Rectangular Test Research Articles

Effects of the synthetic jet on the flow field and heat transfer over a surface-mounted square rib

In this article, a synthetic jet manipulates the flow behavior behind the surface-mounted square rib for heat transfer enhancement. Effects of operating frequencies and amplitudes on the near wake flow field of the rib are studied. Experiments are performed at Re=32000 (based on the Hydraulic diameter of the rectangular test section) with the Synthetic jet flush mounted at the bottom of the test section. Particle Image Velocimeter (PIV) captures a plane's instantaneous and time-averaged spatial flow information. The hotwire anemometer in CTA mode is used for temporal information of the flow field. The effect of synthetic jet on heat transfer downstream of the square rib is measured using Liquid crystal thermography(LCT). The result includes time-averaged velocity magnitude, vorticity, streamlines, turbulence quantities such as turbulence intensity, Reynolds stress, and rms velocities. The concise study indicates that a drastic reduction of reattachment length occurs at frequencies and amplitude of the synthetic jet. The study's unique contribution is the complete removal of the recirculation bubble by using the synthetic jet at a particular upstream position(X/D=-1). At 50 Hz frequency, the maximum heat transfer rate is obtained.

Evaluation of modified turbulent viscosity on shedding dynamic of three-phase cloud cavitation around hydrofoil – numerical/experimental analysis

PurposeThis paper aims to focus on the cavitating flow around the Clark-Y hydrofoil when the dissolved air is taken into account as the third phase. As the RNG k-epsilon model yields poor prediction due to overestimation of viscosity, the modification approaches including density corrected method, filter-based model and filter-based density correction model are used, and the turbulence model is modified. Also, the numerical results are compared with the experimental data.Design/methodology/approachThe cavitating flow is known as a complex multi-phase flow and appeared in the regions where the local pressure drops under saturation vapor pressure. Many researches have been conducted to analyze this phenomenon because of its significant impact on the erosion, vibration, noise, efficiency of turbomachines, etc.FindingsThe experiments are conducted in a rectangular test section equipped with Clark-Y hydrofoil providing cavity visualization, instantaneous pressure and vibration fluctuations. The simulations are carried out for different cavitation numbers with and without dissolved air. The Fast Fourier Transform, continues wavelet transform and temporal-spatial distribution of gray level are implemented to extract and compare the shedding frequency of experiments and numerical predictions and cavitation evolution. It is concluded that the flow structure, shedding frequency and time-averaged characteristics are highly influenced by the dissolved air. Also, the numerical prediction will be more satisfactory when the modified turbulence models are applied.Originality/valueTo the best of the authors’ knowledge, the originality of this study is the modification of the turbulence model for better prediction of cavitating flow, and the validation of numerical results with corresponding experimental data.

Chronic Supplementation of 2S-Hesperidin Improves Acid-Base Status and Decreases Lactate at FatMax, at Ventilatory Threshold 1 and 2 and after an Incremental Test in Amateur Cyclists.

Simple SummaryCurrently, hesperidin is a molecule found mainly in citrus fruits and is being widely researched in the area of chronic disease, but also in the field of sports nutrition. Some studies have shown its antioxidant, anti-inflammatory, lipid and carbohydrate metabolism modulating effects, including the enhancement of nitric oxide synthesis. However, few human studies have demonstrated a positive effect of hesperidin intake, in particular 2S-hesperidin, on sports performance, particularly in anaerobic and aerobic tests. However, the biochemical mechanisms that may be responsible for this enhanced performance have not yet been described. Therefore, one of the aims of this study was to assess whether an eight-week intake of 2S-hesperidin can improve acid-base status and metabolic status (lactate and glucose) in an incremental test in amateur cyclists. The results showed that amateur cyclists chronically supplemented with 2S-hesperidin improved acid-base status and lactate at FatMax, ventilatory thresholds 1 and 2, and in the acute phase of recovery after maximal effort.Chronic supplementation with 2S-hesperidin improves performance; however, the mechanisms underlying this effect have not yet been explored. Therefore, the aim of this study was to assess whether changes in acid-base status may be associated with improved performance after 2S-hesperidin supplementation compared to microcellulose (placebo). Forty amateur cyclists (n = 20 per group) underwent a rectangular test where capillary blood samples were taken at baseline, FatMax1, VT1, VT2, PMAX, FatMax2 and EPOC to measure acid-base parameters. After eight weeks of 2S-hesperidin supplementation (500 mg/d) increased HCO3−, SBC, ABE (p ≤ 0.05) and decreased Lac were found at FatMax1, VT1, FatMax2 and EPOC (p ≤ 0.05), while decreased Lac at VT2 was found with a large effect size (ES = 1.15) compared to placebo. Significant group differences in the area under the curve were observed when comparing pre-post-intervention pH changes (p = 0.02) between groups. Chronic supplementation with 2S-hesperidin improved acid-base status and Lac, both at low-moderate and submaximal intensities, improving recovery after exercise-to-exhaustion in amateur cyclists.

