Instantaneous Diameter Research Articles

Nearly instantaneous stem diameter response to fluctuations in the atmospheric water demand.

Changes in vapour pressure deficit can lead to the depletion and replenishment of stem water pools to buffer water potential variations in the xylem. Yet, the precise velocity at which stem water pools track environmental cues remains poorly explored. Nine eucalyptus seedlings grown in a glasshouse experienced high-frequency environmental oscillations and their stem radial variations (ΔR) were monitored at a 30-s temporal resolution in upper and lower stem locations and on the bark and xylem. The stem ΔR response to vapour pressure deficit changes was nearly instantaneous (<1min), while temperature lagged behind stem ΔR. No temporal differences in the stem ΔR response were observed between locations. Punctual gravimetric measurements confirmed the synchrony between transpiration and stem ΔR dynamics. These results indicate (i) that stem-stored water can respond to the atmospheric evaporative demand much faster than commonly assumed and (ii) that the origin of the water released to the transpiration stream seems critical in determining time lags in stem water pool dynamics. Near-zero time lags may be explained by the high elasticity of eucalyptus woody tissues and the predominant water use from the xylem, circumventing the hydraulic radial barriers to water flow from/to the outer tissues.

Defying the D2-law in fuel droplet combustion under gravity

We show both experimentally and theoretically for the first time that the widely used D2-law for describing the shrinking kinetics of a vaporizing droplet is not the true law for single burning droplets under the influence of gravity. Experimentally, the instantaneous diameter D for such a droplet is identified to obey a new kinetic law: Dn decreases linearly with time t, with the exponent n=2.53±0.30−2.69±0.14 for a variety of common liquid fuels such as alkanes and alcohols of low and high boiling hydrocarbons. Theoretically, we develop a phenomenological theory to show n=8/3≈2.67 well capturing the experimental values. The burning rate constant in this new D8/3-law no longer behaves like the thermal diffusivity α of the gas phase but turns into α3ℓ−7/3/g due to the additional inherent fluid-property-determined buoyancy length ℓ under the influence of the gravitational acceleration g. This non-square power law is purely transport determined. It is a consequence of simultaneous momentum, heat, and mass transfer resulted from buoyant convection setup by the blazing flame around the droplet, insensitive to combustion chemistry and detailed reaction kinetics. This study provides not only renewed insights into the multifaceted droplet combustion phenomenon but also possibly new paradigms for a better understanding or characterization of actual fuel droplet combustion processes in normal gravity environments.

Experimental investigation on tip vortex cavity deformation and flow dynamics using high-speed imaging and laser Doppler velocimetry measurements

Cavitation affects engineering applications relating to aquatic operations. Tip vortex cavitation (TVC) leads to several technical problems, such as efficiency loss and noise. Hence, there is a need for a comprehensive understanding of the formation mechanism, shape distortions, and underlying physical phenomena of TVC. The dispersion relation of inertial waves on inviscid cavitating vortices is a valuable tool for predicting various TVC shapes. This study explains the patterns of flow around the tip of an elliptical foil and the cavity shape deformations under different flow conditions through experimental analysis. Experiments are conducted using a National Advisory Committee for Aeronautics hydrofoil in the cavitation tunnel at Chungnam National University. The appearance, development, and shapes of vortex cavitation are closely examined using high-speed imaging technology. There is good agreement between the vortex cavity shapes captured by this high-speed imaging and those derived in previous studies. Using laser Doppler velocimetry (LDV) measurements and analysis through image processing of high-speed images, we compare the vortex core trajectories in cavitating and non-cavitating conditions. There is a good match between the two, demonstrating the feasibility of predicting the flow behaviors around vortex cavities using LDV data. As the noise from the TVC is considered a significant source of underwater radiated noise we also measured sound pressure level, which exhibits abrupt changes at specific cavitation numbers, supporting the occurrence of the singing vortex phenomenon and highlighting its sensitivity to small variations in flow conditions. Furthermore, we obtain precise measurements of the instantaneous TVC diameter under different cavitation numbers, allowing the physical functionality of distinct TVC shapes to be determined. Our results significantly extend the scientific understanding of the flow around TVC and the fundamental causes of TVC distortions.

