Oscillatory Flow Rate Research Articles

An in vitro experimental investigation of oscillatory flow in the cerebral aqueduct

This in vitro study aims at clarifying the relation between the oscillatory flow of cerebrospinal fluid (CSF) in the cerebral aqueduct, a narrow conduit connecting the third and fourth ventricles, and the corresponding interventricular pressure difference. Dimensional analysis is used in designing an anatomically correct scaled model of the aqueduct flow, with physical similarity maintained by adjusting the flow frequency and the properties of the working fluid. The time-varying pressure difference across the aqueduct corresponding to a given oscillatory flow rate is measured in parametric ranges covering the range of flow conditions commonly encountered in healthy subjects. Parametric dependences are delineated for the time-averaged pressure fluctuations and for the phase lag between the transaqueductal pressure difference and the flow rate, both having clinical relevance. The results are validated through comparisons with predictions obtained with a previously derived computational model. The parametric quantification in this study enables the derivation of a simple formula for the relation between the transaqueductal pressure and the stroke volume. This relationship can be useful in the quantification of transmantle pressure differences based on non-invasive magnetic-resonance-velocimetry measurements of aqueduct flow for investigation of CSF-related disorders.

Impact of residence time distributions in reacting magnesium packed beds on Grignard reagent formation – pump-induced flow behaviour in non-reacting magnesium beds (part 1)

The RTD within a randomly packed bed of non-uniform, non-spherical Mg turnings depends on the properties of the Mg turnings and the pump-induced flow behavior. Using oscillatory flow rates, Bodenstein numbers can be increased by up to 70%.

Control of instability by injection rate oscillations in a radial Hele-Shaw cell

Small spatial perturbations grow into fingers along the unstable interface of a fluid displacing a more viscous fluid in a porous medium or a Hele-Shaw cell. Mitigating this Saffman-Taylor instability increases the efficiency of fluid displacement applications (e.g., oil recovery), whereas amplifying these perturbations is desirable in, e.g., mixing applications. In this work, we investigate the Saffman-Taylor instability through analysis and experiments in which air injected with an oscillatory flow rate outwardly displaces silicone oil in a radial Hele-Shaw cell. A solution for linear instability growth that shows the competing effects of radial growth and surface tension, including wetting effects, is defined given an arbitrary reference condition. We use this solution to define a condition for stability relative to the constant flow rate case and make initial numerical predictions of instability growth by wave number for a variety of oscillations. These solutions are then modified by incorporating reference conditions from experimental data. The morphological evolution of the interface is tracked as the air bubble expands and displaces oil between the plates. Using the resulting images, we analyze and compare the linear growth of perturbations about the mean interfacial radius for constant injection rates with and without superimposed oscillations. Three distinct types of flow rate oscillations are found to modulate experimental linear growth over a constant phase-averaged rate of fluid displacement. In particular, instability growth at the interface is mildly mitigated by adding to the base flow rate provided by a peristaltic pump a second flow with low-frequency oscillations of small magnitude and, to a lesser extent, high-frequency oscillations of large amplitude. In both cases, the increased stability results from the selective suppression of the growth of large wave numbers in the linear regime. Contrarily, intermediate oscillations consistently destabilize the interface and significantly amplify the growth of the most unstable wave numbers of the constant flow rate case. Numerical predictions of low-frequency oscillations of opposite sign (initially decreasing) show promise of even greater mitigation of linear instability growth than that observed in this investigation. Looking forward, proper characterization of the unsteady, wetting, and nonlinear dynamics of instability growth will give further insight into the efficacy of oscillatory injection rates.

Flow pattern transition instabilities in a natural circulation cooling facility

Our research analyzed results from a two-phase natural circulation test facility designed to study the performance of reactor cavity cooling systems, and determined the presence of a flow transition instability. Reactor cavity cooling systems are passive safety system’s designed to remove decay heat from high temperature generation IV reactors. Water-based designs achieve this function by boiling-off a set water inventory held in a storage tank. During normal operation under accident conditions, the two-phase natural circulation facility undergoes a transition from stratified to intermittent flow regimes as the water level in the storage tank is lowered due to inventory evaporation. The transition is accompanied with an oscillatory flow rate due to the differing pressure drops between the flow regimes. The instability ceases after fully transiting into the intermittent flow regime. The presence of the transition was determined with a steady-state drift flux model and wire-mesh sensor data.