Mathematical Models for Predicting the Mechanical Properties of Poly(Lactic Acid) for Load-Bearing Applications

In order to widen the areas of application of poly (lactic acid) (PLA), there has been a multiplicity of experiments. This study attempts to develop mathematical models for predicting the mechanical properties of PLA to reduce the number of experimental runs and material wastage. The melt-cast method produced unreinforced PLA samples with different slenderness ratios (λ) in triplicate using. The samples were subjected to a compression test to obtain the mechanical properties captured at three main points on the stress-strain curve: yield, ultimate stress, and fracture. Regression models were developed from the data obtained at the three points, and their validity was examined by testing them against the previous relevant experimental studies from various authors. The coefficient of determination (R2) and coefficient of correlation (ρ) was also examined for each model to establish their degree of correctness further. Analyses show that the developed models give reasonable approximations of some of the properties examined. The mass (M) and the modulus of elasticity (E) were the most accurately predictable properties with [R2, ρ] of [99.97%, 0.9998] and [91.55%, 0.9568], respectively. Results also show that apart from the melt-cast method, the compressive modulus of PLA (both circular and rectangular cross-sections test samples) produced via injection molding and fused filament fabrication can be predicted with near accuracy using the model developed in this study. This study gives researchers the tools needed to avoid material wastage by having close-to-real values of the mechanical properties of PLA through prediction before carrying out any experiment.

Dynamic Multiprojectile Attack and Killing Effects of Detonation Warheads

Dynamic spatial distribution and killing characteristics of warhead fragments are important topics in the field of weapon effectiveness and protection. However, there is little research on the fragment distribution formed by continuous dynamic attacks of multiple projectiles that explode above the ground. This study analyzes spatial distributions of warhead fragments using witness boards in a rectangular target test. The results show that the fragment distribution of multiple projectiles in continuous dynamic attacks demonstrates a spatial superposition characteristic. The superimposed distribution is the sum of the distributions of two independent fragment distributions. The distribution characteristics are consistent with fragment scattering behavior. Therefore, they can be used to analyze the killing effects of multiple projectiles conveniently. The effects of falling speed, falling angle, and explosion height on the damage range of fragments were explored by a fragment spatial distribution model obtained from experiments. Analysis indicates that the prefabricated fragment distribution conformed to a spatial superposition relationship under dynamic multiprojectile continuous attacks, and the superposition obeyed fragment scattering characteristics. As the projectile falling angle increased at the explosion center, or as the falling height decreased, the positive pressure duration increased gradually. The falling speed had the greatest impact on the specific impulse of overpressure. The falling angle had the greatest impact on the peak value of overpressure. Both the falling angle and the explosion height had the greatest impact on the positive pressure acting time.

Systolic and diastolic function during cycling at the respiratory threshold between elderly and young healthy individuals

The hemodynamic consequences of aging have been extensively investigated during maximal incremental exercise. However, less is known about the effects of aging on hemodynamics during submaximal steady-state exercise. The aim of the present investigation was to compare the hemodynamics of healthy elderly and young subjects during an exercise bout conducted at the gas threshold (GET) intensity. Two groups of healthy, physically active subjects were studied: the elderly group—EG (n = 11; > 60 years old) and the young group—YG (n = 13; < 35 years old). Both groups performed a 5-min rectangular exercise test at the GET intensity. Hemodynamics were measured using echocardiography. The main finding was that stroke volume responses were higher in the YG than the EG (72.5 ± 16.7 vs. 52.4 ± 8.4 ml, respectively). The increased stroke volume capacity in the YG was the consequence of a greater capacity to increase cardiac preload and contractility and, to a lesser extent, to reduce systemic vascular resistance. Importantly, the atrial contribution to ventricular diastolic filling was substantially higher in the YG when compared to the EG.

