Flow Section Research Articles

A unifying bubble-layer-based theoretical model for flow boiling and application to a rod bundle

Current analyses of flow boiling primarily utilize two−/three-dimensional numerical simulations or one-dimensional empirical correlations/models. To develop a quasi-two-dimensional theoretical model, a unifying bubble-layer-based theoretical model is proposed, which can be applicable to the entire flow boiling process, from the single-phase liquid flow to the dryout point. This model considers bubble behaviors in each region and heat and mass transfer at the interfaces of two regions, consisting of conservation equations of mass, momentum, and energy, supplemented by a few empirical correlations. A sensitivity analysis of these correlations is conducted, revealing that the slip ratio correlation and bubble condensation rate correlation have the most significant impacts. Using experimental data on void fraction, the most accurate combination of empirical correlations is identified, with a total absolute error of 27.9 %. The verification ranges are 0.1-8Mpa for pressure, 182-1700 kW/m2 for heat flux, 240-2200 kg/m2s for mass flux, 0.83–1.76 for Prandtl number, and 4.4e3–2.98e5 for Reynold number. Finally, this model is applied to the analysis of the NHR200-II rod bundle, revealing the variations of several two-phase parameters under micro-boiling conditions and the influence of operating conditions on the length proportion of different flow sections, serving as important references for analyzing the impact of boiling on reactor reactivity.

Wind tunnel testing and modelling of a rod-airfoil setup: validation and 3D acoustic imaging

This work revisits the rod-airfoil benchmark experiment from Jacob et al. (2004) with the aim of performing a detailed numerical validation in the nearfield and far field as well as to perform 3D acoustic imaging. The setup consists of a rod near the leading edge of a NACA-0012 airfoil and is placed in a semi-open wind tunnel in anechoic conditions. In addition to a far-field microphone array, the setup is equipped with two planar microphone arrays as well as wall-mounted microphones on the closed wind tunnel section and on the airfoil. The setup is modelled using a second-order finite volume method, and particular attention is devoted to including installation effects and sensor response properties in order to guarantee simulation accuracy. Validation examples are provided, including single microphone spectra as well as the acoustic field reconstructed on the test object by means of 3D acoustic imaging using the planar microphone arrays. Finally, the experimentally-validated numerical model is used as a means to gain further insight into the tested object. For instance, the model allows to separate acoustical and turbulent effects present in the sensors located within the flow section.

Flow boiling in dimpled plate heat exchangers with different geometric parameters: Analysis of asymmetric channels

The evaporators of heat pumps extract heat from the environment. To improve the heat pump performance in cold environments, evaporators must operate with small temperature drops of the heat source, which requires large flow rates of the secondary fluid. This paper discusses dimpled plate heat exchangers (DPHEs) with flexible flow section areas. The flow boiling of R410A is measured in six channels. The flow section area ratios of neighboring channels are 0.86–2.83. To analyze outlet superheat, the two-phase and dryout zones are distinguished using infrared measurement. The dryout zone is a function of the superheat and mass flux, which is quantified. The heat transfer coefficients (HTCs) increase with increasing mass fluxes and heat fluxes. Compared with experimental results from a large scope, the present data fall into the combined regimes of convective boiling and nucleate boiling. Smaller hydraulic diameters slightly enhance the heat transfer. The experimental HTCs are accurately predicted by a correlation of chevron plate heat exchangers (CPHEs). The performances of the DPHEs and CPHE are compared for small temperature drops in cold environments. The DPHEs have superior performance by mitigating the unbalance of mass fluxes. The typical overall heat transfer coefficient is improved by 62%. The improvement depends on the flow section area ratios.

