Equivalent Flow Research Articles

Assessment of thermo-hydraulic performance of inward dimpled tubes with variation in angular orientations

This paper presents a numerical investigation and assessment of thermal and hydraulic performance of dimpled tubes of varying topologies at constant heat flux of 10kW/m2 and Reynolds numbers ranging from 2300 to 15,000. The performance of the tubes consisting of conical, spherical and ellipsoidal dimples with equivalent flow volumes were compared using steady state Reynolds Averaged Navier Stokes simulations. The ellipsoidal dimples, in comparison to other dimple shapes, demonstrated large increment in heat transfer rate. The variation in the orientation of the ellipsoidal dimples was examined to further improve thermal and hydraulic performances of the tube. A 45° inclination angle of ellipsoidal dimple, from its major axis, increased the thermo-hydraulic performance by 58.1% and 20.2% in comparison to smooth tube and 0° ellipsoidal dimpled tube, respectively. Furthermore, Large Eddy Simulations (LES) were carried out to investigate the role geometrical assistance to fluid flow and heat transfer enhancement for the 45° and 90° ellipsoidal dimpled tubes. LES results revealed a flow channel of connected zones of wakes which maximized fluid-surface contact and therefore enhanced the thermal performance of the tube. In addition, correlations for Nusselt number and friction factor for all angular topologies of ellipsoidal dimpled tube have been proposed.

Optimization of the Design of Water Distribution Systems for Variable Pumping Flow Rates

Water supply systems need to be designed in an efficient way, accounting for both construction costs and operational energy expenditures when pumping is required. Since water demand varies depending on the moment’s necessities, especially when it comes to agricultural purposes, water supply systems should also be designed to adequately handle this. This paper presents a straightforward design methodology that using a constant flow rate, the total cost is equivalent to that of the variable demand flow. The methodology is based on the Granados System, which is a very intuitive and practical gradient based procedure. To adapt it to seasonal demand, the concepts of Equivalent Flow Rate and Equivalent Volume are presented and applied in a simple case study. These concepts are computationally straightforward and facilitate the design process of hydraulic drives under demand variability and can be used in multiple methodologies, aside from the Granados System. The Equivalent Flow Rate and Equivalent Volume offer a solution to design procedures that require a constant flow regime, adapting them to more realistic design situations and therefore widening their practical scope.

Influence of altitude on matching characteristic of electronic-controlled pneumatic two-stage turbocharging system with diesel engine

Two-stage turbocharging technology is a solution to reduce turbo lag and improve the performance of engine and matching characteristics at high altitudes. In the present study, an engine testing system was established to study combustion performance and matching characteristics of a regulated two-stage turbocharging system (R2S) at different simulated altitudes. An equivalent turbocharger concept was put forward aiming to simplify the R2S with three bypass valves, and the total equivalent turbine flow area and equivalent efficiency of the R2S were obtained based on a theoretical study. Intake characteristics, combustion process, torque, power and fuel economy of the diesel engine matched with R2S were analyzed at different altitudes. The results showed that compared with 0 m, intake pressure, maximum combustion pressure, cumulative heat release, heat release rate decreased by 36.5%, 33.6%, 33.5%, 21.6%, −8.9% at 4000 r/min, and decreased by 12.3%, 2.9%, 16.4%, 8.8%, −5.4% at the speed of 2000 r/min at the altitude of 5000 m. The torque, fuel consumption and fuel consumption rate decreased by 10.1%, 5.1% and 5.4% at engine speed of 2000 r/min and by 35.7%, 27.6% and 8.9% at engine speed of 4000 r/min at 5000 m.

Detection and Analysis of an Alternate Flow Pattern in a Radial Vaned Diffuser

The flow in the vaned diffuser of an aeronautical centrifugal compressor designed by Safran Helicopter Engines is analyzed through steady and unsteady pressure measurements at different rotation speeds. The analysis leads to the identification of different operating zones thanks to a new variable, the alternate rate ?. It allows the characterization of a specific behavior of the vaned diffuser consisting of an alternate stall pattern in two adjacent channels of the diffuser. While it is close to zero at low speed, the alternate rate reaches a maximum value at a higher speed before collapsing with a further increase in the rotation speed. Depending on the value reached by the alternate rate, three distinct regimes of the flow within the diffuser can be distinguished. For low ? values, the regime is the most common one with an equivalent flow pattern in each channel of the diffuser. For moderate ? values, a mild difference of the flow fields which develop in two adjacent channels can be observed but it remains time independent. Finally, for high values of ?, the alternate pattern is amplified and becomes time dependent, pulsating together with the mild surge of the entire compressor.