Imaging of Permeability Change of Steel Plate Using Rectangular Wave Eddy Current Testing

Imaging of Permeability Change of Steel Plate Using Rectangular Wave Eddy Current Testing

Conceptual Design of Narrow Rectangular Channel Test Section for Research Reactor Application

Conceptual Design of Narrow Rectangular Channel Test Section for Research Reactor Application

Classification of Corrosion Flaws on Front and/or Back Surfaces of Non-magnetic Metal Plates Using a Rectangular Wave Eddy Current Testing System

Classification of Corrosion Flaws on Front and/or Back Surfaces of Non-magnetic Metal Plates Using a Rectangular Wave Eddy Current Testing System

Investigation of Vortex Structure Behavior Induced by Different Drag Reduction Devices in the Near Field

The paper deals with a proposal of possible solutions for wingtip vortex analysis, induced in the near field and performed by visual inspection using smoke screen and laser sheet setup in a subsonic wind tunnel. Wingtip vortices emerge as a result of unevenly distributed lift along the wing when pressure differences above and below the wing are interacting at the wingtips, contributing to generation of induced drag, which significantly affects the aerodynamical efficiency and important factors such as fuel consumption, maximum operational range, maximum achievable speeds, grater endurance etc. The aim of the research is to appropriately design procedures to perform a visual analysis and evaluation of wingtip vortices’ behavior, to establish suitable evaluative parameters, allowing to reliably define the number of vortices, location and area of its individual cores as well as providing the overall size of vortex structures, induced by investigated wingtips and winglets. The visual analysis of six configurations consisting of one net airfoil and five drag reduction devices, commonly used on civil aircraft, was performed in rectangular test section of a subsonic wind tunnel with dimensions of 350 mm × 350 mm. The authors used NACA 4415 airfoil at a flow speed of Re = 17 × 104, with configurations at the angles of attack α = 3°, 9° and 16°, to simulate cruise and non-cruise flight phases. The research proved the use of five proposed evaluative parameters for visual evaluation of vortex structures’ behavior, when using only the visually based setup. The authors also pointed out the limitations and shortcomings of proposed methodology. The results showed that proposed method could not directly provide numerical evaluation of drag component induced by drag reduction devices, but it is an effective tool for identifying the key-characteristics of the vortex at individual angles of attack, i.e., the number of vortices, location of individual areas of interest (cores), their numbers, areas, and dimensions.

Convolution neural network toward Monte Carlo photon dose calculation in radiation therapy.

The Monte Carlo (MC) algorithm has been widely accepted as the most accurate algorithm for dosimetric calculations under various conditions in radiotherapy. However, the calculation time remains an important obstacle hindering the routine use of MC in clinical settings. In this study, full MC three-dimensional dose distributions were obtained with the inputs of the total energy release per unit mass (TERMA) distributions and the electron density (ED) distributions using a convolutional neural network (CNN). A new Dose-mixup data augmentation routine and training strategy are proposed and applied in the training process. Attempts were made to reduce the calculation time while ensuring that the calculation accuracy is comparable to that of the MC. Datasets were generated via the MC with random rectangular field sizes, random iso-centers, and random gantry angles for head and neck computed tomography (CT) images with Mohan 6-MV spectrum photon beams. 1500 samples were generated for the training set, and 150 samples were generated for the validation set. The T-MC Net model was obtained with the Dose-mixup data augmentation routine. The new CTs were used to test the performance of the model in the rectangular fields and the intensity-modulated radiation therapy (IMRT) fields. The mean ± 95% confidence interval of gamma pass rates were calculated. For 150 rectangular field test samples, the 1%/2 mm, 2%/2 mm, and 3%/2 mm criteria gamma pass rates were 90.11% ± 0.65%, 97.65% ± 0.31%, and 99.16% ± 0.19%, respectively. For the 100 IMRT field test samples, the 1%/2 mm, 2%/2 mm, and 3%/2 mm criteria gamma pass rates were 96.48% ± 0.28%, 99.14% ± 0.10%, and 99.63% ± 0.06%, respectively. For the 7-fields IMRT plan, the 1%/2 mm, 2%/2 mm, and 3%/2 mm criteria gamma pass rates were 97.06%, 99.10%, and 99.52%, respectively. For the 9-fields IMRT plan, the 1%/2 mm, 2%/2 mm, and 3%/2 mm criteria gamma pass rates were 98.16%, 99.61%, and 99.89%, respectively. The feasibility of calculating dose distribution using a CNN with the TERMA three-dimensional distribution and ED distribution was established. The dosimetric results were comparable to those of the full MC. The accuracy and speed of the proposed approach make it a potential solution for full MC in radiotherapy. This method may be used as an acceleration engine for the dose algorithm and shows great potential for cases where fast dose calculations are needed.

