Flow Rate Modulation Research Articles

Sensing signal augmentation by flow rate modulation of carrier gas for accurate differentiation of complex odours

ABSTRACT For olfactory sensors, clear differentiation of complex odour samples requires diverse information. To obtain such information, hardware modifications, such as introducing additional channels with different physical/chemical properties, are usually needed. In this study, we present a new approach to augmenting the sensing signals of an olfactory sensor by modulating the flow rate of the carrier gas. The headspace vapour of complex odours is measured using a sensing system of nanomechanical sensor (Membrane-type Surface stress Sensor, MSS). The resulting data set is quantitatively evaluated using the Davies-Bouldin index (DBI) of principal component analysis (PCA). The increasing number of sensing signals obtained at different gas flow rates leads to a decrease in the DBI, achieving better cluster separation between different odours. Such gas flow effects can be attributed to several factors, including the sample evaporation and the equilibrium of the gas-liquid and gas-solid interfaces. Proton-transfer-reaction time-of-flight mass spectrometry (PTR-TOF-MS) experiments reveal that the compositions of odour samples vary with the different gas flow rates. It is demonstrated that a simple technique for modulating gas flow rates can significantly improve the differentiation performance of complex odours, providing an additional degree of freedom in olfactory sensing.

Effect of Flow Rate Modulation on Alginate Emulsification in Multistage Microfluidics.

The encapsulation of stem cells into alginate microspheres is an important aspect of tissue engineering or bioprinting which ensures cell growth and development. We previously demonstrated the encapsulation of stem cells using the hanging drop method. However, this conventional process takes a relatively long time and only produces a small-volume droplet. Here, an experimental approach for alginate emulsification in multistage microfluidics is reported. By using the microfluidic method, the emulsification of alginate in oil can be manipulated by tuning the flow rate for both phases. Two-step droplet emulsification is conducted in a series of polycarbonate and polydimethylsiloxane microfluidic chips. Multistage emulsification of alginate for stem cell encapsulation has been successfully reported in this study under certain flow rates. Fundamental non-dimensional numbers such as Reynolds and capillary are used to evaluate the effect of flow rate on the emulsification process. Reynolds numbers of around 0.5-2.5 for alginate/water and 0.05-0.2 for oil phases were generated in the current study. The capillary number had a maximum value of 0.018 to ensure the formation of plug flow. By using the multistage emulsification system, the flow rates of each process can be tuned independently, offering a wider range of droplet sizes that can be produced. A final droplet size of 500-1000 µm can be produced using flow rates of 0.1-0.5 mL/h and 0.7-2.4 mL/h for the first stage and second stage, respectively.

Programmable Low-Pressure Chromatographic Sub-90 s Assay of Parabens in Cosmetics with Post-Column Chemiluminescence Detection

This work describes a new programmable low-pressure chromatography method with post-column chemiluminescence (CL) detection for the rapid and cost-effective determination of four parabens in cosmetic products. Elution of the target analytes was achieved using a programmable mobile phase prepared by implementing a linear solvent gradient protocol based on appropriate flow rate modulation of 2 MilliGAT pumps. A 5 mm monolithic C18 column was used to separate the parabens. Post-column reaction of the eluted parabens with an acidic Ce(IV)-rhodamine 6G (Rho 6G) medium was carried out by introducing a flow stream of the reactants into the column eluate. The light generated from the CL reaction was detected with a flow-through CL detector fabricated in-house. The whole sequence of operations (including sample injection, generation of the mobile phase, addition of the post-column reaction reagents and signal acquisition) was under full computer control. Various operational parameters (the mobile phase composition and gradient conditions, the CL reagents’ concentrations and flow rates and the length of the reaction coil) were studied. The method was validated and applied to the analysis of various cosmetic products. The proposed approach allows sub-90 s separation of the four parabens and their determination with a limit of quantification of 0.2 μg L−1 with a sample throughput of 24 samples h−1. In addition, the method is economical, makes use of low-cost low-pressure components, is fully automated and produces a low amount of waste.