Application Research of an Automatic Control Seawater Reverse Osmosis (SWRO) System Based on the Siemens PLC

To solve the global environmental problem of a shortage of freshwater resources, seawater desalination is considered one of the most promising solutions. In this research, the main novelty of the seawater desalination system lies in its utilization of a reverse osmosis unit as the core process for producing drinking water. By optimizing the pretreatment section in the process flow, a seawater reverse osmosis (SWRO) control system based on Siemens PLC with a high degree of automation was developed, which has the advantages of convenient maintenance and monitoring. In addition, through research on reverse osmosis systems, the results showed that within two years of operation, the total desalination rates of the primary and secondary reverse osmosis systems were not less than 99% and 97.5%, respectively. Furthermore, the water quality after desalination was tested. When the doses of CaCl2, MgCl2 and NaHCO3 were 20 mg/L, 15 mg/L, and 50 mg/L, respectively, high-quality drinking water was obtained. Finally, a reasonable process plan and corresponding estimates were given for the complex water source conditions. Compared with traditional seawater desalination systems, our system has the advantages of easy operation, efficient water production and lower price. Accordingly, this study will help to solve drinking-water problems in some freshwater-scarce regions.

Abated crowding by fast-tracking the Throughput component of the ED for patients in no need of hospitalization with competency managed personnel

BackgroundEmergency department (ED) crowding is a major patient safety concern and has a negative impact on healthcare systems and healthcare providers. We hypothesized that it would be feasible to control crowding by employing a multifaceted approach consisting of systematically fast-tracking patients who are mostly not in need of a hospital stay as assessed by an initial nurse and treated by decision competent physicians.MethodsData from 120,901 patients registered in a secondary care ED from the 4tth quarter of 2021 to the 1st quarter of 2024 was drawn from the electronic health record’s data warehouse using the SAP Web Intelligence tool and processed in the Python programming language. Crowding was compared before and after ED transformation from a uniform department into a high flow (α) and a low flow (β) section with patient placement in gurneys/chairs or beds, respectively. Patients putatively not in need of hospitalization were identified by nurse, placed in in the α setting and assessed and treated by decision competent physicians. Incidence of crowding, number of patients admitted per day and readmittances within 72 h following ED admission before and after changes were determined. Values are number of patients, mean ± SEM and mean differences with 95% CIs. Statistical significance was ascertained using Student’s two tailed t-test for unpaired values.ResultsBefore and after ED changes crowding of 130% amounted to 123.8 h and 19.3 h in the latter. This is a difference of -104.6 ± 23.9 h with a 95% CI of -159.9 to -49.3, Δ% -84 (p = 0.002).There was the same amount of patients / day amounting to 135.8 and 133.5 patients / day Δ% = -1.7 patients 95% CI -6.3 to 1.6 (p = 0.21).There was no change in readmittances within 72 h before and after changes amounting to 9.0% versus 9.5%, Δ% = 0.5, 95%, CI -0.007 to 1.0 (p > 0.052).ConclusionIt appears feasible to abate crowding with unchanged patient admission and without an increase in readmittances by fast-track assessment and treatment of patients who are not in need of hospitalization.

Study of vortex throttle characteristics with adjustable resistance by rotation of the vortex chamber inlet channel

Abstract The study is aimed at obtaining and analyzing the flow and cavitation characteristics of the proposed control devices, which are in demand in control systems for aircraft and rocket engines, chemical and other technological processes that require a wide range of flow control at high pressure drops. The characteristics of vortex throttling devices with cylindrical and spherical chambers were obtained, providing flow control in the range of 0.1–25 kg/s. A change in flow rate in the range of 3.5–3.8 can be achieved by changing the flow swirl intensity without throttling the flow sections. When vortex devices operate, the threshold for the occurrence of cavitation shifts to the region of small values of P out /P in, and, starting from the values of the geometric characteristic A > 4.5, cavitation is absent throughout the entire range of flow control. The pressure drop at the inlet channel of the vortex chamber does not exceed 10–30 % of the total resistance of the device. The torque on the control roller is small, 1.8–2.8 Nm, regardless of the flow rate.

