Thermoacoustic Effect Research Articles

Cascaded Thermoacoustic amplifier

In this study, we explore the amplification of an incident acoustic wave using the thermoacoustic effect and its applicability for low-temperature energy harvesting. The thermoacoustic effect can be exploited to develop thermoacoustic engines, whose potential for thermal energy harvesting has been extensively studied. In their simplest form, they consist of a porous material inserted in a waveguide, in which a temperature difference is applied and leads to the generation of a thermoacoustic instability. Here, we propose the theoretical and experimental study of an alternative system to the conventional thermoacoustic engine. The system considered here differs from the typical engine in that it exhibits no self-excited instabilities, but only relies on the amplification of an acoustic wave. The experimental set-up consists of a cascaded network of heated porous materials, coupled to an acoustic source and an alternator. This device allows to control several parameters, such as the operating frequency and input power, and it can be designed to achieve a high amplification ratio. Our work offers a new perspective on energy harvesting using the thermoacoustic effect.

Highlighting the effects of gravity in a compact thermoacoustic heat pump

We present a numerical study of gravity impact on thermoacoustic heat pumping effects in a compact cavity used as a refrigeration device. More precisely, we show how gravity acts on the temperature distribution, on the mean temperature heat flux along the stack area and on flow dynamics. Studies are performed in a two-dimensional geometrical configuration which is simplified with respect to common experimental devices but sufficiently detailed to take into account the main physical mechanisms. Fluid motion, heat and mass transfer as well as compression/expansion effects are estimated from the computation of the Navier-Stokes equations in the low-Mach number hypothesis coupled with the heat equation in solid parts. The low-Mach number hypothesis is here relevant because the characteristic scale of the acoustic wavelength is much smaller than the geometrical length scales of the cavity. The operating mode is characterized by a moderate drive ratio, a fluid oscillating motion of moderate amplitude and fixed low frequency, typical of such devices. It is shown that when gravity is included, buoyancy effects modify the temperature and velocity fields as well as heat pumping efficiency.

Nusselt and Reynolds numbers correlation for oscillatory flow of thermoacoustics over heated tube banks

The back-and-forth motion characteristic of the oscillatory flow brings complexity in predicting the heat transfer nature for thermoacoustic wave conditions. Investigating this is crucial as the flow forms the backbone for the thermodynamic cycles of its operation. Often, the steady approximation in calculating heat transfer leads to ambiguity in designing the system. This concern is addressed in this paper via an in-depth analysis of the fluid dynamic behavior and heat transfer characteristics of oscillatory flow within a thermoacoustic framework, spanning experimental works for Reynolds numbers ranging from 300 to 24,000. The investigation focused on a tube bank heat exchanger composed of nine tubes arranged in inline and staggered configurations. Experiments were conducted at constant tube surface temperatures treated at 40 °C and 80 °C, respectively. The distinguishing difference in heat transfer behaviors for oscillatory flow is visualized by the Computational Fluid Dynamics (CFD) models, employing the Reynolds-Averaged Navier Stokes equation with the k-omega turbulence shear stress transport model. The flow never leaves the system, and it cyclically crosses the tubes back and forth with a travel distance that depends on the drive ratio of the flow. The unique nature of the flow forms the foundation for the experimental findings that show a linear relationship between the Nusselt and Reynolds numbers regardless of the configuration of tube banks and tube bank temperature. The Pearson ruler regression analysis was conducted using Matlab R2022b and a Nusselt correlation, Nu = 0.000853RePr⅓, is proposed with a confidence level of 95 %. Notably, the correlation aligns with the constant value known as the Colburn-j factor, with a value of 0.00083. The small Colburn-j value is shown to be the influence of the log-mean temperature difference characteristic of oscillatory flow. It shows a consistent heat transfer process between the heated tubes and surrounding fluid, which is important to sustain the thermoacoustic effect in the system. For future thermoacoustic design, the use of steady heat transfer correlation should be avoided or at least used with caution as the comparative analysis with published works concluded that the Nusselt and Reynolds correlation for steady flow tends to overpredict the heat transfer by two to threefold.

Simulation Analysis of Thermoacoustic Effect of CNT Film with Metasurface-Enhanced Acoustic Autofocusing.