Experimental evidence of H2/O2 propellants powered rotating detonation waves

The paper presents experimental evidence of continuous detonation in a rotating detonation rocket engine (RDRE) powered by H2/O2 propellants. High-speed chemiluminescence imaging is used to characterize the detonation wave dynamics by introducing a tracer in the hydrogen fuel flow. The results show continuous five-wave co-rotating detonations at various equivalence ratios and flow rates demonstrating the potential for H2/O2 propellant based RDREs for upper-stage rocket engines.

Chronic and episodic acidification of streams along the Appalachian Trail corridor, eastern United States

AbstractAcidic atmospheric deposition has adversely affected aquatic ecosystems globally. As emissions and deposition of sulfur (S) and nitrogen (N) have declined in recent decades across North America and Europe, ecosystem recovery is evident in many surface waters. However, persistent chronic and episodic acidification remain important concerns in vulnerable regions. We evaluated acidification in 269 headwater streams during 2010–2012 along the Appalachian Trail (AT) that transits several ecoregions and is located downwind of high levels of S and N emission sources. Discharge was estimated by matching sampled streams to those of a nearby gaged stream and assuming equivalent daily mean flow percentiles. Charge balance acid‐neutralizing capacity (ANC) values were adjusted to the 15th (Q15) and 85th flow percentiles (Q85) by applying the ANC/discharge slope among sample pairs collected at each stream. A site‐based approach was applied to streams sampled twice or more and a second regression‐based approach to streams sampled once to estimate episodic acidification magnitudes as the ANC difference from Q15 to Q85. Streams with ANC <0 μeq/L doubled from 16% to 32% as discharge increased from Q15 to Q85 according to the site‐based approach. The proportion of streams with ANC <0 μeq/L at low flow and high flow decreased from north to south. Base cation dilution explained the greatest amount of episodic acidification among streams and variation in sulfate (SO42−) concentrations was a secondary explanatory variable. Episodic SO42− patterns varied geographically with dilution dominant in northern streams underlain by soils developed in glacial sediment and increased concentrations dominant in southern streams with older, highly weathered soils. Episodic acidification increased as low‐flow ANC increased, exceeding 90 μeq/L in 25% of streams. Episodic increases in ANC were the dominant pattern in streams with low‐flow ANC values <30 μeq/L. Chronic and episodic acidification remain an ecological concern among AT streams. The approach developed here could be applied to estimate the magnitude and extent of chronic and episodic acidification in other regions recovering from decreasing levels of atmospheric S and N deposition.

Microstructure Evolution of Cold Pilgering Stainless Steel Tubes

The 347 stainless steel tube cold rolling test was carried out by a LG60 two‐roll pilger mill. The microstructure evolution was examined by microscope, SEM, and XRD tests. The finite element software DEFORM‐3D has been used to simulate the pilgering process, and the obtained equivalent stress and metal flow were analyzed. The experimental results showed that the internal slip line was randomly distributed, the deformation of the inner wall was more intense than the outer wall structure, and the austenite γ phase was transformed into the α′‐martensitic phase. The simulation results indicated that the direction of metal flow was constantly changing, and the equivalent stress of the inner wall of the steel tube was greater than the equivalent stress of the outer wall. In addition, the slip zone of the inner wall of the characteristic section was more severe than that near the outer wall slip zone. The simulation verified the experimental results to some extent.

The mechanical parameters modeling of heavy steel plate snake/gradient temperature rolling with the same roll diameters

The grains in the center of the heavy steel plate can be refined by the snake/gradient temperature rolling, and the deformation penetration, the microstructure, and the properties of the steel plate will be improved. The existing rolling mechanical models are not suitable for the snake/gradient temperature rolling, so it is necessary to establish the mechanical parameters model of the snake/gradient temperature rolling to instruct production. The yield criterion of rolled material was modified based on the idea of equivalent flow stress. The element stress analyses were carried out based on the uniform normal stress and nonuniform shear stress in the vertical sides of each slab. Then the equilibrium equation of the unit pressure based on the slab method was established on this basis. The deformation region was divided into three layers (the top layer, the bottom layer, and the central layer) and maximum four zones (back slip zone, front slip zone, cross shear zone, and reverse deflection zone) according to the temperature distribution and position of the neutral point, and then the 12 zones were formed during the snake/gradient temperature rolling. The boundary conditions of the existence of the back slip zone, the front slip zone, and the cross shear zone were established according to the relationship between the threading angle and the neutral angle. The accurate mechanical parameters model of the rolling force and rolling torque of the snake/gradient temperature rolling with the same roll diameters was set up on this basis. The ANSYS software has been used in the rolling process simulation by many scholars, and the calculating precision has been verified. So the rolling processes were simulated by the ANSYS software to validate the model precision. The results show that the maximum relative deviation of the rolling force analytic model is less than 7% compared with the numerical method, and the maximum relative deviation of the rolling torque analytic model is less than 11% compared with the measured results. The mechanical parameters model can accurately predict the rolling force and rolling torque during the snake/gradient temperature rolling with the same roll diameters, so as to provide a theoretical basis for the design of rolling mill and the setup of the process parameters.