Analysis of Water Flow through the Active Parts of an Abrasive Water Jet Machine: A Combined Analytical and CFD Approach

This study has the main objective of the analysis of water flow through the active parts (cutting head CH) of an abrasive water jet (AWJ) machine, model YCWJ-380-1520, performed on a high-pressure nozzle (HPN) and mixing tube (MT). The flow is analyzed through the ruby orifice with a diameter of 0.25 mm by assimilating it with a circular pipe. Taking into account the fact that the average flow velocity through the ruby orifice is about 622 m/s, the value of 155,500 according to the Reynolds criterion was obtained. Regarding the turbulent flow regime, the flow section is divided into four zones; for each of them, the limits of flow layers and the maximum values of water velocities were determined. In the second part of this work, a 2D analysis of the flow through the CH assembly was carried out. Since the abrasive inlet tube (AT) also appears in the CH componence, two situations were analyzed in this study, namely, the case when the inlet through AT is restricted and the case when the AT is free. For each case, three values of flow diameters were considered, both for HPN and MT. The water flow characteristics were established and comparisons between theoretical models and CFD simulation were performed.

Disk-Like Surfaces of Section and Symplectic Capacities

We prove that the cylindrical capacity of a dynamically convex domain in \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}${\\mathbb{R}}^{4}$\\end{document} agrees with the least symplectic area of a disk-like global surface of section of the Reeb flow on the boundary of the domain. Moreover, we prove the strong Viterbo conjecture for all convex domains in \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}${\\mathbb{R}}^{4}$\\end{document} which are sufficiently C3 close to the round ball. This generalizes a result of Abbondandolo-Bramham-Hryniewicz-Salomão establishing a systolic inequality for such domains.

High-Speed Schlieren Imaging And PIV Of Unsteady Free Jet Injection With Plume Formation

This work aims to investigate Schlieren image correlation velocimetry for flow field quantification of gaseous jet injection in non-manipulable apparatus like flow chambers. Such flow cases often struggle using tracer-based methods: Seeding particles may locally cause technical problems, or the plant design prevents the principal opportunity of tracer adding, both of which lead to a reduced method repertory. This is specifically the case under flow conditions, where contamination of apparatus internals by seeding particles should be avoided completely. Therefore, in this paper, we explore a seedless, refraction-based method to quantify the velocity field of a jet plume. As an experimental flow case, we examine a transient jet release into a closed compartment under nearly atmospheric conditions. For simplification and greater clarity, the laboratory model geometry is kept essentially two-dimensional, thus we chose a flat-jet nozzle as injection device. The experimental investigations cover high-speed Schlieren imaging and laser sheet visualization, followed by digital image correlation. Combining the traditionally qualitative Schlieren approach for flow visualization with Fast Fourier Transform and cross-correlation algorithms, we calculated the velocity vector field of an unsteady jet plume formation. Furthermore, we determined the axial jet velocity profile at steady-state conditions. Our research findings highlight the applicability of Schlieren image correlation velocimetry to quantify gaseous jet formation at encased flow sections spatially. Concluding, the results coincide with data from particle image velocimetry measurements and point out the potential of expanding flow diagnostics to hitherto hardly explored (industrial) flow cases.

Research of hydrodynamic processes in the flow part of a low-flow thermopressor

This research explores the hydrodynamic processes within the flow section of a low-flow thermopressor as a jet-type heat exchanger that utilizes the instantaneous evaporation of highly dispersed liquid in accelerated superheated gas flow resulting in reducing gas temperature with minimum resistance losses in contrast to conventional surface heat exchanger. The efficiency of thermopressor, as a contact heat exchanger, is highly dependent on the design of the flow section and the water injection nozzle. Geometric characteristics perform a crucial role in shaping gas-dynamic processes along the length of the thermopressor's flow section, influenced by resistance losses and local resistance in the tapering and expanding channel segments. Therefore, the optimum thermopressor design has to ensure minimize pressure losses. Using Computational Fluid Dynamics (CFD), the prototype thermopressor models were simulated and the results were compared with experimental data. The empirical equations for local resistance coefficients of thermopressor diffuser and confuser were received to evaluate the impact of various design parameters. The obtained local resistance coefficients for the confuser ranged from 0.02 to 0.08 and for the diffuser – from 0.08 to 0.32. The practical recommendations on geometric and operating parameters and characteristics for enhancing the efficiency of hydrodynamic processes in thermopressor flow part were given.

