Resonance Tube Research Articles

Study of Quality and Damping Factor at First and Second Resonance of Closed Organ Pipe

The quality factor is a dimensionless physical quantity related to the damping factor present in the medium. The sound is recorded from the resonance tube experiment at the first and second resonating lengths. It is analyzed by PRAAT software to calculate the quality and damping factor. The quality factor varies from 12.50 to 146.70 and 6.32 to 130.95 at first and second resonant length respectively. In case of damping factor, it varies from 3.50x10−3 to 40.00x10−3 and 3.82 x10−3 to 79.11x10−3 at respective first and second resonating length. The ratio of the quality factor of the second resonance to that first resonance varies from 0.49 to 0.97 and for the damping factor that ratio varies from 1.02 to 2.02. The quality factor is higher at the first resonating length than at the second resonating length. The damping factor is lower in the first resonating length than in the second resonating length. From the experiment on the closed organ pipe, it was found that the system is under-damped due to the damping factor of less than one. At the first and second resonating lengths the relation between quality and damping factor is inversely nature.

Parallel dual tuning forks for quartz-enhanced photoacoustic spectroscopy

A recently introduced approach to photoacoustic detection of trace gases utilizing dual quartz tuning forks (D-QTFs) in parallel is described in detail. It investigates the sound vibration mode that is optimal for a small acoustic module. The acoustic module was optimized using COMSOL multiphysics software. The D-QTFs sensor and a half-size resonator module platform were adopted to enhance signal strength. The advantages of the technique compared to the normal QEPAS sensor are that it uses a single resonator tube but realises a 1.25-times signal enhancement. Water vapour was chosen as the target analyte. The achieved noise of 1σ is 1.268 µV compared to the QEPAS noise of 1.196 µV. The presence of parallel forks leads to a decrease in reaction time of ∼17 %. The results of this investigation revealed that a reduced chamber volume and rapid response led to a more pronounced signal response. The sensor's performance can be further enhanced by increasing the laser power and the optical path length. It is widely used in fields with volume constraints.

Highly sensitive temperature sensor using nested hollow-core anti-resonant fibers

A highly sensitive temperature sensor based on composite nested negative curvature hollow-core fiber is proposed. Three resonant tubes are nested inside the cladding tubes to induce a resonant coupling between the fundamental core mode and the dielectric mode of the nested resonant tube. Three glass-sheet conjoined nested tubes are introduced to suppress the comparatively low loss higher-order mode LP02. All the air-holes are filled with temperature-sensitive liquid of ethanol. As the temperature changes, the resonant dip in the transmission spectrum corresponding to the coupling will shift. Numerical simulation results indicate that the temperature sensitivity is 3.36 nm °C−1 in the range of 20 °C–40 °C. Since there is no need of any special post-processing, such as selective infiltration or material coating for the sensors proposed, the sensor provides a promising mechanism for the optical fiber temperature sensing.

Numerical and experimental investigations on coiled resonance tube of a duplex Stirling cryocooler

Duplex Stirling cryocooler is promising in mitigating methane emission due to its environmentally-friendly working gas, high thermal efficiency and high adaptivity to varying methane concentration. In this work, a coiled resonance tube is introduced to supplant the conventional straight tube in a resonance tube coupled duplex free-piston Stirling cryocooler (RT-DFPSC) to reduce footprint and elevate power density. At first, an experimental setup was built employing resistance-compliance acoustic load to produce the analogical acoustic field. It was observed from experiments that on a coiled resonance tube, an acoustic power transfer efficiency of 35% was obtained. Based on the experiments, a three-dimensional computational fluid dynamics (CFD) model was subsequently developed to pinpoint the loss mechanism. Due to the interaction of centrifugal, viscous and inertial force, there are two secondary flow vortices in the cross-section of the coiled resonance tube during the reversing flow, accounting for the primary loss. Furthermore, the acoustic loss of the coiled resonance tube increases with the decrease of the coiled diameter, while the spiral pitch has minimal effect on the acoustic and flow field. Typically, the acoustic loss of a coiled resonance tube with a diameter of 0.8 m increases by approximately 9% compared to that of a straight tube. Finally, a one-dimensional equivalent model of the coiled resonance tube was established and integrated into a one-dimensional system-level model. Compared to the straight RT-DFPSC, a system with a coiled tube resonance tube demonstrates a cooling capacity and overall exergy efficiency reduction by 465.2 W and 2.4%, respectively.

