Steady Flow Rate Research Articles

Particle and inhalation exposure in human and monkey computational airway models

Regional deposition of inhaled aerosols is essential for assessing health risks from toxic exposure. Upper airway physiology plays a significant role in respiratory defense by filtering micrometer particles, whose deposition mechanism is predominantly inertial impaction and is mainly controlled by airflow characteristics. The monkey is commonly used in tests that study inhalation toxicity as well as in preclinical tests as human surrogates due to their anatomical similarities to humans. Therefore, accurate predictions and an understanding of the inhaled particles and their distribution in monkeys are essential for extrapolating laboratory animal data to humans. The study goals were as follows: (1) to predict the particle deposition based on aerodynamic diameters (1–10 µm) and various steady inspiratory flow rates in computational models of monkey and human upper airways; and (2) to investigate potential differences in inhalation flow and particle deposition between humans and monkeys by comparing numerical simulation results with similar in-vitro and in-vivo measurements from recent literature. The deposition fractions of the monkey’s numerical airway model agreed well with in-vitro and human model data when equivalent Stokes numbers were compared, based on the minimum cross-sectional area as representative of length scale. Vestibule removal efficiencies were predicted to be higher in the monkey model compared with the human model. Our results revealed that the particle transportations were sensitive to the anatomical structure, airway geometry, airflow rates, inflow boundary conditions and particle size.

Nonlinear dynamic analysis of parallel three uniformly heated channels with water at supercritical pressures

This study develops a nonlinear dynamic model of parallel supercritical uniformly heated channels based on three-region methodology coupled with polynomial profile approximations between flow density and flow enthalpy. The validation results against the experimental data indicate that the present model has the capability to investigate the stability issues of parallel uniformly heated channels with supercritical water. Nonlinear characteristics, stability maps and parametric effects of three uniformly heated channels with supercritical water are investigated. The results illustrate that channel-to-channel interactions among three channels will drive the system more unstable due to a more asymmetric power distribution. In addition, the hottest channel with the highest steady state flow rate would oscillate with the largest amplitude and out-of-phase with the other less heated channels under constant total inlet flow rate condition. This study also reveals that the nonlinear oscillations between inlet flow velocity and outlet flow velocity in each channel tend to present out-of-phase. It could demonstrate that increasing the pressure drop of heavy fluid region (region 1) would stabilize the system, while increasing the pressure drop of light fluid region (region 3) would destabilize the system. The parametric studies on system stability of three uniformly heated channels suggest that increasing inlet flow resistance or enlarging the channel diameter would stabilize the system, while increasing outlet flow resistance or lengthening the channel length would destabilize the system.

Continuous Laminaribiose Production Using an Immobilized Bienzymatic System in a Packed Bed Reactor.

The first continuous production system of laminaribiose from sucrose and glucose in a bienzymatic reaction is reported in this study. Immobilized laminaribiose phosphorylase and sucrose phosphorylase were used in a packed bed reactor system comprising of a 3-cm glass column at 35°C with a steady feeding flow rate of 0.1ml/min. Factors affecting product formation including enzyme ratio, peal concept (both enzymes in one pearl or in separate pearls), and pearl size were studied. An enzyme ratio of 2:1 of laminaribiose phosphorylase (LP) to sucrose phosphorylase (SP) when encapsulated separately in bigger size peals resulted in higher concentration of product. Laminaribiose (0.4g/(Lh)) is produced in the optimized system at steady state. The reaction system proved to be operationally stable throughout 10days of continuous processing. A half-life time of more than 9days was observed for both biocatalysts.