ANALISIS KEMACETAN SIMPANG TAK BERSINYAL JALAN PADAT KARYA – JALAN SUMATERA KOTA PRABUMULIH MENGGUNAKAN PKJI 2023

There will undoubtedly be heavy traffic in this location, especially at the intersection of Jalan Padat Karya, as Prabumulih is one of the cross-Sumatra cities with heavy traffic. The second economic hub of Prabumulih City is the Karya Intensive Road. When primary data collecting takes place in the field, descriptive and quantitative research methodology is employed. 7 days a week, Monday through Sunday, from 07.00 to 18.00. Road width measurements are made on the spot at each approach using a measuring tool. Following the collection of all primary and secondary data, analysis will be conducted utilizing PTV Vissim Version Student for traffic modeling and the 2023 PKJI Book. Intersection performance analysis using PKJI 2023 produces results traffic flow is 836.2 pcu/hour, free flow speed is 43.70 km/hour, capacity of 1468 pcu/hour, degree of saturation of 0.85. Based on the results above, the service level flow section is D. The intersection model after being given a signal changes if using APILL with 2 phases because of the level of service that occurs changed to level A.

Effect of jet ejector geometry on the supply of a pumping unit preventing wax-deposit

Relevance. Today oil production by installations of electric centrifugal pumps is one of the leading methods of mechanized oil production. The mechanized operation of hard-to-recover oil objects is complicated by the high viscosity of reservoir oil, the formation of wax-deposits in the wellbore. This leads to an increase in hydraulic resistances due to a decrease in the flow section of pipes and other pumping equipment components, a decrease in the productivity of wells and the efficiency of pumping production. In this regard, an urgent task is to develop and improve methods and devices for preventing deposits of wax-deposits in wells. Object. Downhole pumping unit for dosing reagent (inhibitor of wax-deposits) into the well, which is a combination of two technical devices – a pump dosing the reagent and a jet pump. Aim. To analyze the influence of the design parameters of the dosing unit on the efficiency of its operation (reagent consumption, liquid cavitation coefficient in the jet pump). Methods. Mathematical modeling of the operation of a downhole dosing unit for the supply of reagent, based on the application of the laws of conservation of mass and quantity of motion, as well as Bernoulli's law for a moving flow in a jet pump. Results. Based on the simulation results, the nature of the influence of the design parameters of the developed installation on the reagent consumption is established. It is established that the maximum flow rate of the reagent is achieved with a mixing chamber diameter of about 22 mm; an increase in diameter relative to the specified value leads to a decrease in the degree of local pressure reduction, a decrease in the diameter of the mixing chamber – a drop in flow due to an increase in the flow rate in the chamber and an increase in hydraulic resistance. It was found that an increase in the supply of electric centrifugal pumps in the considered range of 100–200 m3 per day has practically no effect on the reagent consumption when the mixing chamber diameter is more than 30 mm. It was found that at confuser length values exceeding 210 mm, the cavitation coefficient, regardless of the mixing chamber diameter, exceeds one, which indicates a smooth and uniform pressure reduction in the device body. In general, it is shown that by regulating the design parameters of a downhole metering unit, it is possible to ensure the required reagent consumption at a known electric centrifugal pump supply (well flow rate).

Numerical Study of Wind Flow Behavior Around High-Rise Buildings Using Computational Fluid Dynamics (CFD)