Analysis of non-linear losses in a parallel plate thermoacoustic stack

PurposeThis study aims to analyse the non-linear losses of a porous media (stack) composed by parallel plates and inserted in a resonator tube in oscillatory flows by proposing numerical correlations between pressure gradient and velocity.Design/methodology/approachThe numerical correlations origin from computational fluid dynamics simulations, conducted at the microscopic scale, in which three fluid channels representing the porous media are taken into account. More specifically, for a specific frequency and stack porosity, the oscillating pressure input is varied, and the velocity and the pressure-drop are post-processed in the frequency domain (Fast Fourier Transform analysis).FindingsIt emerges that the viscous component of pressure drop follows a quadratic trend with respect to velocity inside the stack, while the inertial component is linear also at high-velocity regimes. Furthermore, the non-linear coefficient b of the correlation ax + bx2 (related to the Forchheimer coefficient) is discovered to be dependent on frequency. The largest value of the b is found at low frequencies as the fluid particle displacement is comparable to the stack length. Furthermore, the lower the porosity the higher the Forchheimer term because the velocity gradients at the stack geometrical discontinuities are more pronounced.Originality/valueThe main novelty of this work is that, for the first time, non-linear losses of a parallel plate stack are investigated from a macroscopic point of view and summarised into a non-linear correlation, similar to the steady-state and well-known Darcy–Forchheimer law. The main difference is that it considers the frequency dependence of both Darcy and Forchheimer terms. The results can be used to enhance the analysis and design of thermoacoustic devices, which use the kind of stacks studied in the present work.

Determination of gas parameters in resonant pipes and channels of engines with a periodic workflow using the piston analogy method

This paper investigates a process of gas flow in the resonant tube of an engine with a periodic workflow. Analysis of various flow models and comparison of known data have shown that the problems of constructing closed 0-dimensional models of the operating cycle for some types of engines remain unresolved. Given this, the question arises about the dimensionality of models of individual engine elements, including the resonant pipe model, which must be included in the general model of the cycle, especially at the initial stage of its development. To solve the identified problems, a mathematical model of air flow has been improved, built on the basis of an analogy with a '"liquid" piston. Unlike existing ones, the piston analogy model allows one to calculate the instantaneous velocity averaged over the length of the pipe using a numerical solution of the differential equation for velocity. To test the model built, an alternative finite-difference 1-dimensional gas-dynamic model was selected, with the help of which a test simulation of air flow in a pipe was performed. It has been established that the piston model allows one to find the flow velocity with an accuracy of 5 % for a pressure drop varying according to a sinusoidal law. The permissible limits for changes in the oscillation frequency and pipe length were found, at which the piston model has a minimum error. Based on the results of the study, it was concluded that with a small mass and inertia of the liquid piston, the proposed model gives results close to those provided by more complex models with higher dimensionality. This indicates the possibility of using a piston model for elements such as pipes as part of a 0-dimensional thermodynamic model of engines with a periodic operating process as an approximate alternative to traditional 1-dimensional flow models

An Experimental Study of Thermoacoustic Couples

In this study, a simple thermoacoustic refrigerator system experiment set was established by using the design parameters in accordance with the relevant literature. In the experimental setup, a loudspeaker was used as acoustic power source and a suitable frequency value was determined for the system. Three kinds of stack materials with different thermal conductivity coefficients, respectively, mylar, cotton and glass wool were placed in the resonance tube. The temperature values at both ends of the stack material were measured by placed temperature gauges. In the measurements made within the same time period, the temperature differences were measured as 5.2°C for mylar, 4.7°C for cotton and 4.3°C for glass wool, respectively. It was determined that the highest temperature difference was in the mylar material.

Low-frequency Resonant Photoacoustic Gas Sensor by Employing Hollow Core Fiber-Based O-Shaped Multipass Cells.

A low-frequency flexible resonant photoacoustic (PA) gas sensor using an O-shaped multipass cell is demonstrated. The PA sensor employed a flexible gradually tapered leaky hollow core fiber (LHCF). The LHCF was bent to be an end-to-end structure to make full use of the incident light. Additionally, the two ends of the LHCF were put inside a single buffer chamber, yielding an equivalent H-type acoustic resonator. The geometric size was reduced thanks to the bending structure. The geometric length of the LHCF was 500 mm. A micro-electro-mechanical-systems electrical microphone was installed at the center of the resonant tube to detect the PA signal. The proposed PA gas sensor exhibited a first-order longitudinal resonance frequency of 408 Hz. Trace acetylene (C2H2) was used as the target gas. The minimum detectable limit was calculated to be 25.8 parts-per-billion (ppb) with an average time of 400 s, which was 1.93 times higher than that of a single-pass PA gas sensor. The normalized noise-equivalent absorption coefficient and the PA cell constant were calculated to be 9.6 × 10-9 W·cm-1·Hz-1/2 and 8295 Pa/W·cm-1, respectively. The PA gas sensor owns a low resonance frequency and can be used for detection of most of the polar gaseous molecules, especially suitable for gas molecules with a long V-T relation time, such as carbon monoxide and carbon dioxide.