Air-Pinch PWM Valve to Regulate Flow Rate of Hollow-Cone Nozzles for Variable-Rate Sprayers

Highlights Air-pinch PWM valve was investigated as an alternative to electric PWM valves to manipulate hollow-cone nozzles. Air-pinch and electric PWM valves performed comparable accuracy in flow rate modulations. Droplet sizes from hollow-cone nozzles with both PWM valves were comparable across DUCs ranging from 20% to 100%. Air-pinch PWM valve had great potential of use due to its capacity to isolate the internal parts of the valve from chemicals. Abstract. Electric pulse width modulation (PWM) solenoid valves are commonly used to regulate nozzle flow rates to achieve precision variable-rate spray applications. However, some pesticide formulations, such as wettable powders and adhesive additives, can potentially cause a malfunction such that the valve cannot completely shut off during flow rate modulation if spray lines are not cleaned thoroughly after spray applications. An air-pinch PWM valve was evaluated as a potential alternative to conventional PWM valves to modulate the flow rates of hollow-cone nozzles used on air-assisted orchard sprayers. With the air-pinch valve, spray mixtures only passed through a flexible tube to avoid chemicals directly contacting the moving components inside the valve chamber. The flow rate modulation was performed by pinching and releasing the tube back and forth with air-pilot PWM actions. Evaluations included the flow rate modulation capability along with droplet size distributions from three disc-core hollow-cone nozzles coupled with the PWM pinch valve and compared with a conventional electric PWM valve. Both air-pinch and electric PWM valves performed comparably in the flow rate modulation accuracy and droplet size distribution for hollow-cone nozzles operated at 414 and 827 kPa pressures across the duty cycles (DUCs) ranging from 10% to 100%, except for the air-pinch valve that could not activate at 10% DUC. The flow rates of nozzles modulated with both PWM valves at all DUCs were 5.3% greater on average than the target flow rates, while the flow rates were similar at 90% and 100% DUCs. Droplet size classifications based on ASABE Standard S-572.3 were generally consistent across DUCs ranging from 20% to 100% for the same nozzle and pressure with the air-pinch PWM valve and from 10% to 100% with the conventional electric PWM valve. The consistency of droplet sizes across DUCs and accuracy of flow rate modulations demonstrated the potential advantage of using the air-pinch PWM solenoid valve as an alternative for precision variable-rate sprayers to accurately apply different chemicals. Keywords: Droplet size, Flow rate control, Pesticide, Pinch valve, Precision farming, Pulse width modulation.

Assessment of PWM Solenoid Valves to Manipulate Hollow-Cone Nozzles with Different Modulation Frequencies

HighlightsTwelve industrial PWM valves were investigated to manipulate high-pressure agricultural hollow-cone nozzles.Modulation frequencies ranged between 5 and 50 Hz and duty cycles between 10% and 100%.Upstream and downstream pressure profiles were used to determine maximum duty cycle ranges.Two out of 12 PWM valves could be potentially used for future variable-rate orchard sprayer designs.Abstract. Integration of high-speed pulse-width-modulation (PWM) solenoid valves into variable-rate orchard sprayers is needed to accurately regulate spray outputs for matching changes in plant canopy structure characteristics. Capability of 12 PWM valves to modulate hollow-cone nozzles for variable-rate applications was investigated with PWM frequencies of 5 to 50 Hz and duty cycles of 10% to 100%. The PWM valves were assembled on a laboratory spray system with a hollow-cone disc-core nozzle of 2.84 L min-1 flow capacity operated at 1380 kPa pressure. The upstream and downstream pressures on the PWM valves were recorded and analyzed to determine the maximum functional duty cycle ranges and maximum PWM frequency at which the PWM valves could manipulate the nozzle functionally. Test results showed that there were noticeable differences in the modulation capability among the 12 PWM valves due to their design differences. Two out of 12 valves were able to manipulate the hollow-cone nozzles with duty cycles ranging from 30% or 40% to 70% at the modulation frequency of 40 Hz. These two PWM valves performed the highest capability among the 12 valves to manipulate the hollow-cone nozzle. As a result, these two valves would be selected for future investigations on their flow rate modulation accuracy and droplet size distributions before they could be recommended for adaptation in the variable-rate orchard sprayers. Keywords: Duty cycle, Flow control, Orchard sprayer, Pesticide, Precision farming, Pulse width modulation.