Input oscillometry and the forced oscillation technique for assessing lung function in preschool children with asthma

Preschool children with asthma present a challenge in lung function testing, as they cannot readily cooperate with spirometry. The forced oscillation technique (FOT) measures passive pressures and flows delivered by a loudspeaker to a facemask, at frequencies much higher than those occurring physiologically. This in turn allows for rapid collection of data from a spontaneously breathing child in a timespan of seconds. However, at very rapid oscillatory flow rates, the mechanical properties opposing flows into and out of the respiratory system (collectively termed the respiratory system impedance, and comprised of elastic, resistive and inertial components) are very different from at normal breathing frequencies, with elastic properties being less important and inertial properties being more important. An understanding of how the respiratory system behaves at high frequencies is essential to understanding the physiological basis of this technique. This article presents a way to understand these oscillatory mechanics of the respiratory system. It then describes studies of the FOT in normal preschool children and in children with asthma. The technique can also measure the separate contributions of the central and peripheral airways, as well as assess for changes after bronchodilator administration. The FOT holds promise for the objective measurement of lung function in children who are too young to reliably perform spirometry.

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.

Integrated nozzle - flapper valve with piezoelectric actuator and isothermal chamber: a feedback linearization multi control device

This paper introduces a new nozzle-flapper valve with isothermal chamber using piezoelectric actuator. It controls the pressure and flow rate simply, effectively and separately. The proposed valve uses isothermal chamber presenting practical isothermal condition due to its large heat transfer interfaces filled by metal wool. The valve uses stacked type piezoelectric actuator with unique advantages. By using this valve, a simple method has been fulfilled to control flow rate or pressure of ideal gases in a pneumatic actuators. Experimental results demonstrated applications of the proposed valve to control either pressure or flow rate in pneumatic circuits. This valve can be also used in the pilot stage valve to actuate the main stage of a much bigger pneumatic valve. Designated structure contains only one pressure sensor installed on the isothermal control chamber, capable of controlling both pressure and flow rate. The desired output mass flow rate of the valve is controlled by the pressure changes during positioning of piezoelectric actuator at proper position. The proposed valve can control steady and unsteady oscillatory flow rate and pressure effectively, using nonlinear control method such as feedback linearization approach. Its effectiveness is demonstrated and validated through simulation and experiments.

Dynamics of viscous liquid bridges inside microchannels subject to external oscillatory flow.

We report on two-dimensional simulations of liquid bridges' dynamics inside microchannels of uniform wettability and subject to an external oscillatory flow rate. The oscillatory flow results in a zero net flow rate and its effects are compared to those of a stationary system. To handle the three phase contact lines motion, Cahn-Hilliard diffuse-interface formulation was used and the flow equations were solved using the finite element method with adaptively refined unstructured grids. The results indicate that the liquid bridge responds in three different ways depending on the substrate wettability properties and the frequency of the oscillatory flow. In particular below a critical frequency, the liquid bridge will rupture when the channel walls are philic or detach from the surface when they are phobic. However, at high frequencies, the liquid bridge shows a perpetual periodic oscillatory motion for both philic and phobic surfaces. Furthermore, an increase in the frequency of the flow velocity results in stabilization effects and a behavior approaching that of the stationary system where no rupture or detachment can be observed. This stable behavior is the direct result of less deformation of the liquid bridge due to the fast flow direction change and motion of contact lines on the solid substrate. Moreover, it was found that the flow velocity is out of phase with the footprint and throat lengths and that the latter two also show a phase difference. These differences were explained in terms of the motion of the two contact lines on the solid substrates and the deformation of the two fluid-fluid interfaces.