Structural optimization of resonance tubes for a looped thermoacoustic engine with multiple heat sources

The advantage of coupling different heat sources with each thermoacoustic core unit in a three-stage looped traveling-wave thermoacoustic system is used to solve the application problem of multiple waste heat sources. The effects of the heat-side heat exchanger temperature, the resonance tube radius and length, and their interaction terms on the thermoacoustic thermodynamic properties are analyzed using response surface methodology on the premise that thermoacoustic core structures remain unchanged. The results indicate that prediction deviations for acoustic power, thermoacoustic conversion efficiency, and relative Carnot efficiency are within ±9%, ±3%, and ±3%, respectively. The acoustic power can be improved by increasing the hot-side heat exchanger temperature and the resonance tube radius. Under the same heat source conditions, the acoustic power, thermoacoustic conversion efficiency, and relative Carnot efficiency of the optimized thermoacoustic system show the highest increases of 49.63%, 4.82%, and 3.20%, respectively, compared to the non-optimized thermoacoustic system. The optimized variable-temperature system not only has higher thermodynamic efficiency compared with the optimized constant-temperature system but also can realize the complementary regulation among the thermoacoustic engine units by matching decreasing-gradient variable temperature and increasing-gradient variable radii and effectively broaden the working temperature range of the looped thermoacoustic system.

Design of a negative curvature hollow-core fiber for transmitting a single-mode dark hollow beam

We propose a nested negative curvature hollow-core fiber that can stably transmit a single-mode (LP11 mode) dark hollow beam with low loss. A pair of resonant tubes is nested inside the cladding tubes in the horizontal direction to enhance the confinement loss of the fundamental mode LP01. Two pairs of glass sheets at different positions within the four cladding tubes in the non-horizontal direction are introduced to suppress the comparatively low loss higher-order modes LP21 and LP02. The numerical simulation results indicate that the loss ratio between the fundamental mode and LP11 mode can reach 28703 when the transmission wavelength is 1.54 µm, and the LP11 mode has the lowest confinement loss of 0.0049 dB/m. Meanwhile, the loss ratios of higher-order modes such as LP21, LP02, and LP31 with the target LP11 mode are above 100. The effective bandwidth of single-mode dark hollow beam transmission can reach 5 nm. This provides an optical fiber solution for single-mode dark hollow beam transmission, which has potential applications in atomic optics, quantum information, and nonlinear optics.

Pengaruh Variasi Jenis Bahan Terhadap Pengurangan Taraf Intensitas Bunyi

Acoustic materials such as plastic carpet, gypsum board, styrofoam and plywood can be used to reduce sound intensity. Nevertheless, the existing research has generally focused on single-ingredient studies. In this research, the optimum thickness of each material will be sought based on its efficiency in reducing the sound intensity level. Besides that, the efficiency of various types of materials will also be tested for reducing the level of sound intensity. In this study, a resonator tube was used in making measurements. Acoustic materials used as test materials, both single materials and combined materials, can be placed in the resonator tube. The distance between the sound source and the detector is 30 cm, with the position of the detector right behind the acoustic material. Tests on a single material show that the measured sound intensity level decreases in proportion to the thickness of the acoustic material, with styrofoam has the lowest efficiency. Meanwhile, the combined material that combines plastic carpet material at a frequency of 2000 Hz has an efficiency value that tends to be higher than the combination of materials without carpet with efficiency >30%. However, at a frequency of 1500 Hz, all combined materials have efficiency values that are not significantly different. All models of material combinations are proven to be able to reduce sound intensity levels compared to single materials. Thus, it can be concluded that the combined material has the potential as an efficient acoustic material.

Optimal cross-sectional area ratio between porous material and resonance tube for the onset of self-excited oscillations in standing-wave thermoacoustic engines

Optimal cross-sectional area ratio between porous material and resonance tube for the onset of self-excited oscillations in standing-wave thermoacoustic engines

Research on an Optimized Quarter-Wavelength Resonator-Based Triboelectric Nanogenerator for Efficient Low-Frequency Acoustic Energy Harvesting.