Observation of departure from nucleate boiling under flow using optical visualization and IR thermometry

Departure from nucleate boiling (DNB) is a limiting phenomenon in the safety of nuclear reactors. Several mechanistic models have been suggested for predicting the critical heat flux at the DNB. However, existing experiments could not fully reveal the underlying phenomena of mechanistic models. In this study, we closely examined the phenomenon of rewetting failure of a dry patch during DNB to provide a deeper understanding of the mechanism of DNB occurrence and to assist in subsequent mechanistic modeling. Specifically, we utilized the total reflection technique and IR thermometry to obtain the synchronized side-view, total reflection view, temperature, and heat flux profile images at the DNB. We established a water flow loop under atmospheric pressure with a vertical rectangular test section comprising an ITO heater coated on a sapphire substrate. The ITO heater was 10 mm wide and 120 mm long. The long length of the ITO heater enabled the development of elongated bubbles upstream of the DNB location. A series of tests were conducted under various flow rates. Slug flow was observed in all tests conducted. An alternate passage of elongated bubbles and water slugs led to expansion and shrinkage of the dry patches. At the DNB, the dry patch size continued to increase, but the developing pattern was dependent on the flow rate. The peripheral temperature of the dry patches at the DNB was found to be ∼150°C.

Evaluation of physical properties of polyamide and methacrylate based denture base resins polymerized by different techniques.

This study aims to comparatively evaluate the flexural strength, internal adaptation, elastic modulus, and maximum deflection of a newly introduced, strengthened injection-molded semi-flexed polyamide resin (Deflex) and a conventional heat-cured resin containing cross-linking polymethyl methacrylate denture base polymers (QC-20). A vinyl polysiloxane film replicating the gap between the denture base and the metallic master model of an edentulous maxilla was weighed using an analytical balance with an accuracy of 0.0001 g for the measurement of internal adaptation. The measurements were performed immediately after surface finishing. Seven rectangular test samples measuring 65 × 10 × 3.3 mm3 were set up for flexural strength test. Flexural strength test (three-point bending test) was performed using a universal machine under axial load at a crosshead speed of 5 mm/min. One-way ANOVA (α = 0.05) following by t tests was utilized in statistical analysis. The difference between the flexural strength of the denture base resins of Deflex and QC-20 was found to be statistically significant. The injection-molded resin demonstrated better internal adaptation compared to the conventional heat-polymerized resin. Evaluation of the physical test results revealed that the polyamide samples were more flexible than polymethyl methacrylate and did not break during flexural strength tests. Some properties of denture base resins, such as resin types, internal adaptation, and mechanical strength, may play a significant role in clinical performance of complete dentures and removable partial prostheses. Because of the superior flexural strength properties and internal adaptation characteristics, Deflex may prove to be a useful alternative to conventional denture base resin.