Thermoacoustic instability and flame transfer function in a lean direct injection model gas turbine combustor

This paper discusses the combustion dynamic characteristics of hydrogen/methane flames and the flame response to fuel flow fluctuation in a model lean-direct injection gas turbine combustor. The results show that a higher frequency longitudinal thermoacoustic instability is triggered as hydrogen/methane ratios increase. The mode shift is accompanied by shortening flame length and hence decreasing convection time delay between fuel injection and flame location. The flame transfer function (FTF) subject to fuel flow rate modulation is determined over a range of frequencies for hydrogen/methane volume ratios of 25:75, 50:50, and 75:25 at a fixed equivalence ratio of 0.55. The input and output of the FTF are the velocity fluctuation of fuel-mixture at the inlet of the burner and the heat release fluctuation of flame in the combustion zone, respectively. Because of the difficulty of measuring fuel flow velocity at the inlet of the combustor while the flame exists, the fuel transfer function (FLTF) is measured and used along with the intermediate flame transfer function (ITF) to determine the FTF. The transfer functions are measured at frequencies up to 600 Hz and the FTF above 600 Hz is determined from the flame response at higher harmonic frequencies. Results of the FLTF measurement show that an acoustic resonance is formed within the fuel injector and the resonance frequency changes with the hydrogen/methane ratio as well as the length of the fuel feedline. The gain of FTF at a given frequency decreases as the hydrogen content increases and the absolute value of the slope of the phase plot, which is related to the convection time delay between fuel injector tip and flame location, decreases as the hydrogen enrichment ratio increases. Using the measured FTF as input to an open-source simulator, the occurrence of instability is predicted and compared with experimental results. The modeling results agree very well with the experimental data in predicting the occurrence of unstable combustion, the frequency at which unstable combustion occurs, and the acoustic mode inside the combustor.

Flutter instability in an internal flow energy harvester

Abstract

Amplitude modulated flow analysis for speciation—Proof of concept by quantification of Fe2+ and Fe3+ ions

We propose a novel concept of flow-based analysis for spectrophotometric speciation based on flow rate modulation and fast Fourier transform (FFT). A redox reagent solution's and a sample solution's flow rates are varied by sinusoidal control signals with periods of T and 0.5T, respectively. Both solutions are merged with a color reagent, while the total flow rate is held constant. Downstream, the absorbance of the mixed solution is measured and acquired as the detector output voltage (Vd). The Vd is analyzed by FFT with the window's time length of T. One species that directly reacts with the color reagent contributes only to the amplitude (A2) of the second harmonic wave component in Vd. The other species that needs the redox conversion before the coloration contributes to the amplitude (A1) of the fundamental wave component, in addition to A2. The former species+' concentration can be estimated from A2 by taking the latter's contribution to A2 into account. The latter species’ concentration can be determined only from A1. The proposed concept was demonstrated by applying it to the speciation of Fe2+ and Fe3+ by an o-phenanthroline spectrophotometry, where Fe3+ was reduced to Fe2+ by L-ascorbic acid before the coloration.