Application and comparison of level control strategies in the slug flow problem using a mathematical model of the process

This paper presents the application of the error-squared level control strategy Proportional Integral (PI) in the slug flow problem in oil production industry. For this purpose the dynamic model has been used for a pipeline-separator under slug flow with five Ordinary Differential Equations (ODEs), coupled, non-linear. The application of the error-squared level control strategy PI is performed through the methodology by bands, whose objective is to damp the oscillatory flow rate of the load that occur in production separators for equipment downstream of the process. This strategy is compared with the level control strategy PI conventional, widely used in industrial processes; and with the level control strategy PI, also, in the methodology by bands. Simulation results showed that the error-squared level control strategy PI in the methodology by bands, presented better results when compared with the level control strategy PI conventional, because reduced flow fluctuations caused by slug flow; and with the level control strategy PI in the methodology by bands, it probably happened because the first has highly respected the defined bands.

Measurement-integrated simulation of wall pressure measurements using a turbulent model for analyzing oscillating orifice flow in a circular pipe

The development of a highly functionalized orifice flowmeter with high accuracy under realistic conditions is desired. This paper presents a method for analyzing oscillating air flow through an orifice in a circular pipe. A measurement-integrated (MI) simulation using a standard k– ε model was used to reduce the computation time. In a previous study, the feedback law of the MI simulation was determined by considering the effect of the computational fluid dynamics (CFD) grid on contracted flow. However, the previous method required the measurement of inlet flow rate, which is not feasible in many applications. Therefore, an MI simulation was proposed that only requires wall pressures, which are much simpler to measure than flow rate. In this MI simulation, the wall pressure downstream of an orifice was measured, and a new proportional–integral controller feedback algorithm was developed to control the inlet flow rate in the computed flow field. The proposed MI simulations were performed for steady and oscillatory flow rates up to 10 Hz. It was found that this MI simulation provides accurate solutions at a significantly shorter computation time than conventional CFD analysis.

Effects of Changes in Lung Volume on Oscillatory Flow Rate During High‐Frequency Chest Wall Oscillation

The effectiveness of high-frequency chest wall oscillation (HFCWO) in mucolysis and mucous clearance is thought to be dependant on oscillatory flow rate (Fosc). Therefore, increasing Fosc during HFCWO may have a clinical benefit. To examine effects of continuous positive airway pressure (CPAP) on Fosc at two oscillation frequencies in healthy subjects and patients with airway obstruction. Five healthy subjects and six patients with airway obstruction underwent 12 randomized trials of HFCWO (CPAP levels of 0 cm H2O, 2 cm H2O, 4 cm H2O, 6 cm H2O, 8 cm H2O and 10 cm H2O at frequencies of 10 Hz and 15 Hz) within a body plethysmograph, allowing measurements of changes in lung volume. Fosc was measured by reverse plethysmography using a 20 L isothermic chamber near the mouth. At the end of each randomized trial, an inspiratory capacity manoeuvre was used to determine end-expiratory lung volume (EELV). EELV increased significantly (P<0.05) with each level of CPAP regardless of oscillation frequency. Fosc also significantly increased with CPAP (P<0.05) and it was correlated with EELV (r=0.7935, P<0.05) in obstructed patients but not in healthy subjects (r=0.125, P=0.343). There were no significant differences in perceived comfort across the levels of CPAP. Significant increases in Fosc with CPAP-induced increases in lung volume were observed, suggesting that CPAP may be useful as a therapeutic adjunct in patients who have obstructive airway disease and who require HFCWO.

Discussions on Accuracy of Modified KDP Method Applied to Simulataneous Measurements of Unsteady Flow Rates, Pressures and Impedances for Pulsating Oil Flows in a Pipe

When a liquid flow in a pipe is accelerated or decelerated, a differential pressure is kinetically induced between two separate sections of the liquid column. This fact has been utilized to measure an unsteady flow rate, and that way of measurement is called “Kinetic Differential Pressure (KDP) Method”. In the present paper, the KDP method is modified so as to find oscillatory flow rates, pressures and hydraulic impedances simultaneously at any section in pulsating pipe flows of oil from the pressure data detected at two fixed sections of the pipe. Through being applied to measurements of impedances of a pipe with a closed end and a Helmholtz resonator, the modified KDP method has proved effective enough for pratical use. In actual measurements, it turned out more recommendable from the viewpoint of accuracy to employ differential pressures obtained by electrical subtraction between outputs of the two pressure transducers than to rely upon pressure data alone.