Evaluation of nanofluids for enhancing critical heat flux for in-vessel retention during sever reactor accidents

ABSTRACT In-vessel retention (IVR) of a molten core through external cooling of the reactor vessel is a severe accident management strategy at nuclear power plants. The enhancement of critical heat flux (CHF) is one of the measures to improve the success probability of IVR. A nanofluid, in which nanoparticles are dispersed in a liquid, is known to reliably enhance CHF, mainly under pool boiling conditions. However, to apply nanofluids to IVR, it is necessary to clarify the effect of CHF enhancement under convection boiling similar to that in an actual IVR event. Therefore, CHF tests were conducted using a rectangular test section 50 mm wide × 50 mm deep × 600 mm long under conditions simulating severe accidents. From the CHF data obtained for various nanofluid parameters under typical severe accident conditions, each parameter’s effect on CHF enhancement was clarified. It was found that CHF was improved by 50% or more by a nanofluid as compared with deionized water. Furthermore, the CHF of nanofluid obtained in the tests simulating the actual severe accident conditions increased from 30% to 50% compared with that of deionized water, suggesting that CHF can be enhanced by nanofluids even in an actual plant.

Experimental Research on Noise Load Characteristics of Supersonic Jets in Rectangular Nozzles with Different Mach Numbers

Aiming at the jet noise problem of the rectangular supersonic nozzle, rectangular nozzle test models with Mach numbers of 1.35 and 1.65 were designed and processed. Using the jet noise test platform in a full anechoic chamber, the nozzle supersonic jet noise characteristic test was carried out. The test results show that the surface noise load of the model gradually increases along the nozzle axis; the unsteady flow field structure at the nozzle exit position has complex evolution, with strong turbulent pulsation and high noise load; the directivity trend of the far-field noise total pressure level of the two nozzles is basically the same, and the directivity is obvious in the upstream and 90° direction of the nozzles; from the far-field sound pressure spectrum, it can be seen that the far-field noise is composed of broadband noise and discrete frequency noise. The amplitude of the second order frequency varies significantly from 70° to 90° of upstream, and the fourth harmonic frequency of the whistling mode is captured in the direction of 90°.

Experimental performance comparison between circular and elliptical tubes in evaporative condensers

AbstractIn refrigeration systems, evaporative condensers have two main advantages compared to other condensation heat exchangers: They operate at lower condensation temperature than traditional air-cooled condensers and require a lower quantity of water and pumping power compared to evaporative towers. The heat and mass transfer that occur on tube batteries are difficult to study. The aim of this work is to apply an experimental approach to investigate the performance of an evaporative condenser on a reduced scale by means of a test bench, consisting of a transparent duct with a rectangular test section in which electric heaters, inside elliptical pipes (major axis 32 mm, minor axis 23 mm), simulate the presence of the refrigerant during condensation. By keeping the water conditions fixed and constant, the operating conditions of the air and the inclination of the heat transfer geometry were varied, and this allowed to carry out a sensitivity analysis, depending on some of the main parameters that influence the thermo-fluid dynamic phenomena, as well as a performance comparison. The results showed that the heat transfer increases with the tube surface exposed directly to the air as a result of the increase in their inclination, that has been varied in the range 0–20°. For the investigated conditions, the average increase, resulting by the inclination, is 28%.

Development of the antenna adjustable power coupler for 325 MHz superconducting cavities

In this paper, we present the multi-physics design and high-power tests of a fundamental power coupler for superconducting cavities. The fabricated power coupler was a coaxial capacitive-type coupler based on a conventional 318-inch Electronic Industries Alliance 50-Ω coaxial transmission line with a titanium nitride (TiN)-coated single ceramic window. The coupler had three diagnostic ports for vacuum, arc, and electron pick-ups to monitor radio frequency (RF) breakdowns. To reduce the thermal load required to reach the cryogenic temperature, the thermal intercepts were located at 4.5 K and 40 K for liquid helium use and at 4.5 K and 77 K for liquid helium and nitrogen use. A transition box for adjusting the antenna penetration depth and matching impedance was designed. A high-power test was performed with a 20 kW and 325 MHz solid-state power amplifier. The power coupler was connected to a rectangular test cavity with high vacuum and various measuring equipment, such as an arc detector, a power meter, and an electron pick-up probe. The interlock system under vacuum and arc instrumentations prevented the RF window from breaking the power coupler window during the high-power test. We conducted high-power tests for more than 12 h at 12 kW in a 325 MHz continuous wave mode to verify the performance of the designed power coupler.