Sound wave is an extensively existing mechanical wave, especially in marine and industrial plants where low-frequency acoustic waves are ubiquitous. The effective collection and utilization of sound waves provide a fresh new approach to supply power for the distributed nodes of the rapidly developing Internet of Things technology. In this paper, a novel acoustic triboelectric nanogenerator (QWR-TENG) was proposed for efficient low-frequency acoustic energy harvesting. QWR-TENG consisted of a quarter-wavelength resonant tube, a uniformly perforated aluminum film, an FEP membrane, and a conductive carbon nanotube coating. Simulation and experimental studies showed that QWR-TENG has two resonance peaks in the low-frequency range, which effectively extends the response bandwidth of acoustic-electrical conversion. The structural optimized QWR-TENG has excellent electrical output performance, and the maximum output voltage, short-circuit current and transferred charge are 255 V, 67 μA, and 153 nC, respectively, under the acoustic frequency of 90 Hz and sound pressure level of 100 dB. On this basis, a conical energy concentrator was introduced to the entrance of the acoustic tube, and a composite quarter-wavelength resonator-based triboelectric nanogenerator (CQWR-TENG) was designed to further enhance the electrical output. Results showed that the maximum output power and the power density per unit pressure of CQWR-TENG reached 13.47 mW and 2.27 WPa-1m-2, respectively. Application demonstrations indicated that QWR/CQWR-TENG has good capacitor charging performance and is expected to realize power supply for distributed sensor nodes and other small electrical devices.

State of the art of rational design of efficient mufflers

An efficient exhaust muffler needs to satisfy the rather conflicting requirements of adequate insertion loss (IL) with limited back pressure, weight, size and cost. The unmuffled exhaust noise of an internal combustion engine peaks at the engine firing frequency and the first few harmonics thereof. Designing the muffler (a wide-band low pass acoustical filter) for such low frequencies is quite a challenge. Therefore, design of efficient mufflers has remained an art as well as science. During the last two decades or so, however, (a) multi-hole cross-flow perforates, (b) multiply connected perforated pipes and baffles, and (c) the double-tuned, grazing-flow concentric tube resonators have emerged as promising constituent elements. In this paper, elements (a) and (c) have been combined ingeniously to synthesize efficient muffler configuration for diesel generator (DG) sets as well as automotive engines. Relatively simpler lumped parameter approximation for perforates opening into cavities, electro-acoustic analogies, and the simple expansion chamber equivalence of the double-tuned concentric tube resonator have been used to develop a rational design methodology. A novel feature of this methodology is incorporation of the given back-pressure limit into the acoustic design process. The resulting muffler configurations are robust and can be scaled up (and down) easily for IL as well as back pressure.

Immediate effects of a semi-occluded water-resistance ventilation mask on vocal outcomes in women with dysphonia

IntroductionSemi-occluded vocal tract exercises (SOVTEs) are frequently used exercises in voice therapy. An important shortcoming to most SOVTEs is the inability to include continuous speech in these exercises. A variation of water-resistance therapy (WRT), during which a patient phonates through a resonance tube ending in water, was developed to include continuous speech: the semi-occluded water resistance ventilation mask (SOVM-WR). The current study investigated the immediate effects of this innovative technique on vocal outcomes of women with dysphonia. MethodsA pretest-posttest randomized controlled trial was performed. Twenty female participants were randomly assigned to the experimental SOVM-WR group or the WRT (control) group. A blinded multidimensional voice assessment was conducted before and after a 30-minute therapy session with the assigned technique. ResultsNo significant changes were found in acoustic or auditory-perceptual vocal outcomes in either of the groups, except for a significant increase in lowest frequency in both groups. Patient-reported outcomes (PROMs) showed significant improvements of vocal comfort, vocal effort, and voice quality in both groups, and participants indicated that they would use the techniques at home. ConclusionsThe similar results of the SOVM-WR to WRT and promising PROMs confirm its suitability as an alternative to the latter technique. Potential reasons for a lack of improvement of objective and auditory-perceptual vocal outcomes are vocal fatigue, tube dimensions and immersion, and the small sample size. Large-scale and longitudinal research is needed to examine whether the SOVM-WR has a higher transfer to spontaneous speech than WRT after a full therapy program.

Quartz-enhanced photoacoustic spectroscopy (QEPAS) and Beat Frequency-QEPAS techniques for air pollutants detection: A comparison in terms of sensitivity and acquisition time

In this work, a comparison between Quartz Enhanced Photoacoustic Spectroscopy (QEPAS) and Beat Frequency-QEPAS (BF-QEPAS) techniques for environmental monitoring of pollutants is reported. A spectrophone composed of a T-shaped Quartz Tuning Fork (QTF) coupled with resonator tubes was employed as a detection module. An interband cascade laser has been used as an exciting source, allowing the targeting of two NO absorption features, located at 1900.07 cm−1 and 1900.52 cm−1, and a water vapor absorption feature, located at 1901.76 cm−1. Minimum detection limits of 90 ppb and 180 ppb were achieved with QEPAS and BF-QEPAS techniques, respectively, for NO detection. The capability to detect multiple components in the same gas mixture using BF-QEPAS was also demonstrated.