Dynamic Behavior of Droplet Impact on Laminar Superheated Particles.

The impact of droplets on particles involves a wide range of complex phenomena and mechanisms, including bubble nucleation, crater formation, fluidization, and more intricate changes in the boiling regime when impacting superheated particles. In this study, we focus on droplet impact behavior on superheated laminar particles at various temperatures and define six typical characteristic patterns of a single droplet impact on superheated laminar particles, including film evaporation, bubbly boiling, immersion boiling, sputter boiling, transition boiling, and film boiling. It is worth noting that the variations of inertial force FI caused by gravity, the capillary force FC generated by the pores of the droplets, and the dewetting force by the vapor phase FV are the main contributors to different evaporation regimes. Interestingly, we find that the Leidenfrost point (LFP) of droplets on the laminar superheated particles decreases with particle size, which is related to the effect of the pore space generated between the laminar particles. Finally, the effect of temperature, particle size, and Weber number (We) on the dynamic behavior of droplet impact is revealed. Experimental results show that the instantaneous diameter of droplets is inversely proportional to the change of height, with different patterns of maximum spreading diameter and maximum bounce height at different particle sizes, while the maximum spreading velocity and maximum bounce velocity are independent of particle size. We believe the present work would provide a broader knowledge and comprehension of the droplet impact on heated particles and promote the development of the safety and productivity of industrial processes such as fluid catalytic cracking, spray drying, and spray cooling.

Evaporation flow characteristics of respiratory droplets: Dynamic property under multifarious ambient conditions

This study numerically investigated the impact of ambient conditions on the evaporation process of full-range cough expelled droplets. The multi-component Eulerian-Lagrangian framework was adopted to simulate droplet evaporation within the inhomogeneous humidity fields. The results found that effect of ambient relative humidity (RH) on droplet evaporation was more pronounced than that of temperature. When the ambient relative humidity was higher than 40%RH, the evaporation of droplets with a diameter smaller than 100 μm would be significantly decelerated. Meanwhile, in normal indoor environments, 175μm could be a marginal diameter, in which droplets with larger initial diameters would probably not be fully evaporated before settling to the ground. Moreover, a novel cost-efficient approach, representing the instantaneous droplet diameter by functions of dt=φ(RH,t,T), was developed to fulfil the time-dependent dynamic size distributions of evaporated droplets under various ambient conditions directly from the data by this study. The implementation of this approach into User Defined Function (UDF) was demonstrated and it would significantly reduce the computational resource on simulating droplet-related scenarios as it does not require costly calculations on the evaporation processes of each droplet repeatedly in every simulation. This development is limited to cough droplets so far and further fulfilment on droplets database regarding other respiratory behaviours would be highly suggested.

Non-linear necking behaviour of S275 to S960 structural steels under monotonic tension

For cylindrical coupons of structural steels under tension, gradual reductions in their cross-sections, commonly known as necking, occurred at an elongation that the maximum force is attained. Non-uniform stress and strain distributions in the critical cross-sections of the necking regions have been known for more than 70 years; however, the values of these stresses cannot be directly measured in experiments so far. This paper presents a systematic investigation into the post-necking structural responses of the S275 to S960 steels under monotonic tension forces through the Instantaneous Area (iArea) Method proposed by the authors. In order to examine post-necking deformation characteristics of structural steels up to fracture, a total of 15 standard tensile tests on proportional cylindrical coupons of these steels were carried out carefully to obtain their force–elongation (F – e) curves while precision measurements were made to obtain their instantaneous dimensions. Complementary advanced finite element models are then established to predict non-linear stress and strain distributions at the critical cross-sections of the necking regions. Through a process of successive approximation, a series of correction factors are obtained to allow for the effects of these non-uniform stress and strain distributions respectively onto the post-necking structural responses of the coupons. Hence, the predicted force–elongation (F - e) curves of the coupons are demonstrated to follow the measured curves closely throughout the entire deformation ranges. More importantly, the predicted instantaneous diameters dgi are shown to have a good agreement with the measured values at various deformation stages up to fracture.