Chaos in a non-autonomous nonlinear system describing asymmetric water wheels

We derive a water wheel model from first principles under the assumption of an asymmetric water wheel for which the water inflow rate is in general unsteady (modeled by an arbitrary function of time). Our model allows one to recover the asymmetric water wheel with steady flow rate, as well as the symmetric water wheel, as special cases. Under physically reasonable assumptions, we then reduce the underlying model into a non-autonomous nonlinear system. In order to determine parameter regimes giving chaotic dynamics in this non-autonomous nonlinear system, we consider an application of competitive modes analysis. In order to apply this method to a non-autonomous system, we are required to generalize the competitive modes analysis so that it is applicable to non-autonomous systems. The non-autonomous nonlinear water wheel model is shown to satisfy competitive modes conditions for chaos in certain parameter regimes, and we employ the obtained parameter regimes to construct the chaotic attractors. As anticipated, the asymmetric unsteady water wheel exhibits more disorder than does the asymmetric steady water wheel, which in turn is less regular than the symmetric steady state water wheel. Our results suggest that chaos should be fairly ubiquitous in the asymmetric water wheel model with unsteady inflow of water.

Modeling Inspiratory Flow in a Porcine Lung Airway.

Inspiratory flow in a multigeneration pig lung airways was numerically studied at a steady inlet flow rate of 3.2 × 10-4 m3/s corresponding to a Reynolds number of 1150 in the trachea. The model was validated by comparing velocity distributions with previous measurements and simulations in simplified airway geometries. Simulation results provided detailed maps of the axial and secondary flow patterns at different cross sections of the airway tree. The vortex core regions in the airways were visualized using absolute helicity values and suggested the presence of secondary flow vortices where two counter-rotating vortices were observed at the main bifurcation and in many other bifurcations. Both laminar and turbulent flows were considered. Results showed that axial and secondary flows were comparable in the laminar and turbulent cases. Turbulent kinetic energy (TKE) vanished in the more distal airways, which indicates that the flow in these airways approaches laminar flow conditions. The simulation results suggested viscous pressure drop values comparable to earlier studies. The monopodial asymmetric nature of airway branching in pigs resulted in airflow patterns that are different from the less asymmetric human airways. The major daughters of the pig airways tended to have high airflow ratios, which may lead to different particle distribution and sound generation patterns. These differences need to be taken into consideration when interpreting the results of animal studies involving pigs before generalizing these results to humans.

A clip-on electroosmotic pump for oscillating flow in microfluidic cell culture devices

Recent advances in microfluidic devices put a high demand on small, robust and reliable pumps suitable for high-throughput applications. Here we demonstrate a compact, low-cost, directly attachable (clip-on) electroosmotic pump that couples with standard Luer connectors on a microfluidic device. The pump is easy to make and consists of a porous polycarbonate membrane and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) electrodes. The soft electrode and membrane materials make it possible to incorporate the pump into a standard syringe filter holder, which in turn can be attached to commercial chips. The pump is less than half the size of the microscope slide used for many commercial lab-on-a-chip devices, meaning that these pumps can be used to control fluid flow in individual reactors in highly parallelized chemistry and biology experiments. Flow rates at various electric current and device dimensions are reported. We demonstrate the feasibility and safety of the pump for biological experiments by exposing endothelial cells to oscillating shear stress (up to 5 dyn/cm2) and by controlling the movement of both micro- and macroparticles, generating steady or oscillatory flow rates up to ± 400 μL/min.

Prediction of bed profile due to complexity of sediment properties in the channel

Numerous data on bed profile have been investigated yet the analysis to predict bed profile formation especially related to sediment properties are still insufficient. Objectives of this study to determine significant bed elevation profile pattern formed based on the complexity of sediment properties especially related to sediment size. The investigation is made by carried out a computer simulation of straight channel pattern with the fixed bank and movable sand bed. The study included the various hydraulic characteristics with steady flow rates and sediment properties. The simulations focus on three different sediment sizes with other variables namely channel size, flow rate and bed slope were kept constant. Analysis has included the discussion on a significant difference of bed elevation profile formed along the lateral and longitudinal distance. As a conclusion, the sediment size alone does not significantly change the bed elevation profile as its only gave minor effect to the bed profile changes.