Metamaterial based miniaturized broadband acoustic absorber

A miniaturized, broadband (800–5000 Hz) absorber with >95% absorption is proposed and realized. The absorber is designed using quarter-wavelength resonator tubes coiled as a rectangular “meta-atom.” The study describes the basic theoretical aspects of the absorber and compares it with the numerical simulations, fabrication, and experimental validation. The meta-atom, simple in design and made with fabrication-friendly materials, can provide greater spatial coverage through tiling over large surfaces.

A Simple Approach to Connecting Pt100 by Utilizing an Electroacoustic Resonance Tube

Temperature transducers are frequently employed to keep track of process variables with different kinds of industrial controllers. One of the widely used temperature sensors is Pt100. A novel approach of utilizing an electroacoustic transducer in signal conditioning for Pt100 is proposed in this paper. A "signal conditioner" is a resonance tube filled with air, which is operated in a free resonance mode. The Pt100 wires are connected to one of the leads of the speaker in the resonance tube where the temperature changes, which is related to Pt100 resistance. The resistance affects the amplitude of the standing wave that is detected by an electrolyte microphone. An algorithm for measuring the amplitude of the speaker signal is described, as well as the building and functioning of the electroacoustic resonance tube signal conditioner. The microphone signal is acquired as a voltage using LabVIEW software. A virtual instrument (VI) developed under LabVIEW provides a measure of the voltage using standard VIs. The findings of the experiments reveal a link between the measured amplitude of the standing wave within the tube and the change in Pt100 resistance as the ambient temperature changes. Additionally, the suggested method may interface with any computer system when a sound card is added to it without the need for any extra measuring tools. The maximum nonlinearity error at full-scale deflection (FSD) is estimated at roughly 3.77%, and the experimental results and a regression model are used to assess the relative inaccuracy of the developed signal conditioner. When comparing the proposed approach with well-known approaches for Pt100 signal conditioning, the proposed one has several advantages such as its simplicity of connecting Pt100 to a personal computer directly via the sound card of any personal computer. In addition, there is no need for a reference resistance to perform a temperature measurement using such a signal conditioner.

Experimental investigation on the performance of a novel resonance-assisted ejector under low pressurization

It is of great significance and value to apply different techniques to optimize the entrained performance of an ejector. In this paper, a novel resonance-assisted ejector is proposed by applying a mixing enhancement technique. Experimental studies were conducted to investigate the oscillation effect on the performance of the ejector under different geometries and operating conditions. The results show that adding high-frequency oscillations to the primary flow can provide up to a 14% improvement in entrainment performance. As the length of the resonance tube increases, the performance tends to increase and then decrease. The performance is sensitive to variations in the distance between the nozzle of the resonance generator and the inlet of the resonance tube. The shorter the distance, the greater the performance improvement. The critical pressure ratio of the resonance generator is approximately 5.5. The entrained performance enhancement rate increases gradually over the critical pressure ratio. Entrainment enhancement caused by resonance generator can be eliminated with small mixing cross-sectional areas. The oscillation effect enhances the entrained performance at different backpressures, and the higher the pressure the greater the enhancement rate. This paper provides new ideas for the optimization of ejector performance.

Experimental Investigation of Microcontroller-Based Acoustic Temperature Transducer Systems

Temperature transducers are commonly used to monitor process parameters that are controlled by various types of industrial controllers. The purpose of this study is to design and model a simple microcontroller-based acoustic temperature transducer based on the variations of resonance conditions in a cylindrical resonance tube. The transducer's operation is based on the generation of an acoustic standing wave in the free resonance mode of generation within a cylindrical resonance tube which is converted into a train of pulses using Schmitt trigger circuit. The frequency of the generated standing wave (i.e., the train of pulses) is measured by the Arduino Uno microcontroller, where a digital pin is used to acquire pulses that are counted using a build-in software function in an Arduino IDE environment. Experimental results are performed for three sizes of diameters to investigate the effect of the diameter of resonance tube on the obtained results. The maximum nonlinearity error according to Full-Scale Deflection (FSD) is about 2.3 percent, and the relative error of the transducer is evaluated using experimental findings and the regression model. The circuit simplicity and design of the suggested transducer, as well as the linearity of its measurements, are notable.