Embedded Soft Inductive Sensors to Measure Arterial Expansion of Tubular Diameters in Vascular Phantoms

Measuring diameter change in flexible tubular structures embedded in opaque material is challenging. In this article, we present a soft braided coil embedded in an elastomer tube as a method to continuously measure such a change in diameter. By measuring the inductance change in the braided coil, we estimate the instantaneous diameter with a simple inductance model. In applying this method, we demonstrate that diameter waves in a vascular phantom, a model of a radial artery embedded in a viscoelastic wrist structure, can be recorded continuously. Four sensors were made, and their ability to measure physiologically relevant simulated pulse waves was assessed. Several pressure pulse profiles were generated using a precision digital pump. Inductance of the coil was measured simultaneously as the change in diameter was recorded using an optical laser/mirror deflection measurement. One sensor was then embedded in a vascular phantom model of the human wrist. The diameter of the simulated radial artery was recorded via ultrasound and estimated from coil inductance measurements. The diameter estimates from the inductance model corresponded well with the comparator in both experimental setups. We demonstrate that our method is a viable alternative to ultrasound in recording diameter waves in artery models. This opens opportunities in empirical investigations of physiologically interesting fluid-structure interaction. This method can provide new ability to measure diameter changes in tubular systems where access is obstructed.

Technical Validation and Usability of a Portable Ultrasound-Based System for Carotid Assessment of Vascular Ageing: A Pilot Study

The objective of this work was to investigate technical validation and usability of an innovative, technically simple, easy-to-use, and portable integrated system to assess carotid function and structure by ultrasound. The studied system integrated a hardware (the Interson SP-L01 embedded ultrasound probe [Interson, Pleasanton, CA, USA]) and a software measuring the instantaneous diameter of the carotid artery in real-time from B-mode ultrasound image sequences (Carotid Studio, by Quipu Srl [Pisa, Italy]). Technical validation was evaluated by intra-operator reproducibility of two measurements acquired by an expert operator, and agreement with state-of-the-art technique (Mylab25 by Esaote SpA [Genova, Italy], Carotid Studio 4.3 by Quipu Srl) was evaluated in laboratory settings in 12 healthy volunteers; usability of the portable integrated system was investigated by administering questionnaires to users and the results were reported with scores based on a five-point scale. Twelve (12) healthy volunteers (five men, mean age 44.5±13.6 years, free of cardiovascular disease or risk factors), were recruited. Agreement with state-of-the-art technique was satisfactory, with no significant bias. Coefficient of variation (intra-operator reproducibility) was 3.2% (2.5% SD) for intima-media thickness, 0.9% (0.7% SD) for diameter, and 2.5% (2.2% SD) for distension. Usability questionnaires showed an overall positive judgement of the integrated system with respect to the traditional one, obtaining an average score greater than 4 (on a five-point scale). A portable, innovative prototype to easily assess ultrasound carotid parameters of vascular ageing was successfully designed, developed, and demonstrated to be comparable with state-of-the art technique. Usability was also satisfactory.

Greater arterial wall viscosity in endurance-trained men.

The age-associated increase in arterial wall viscosity (AWV) is attenuated by high cardiorespiratory fitness level. However, AWV in endurance-trained athletes have not been determined. We designed a cross sectional study to compare central AWV and compliance between endurance-trained young athletes and age-matched control men. Twenty-one endurance-trained men (age 20.7 ± 0.3years) and 20 age-matched healthy control men (age 21.6 ± 0.4years) were studied. The common carotid artery was measured noninvasively by tonometry and automatic tracking of B-mode images to obtain instantaneous pressure and diameter hysteresis loops, and we calculated the dynamic carotid arterial compliance, static (effective and isobaric) compliance, and viscosity index. The AWV index in the endurance-trained men was larger than the control peers (2285 ± 181 vs. 1429 ± 124mmHg·s/mm: P < 0.001). In addition, dynamic and static compliance were not statistically different between both groups. The present study indicated that the central AWV in endurance-trained athletes was greater than age-matched healthy control men. We believe that the AWV, as well as arterial compliance, is an important element for assessing vascular adaptation to endurance training.