Finger instability of oscillating liquid–liquid interface in radial Hele-Shaw cell

The dynamics of the interface between two immiscible liquids with a high viscosity contrast is studied experimentally when the liquids are pumped through a radial Hele-Shaw cell. Two cases are considered: a monotonous radial displacement of the viscous fluid, when the classical Saffman–Taylor instability develops, and an oscillatory interface motion due to harmonic flowrate modulation in the absence of the average displacement flow. At small amplitudes of flowrate modulation, the interface performs axisymmetric radial oscillations, maintaining the ring shape during the entire period, while with an increase in the amplitude, it loses stability in a threshold manner. In the phase of fluid displacement, finger instability develops at the interface in the form of an azimuthally periodic structure during a fraction of the period. Fingers reach the greatest length in the phase of maximum fluid displacement, while in the contraction phase (maximum displacement toward the cell center), the interface restores its concentric shape. The threshold for the occurrence of finger instability is determined by the relative amplitude of interface oscillations and under conditions of high contrast of viscosities (one liquid oscillates following the “viscous” law and the other obeys the “inviscid” law) coincides at different oscillation frequencies and different average radii of the interface. The discovered type of instability is new and is studied for the first time. A comparison of the wavelengths of the pulsating fingers with the well-known case of continuous displacement of a viscous fluid in a Hele-Shaw cell indicates that the Saffman–Taylor instability mechanism underlies the observed phenomenon.

Optimal rule-based control for the management of thermal energy storage in a Canadian solar district heating system

Solar district heating systems are a promising solution to facilitate the adoption of large-scale, solar energy-based technologies. Thermal energy storage devices could also play an instrumental role to manage the mismatch between solar energy resources and community heating loads; however, controlling such systems is no easy task. In this paper, a novel heuristic reactive control strategy is developed to properly manage the thermal energy storage capacity, at both the short-term and the long-term, in a Canadian solar district heating system (the Drake Landing Solar Community). This strategy targets the optimization of: (a) the temperature difference across solar collectors and (b) the flow rate modulation of the variable speed pump linking the short-term and the seasonal thermal energy storage devices. A simulation is used to compare this new control approach with the conventional control strategy currently in place. Results are assessed for the year 2017–18 in terms of energy, cost and greenhouse gas emissions. Despite a 10% increase in natural gas consumption, electricity use was decreased by 43%; reductions of 34% and 29% were respectively achieved in terms of energy cost and GHG emissions.

Volume velocity in a canine larynx model using time‑resolved tomographic particle image velocimetry.

In the classic source-filter theory, the source of sound is flow modulation. "Flow" is the flow rate (Q) and flow modulation is dQ/dt. Other investigators have argued, using theoretical, computational, and mechanical models of the larynx, that there are additional sources of sound. To determine the acoustic role of dQ/dt in a tissue model, Q needs to be accurately measured within a few millimeters of the glottal exit; however, no direct measures of Q currently exist. The goal of this study is to obtain this waveform in an excised canine larynx model using time-resolved tomographic particle image velocimetry. The flow rate data are captured simultaneously with acoustic measurements to determine relations with vocal characteristics. The results show that glottal waveform characteristics such as maximum flow declination rate are proportional to the subglottal pressure, fundamental frequency, and acoustic intensity. These findings are important as they use direct measurements of the volume flow at the glottal exit to validate some of the assumptions used in the source-filter theory. In addition, future work will address the accuracy of indirect clinical measurement techniques, such as the Rothenberg mask.

Improvement of the interfaces in AlGaN/AlN superlattice grown by NH3 flow-rate modulation epitaxy

AlGaN/AlN superlattices (SLs) are key building blocks for vertical emitting devices, especially in the deep UV spectral range. Abrupt interfaces of 30-pair AlGaN/AlN (6.6 nm/3.3 nm) SLs with an average Al composition of 55.3% have been grown by NH3 flow-rate modulation epitaxy (FME). The interface and surface morphology can be largely improved using this growth technique due to enhancement of the surface migration of Al atoms. Moreover, basal stacking faults at the interfaces are observed by high resolution transmission electron microscopy. A stress relieving model has been proposed to explain the forming of BSFs.

The Relationship Between Blood Flow and Motor Unit Firing Rates in Response to Fatiguing Exercise Post-stroke.