Development and validation of analytical method for vildagliptinencapsulated poly-ε-caprolactone microparticles

Statistical experimental designs (DoE) are used as an advancement over conventional ‘One Variable at Time’ (OVAT) experimental approach. It provides more accurate results in fewer runs compared to conventional methods. In the present work a simple, rapid, precise and highly accurate RP-HPLC method was developed and validated for vildagliptin (VLG) in VLG-poly-ε-caprolactone (PCL) microparticles by using Box-Behnken design (BBD). Microparticles (MPs) were prepared by W/O/W solvent evaporation method. The prepared MPs were characterized by employing scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR).The RP-HPLC separation was carried out on HyperClone TM C18 column (250 mm x 4.6 mm I.D., 5μm) with mobile phase consisting of mixture of Phosphate buffer (0.01 M, pH 7): acetonitrile (75:25,v/v) and UV detection set at 203 nm with steady flow rate of 1.0 ml/min. The measurement was linearly correlated with concentration in the 10 - 100 μg/ml range (r > 0.9999). The proposed method was applied for the analysis of VLG in developed MPs. The results showed that the method is suitable to determine VLG in microparticle formulation without any interference from the formulation variables.

Communication—Evaporation Driven Micro/Nanofluidic Pumping Device

A compact portable nanofluidic pump that enables precise manipulation of ultra-small amount of liquid is highly desirable for the trend in miniaturization. Here we develop an integrated micro/nanofluidic pumping device utilizing nanopillar structures with diminishing intervals and locally controlled evaporation. A continuous and steady flow rate of 2.7 pL/s was achieved for more than 12 h without external mechanical power source. The liquid transports in the nanofluidic channels were controllable by adjusting the temperature of evaporation surface. The picoliter-scale flow rates meet the demands for performing nanofluidic immunoassays and other interdisciplinary applications.

Damping hydrodynamic fluctuations in microfluidic systems

In this article, we report a method to damp microfluidic hydrodynamic fluctuations caused by flow sources. We demonstrate that compliance of elastomeric off-chip tubings can be used to damp fluctuations and lead to steady flow rates. We analyze the whole microfluidic system using electrical circuit analogies, and demonstrate that off-chip compliances are significant, especially for displacement pump driven systems. We apply this hydrodynamic damping method to microfluidic droplet generation. Our results show that highly monodisperse microdroplets can be obtained by syringe pump driven systems utilizing this damping effect. We reached a coefficient of variation of 0.39% for the microdroplet area using a standard T-junction geometry. Additionally, we demonstrated that pressure pumps inherently use this effect, and have so far led the high performances reported in the literature in terms of droplet monodispersity. The presented off-chip hydrodynamic damping method is not only low-cost and practical, but can also be used in elastomeric and rigid microchannels without need to introduce additional components to the fluidic circuit.

Active Control of Noise from Hot Supersonic Jets

This paper presents diagnostic experiments aimed at understanding and mitigating supersonic jet noise from the coherent wave-packet structures that are the source of peak aft-angle mixing noise. Both isothermal and heated, nearly perfectly expanded, Mach 1.5 jets were forced in the near-nozzle region with air injection generated by a spinning-valve device designed to excite the jet at frequencies approaching those of the dominant turbulent structures. Substantial reductions in the peak aft-angle radiation were achieved with steady blowing at amplitudes corresponding to 2–6% of the mass flow rate of the primary jet. The noise benefit saturated at mass flow rates above 4%, with as much as a 6 dB reduction in overall sound pressure level at aft angles. Increasing the mass flow rates yielded a monotonically increasing high-frequency noise penalty at the sideline, where noise levels in the natural jet were already 15 dB lower than the aft-angle peak, so that the penalty due to actuation was minor. Although both steady and periodic unsteady mass injections were produced by the spinning valve when it rotated, it was calibrated to hold the steady mass flow rate constant as the frequency of unsteady blowing was changed. In this way, the effect of steady and unsteady blowings on the acoustic field could be decoupled. It is shown that the noise benefit was uniquely associated with the steady component of blowing, whereas the unsteady component resulted in additive tones in the spectra. This implied linearity is consistent with theory and experiments showing that the wave-packet structures, which give rise to the dominant aft-angle radiation, evolve in the turbulent mean flowfield in a nearly linear fashion from their origin in the near-nozzle region. The interpretation of noise reduction is that the steady component of blowing spreads the mean flow more rapidly, resulting in weaker wave packets. Periodic unsteady blowing forces coherent wave packets that are largely uncorrelated from the random natural ones, which then leads to the observed additive tones.