The development of civil construction technology in Indonesia is progressing along with the rise in high-rise building construction. The emergence of high-rise buildings has altered wind flow characteristics, leading to phenomena that can directly impact surrounding structures. One of the observable phenomena is the wind speed amplification caused by the narrowing of the wind flow section, known as the Venturi effect. This study aims to compare the outcomes of two Computational Fluid Dynamics (CFD) methods—Reynolds-Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES)—against experimental results. The study employs a model of four buildings of similar height and symmetrical positioning, with a 72 mm passage width, to verify numerical simulations against experimental data. The RANS method yields a maximum wind speed amplification of 14.9% along the passage's centerline, which remains below the experimental prediction of 25.5% in Zone A. Conversely, the LES results show a higher wind speed amplification, reaching 40.2%, surpassing the experimental findings. Nevertheless, LES identifies a similar location for wind speed amplification observed in Zone A. Additionally, CFD simulations were conducted to analyze the effects of passage width, revealing that a passage width of 54 mm produces the highest wind speed amplification, with a ratio value of passage width to building influence scale (L/S) of 0.481. Further research on building model scale may be necessary to verify CFD accuracy compared to the actual scale. However, such simulations demand exceedingly high computational resources with current technology.

Design and study of the flow section of a variable microchannel reformer based on the coupling law of reforming with flow, heat and mass transfer

In the amplification mode, microscale reforming reactions are controlled by the transfer rate. To avoid the amplification effect, the process coupling mechanism in the microchannel reactor must be studied to take full advantage of its precise control. This paper studies the coupling effect between the flow process and the reforming process in the microchannel and constructs a computational model of the flow coupling. A study was conducted on the influence of the coupling effect on the conversion rate, based on a combination of reliability verification and experiments. The following conclusions were obtained: the coupling effect in the reactive flow field was quantified based on the characteristic time of the flow process and the reaction process (Da number), and the microchannel was divided into three parts. The methanol conversion rate of the burst-expansion scheme was increased to more than 6%, and the USAER (unit surface area enhancement rate) reached 7.7. The USAER of the protrusion-expansion scheme can reach 8.342, with a potential for an 10% increase in conversion rate. The distribution of the three-segmented variable cross-section has the most effective regulation effect. The USAER of the protrusion-expansion scheme reaches 9.11, with a conversion rate that can be increased by 7%.

Influence of Incident Shock on Fuel Mixing in Scramjet

During the operation of hypersonic vehicles, a reciprocal coupling effect is manifested between the inlet and the combustion chamber. This results in an unavoidable non-uniformity of conditions at the combustion chamber’s entrance, which, in turn, influences the fuel mixing within the chamber. The present study employed the Reynolds-averaged Navier–Stokes (RANS) equations to perform a numerical simulation of an X-51-like vehicle, with a focus on examining the impact of isolation section length and multi-injection strategies on the fuel mixing characteristics within the combustion chamber under conditions of non-uniform inflow. The findings indicated that a supersonic non-uniform inlet triggers incident shock waves, leading to a non-uniform pressure distribution across the flow section. Moreover, the position of injection was found to be pivotal in regulating penetration depth and mixing efficiency. The incident shock wave, bow shock, and boundary layer separation shock interacted with each other to increase local pressure. The coupling of high and low pressures generated an adverse pressure gradient that led to boundary layer separation, which further enhanced fuel penetration depth.

Analysis of Flow Fluctuation of Confined Backward-Facing Step Based on Pulsation Tracking Network Method

Abstract Backward-facing step is a common flow model in hydraulic machinery. Its main feature is that there is a sudden expansion structure at the downstream of the flow channel, which causes the flow instability and is easy to form a vortex behind the sudden expansion section. At present, there are many studies on backstage step flow, but the dominant frequency fluctuation of its flow information has not been noticed. Based on the pulsation tracking network (PTN) method, the numerical simulation of a typical backstage step flow is carried out in this paper. The numerical simulation results are in good agreement with the experimental results. The results of numerical simulation are analyzed in frequency domain by using FFT to obtain the main frequency distribution of flow information on the typical section of the backstage step flow and the distribution of pulsation amplitude at each frequency. It explores a new direction for future research.