This study introduces a novel thermoacoustic (TA) focusing system enhanced by Airy beam-based acoustic metasurfaces, significantly improving acoustic focusing and efficiency. The system integrates a TA emitter, fabricated from carbon nanotube (CNT) films, with a binary acoustic metasurface capable of generating quasi-Airy beams. Through finite element simulations, the system's heat conduction, acoustic focusing, and self-healing properties were thoroughly analyzed. The results demonstrate that the system achieves superior sub-wavelength focusing, tunable focal length via frequency control, and robust self-healing, even in the presence of obstacles. These findings address current limitations in TA emitters and suggest broader applications in medical ultrasound and advanced technology.

Non-contact defect imaging of carbon fiber composites using laser excited acoustic shearography

The performance of carbon fiber reinforced polymer (CFRP) composites is significantly affected by the presence of subsurface defects, which originate from manufacturing processes or during operations. Although many non-destructive testing (NDT) methods have been employed to inspect CFRP materials and structures, the existing techniques are often time-consuming and sometimes require contact measurement. This paper presents a non-contact and rapid inspection method utilizing laser-excited acoustic shearography to detect subsurface defects in CFRP composites. In this method, a pulsed nanosecond laser is used to generate ultrasonic waves through thermoacoustic effect, and a shearography sensor is used to image the full-field wave-defect interactions. It is found that the proposed method can efficiently image various subsurface defect sizes in a non-contact way. The identified defects were validated through comparison with X-ray computed tomography (XCT).

Study on heat transfer law of moving temperature variable gas in thermoacoustic plate stack

Taking gas and the heat transfer process between gas and plate as the research object, the mathematical model of heat transfer in one working cycle by moving variable temperature air mass under the action of sound field is established, which provides a new idea for understanding thermoacoustic effect. The influence factors in the model are analyzed and it is found that the amplitude of the air mass has a significant influence on the heat transfer, and the heat transfer of the air mass in one working cycle is proportional to the square of the amplitude. In a certain working environment, the thermoacoustic refrigerator has a critical operating frequency, and only when the operating frequency is greater than the critical frequency can refrigeration be realized. The critical operating frequency is independent of the amplitude and increases with the increase of the stack temperature gradient. With the pressure belly point as the reference position, the greater the distance from the reference position, the greater the critical operating frequency. On this basis, the idea of short plate overlapping is put forward and the formation mechanism of temperature difference between two ends of plate overlapping is explained.

Multiphysics analysis of a high-intensity ultrasound system applied to a three-layer animal tissue

High-intensity ultrasound systems for medical therapy must be carefully designed, implemented, and applied to avoid tissue damage or injury considering stimulation and relaxation time, frequency, and intensity of ultrasound. Based on these concerns and considering a test three-layer animal tissue consisting of skin, muscle, and bone, we determined the frequency and intensity at which ultrasound effectively stimulates the test animal tissues. In addition, from these ultrasound frequencies and intensities, and taking care the critical temperature recommended to preserve the integrity of the human tissue and avoid any tissue injury, we determine the stimulation and relaxation times. For this purpose, we performed a multiphysics simulation that describes the spatial and temporal dynamics of the thermoacoustic effect of ultrasound applied to test animal tissues. To practically demonstrate this ultrasound behavior, we perform an experimental setup based on an electronic HITU device designed and implemented to freely adjust the ultrasound intensity and frequency, as well as the stimulation time of the test animal tissues. Finally, we conclude that, depending on the test tissue, an ultrasound therapy system should allow the selection of the intensity and frequency of applied ultrasound, as well as the stimulation time to avoid tissue injury, which can be considered by health ministries around the world.

Погодно-климатический аспект стратегии устойчивого развития экосистем горных территорий

Introduction. The results of an analysis of information about threats to the development of civilization from the consequences of global warming and the effectiveness of projects presented to society to prevent it are presented. Research methods and materials. The method of inductive-deductive content analysis of scientific publications on the problems of global warming and the effectiveness of known methods for adjusting the heat balance of the planet was used. Research results. The high sensitivity of the thermal balance of the earth’s shell to cloud albedo and the complex dependence of cloud albedo on combinations of different types of clouds and on the frequency of cyclone formation have been established. Discussion of research results. Projects presented by various initiative groups to prevent global warming are assessed as unpromising. Conclusions on the article. An alternative method for adjusting cloud albedo is presented based on the use of thermoacoustic instability of atmospheric moisture. The method uses not a material substrate, but a phase of acoustic vibrations to influence the atmosphere. As a result, the use of the method is not accompanied by an increase in the entropy of the terrestrial ecosystem. Suggestions for practical applications and directions for future research. The application of the acoustic method is carried out in the form of remote initiation in the atmosphere of direct and reverse thermoacoustic effects using narrowly directed acoustic radiation from a ground-based installation and is characterized by high scalability, constant readiness for use and the absence of supporting infrastructure.