State-of-the-art computer code RELAP5 validation with RBMK-related separate phenomena data

Validation of the RBMK model, developed by employing best estimate system computer code RELAP5 is performed by employing the data from NPPs operation or from integral and separate effects facilities. Validation of the models on the basis of separate phenomena is necessary to perform due to the fact that RELAP5 code has been developed for PWRs, which operate at different conditions (pressure, temperature, coolant void fraction, etc.) from RBMKs. In addition to that, there is a number of phenomena specific for RBMK type reactors (oscillatory flow rate behaviour in parallel channels, flow stagnation in channels, stratification in long horizontal piping, etc.), which have not been studied during RELAP5 validation for PWRs. In the paper, RELAP5 models for separate effects related to RBMK-1500 are presented and modelling of transients is performed. Obtained results are compared with experimental data.

マイクロフローセンサを用いた管内一点の流速からの気体の振動流量計測

マイクロフローセンサを用いた管内一点の流速からの気体の振動流量計測

A Measurement of the Bi-directional Oscillatory Flow Rate by Using a Drag Force on Circular Drag Plates

A Measurement of the Bi-directional Oscillatory Flow Rate by Using a Drag Force on Circular Drag Plates

Yeast cell microfiltration: Flux enhancement in baffled and pulsatile flow systems

The filtration performance of yeast cell harvesting was greatly improved by using an oscillatory flow mixing technique in both tubular and flat sheet membrane systems; flux increases of several fold were achieved. The effects of various operating parameters such as frequency, amplitude and ratio of net forward flow rate to oscillatory flow rate were investigated. A simple alternative to the dual head pump, which involved the use of solenoid valves for producing flow reversal, was developed. The flux was significantly increased using this new operating mode. As the only increase of power consumption was from inertia loss due to change of flow direction the additional power consumption is minimal.

Lung hyperinflation in isolated dog lungs during high-frequency oscillation

To study the phenomenon of lung hyperinflation (LHI), i.e., an increase in lung volume without a concomitant rise in airway pressure, we measured lung volume changes in isolated dog lungs during high-frequency oscillation (HFO) with air, He, and SF6 and with mean tracheal pressure controlled at 2.5, 5.0, and 7.5 cmH2O. The tidal volume and frequency used were 1.5 ml/kg body wt and 20 Hz, respectively. LHI was observed during HFO in all cases except for a few trials with He. The degree of LHI was inversely related to mean tracheal pressure and varied directly with gas density. Maximum expiratory flow rate (Vmax) was measured during forced expiration induced by a vacuum source (-150 cmH2O) at the trachea. Vmax was consistently higher than the peak oscillatory flow rate (Vosc) during HFO, demonstrating that overall expiratory flow limitation did not cause LHI in isolated dog lungs. Asymmetry of inspiratory and expiratory impedances seems to be one cause of LHI, although other factors are involved.

振動流量計測法の一提案

振動流量計測法の一提案

Effective pulmonary ventilation with small-volume oscillations at high frequency.

At high oscillation frequencies (4 to 30 hertz), effective alveolar ventilation can be achieved with tidal volumes much smaller than the anatomic dead space. An explanation of this phenomenon is given in terms of the combined effects of diffusion and convection and in terms of data consistent with the hypothesis. Theory and experimental results both show that the significant variable determining the effectiveness of gas exchange is the amplitude of the oscillatory flow rate independent of the individual values of frequency and stroke volume.

Finite Element Analysis of Cascade Flow with Oscillatory Flow Rate

Finite Element Analysis of Cascade Flow with Oscillatory Flow Rate