Restitution methodology for space and time dependent solid-fuel port diameter evolution in hybrid rocket engines

A post-processing tool for experimental data is developed to rebuild the instantaneous and local distributions of the fuel port diameter and the fuel regression rate throughout the port conduct during a firing test. The main objective is to use the developed methodology to be able, at a given instant during the firing test, to simulate a hybrid rocket engine configuration and to validate the related numerical modeling. The methodology is based on the coupling between the instantaneous fuel mass flow rate obtained by a ballistic reconstruction technique and the port diameter measurement throughout the port conduct after the firing test. The ballistic reconstruction method is adapted and applied to an experimental hybrid rocket, using hydrogen peroxide/high density polyethlylene propellants, with a catalytic injector (HYCAT). Firstly, a set of representative firing tests is selected from the HYCAT hybrid rocket engine testing campaign. Secondly, an analytical approach leads to instantaneous evolutions of the fuel port diameter and the fuel regression rate profiles throughout the fuel port conduct. The rebuilt profiles of the instantaneous port diameter show the ability of the methodology to restore the space and time distribution of the fuel port diameter. Nevertheless, the fuel regression rate distributions show some limitations of the methodology even though the average is coherent with the ballistic reconstruction trends.

Spray Flame Characteristics of Bio-Derived Fuels in a Simulated Gas Turbine Burner

Abstract Fuel injection plays an important role in liquid-fueled gas turbine combustion. The strong interdependence of liquid breakup and atomization, turbulent dispersion of these droplets, droplet evaporation, and fuel–air mixing make the spray modeling an extremely challenging task. The physical processes are even more difficult to predict for alternative fuels with different thermophysical properties. In this study, spray flames of unheated and preheated vegetable oil (VO) produced by an air-blast (AB) atomizer in a swirl stabilized combustor are investigated experimentally. Phase Doppler particle analyzer (PDPA) is used to measure the instantaneous diameter and axial velocity of droplets at different axial and radial locations in both flames. Experiments are conducted at an equivalence ratio of 0.79 and atomizing air to liquid ratio by a mass of 2.5 to obtain stable VO flames. Radial profiles of mean axial velocity and Sauter mean diameter (SMD) are presented to show the effect of fuel preheating. Joint probability density functions (joint PDF) are presented to show the correlation between droplet diameter and axial velocity. Results are analyzed to show that both sprays exhibit self-similar droplet diameter distributions at different axial and radial locations when normalized properly. Thus, the vast amount of PDPA data in the spray can be reduced to simple distribution functions. A method to reconstruct the joint PDF from experimentally determined distribution functions is presented. We envision that the joint PDF approach outlined in this study could be implemented in high-fidelity computational fluid dynamic models to improve spray predictions in future studies.

A new simple formulation for instantaneous coil diameter of a SMA helical spring

Helical coil tension springs made of shape memory alloy (SMA) materials generally undergo large deflection under loading during which their mean coil diameter changes noticeably. In the design of these helical coil springs, it is necessary to identify the real behaviour which may be affected by the variation in actual coil diameter. Therefore, a simple formulation is proposed in this paper for predicting instantaneous coil diameter. The predictions from present formulation match very closely with experimental measurements. The proposed formulation is relatively easy to adopt for design calculations. The effects of varying coil diameter on the spring characteristics are also discussed. This is very general and can be used for any helical spring which undergoes small or large deflections, although the proposed formulation is derived for SMA helical spring.

A new simple formulation for instantaneous coil diameter of a SMA helical spring

Helical coil tension springs made of shape memory alloy (SMA) materials generally undergo large deflection under loading during which their mean coil diameter changes noticeably. In the design of these helical coil springs, it is necessary to identify the real behaviour which may be affected by the variation in actual coil diameter. Therefore, a simple formulation is proposed in this paper for predicting instantaneous coil diameter. The predictions from present formulation match very closely with experimental measurements. The proposed formulation is relatively easy to adopt for design calculations. The effects of varying coil diameter on the spring characteristics are also discussed. This is very general and can be used for any helical spring which undergoes small or large deflections, although the proposed formulation is derived for SMA helical spring.