Frozen sound: An ultra-low frequency and ultra-broadband non-reciprocal acoustic absorber

The absorption of airborne sound is still a subject of active research, and even more since the emergence of acoustic metamaterials. Although being subwavelength, the screen barriers developed so far cannot absorb more than 50% of an incident wave at very low frequencies (<100 Hz). Here, we explore the design of a subwavelength and broadband absorbing screen based on thermoacoustic energy conversion. The system consists of a porous layer kept at room temperature on one side while the other side is cooled down to a very low temperature using liquid nitrogen. At the absorbing screen, the sound wave experiences both a pressure jump caused by viscous drag, and a velocity jump caused by thermoacoustic energy conversion breaking reciprocity and allowing a one-sided absorption up to 95 % even in the infrasound regime. By overcoming the ordinary low frequency absorption limit, thermoacoustic effects open the door to the design of innovative devices.

Monitoring method of phase transition interface for natural gas hydrate based on thermoacoustic effect

In the drilling and exploitation for natural gas hydrate, the decomposition of combustible ices creates the interface between their solid state and liquid state, which would play an important role in the dynamic monitoring while exploitation. In this paper, a monitoring method based on the thermoacoustic effect is proposed to detect the position of the interface. The mechanism of the thermoacoustic coupling is introduced into the natural gas hydrate, that is, the physical model of thermoacoustic effect is established and detailed when the hydrate is excited by a strong electrical pulse. Two kinds of acoustic sources, the thermoelastic source and the phase transition acoustic source, are proposed to explain the obviously enhanced acoustic signals. By modeling and simulating, it is verified that the acoustic signals can be generated by the phase transition around the interface in hydrate. At the same time, many influencing factors on the thermoacoustic signals are researched based on simulations, such as the size of hydrate, the latent heat absorption coefficient and the amplitude of the transient electrical pulse. Finally, the experimental system both for hydrate generation and for thermoacoustic monitoring is built. We prepared carbon dioxide hydrate in a high-pressure reactor at an initial pressure of 5 MPa and temperature of −5 °C. Then take the hydrate into the environment of room temperature and standard pressure, apply the transient electrical pulse to the hydrate and use the ultrasonic probe to detect the acoustic signals. The results show that acoustic signals emitted from the position of the solid-liquid interface can be employed to monitor the hydrate decomposition experimentally and actually.

More silicon-deep in the nanovalley-

Some topics on the studies of nanostructured Si are presented. The emphasis is laid on the unique features of nano-Si systems in relation to Si quantum dots (Si-QDs), nano-textures, and their functional applications (such as hybrid solar cell, hetero epitaxy, pore filling, quasiballistic electron emitter, thermoacoustic effect, and phononics. Focusing on the close relation of Si to human body, nutritional, biometric, and medical importance of nanostructured Si is also addressed.

Pyrolyzed Silk Carbon Fabric-Enabled Wearable Functional Actuators With Heating and Sound-Emitting Capabilities

Textile-based wearable electronics are widely favored by researchers due to their superior comfort. However, there are few studies on textile-based flexible actuators with multiple uses. In this article, a highly flexible actuator with heating and sound-emitting capabilities enabled by pyrolyzed silk carbon fabrics is developed. The functionalized fabrics with ideal physical properties are prepared by a high-temperature reduction method, which is simple and efficient. Its electrothermal and photothermal effects endow the device with heating function. The steady-state temperature can reach 188 °C and 280 °C under 0.80-W/cm2 electricity power density and 1.46-W/cm2 laser power density with high stability, respectively. By taking advantage of thermoacoustic effect, it can also produce intuitive sound messages. Test results show that acoustic properties are in good agreement with theoretical model. The output sound pressure level can be stabilized at about 55 dB in the range of 8–20 kHz under 101-mW power. The actuator carries great potentials in wearable thermal and acoustic applications.