Geometry and airflow dynamics analysis in the nasal cavity during inhalation

BackgroundA major issue among computational respiratory studies is the wide variety of nasal morphologies being studied, caused by both inter-population and inter-subject variations. MethodSix nasal cavity geometries exhibiting diverse geometry variations were subjected to steady inhalation flow rate of 15L/min. to determine if any consistent flow behaviour could be found. FindingsDespite vastly different geometries we were able to identify consistent flow patterns including relatively high velocity in the nasal valve region, followed by flow continuing predominantly in the inferior half of the airway. We also found conformity among models where the inhaled air reached a near-conditioned state by the middle of the nasal cavity. Air from the front of the face reached the olfactory regions while air from the lateral sides of the face moved through the inferior half of the nasal cavity. InterpretationThe ability to predict gross flow features provides a baseline flow field to compare against. This contributes towards establishing well defined flow predictions and be used as a comparison for future larger studies.

Rheological, sensory, and microstructural properties of fresh and frozen/thawed mashed potatoes enriched with different proteins

ABSTRACTIn this study, the effect of the addition of soybean protein isolate (SPI), whey protein isolate (WPI), whole milk powder (WMP), and sodium caseinate (SC) on the rheological, physical, sensory, and structural properties of fresh and frozen/thawed mashed potatoes formulated with added cryoprotectants [kappa-carrageenan (κ-C) and xanthan gum (XG)] was compared. Steady shear flow rate curves indicated a non-Newtonian fluid and exhibited typical shear thinning (pseudoplastic) behavior (n < 1) with all added proteins. The results showed that there is no significant change in the apparent viscosity (ηapp) of fresh mashed potatoes (FMP) and frozen/thawed mashed potatoes (F/TMP) with added WMP and SC at a concentration of 5 g/kg. While the addition of SPI at a concentration of 10 g/kg increased the ηapp and pseudoplasticity, which indicates that the SPI behaves as harder fillers. Based on the sensory evaluation results, WPI and WMP could incorporate to FMP without losing the sensory quality of the product. F/TMP samples with addition of SPI were judged more acceptable than other processed samples, evidencing the ability of this protein to reduce the influence of freeze/thaw process.

In situ measurements of soil saturated hydraulic conductivity: Assessment of reliability through rainfall-runoff experiments

The saturated hydraulic conductivity, Ks, is a soil property that has a key role in the partitioning of rainfall into surface runoff and infiltration. The commonly used instruments and methods for in situ measurements of Ks have frequently provided conflicting results. Comparison of Ks estimates obtained by three classical devices—namely, the double ring infiltrometer (DRI), the Guelph version of the constant-head well permeameter (GUELPH-CHP) and the CSIRO version of the tension permeameter (CSIRO-TP) is presented. A distinguishing feature in this study is the use of steady deep flow rates, obtained from controlled rainfall–runoff experiments, as benchmark values of Ks at local and field-plot scales, thereby enabling an assessment of these methods in reliably reproducing repeatable values and in their capability of determining plot-scale variation of Ks. We find that the DRI grossly overestimates Ks, the GUELPH-CHP gives conflicting estimates of Ks with substantial overestimation in laboratory experiments and underestimation at the plot scale, whereas the CSIRO-TP yields average Ks values with significant errors of 24% in the plot scale experiment and 66% in laboratory experiments. Although the DRI would likely yield a better estimate of the nature of variability than the GUELPH-CHP and CSIRO-TP, a separate calibration may be warranted to correct for the overestimation of Ks values. The reasons for such discrepancies within and between the measurement methods are not yet fully understood and serve as motivation for future work to better characterize the uncertainty associated with individual measurements of Ks using these methods and the characterization of field scale variability from multiple local measurements.