Research on internal flow characteristics of the planar conical tube for valveless piezoelectric micropump

Abstract As the most commonly used driving and executing components in microfluidic systems, valveless piezoelectric micropumps have broad application prospects in numerous fields. The steady and unsteady characteristics of planar conical tubes for valveless piezoelectric micropumps were simulated using CFX software at different pressure amplitudes and driving frequencies. The aim was to obtain the factors affecting the flow performance of the valveless piezoelectric micropump. The results show that the numbers of Remax in both diffusion and contraction directions of the planar conical tube increase with increasing pressure. When the number of Wo is lower, the number of Remax under a steady state is approximately equal to that under an unsteady state, and the maximum relative deviation is only 0.25%. The greater the Wo number, the smaller the velocity on the minimum flow section, and the more significant the velocity change. The rectification efficiency η of the valveless piezoelectric micropump and the efficiency λ of the planar conical tube both increase with increasing pressure under steady conditions, and the maximum values can be reached at 11.2% and 1.56, respectively.

Multi-mode Optimization of Diesel Engine Turbocharging

The thermogasdynamic engine system consisting of a number of subsystems of varying complexity is considered. The solution to the optimization problem in general is carried out by a multi-step iterative process of exchanging information between the levels repeatedly with refinement for all successive iterations of the initial data. Mathematical models of gas-dynamic processes in the flow section in variable modes, the simulation model of a gas turbine engine, and the model of multi-mode optimization of a gas turbine engine have been developed. The optimization of general-mode parameters is carried out in the space of points each of which reaches a minimum expression for the mode parameters.

Modeling and simulation of air-water upward annular flow characteristics in a vertical tube using CFD

Annular flow refers to a special type of two-phase flow pattern in which liquid flows as a thin film at the periphery of a pipe, tube, or conduit, and gas with relatively high velocity flows at the center of the flow section. This gas also includes dispersed liquid droplets. The liquid film flow rate continuously changes inside the tube due to two processes-entrainment and deposition. To determine the liquid holdup, pressure drop, the onset of dryout, and heat transfer characteristics in annular flow, it is important to have proper knowledge of flow characteristics. Especially a better understanding of entrainment fraction is important for the heat transfer and safe operation of two-phase flow systems operating in an annular two-phase flow regime. Therefore, the objective of this work is to develop a computational model for the simulation of the annular two-phase flow regime and assess the various existing models for the entrainment rate. In this work, Computational Fluid Dynamics (CFD) in ANSYS FLUENT has been applied to determine annular flow characteristics such as liquid film thickness, film velocity, entrainment rate, deposition rate, and entrainment fraction for various gas-liquid flow conditions in a vertical upward tube. The gas core with droplets was simulated using the Discrete Phase Model (DPM) which is based on the Eulerian-Lagrangian approach. The Eulerian Wall Film (EWF) model was utilized to simulate liquid film on the tube wall. Three different models of Entrainment rate were implemented and assessed through user-defined functions (UDF) in ANSYS. Finally, entrainment for fully developed flow was determined and compared with the experimental data available in the literature. From the simulations, it was obtained that the Bertodano correlation performed best in predicting entrainment fraction and the results were within the ±30 % limit when compared to experimental data.

Design and experimental analysis of a new vertical ultra-low-head hydro turbine with the variation of outlet flow level on the head drop section of an open canal

Hydropower generation from ultra-low-head water resources is the salient category. The power can be tapped through different non-conventional turbines and is developing these days with different features. This research aims to develop a technology that applies to ultra-low-head resources from conceptualization to laboratory testing. Among several ultra-low-head water resources, it is concentrated on the power generation from the head drop section of the open canal flow through a new hydro turbine. A vertical shaft turbine with an axial flow type of runner having fixed, flat, and constant blade thickness including fixed guide vanes has been designed conventionally for 0.5 m of head and 0.088 m3/s of discharge. Several experiments have been conducted with fixing the level of flow outlet control from 0.0 m to 0.5 m creating the runner from free to submerged conditions is the novelty of this research. The results obtained for all the independent and dependent variables are presented and discussed for a constant flow of 0.088 m3/s and constant speed of 115 rpm conditions. The uncertainty on measurement was found ±1.85 % and the overall maximum efficiency obtained was 53.8 % for flow 10 % above the design flow. The research has concluded the use of outlet flow control is necessary to achieve the maximum efficiency of the turbine at a specific height and the overall efficiency can be advanced further through the optimization of blade profile.