Magneto-thermal-acoustic imaging of magnetic nanoparticles with tissue structure imaging function

Magneto-thermal-acoustic imaging with magnetic nanoparticles (MNPs) is a novel medical imaging modality based on the thermoacoustic (TA) effect of MNPs. We proposed a new dual-modality imaging strategy that combines the TA and echo signals. Based on the synthetic aperture method, we used TA signals to image cancer tissues labeled with MNPs and applied echo signals to achieve tissue structure imaging. In the simulation, we constructed a breast cancer model and assumed that cancer tissue was labeled with MNPs. Under a limited field of view, the TA and echo signals were collected using a multi-element transducer array. By fusing the imaging results of the TA and echo signals, we obtained a boundary distribution map of the breast cancer model, and accurately located the tumor tissue. In this experiment, we built a multi-channel acquisition system. Pork tissue labeled with MNPs was used as the breast cancer phantom. We collected a total of 120 TA and echo signals at 1 mm intervals using a multi-element transducer array and faithfully imaged the boundary distribution map of the phantom. Compared with the traditional linear back projection method based on focused transducers, we demonstrated that the proposed method not only improves the lateral resolution of the image, but also makes accurate cancer identification easier. This provides a promising medical imaging technology for clinical applications.

RESEARCH ON MAGNETICALLY MEDIATED THERMOACOUSTIC IMAGING BASED ON B-SCAN

Magnetically Mediated Thermoacoustic Imaging (MMTAI) is a new imaging technology that uses the thermoacoustic effect of electromagnetic fields. It is capable of a high resolution in ultrasonic imaging and high contrast in electrical impedance imaging. It has considerable potential applications in the early diagnosis of diseases. First, this paper describes the theoretical analysis and numerical simulation of MMTAI. For B-scan thermoacoustic imaging, the thermoacoustic image of a two-dimensional model is simulated and analyzed. The numerical simulation results provide theoretical guidance for the design of the experiment. Second, the B-scan experimental system of MMTAI is designed and built. The imaging experiment was carried out using an imitation gel that contains sodium chloride as the target, and the imaging results were basically consistent with the conductivity distribution of the target. Numerical simulation and physical experiments verify the feasibility of the MMTAI method for low conductivity media. This preliminary study has shown the feasibility of the technique to detect conductivity boundaries, making it relevant for the future application of this method in the field of biomedical imaging.

3D Single-Layer-Dominated Graphene Foam for High-Resolution Strain Sensing and Self-Monitoring Shape Memory Composite.

Flexible intelligent materials are desired to effectively regulate their own deformation and accurately sense their immediate morphology at the same time. Graphene foam is an attractive material for strain sensing and electrical/thermal performance control due to its outstanding mechanical, electrical, and thermal properties. However, graphene-foam-based materials with both strain sensing and deformation control capabilities are rarely reported. Here, a multiscale design of graphene foam with a single-layer-graphene-dominated microstructure and resilient 3D network architecture, which leads to exceptional strain sensing performance as well as modulation ability of the electrical and thermal conductivity for shape memory polymers, is reported. The graphene foams exhibit a strain detection limit of 0.033%, a rapid response of 53ms, long-term stability over 10 000 cycles, significant thermoacoustic effect, and great heat-generation and heat-diffusion ability. By combining these advantages, an electro-activated shape-memory composite that is capable of monitoring its own shape state during its morphing process, is demonstrated.

Performance analysis of thermoacoustic plasma MHD generation

We develop a quasi-one-dimensional theoretical model describing the oscillatory plasma MHD conversion in a channel with parallel electrodes. Based on the model, a thermoacoustic plasma MHD generation system with a looped configuration is proposed and the characteristics of the operation of the system are investigated. Our results show that, for efficient oscillatory MHD generation, the channel dimension of the MHD duct should be much larger than the penetration depth (a proper Womersley number is above 100), otherwise the thermoacoustic effect will play a major role and consume considerable energy. Further, the electromagnetic induction parameter should be larger than 100S⋅T2/m, so that a majority of the kinetic energy of the oscillatory plasma can be harnessed for energy conversion. Moreover, a load ratio between 0.6 to 0.8 is suggested for the presented system, with which an efficiency above 20% can be achieved when the electromagnetic induction parameter is 500S⋅T2/m. In the optimal case, an efficiency of 24% can be obtained, with the corresponding output electricity of 1644 W. These results shed light on the feasibility of the closed-cycle MHD generation without any moving part, which endows the system with advantages of high reliability and long lifetime.