Computational fluid dynamics analysis of buoyancy-aided turbulent mixed convection inside a heated vertical rectangular duct

Heat transfer in buoyancy-aided turbulent mixed convection inside a vertical rectangular duct with air was investigated through steady-state computational fluid dynamics (CFD) analysis with Reynolds-averaged Navier–Stokes turbulence models. Heat transfer can occur in the passive safety system of a nuclear reactor, which uses natural circulation as an initial driving force owing to its relatively low flow rate and strong heat flux condition. One example is the reactor cavity cooling system in a very high temperature gas-cooled nuclear reactor, whose high operating temperature enables high-efficiency power generation and hydrogen production. In buoyancy-aided turbulent mixed convection, heat transfer can deteriorate under specific conditions. Therefore, heat transfer must be analyzed because its deterioration can affect the performance of the safety system, which has an influence on the safety of the nuclear reactor. In this study, the results of a CFD analysis were compared with experimental results obtained from the riser heat transfer experimental facility, which is an experimental heat transfer facility with a 4.0 vertical rectangular duct test section. The CFD analyses were performed using a realizable k–ε model and a v2–f model, and the results were compared with the experimental results. It was confirmed that the results of the v2–f model exhibited good agreement with the experimental results. Based on this fact, four additional idealized cases were calculated using the v2–f model to investigate heat transfer deterioration in the turbulent mixed-convection regime. The calculation results revealed that the gradient of the velocity profile from the wall toward the center was reduced outside the near-wall region owing to buoyancy, which led to a reduction in the shear stress, turbulence generation, and heat transfer. In addition, the velocity gradient beyond the near-wall region reached a negative value above a certain buoyancy number, and turbulence generation and heat transfer started to recover. This analysis of heat transfer deterioration can provide insight into the construction of a heat-transfer coefficient correlation for buoyancy-aided turbulent mixed convection, and it will contribute to the development of heat transfer predictions and the evaluation of safety systems in nuclear reactors.

Characterization of Hydrogen-Bonded Liquid Crystal Materials in the Millimeter-Wave Region

A novel liquid crystal (LC) materials consisting of hydrogen bonding are investigated in the millimeter-wave (MMW) frequency region of electromagnetic wave spectra. Relative permittivity (or refractive index) and loss tangent (or absorption coefficient) are evaluated using a rectangular waveguide test cell and are compared with those values of conventional LC materials. The most unusual result is that the refractive index anisotropy increases significantly in the MMW region comparing with that for visible light, which is contrary to what is observed in the conventional LC materials. Although the anisotropy, which determines the tunability of LC devices, is not so large in this stage, the loss tangent is as small as, or better than, those of the excellent conventional-type LC materials synthesized for the microwave applications. We find out a potential of the hydrogen-bonded LCs as one of the best classes of LC materials for MMW application.

A New Apparatus for Studying Laterally Restrained Swell of Compacted Clay with Lateral Pressure Measurement

Abstract Wetting of compacted clays, and their subsequent swelling, often results in damage to structures and infrastructures. In some cases, for example, if the clay is adjacent to a structure such as a retaining wall, pile, or pipeline, lateral swell is restrained, resulting in heave in the vertical direction and development of swelling pressure laterally. Standard procedures for testing the swell of clays on wetting are limited to the definition of a vertical pressure-swell relationship. This paper presents an investigation of the laterally restrained swell of a highly plastic compacted clay in a new rectangular test cell designed to provide additional and more reliable test information. Lateral soil pressure is measured using null pressure gauges flush with the cell walls. Cell sidewall friction is evaluated by measuring the load applied to the specimen top and the load reaching its base, and it is minimized by incorporating friction reduction measures. It was found that pressure-swell curves, based on vertical pressure, horizontal pressure, and mean pressure, all plot as straight lines on a semi-log basis. Although inundation of the test specimen is standard practice for swelling tests, this procedure represents an extreme wetting condition in the field. The study demonstrates that swell is affected by the characteristics of the hydraulic head responsible for wetting the soil; wetting by suction alone, or by combination of suction and gravity head, result in different degrees of swell.