Combined constitutive model for creep and steady flow rate of frozen soil in an unconfined condition

A combined constitutive model is developed for the creep behavior of frozen soil in an unconfined condition. The model is obtained by coupling two stress- and time-dependent models, which are responsible for the primary and tertiary creep stages. The model parameters are dependent on temperature and can be readily determined from the strain rate–time curves at two creep stresses. The model performance is demonstrated by simulating the complete strain–time and strain rate–time curves (including primary, secondary, and tertiary stages) of frozen sand and frozen clay in uniaxial creep tests under different creep stresses. Moreover, two equations are obtained from the combined model. One shows a good capability in describing the relationship between creep strength and the time to creep failure. The other makes an excellent prediction of the steady flow rate in a typical creep process. Both equations can reflect the effects of stress and temperature on the creep behavior of frozen soil.

Localised dynamics of laminar pulsatile flow in a rectangular channel

The exploitation of flow pulsation in low-Reynolds number micro/minichannel flows is a potentially useful technique for enhancing cooling of high power photonics and electronics devices. Although the mechanical and thermal problems are inextricably linked, decoupling of the local instantaneous parameters provides insight into underlying mechanisms. The current study performs complementary experimental and analytical analyses to verify novel representations of the pulsating channel flow solutions, which conveniently decompose hydrodynamic parameters into amplitude and phase values relative to a prescribed flow rate, for sinusoidally-pulsating flows of Womersley numbers 1.4 ≤ Wo ≤ 7.0 and a fixed ratio of oscillating flow rate amplitude to steady flow rate equal to 0.9. To the best of the authors’ knowledge, the velocity measurements – taken using particle image velocimetry – constitute the first experimental verification of theory over two dimensions of a rectangular channel. Furthermore, the wall shear stress measurements add to the very limited number of studies that exist for any vessel geometry. The amplification of the modulation component of wall shear stress relative to a steady flow (with flow rate equal to the amplitude of the oscillating flow rate) is an important thermal indicator that may be coupled with future heat transfer measurements. The positive half-cycle time- and space-averaged value is found to increase with frequency owing to growing phase delays and higher amplitudes in the near-wall region of the velocity profiles. Furthermore, the local time-dependent amplification varies depending on the regime of unsteadiness: (i) For quasi-steady flows, the local values are similar during acceleration and deceleration though amplification is greater near the corners over the interval 0 – 0.5π. (ii) At intermediate frequencies, local behaviour begins to differ during accelerating and decelerating periods and the interval of greater wall shear stress near the corners lengthens. (iii) Plug-like flows experience universally high amplifications, with wall shear stress greater near the corners for the majority of the positive half-cycle. The overall fluid mechanical performance of pulsating flow, measured by the ratio of bulk mean wall shear stress and pressure gradient amplifications, is found to reduce from an initial value of 0.97 at Wo = 1.4 to 0.28 at Wo = 7.0, demonstrating the increasing work input required to overcome inertia.

Dynamic and heat transfer of a Pr < 1 thermal flow around a fin on the thermal wall

A Pr<1 thermal flow around a fin at different positions on the thermal wall is investigated using scaling analysis and numerical simulation. Dynamic and heat transfer of the thermal flow around the fin with unsteady and steady flow rates are analyzed and possible flow regimes are identified. The scaling relations of the thermal flow around the fin are obtained, which are dependent on the fin position, the Prandtl number and the Rayleigh number. The velocity and thickness scales of the intrusion and the plume around the fin are also validated by numerical simulation. The numerical results are consistent with the scaling predictions.