Experimental determination of local head loss of non-coaxial emitters in thin-wall lay-flat polyethylene pipes

The hydraulic performance of thin-wall lay-flat polyethylene pipes with non-coaxial emitters were evaluated in this study. Two experiments were performed to measure the dimensional variation of commercially available lay-flat drip irrigation pipes. A model for estimating the corresponding local head loss was developed and validated using dimensional analysis. The model was then implemented in a finite element algorithm to analyse the hydraulic performance of this type of pipes. Finally, a design example was provided. The results revealed that, for a wall thickness of 0.13 and 0.20 mm, the pipe height and width tended to be equal above a relatively low pressure, and the pipe cross-section rapidly inflated from a quasi-rectangular form to circular. For thicker walls, the equivalent diameter (four times the hydraulic radius) increased continuously with increasing pressure head but it hardly reached its nominal diameter (16 mm). The proposed model indicated that the local head loss was affected by the equivalent diameter, emitter geometry, and flow velocity. The model had high accuracy in determining the local head loss. The estimated results were in close agreement with the measured data. According to the numerical simulation, the ratio of local head loss to total loss along a pipe was up to 74.71%. The design results, when using an earlier model, demonstrated a longer maximum lateral length, since the model did not consider further contraction of the flow caused by pipe deformation. However, the model proposed here could be used in the design of systems for thin-wall lay-flat polyethylene pipes.

On Linear Analysis of the Power Flow Equations for DC and AC Grids With CPLs

This express brief presents an approximation of the power flow problem for alternating-current (ac) and directcurrent (dc) distribution networks by using a linear representation of the hyperbolic constraints i = p/v ↔ II* = ℤ/V related to the power balance at each constant power load node. Taylor's or Laurent's series expansion methods are not required to obtain an equivalent linear power flow model. The proposed linear method allows us to achieve a high quality approximation of the power flow modeling without iterative procedures. Our simulation results show the accurate estimation of the voltage profile in distribution networks by the proposed linear approach in comparison to existing methods in specialized literature for ac and dc networks, including linear estimators or classical numerical methods, such as Gauss-Seidel and Newton-Raphson approaches. Numerical implementation of those approaches is carried out in the MATLAB 2017a programming environment.

A critical productivity equation of horizontal wells in a bottom water drive reservoir with low-permeability interbeds

It has been proved by laboratory and field experiments that the low-permeability interbed under the horizontal section is able to restrain bottom water cresting efficiently. However, the effect of the lower permeability interbeds is barely considered when computing the critical productivity of a horizontal well in a bottom drive reservoir. As a modification, this article presents a new critical productivity equation for horizontal wells by using equivalent flow resistance method. In this paper, the 3-dimensional seepage field is split into a 2-dimensional (2D) inner seepage filed and a 2D outer one. The production rate in the outer seepage field is achieved by Dupuit critical production equation, and the productivity equation in the inner field is obtained by using imaging principle. Then, the critical productivity of a horizontal well with low-permeability interbed is achieved and the water breakthrough is able to be predicted. The case study is conducted to demonstrate that the low-permeability interbed can restrain the rate of water cresting and delay the water breakthrough efficiently.

Reweighting Signal Spectra to Improve Spatial Sensitivity for an Electrostatic Sensor.

The ring-shaped electrostatic sensor is a gas–solid flow measurement system, which has a problem of flow profile dependency. To deal with this problem, a method was introduced in this paper, which was to repeatedly use the successive “tails” of the sensor’s overall output power spectrum to identify elementary frequency components corresponding to the equivalent roping flow streams. From the radial locations of these equivalent flow streams, the decomposed power frequency spectral components were then reweighted accordingly. Through such signal processing, an improved electrostatic sensor spatial sensitivity was achieved without modifying the sensor’s structure. The method of interpolation was presented and discussed, and the effect of velocity profile on the proposed method was evaluated under different velocity profiles.