We quantified the relationship between the change in post-contraction blood flow with motor unit firing rates and metrics of fatigue during intermittent, sub-maximal fatiguing contractions of the knee extensor muscles after stroke. Ten chronic stroke survivors (>1-year post-stroke) and nine controls participated. Throughout fatiguing contractions, the discharge timings of individual motor units were identified by decomposition of high-density surface EMG signals. After five consecutive contractions, a blood flow measurement through the femoral artery was obtained using an ultrasound machine and probe designed for vascular measurements. There was a greater increase of motor unit firing rates from the beginning of the fatigue protocol to the end of the fatigue protocol for the control group compared to the stroke group (14.97 ± 3.78% vs. 1.99 ± 11.90%, p = 0.023). While blood flow increased with fatigue for both groups (p = 0.003), the magnitude of post-contraction blood flow was significantly greater for the control group compared to the stroke group (p = 0.004). We found that despite the lower magnitude of muscle perfusion through the femoral artery in the stroke group, blood flow has a greater impact on peripheral fatigue for the control group; however, we observed a significant correlation between change in blood flow and motor unit firing rate modulation (r2 = 0.654, p = 0.004) during fatigue in the stroke group and not the control group (r2 = 0.024, p < 0.768). Taken together, this data showed a disruption between motor unit firing rates and post-contraction blood flow in the stroke group, suggesting that there may be a disruption to common inputs to both the reticular system and the corticospinal tract. This study provides novel insights in the relationship between the hyperemic response to exercise and motor unit firing behavior for post-stroke force production and may provide new approaches for recovery by improving both blood flow and muscle activation simultaneously.

High-repetition-rate burst-mode-laser diagnostics of an unconfined lean premixed swirling flame under external acoustic excitation.

Lean premixed swirling flames are important in practical combustors, but a commonly encountered problem of practical swirl combustors is thermo-acoustic instability, which may cause internal structure damage to combustors. In this research, a high-repetition-rate burst-mode laser is used for simultaneous particle image velocimetry and planar laser-induced fluorescence measurement in an unconfined acoustically excited swirl burner. The time-resolved flow field and transient flame response to the acoustic perturbation are visualized at 20 kHz, offering insight into the heat release rate oscillation. The premixed mixture flow rate and acoustic modulation are varied to study the effects of Reynolds number, Strouhal number, and acoustic modulation amplitude on the swirling flame. The results suggest that the Strouhal number has a notable effect on the periodic movements of the inner recirculation zone and swirling flame configuration.

Enhanced p-type conduction in AlGaN grown by metal-source flow-rate modulation epitaxy

A metal-source flow-rate modulation epitaxy method is reported to enhance the hole concentration of Mg-doped AlGaN grown by metal organic chemical vapor deposition. The hole concentration of p-type AlGaN (Al content 0.43) is increased to 2.3 × 1017 cm−3 at room temperature by this method, which is about ten times higher than that of the conventional growth. The resistivity was found to be as low as 12.7 Ω·cm. Furthermore, the effective acceptor activation energy (EA) in the AlGaN films (Al content 0.32–0.43) was determined to be 20–22 meV, several times smaller than EA in p-GaN. Secondary ion mass spectroscopy measurements demonstrated that uniformly Mg-doped AlGaN structures with spatially modulated Al compositions were formed using this technique. It is suggested that the enhancement of hole concentration benefits from the modulation of the valence band edge.

CO2 Conversion Enhancement in a Periodically Operated Sabatier Reactor: Nonlinear Frequency Response Analysis and Simulation‐based Study

AbstractConversion of CO2 into synthetic CH4 via thermocatalytic hydrogenation (the Sabatier reaction), has recently gained increasing interest as a possible route for CO2 utilization and energy storage pathway. Herein, we analyze the possibility of increasing the CO2 conversion through periodic operation of the reactor. The analysis is performed by using the Nonlinear Frequency Response (NFR) method, a recently developed analytical technique, suitable for fast evaluation of periodic reactor operations. The NFR analysis predicts a significant conversion gain (up to 50 %) for certain frequencies of the feed flow rate modulation. This prediction is validated by numerical simulations with a reaction rate expression obtained by CO2 conversion experiments using a Ni/Al2O3 catalysts. Both the NFR analysis and numerical simulations predict that it is possible to obtain 70 % CO2 conversion at 500 K, 5 bar, and average space velocity of 7600 h−1 by a periodic modulation of the feed flow rate, as compared to the corresponding steady state CO2 conversion of 43 %.