High resolution focused-ultrasound-induced thermoacoustic imaging

We report a new imaging modality, focused-ultrasound-induced thermoacoustic imaging (FUTAI). FUTAI provides high imaging resolution and unique contrast of acoustic absorption and thermodynamic properties of tissue. When a short pulse of the focused ultrasound beam is applied to biological tissue, the tissue will absorb the energy of the incident ultrasound causing a rapid change in local temperature, which leads to thermoelastic expansion and generates acoustic waves. In this work, we investigated this focused-ultrasound-induced thermoacoustic effect through theoretical simulation and experimental validation. A novel imaging modality FUTAI is proposed and demonstrated for the first time. By scanning the focus of the incident ultrasound beam, a 2D or 3D image of tissue properties can be formed. FUTAI provides better resolution compared to traditional B-mode ultrasound imaging, and deeper imaging depth compared to photoacoustic imaging. Additionally, since FUTAI is sensitive to acoustic absorption, it has unique advantages in guiding therapies like high intensity focused ultrasound (HIFU) in which treatment efficiency is determined by the acoustic absorption property. In this work, we also proposed a new method to localize the focus of HIFU with high accuracy using FUTAI. The results indicate that FUTAI has great potential in applications such as noninvasive imaging and therapy guidance.

Analysis of influencing factors of excitation parameters for magnetoacoustic tomography with current injection

Magneto-acoustic tomography with current injection (MAT-CI) is a type of hybrid imaging; under the excitation of the static magnetic field, the thermoacoustic effect and the Lorentz force effect will exist at the same time. Therefore, the detected signal is a mixed signal generated by the simultaneous action of the two effects, but the influence of excitation parameters on the two effects is different. In this paper, for objects with different conductivity, the proportion of thermoacoustic signal (TA) and magneto-acoustic signal (MA) in the mixed signal is quantitatively analyzed in terms of three aspects: the magnetic induction intensity, pulse excitation and injection current polarity. Experimental and simulation analyses show that the intensity ratio of MA to TA is not affected when the conductivity varies from 0.1 S/m to 1.5 S/m and other conditions remain unchanged. When the amplitude of the pulse excitation and the strength of the magnetic induction are different, the growth rates of MA and TA are different, which has a significant impact on the proportion of the two signals in the mixed signal. At the same time, due to the Lorentz force effect, MA is affected by the polarity of the injected current and the direction of the static magnetic field. The combination of the static magnetic field and the injected current can not only distinguish the two signals in the mixed signal, but also effectively enhance the intensity of the mixed signal and improve the quality of the reconstructed image.

Thermoacoustic effects on the propagation of non-planar sound in a circular duct

This paper examines thermoacoustic effects on the propagation of non-planar sound in a circular duct subjected to an axial temperature gradient. Of particular concern are thermoviscous diffusive effects, which are taken into account by the boundary-layer approximation in a framework of the linear theory. For disturbances expanded into Fourier and Fourier–Bessel series in the azimuthal and radial directions, respectively, the pressure in each mode is described by a one-dimensional, dispersive wave equation, if non-diffusive propagation is assumed. When the diffusive effects are included, each radial mode is coupled to the other radial modes through the boundary layer. Focusing on a single azimuthal and radial mode only, the dispersion relation for the propagation along an infinite duct of a uniform gas is first derived. Effects of the temperature gradient are then examined by solving boundary-value problems for a duct of finite length in four typical cases. Assuming that the wall temperature increases exponentially along the duct, eigenfrequencies and decay rates in the lowest axial mode are obtained as well as axial distributions of the sound pressure and the axial velocity in the duct. The frequency and the decay rate increase as the temperature ratio at both ends becomes higher. It is found from the acoustic energy equation that the dispersion combined with the diffusion acts to reduce the damping and that the temperature gradient makes little contribution to the production of the energy. However, it is unveiled that the non-uniformity in temperature yields thermoacoustic sound confinement in the vicinity of the cold end.

Asymmetric transmission and coherent perfect absorption in a periodic array of thermoacoustic cells

This paper describes some exotic scattering properties of a one-dimensional network of thermoacoustic cells and characterizes them experimentally. The considered two-port consists of a waveguide containing a periodic arrangement of porous materials subjected to temperature gradients and separated by empty sections. The interaction of an acoustic wave with the temperature gradients leads to an inherently nonreciprocal phenomenon known as the thermoacoustic effect. It is shown that this effect can be exploited for the design of systems with exotic acoustic scattering properties through two experimental demonstrations. The first example showcases a balanced asymmetric transmitter with transmission coefficients inverse of each other, yielding a nonreciprocity factor of 18 dB, without reflections. The second example shows a coherent perfect absorber, where maximum absorption is achieved for a wide range of temperature gradients by controlling the relative amplitudes and phasing of incoming waves.