Enhancing the flame stability in a slot burner using yttrium-doped zirconia coating

Quenching experiments using a slot burner and surface analysis were conducted to analyze the effects of two materials (ZrO2 and 13.5 wt%Y2O3-doped ZrO2 (13.5YSZ)) deposited on stainless steel 304 (STS304) substrate on the flame stability of premixed methane/air mixtures of varying equivalence ratio and flow velocity at a wall temperature range of 373 K to 773 K. Results showed that these two types of coatings are beneficial for decreasing the quenching distance and extending the flame stability limit. Moreover, doping 13.5 wt%Y2O3 into ZrO2 coating was more conducive to reduce quenching data and broaden lower flammability limits in the fuel-lean side. Surface analyses reflected that the superior mobility of lattice oxygen for 13.5YSZ coating plays a crucial role in improving the quenching characteristics due to the formation of extrinsic active oxygen vacancies. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) verified that the methane oxidation process can be accelerated over the two coating surfaces due to the high catalytic performance. Finally, one migration route of oxygen ions consisting of the dynamic oxygen diffusion and replenishment pathways was proposed to discuss the underlying mechanism of flame stability improvement when using yttrium-stabilized zirconia composite coatings in a narrow channel.

Transient numerical simulation of airflow and fibrous particles in a human upper airway model

In this study, the unsteady airflow field in a realistic model of human upper airways during the breathing cycle and the fibrous particle transport and deposition were investigated using the CFD method. An anatomically realistic model of airway passage including vestibule to the end of the trachea was constructed from the CT images of a 24-year-old healthy woman. Several user-defined functions (UDFs) were developed and incorporated into the discrete phase model (DPM) of ANSYS Fluent code and were used for the evaluation of ellipsoidal particle motion in transient airflows. The developed UDF was used to solve the coupled translational and rotational equations of motion of ellipsoidal fibers and to analyze their dispersion and deposition in the upper airways. The total and regional depositions for a range of fiber sizes were evaluated. The transient particle deposition fraction was compared with those obtained for the equivalent steady flow condition. In addition, the fraction of ellipsoidal fibers that penetrate the lower respiratory tract under cyclic breathing was calculated and compared with the steady flow simulation. The presented results showed that the steady simulation with an appropriate equivalent airflow rate can predict the total fibrous particle deposition during cyclic breathing with reasonable accuracy. The steady simulations, however, cannot properly predict the regional particle deposition under transient flows. In particular, the comparison between steady and transient penetration fraction reveals that the steady breathing model fails to accurately predict the penetration fraction of ellipsoidal fibers into the lower respiratory tract.

On microboudin paleopiezometers and their applications to constrain stress variations in tectonites

Accounting for interfacial shear-induced near-end fracturing, we propose a new microboudin piezometer, τe = τ/C = 0.25/(L/W), where τ is the shear flow stress of the ductile matrix (e.g., polycrystalline quartz), C is the tensile fracture strength of a columnar mineral (e.g., tourmaline), which ranges generally between E/1000 to E/250 (E is Young's modulus), τe is a dimensionless parameter named ‘equivalent shear strength’, and L/W is the mean length/width ratio of the microboudins formed by near-end fracturing. This provides a straightforward method of estimating the magnitude of shear flow stresses responsible for ductile deformation of natural rocks. The piezometer is easy to apply because it does not require the use of TEM, SEM-EBSD or the identification of prevailing deformation mechanism (e.g., dislocation creep, diffusion creep, hardening or weakening). The samples from the Gaoligong metamorphic belt (Yunnan, China) yield the equivalent shear flow stresses of 0.145–0.424 (36–106 MPa if taking C = E/800 or 250 MPa) for felsic gneisses, mylonites and phyllonites. The earlier formed microboudins had consistently a larger mean length/width ratio than the later formed ones, suggesting that the rocks recorded a tectonic history of continuous hardening prior to the cessation of quartz plasticity.

