACTIn the study, a pilot-scale liquid-solid fluidized bed (LSFB) apparatus was modified by adding an aeration unit, which enabled us to test the effect of air addition on LSFB separation performance for fine coal (0.25 ~ 1.00 mm). Upward water flow velocity, aeration volume and flotation reagent (Kerosene and 2-Caprylic alcohol) dosage varied throughout the experiment. The optimum results from the three experimental conditions (without aeration, with aeration only, with aeration and reagent) were compared by their respective probable error (Ep) values. The Ep values of the three experimental conditions were 0.109, 0.08 and 0.07, respectively. The results indicated that the addition of air obviously enhanced LSFB performance, while the addition of flotation reagent further improved the separation result.