The Effects of Tooth Brushing on Whole Salivary Flow Rate in Older Adults.

Objectives (1) To determine whether manual (MTB), or electric, tooth brushing (ETB) modulates whole salivary flow rate in older adults who are free of systemic disease. (2) To determine the duration of the brushing-related modulation of salivary flow rate. (3) To compare salivary flow rate modulation associated with MTB and ETB. Method Twenty-one adults aged 60 years and older participated in two experimental sessions during which they used a manual, or electric, toothbrush to brush their teeth, tongue, and palate. Whole salivary flow rates were determined using the draining method before, during, and after brushing. Differences in salivary flow rates across time periods, and between conditions, were examined using paired samples t-tests applying a Holm-Bonferroni sequential procedure (pcorr < 0.0045). The relationship between tooth brushing and age with respect to maximum salivary flow rate increase was examined using Pearson's correlation coefficient (p < 0.05). Results/Conclusion Whole salivary flow rates increased during, and for up to 5 minutes following, tooth brushing in adults aged 60 years and older who were free of systemic disease. The salivary effects of MTB and ETB were not significantly different. A moderate, positive correlation was observed between tooth-brushing-related maximum salivary flow rate increase and age.

Surface supersaturation in flow-rate modulation epitaxy of GaN

Hillocks on N-face GaN (0001¯) films are effectively eliminated by group-III-source flow-rate modulation epitaxy (FME), wherein the flow-rate of group-III sources are sequentially modulated under a constant supply of NH3. A hillock-free smooth surface obtained by group-III-source FME is attributed to the enhancement of step-flow growth. We found that a hillock originates from a micropipe and grows by spiral growth around the micropipe. The spiral growth rate rapidly decreases with decreasing the degree of surface supersaturation σ, while the step-flow growth rate decreases linearly. For group-III-source FME, wherein σ is lower than conventional continuous growth, the spiral growth rate could be lower than the step-flow growth one so that the formation of hillocks is suppressed.

Growth of InGaAs nanowires on Ge(111) by selective-area metal-organic vapor-phase epitaxy

We report the growth of InGaAs nanowires (NWs) on Ge(111) substrates using selective-area metal-organic vapor-phase epitaxy (SA-MOVPE) for novel InGaAs/Ge hybrid complementary metal-oxide-semiconductor (CMOS) applications. Ge(111) substrates with periodic arrays of mask opening were prepared, and InGaAs was selectively grown on the opening region of Ge(111). A uniform array of InGaAs NWs with a diameter around 100nm was successfully grown using appropriate preparation of the initial surfaces with an AsH3 thermal treatment and flow-rate modulation epitaxy (FME). We found that optimizing partial pressure of AsH3 and the number of FME cycles improved the yield of vertical InGaAs NWs. Line-scan profile analysis of energy dispersive X-ray (EDX) spectrometry showed that the In composition in the InGaAs NW was almost constant from the bottom to the top. Transmission electron microscope (TEM) analysis revealed that the interface between InGaAs NW and Ge had misfit dislocations, but their distance was longer than that expected from the difference in their lattice constants.

N-face GaN films with hillock-free smooth surfaces grown by group-III-source flow-rate modulation epitaxy

N-face GaN films were grown by group-III-source flow-rate modulation epitaxy (FME), wherein the flow-rate of group-III sources are sequentially modulated under a constant supply of NH3. By using GaN bulk substrates with a low misscut angle (∼0.3°), hillock-free N-face GaN surfaces are achieved over almost the whole sample area (10 × 5 mm2). A smooth surface with the root mean square roughness of 0.39 nm exhibits the step-and-terrace structure. Group-III-source FME also reduces carbon impurities in the films, resulting in weakened blue and yellow deep emissions in the photoluminescence spectrum.