Reliability evaluation of integrated electricity\u2013gas system utilizing network equivalent and integrated optimal power flow techniques

The wide utilization of gas-fired generation and the rapid development of power-to-gas technologies have led to the intensified integration of electricity and gas systems. The random failures of components in either electricity or gas system may have a considerable impact on the reliabilities of both systems. Therefore, it is necessary to evaluate the reliabilities of electricity and gas systems considering their integration. In this paper, a novel reliability evaluation method for integrated electricity–gas systems (IEGSs) is proposed. First, reliability network equivalents are utilized to represent reliability models of gas-fired generating units, gas sources (GSs), power-to-gas facilities, and other conventional generating units in IEGS. A contingency management schema is then developed considering the coupling between electricity and gas systems based on an optimal power flow technique. Finally, the time-sequential Monte Carlo simulation approach is used to model the chronological characteristics of the corresponding reliability network equivalents. The proposed method is capable to evaluate customers’ reliabilities in IEGS, which is illustrated on an integrated IEEE Reliability Test System and Belgium gas transmission system.

Monitoring lung function in patients with chronic graft versus host disease: a pilot study.

Bronchiolitis obliterans syndrome (BOS) following allogenic haematopoietic stem cell transplant is considered the manifestation of chronic graft versus host disease (cGvHD) in the lung, and affects about 14% of patients with cGvHD, mainly in the first 2 years after transplant. Despite advances in assessment, diagnosis and treatment, the clinical prognosis remains poor for patients with pulmonary manifestations of cGvHD. A pilot study of 50 patients was devised to establish whether a relationship exists between forced expiratory volume in 1 second (FEV1) via pulmonary function test (PFT) and the equivalent peak expiratory flow (PEF) via peak flow handheld spirometry in cGvHD patients receiving extracorporeal photopheresis (ECP). Only PEF observed within 2 days of PFT could be compared with data at month 3, 6, 9 and 12. This pilot study illustrated that monitoring via handheld peak flow readings has the potential to become an acceptable method of monitoring lung function longitudinally in cGvHD patients.

Adjusted saturation flow of some signalized intersection in Semarang, Indonesia

Indonesian Highway Capacity Manual or IHCM (1997) is a manual used to analyse performance of Indonesia’s road network. It has been more than 20 years since the manual is firstly published, so that some parameters such as passenger car equivalent (pce) and base saturation flow (S0) are no longer in accordance with actual conditions, which is indicated by significant differences between IHCM analysis results and empirical data. Several studies have been conducted in many cities and rural areas across Indonesia to explore pce, base saturation flow or other adjustment factors, in order to update IHCM, so in general, this manual will be more appropriate for current traffic conditions. This study is aimed at obtaining adjusted saturation flow from three signalized intersections in Semarang City, based on a comparison between predicted queue lengths and the empirical ones. Using the vehicle departure time slice data for green time, the pce and saturation flow was adjusted using regression method. Adjusted saturation flow at the observed intersection can be simplified in equation S = 506.48 We + 1857.9. Addition of variables still needs to be considered to gain a more general equation.

Quantitative criteria for identifying main flow channels in complex porous media

To identify the type of main flow channels of complex porous media in oil and gas reservoirs, the “main flow channel index” is defined as the ratio of comprehensive permeability obtained from well test to matrix permeability obtained from core analysis or well logging. Meanwhile, a mathematical model is established based on equivalent flow assumption, the classification method for main flow channels is put forward, and quantitative characterization of main flow channels is realized. The method has been verified by analysis of typical gas reservoirs. The study results show that the “main flow channel index” can quantitatively classify types of flow channels. If the index is less than 3, the matrix pore is the main flow channel; if the index is between 3 and 20, the fracture is the main flow channel and the matrix pore acts as the supplement one; if the index is more than 20, the fracture is the only seepage channel. The dynamic analysis of typical gas reservoirs shows that the “main flow channel index” can be used to identify the type of flow channel in complex porous media, guiding the classified development of gas reservoirs, and avoiding development risk.

Squeeze Flow of Bingham Fluids through Reticulated, Compressed Foams

The paper presents experimental and theoretical results for the planar squeeze flow of a finite volume of viscoplastic material through a highly deformable porous layer. The central zone of an annular disc made of a reticulated polyurethane foam with high porosity (ε > 0.97) was fully filled with tooth paste. The porous disc placed between two flat, impermeable, parallel, and rigid discs was subjected to compression and the normal force was recorded. After compression, the radial extension of the squeezed fluid was measured. The visualisation of the compressed disc managed to provide evidence of a tortuous flow inside the porous structure. An original analytical model is proposed for the prediction of the front of the flow inside the porous layer and corresponding resistant normal force. The model combines the Covey and Stanmore (1981) model for squeeze flow of a Bingham fluid inside the central zone, with an original approach for flow through the reticulated foams, based on the concept of “equivalent flow tubes” with variable tortuosity. This explorative investigation is of interest for innovative shock absorbers. The model validity covers both low and high plasticity numbers and was experimentally validated for low speed.