SMART-ITL 1 계열 피동안전계통을 이용한 유동분사기 성능에 대한 실험연구

노심보충탱크 상부에 설치되는 유동분사기 형상에 따른 냉각수 주입특성 및 탱크 내에서의 열수력 현상 변화를 파악하기 위한 안전주입배관 2인치 파단 소형냉각재상실사고(SBLOCA) 모의시험이 잔열 및 피동잔열제거계통(PRHRS) 모의 없이 수행되었다. 두 가지 형상의 유동분사기를 설치하고 수행한 각각의 시험은 거의 유사한 초기 및 경계조건에서 수행되었으며, 이로 인해 반복시험에 대한 재현성이 충족되었다고 판단된다. 시험결과는 유동분사기의 종류(본 시험에서는 구멍의 개수에 해당)에 관계없이 유사한 열수력학적 거동을 보였으며, 초기 주입유량 관점에서는 구멍의 개수가 2배인 B형이 A형에 비해 좀 더 우수한 주입 성능을 보였다. 노심보충탱크 격리 밸브가 개방된 후 압력평형배관을 통해 유입되는 고온의 원자로냉각재는 상부 헤더에서 상대적으로 저온인 <TEX>$50^{\circ}C$</TEX> 물과 혼합되면서 증기 응축과 같은 상변화에 의한 압력 변동을 동반하는 다차원 열유동 현상을 일으키게 된다. 이로 인해 초반부 노심보충탱크 주입 유량은 상온운전 조건에서 보다는 작게 되고, 일정시간 경과 후에는 유사한 주입유량 특성을 보였다. In order to estimate the effect of flow distributors connected to an upper nozzle of CMT(Core Makeup Tank) on the thermal-hydraulic characteristics in the tank, a simplified 2 inch Small Break Loss of Coolant Accident(SBLOCA) was simulated by skipping the decay power and Passive Residual Heat Removal System(PRHRS) actuation. The CMT is a part of safety injection systems in the SMART (System Integrated Modular Advanced Reactor). Each test was performed with reliable boundary conditions. It means that the pressure distribution is provided with repeatable and reproducible behavior during SBLOCA simulations. The maximum flow rates were achieved at around 350 seconds after the initial opening of the isolation valve installed in CMT. After a short period of decreased flow rate, it attained a steady injection flow rate after about 1,250 seconds. This unstable injection period of the CMT coolant is due to the condensation of steam injected into the upper part of CMT. The steady injection flow rate was about 8.4% higher with B-type distributor than that with A-type distributor. The gravity injection during hot condition tests were in good agreement with that during cold condition tests except for the early stages.

Start-up flow behavior of pipelines transporting waxy crude oil emulsion

Water-in-waxy crude oil emulsion tends to gelatinize under shutdown conditions when the atmospheric temperature or sea water temperature is lower than its pour point, threatening pipeline restart safety. Based on previous researches about the complex rheological properties of waxy crude oil emulsion gel, elasto-viscoplastic thixotropic models were first compared with each other according to experimental results, and the model proposed by Teng was screened out to be the most accurate one that could describe the whole response after shear loading. Then the effects of rheological changes on pipeline start-up flow after the formation of emulsion gel were computed numerically with the help of this thixotropic model. It was found out through a case study of a 50km long pipeline that the time for the flow to start and from start state to steady state at terminal of the pipeline transporting 30% water cut emulsion gel increases by 5.8 times and 2.1 times respectively when compared with the time for original crude oil. Meanwhile, the steady flow rate after start-up decreases dramatically by 85.9%. The pipeline transporting waxy crude oil could be restarted successfully at the pressure of 1.0MPa, while it need to be pressurized to 5.0MPa to resume flow when its 60% water cut emulsion gel is formed. All these results indicate that the emulsification of waxy crude oil makes pipeline restart more difficult, and the lengthening of the pipeline magnifies the influence of the emulsification. Therefore, the possibility of wax precipitation in crude oil emulsion and further the structural characteristics of the formed emulsion gel have to be taken into consideration during multiphase pipeline shutdown.

Centerline Bed Elevation Profile of Sand Bed Channel due to Bar Formation

Numerous data on bar formation have been accumulated yet the methods to predict bar geometry especially bar height are still insufficient. Objectives of this study to determine the trend in term of a significant difference of centreline bed elevation profile along the longitudinal distance. This can be investigate by carried out an experimental work in an erodible sand bed channel using a large-scale physical river model. The study included the various hydraulic characteristics with steady flow rates and sediment supply. An experimental work consists of four matrices of flow rate and channel width with other variables namely grains size and bed slope were kept constant. Analysis have included the discussion on a significant difference of centreline bed elevation profile along the longitudinal distance. As a conclusion the higher velocity in the smaller channel width have induced erosion of the banks that resulted in elevation increase while the larger flow rates have contributed to higher elevation.