Numerical and Experimental Studies of Compression-Tested Copper: Proposal for a New Friction Correction

New empirical relationship is proposed to calculate instantaneous maximum diameters on the sample during compression test. The proposal is a relationship between instantaneous maximum diameter, friction coefficient, initial dimensions of the sample and the displacement during the compression test. Seventeen compression tests were carried out to copper cylindrical samples without lubrication at room temperature to obtain this new empirical relationship. Numerical simulations were carried out taking into a count this new relationship for numerical validation. The maximum diameters calculated with this new empirical relationship are the same to the experimental measurements. The mechanical behavior calculated with this new relationship and with the friction corrections of Rowe and Dieter are similar. The simulations are similar to the experiments, with differences lower than 4.21%. The simulation shows higher hardening in the middle of the sample than on the bottom. Numerical simulations show that, possibly, the friction coefficient between sample and dies changes meanwhile the sample is hardening.

Hysteretic behaviour of high strength S690 steel materials under low cycle high strain tests

This paper describes a detailed experimental investigation into structural behaviour of S690 steel materials under both monotonic and cyclic loading conditions. In addition to 6 monotonic tensile tests, which were conducted to establish basic mechanical properties, 36 cyclic tests were then carried out in order to examine hysteretic behaviour of the S690 steel materials under various target strains and loading frequencies. The experimental arrangements used for the monotonic and the cyclic tests are described, and a detailed account of the test results is provided. The monotonic tests showed that all the S690 steel specimens satisfied the ductility requirements stipulated in current European provisions which are typically based solely on monotonic behaviour. In the cyclic tests, most specimens were able to complete 20 cycles with target strain amplitudes of ±2.5%, ±5.0%, ±7.5%, and ±10.0%, under loading frequencies of 0.1, 0.5, 1.0 and 2.0 Hz. However, some specimens fractured at the 20th cycle when the target strains were ±10.0% irrespective of the loading frequency. Additionally, significant strength enhancement due to strain hardening was observed and quantified in the cyclic tests, depending on the level of target strains. The results additionally illustrated the importance of using actual instantaneous cross-sectional diameters for evaluating true stresses in order to obtain actual representative hysteretic curves.In general, the study highlights the importance of establishing seismic ductility requirements based on cyclic tests, particularly for high strength steel materials. It also provides a detailed assessment of the hysteretic characteristics, which can be directly employed to develop reliable constitutive models for high strength S690 steel materials under seismic loading conditions.

Simulation of the spreading of a gas-propelled micro-droplet upon impact on a dry surface using a lattice-Boltzmann approach

Spray cooling is one of the most promising methods of cooling high heat flux electronics. Depending on the type of the nozzle, spray cooling can be categorized as single-phase or two-phase. In the latter, which is known to be more effective, a secondary gas is used to further pressurize the liquid and form smaller droplets at higher velocities. The gas is also assumed to assist the spreading phase by imposing normal and tangential forces on the droplet free surface which adds to the complicated hydrodynamics of the droplet impact. Moreover, the order of magnitude of droplet size in spray cooling is 10−6 m, thereby introducing a low Weber and Reynolds numbers’ impact regime which heretofore has not been well understood. A 3D lattice Boltzmann method was implemented to simulate the impact of a single micro-droplet on a dry surface both in ambient air and under a stagnation gas flow. Two cases were closely compared and correlations were proposed for the instantaneous spreading diameter. Contrary to recent findings at higher impact Weber and Reynolds numbers, it was found that a stagnation flow only significantly affects the spreading phase for Ca* ≥ 0.35 but has little influence on the receding physics.

Hemodynamic analysis of radiation-induced damage in common carotid arteries by using color Doppler ultrasonography.

PurposeThe aim of this study was to assess vascular changes and blood flow abnormalities in the common carotid arteries of patients with head and neck cancers after external radiotherapy, using color Doppler ultrasonography.MethodsWe studied 24 patients treated with external radiotherapy for various head and neck cancers. In order to study the acute effects of irradiation on common carotid blood flow and arterial diameter changes, color Doppler ultrasonography parameters such as peak systolic velocity, end diastolic velocity, mean velocity, systolic-to-diastolic velocity (S/D) ratio, pulsatility index (PI), resistive index (RI), and instantaneous diameter changes were evaluated before and after external radiotherapy. Additionally, the blood volume flow (VF) values in the peak systolic and end diastolic phases, as well as mean velocity, were evaluated throughout three cardiac cycles using B-mode ultrasonic image processing.ResultsThe findings showed significant changes in the S/D ratio, PI, and RI of the common carotid arteries before and after external radiotherapy (P<0.05). Moreover, a significant decrease in artery diameter and blood VF was observed after radiotherapy relative to the pretreatment values. A significant correlation was found between the blood VF values estimated using ultrasonic measurements and mathematical methods throughout three cardiac cycles.ConclusionThe hemodynamic parameters of the common carotid arteries changed during radiotherapy. These arterial changes may lead to late adverse effects of radiotherapy, such as ischemic strokes and ischemic attacks.

Identification of the impact regimes of a liquid droplet propelled by a gas stream impinging onto a dry surface at moderate to high Weber number

In “vapor assisted” spray cooling it is well known that the droplet spray is more effective in cooling when smaller droplets are formed and propelled by a vapor phase towards the target surface. In the ideal spray evaporative cooling regime, the droplet impacts, spreads into a thin film, and then evaporates. In the presence of a carrier vapor, the vapor phase may affect the droplet dynamics by accelerating the droplet and by imposing hydrodynamic forces on the free surface during spreading and receding. There is a lack of understanding of the complicated physics at play. In the present study, the impact of a water droplet propelled by an air stream onto a dry smooth unheated surface was experimentally investigated. It was observed that higher impact Weber numbers led to a larger diameter and thinner film thickness. It was found that the gas stream did not significantly influence the spreading phase. However, the propellant gas noticeably decreased the droplet receding phase, delayed the onset of droplet splashing, and increased the upper Weber number limit for the droplet spreading regime. An analytic model using an energy balance approach was developed to predict dynamic and instantaneous droplet diameter and the agreement with the experimental observations was within 5% in the spreading phase, with poorer agreement in the receding phase due to the assumption of constant receding contact angle.

Molecular Dynamics Simulations of Ibuprofen Release from pH-Gated Silica Nanochannels.

The iboprufen delivery process from cylindrical silica pores of 3 nm diameter, with polyamine chains anchored at the pore outlets, was investigated by means of massive molecular dynamics simulations. Effects from pH were introduced by considering polyamine chains with different degrees of protonation. High, low, and intermediate pH environments were investigated. The increment of the acidity of the environment leads to a significant decrease of the pore aperture, yielding an effective diameter, for the lowest pH case, that is 3.5 times smaller than the one associated with the highest pH one. Using a biased sampling procedure, Gibbs free energy profiles for the ibuprofen delivery process were obtained. The joint analysis of the corresponding profiles, time evolution of the ibuprofen position within the channel, orientation of the molecule, and instantaneous effective diameter of the gate suggest a three-step mechanism for ibuprofen delivery. A complementary analysis of the translational mobility of ibuprofen along the axial direction of the channel revealed a subdiffusive dynamics in the low and intermediate pH cases. Deviations from Brownian diffusive dynamics are discussed and compared with direct experimental results.

Similarities of arterial collagen pressure-diameter relationship in ovine femoral arteries and PLLA vascular grafts.

In-vivo implanted vascular grafts fail due to the mechanical mismatch between the native vessel and the implant. The biomechanical characterization of native vessels provides valuable information towards the development of synthetic grafts. Five samples of electrospun nanofibrous poly(L-lactic acid)(PLLA) tubular structures were subjected to physiological pulsating pressure using an experimental setup. Four ovine femoral arteries were also tested in the experimental setup under the same conditions. Instantaneous diameter and pressure signals were obtained using gold standard techniques, in order to estimate the dynamic pressure-strain elastic modulus (E(Pε)) of both native vessels and grafts. Synthetic grafts showed a significant increase of E(Pε) (10.57±0.97 to 17.63±2.61 10(6) dyn/cm(2)) when pressure was increased from a range of 50-90 mmHg (elastin-response range) to a range of 100-130 mmHg (collagen-response range). Furthermore, femoral arteries also exhibited a significant increase of EPε (1.66±0.30 to 15.76±4.78 10(6) dyn/cm(2)) with the same pressure variation, showing that both native vessels and synthetic grafts have a similar behavior in the collagen-acting range. The mechanical behavior of PLLA vascular grafts was characterized In vitro. However, the procedure can be easily extrapolated to In vivo experiences in conscious and chronically instrumented animals.