声波除灰技术的理论及应用

声波除灰技术是近年来发展起来的一项新技术，已广泛用于电厂、石化及一般工业锅炉。该技术有很多优于其他除灰技术的优点，但有些作用机理尚需进一步研究。本文重点介绍声波除灰技术的物理声学基础、除灰机理、技术特点及应用情况，并提出具体的结论和建议。     

直线电机驱动回热器性能研究

本文提出并搭建了一种采用直线电机驱动的回热器热声转换实验台,通过调节负载阻抗改变回热器处声场条件,研究回热器在不同声场下热声转换特性。文中首先对实验系统进行了数值模拟,结果表明,回热器存在最优的工作声场,但由于有限水力半径因素,最优声场会偏离行波相位。计算中系统获得了最大1300 W净输出声功,热声效率达到35%。之后进行的实验实现了回热器处声场的调节,验证了回热器的声功放大作用,并获得了与数值计算相同的趋势。     

结构振动模态声辐射理论及试验研究

从结构振动声辐射的一般规律、自由声场的声功率辐射理论和结构振动模态原理入手,对结构振动模态的声辐射与外加激励、模态参数之间的关系进行了理论推导和研究,得到,当激振点不变,振动模态辐射的平均声压级的变化量与激振力级的变化量之比为1;若激振力不变,任意两点处激振振动模态辐射的平均声压级的变化量与相应点振型元素级的变化量之比为1.对以上结果试验验证表明:理论值与实测值基本相符.     

双频温控式声化学反应器的研制

介绍一种双频温控式声化学反应器。采用水循环降温方法，使变幅杆式反应头能在大功率状态下长时间稳定辐射，并能有效地将声化学反应器内因超声热效应引起的温升控制在5℃左右。利用自动控制及转换电路，使声源既能在20kHz或35kHz中任一单频辐射工作，又能双频自动交替辐射工作，且工作性能稳定，输出电功率在0-800W可调。     

行波和驻波模式下热声振荡的临界温度梯度

热声机械作为一种能量转化装置。其效率于传统发动机还有较大差距。本文讨论了热声发动机在驻波和行波两种不同工作状态下,其声功率产生的临界温度梯度与流道尺寸和工作介质的关系,得出了两种模式下最佳的工作条件。结果表明;采用行波形式的热声发动机结构,可以有效降低临界温度梯度,提高热致声的效率,同时可以利用一些低品位来做为热声发动机的高温端。     

声化学反应器研究进展

自八十年代后期以来，超声应用于有机合成、金属有机化学、电化学、聚合物化学等领域，取得了大量研究成果，引起了越来越多的化学工作者的兴趣[1-4]．利用超声波获取化学效应时，有许多实验参数需要加以控制，诸如超声频率、声强、处理时间、体系温度、外部压力、溶剂以及反应物浓度等．因此，为了适应声化学研究的需要，必须设计合适的反应器．国际上在这方面的研究十分活跃[5-11]，近年来研制和发展了许多新型的声化学反应器．本文拟对近年来国际上出现的实验室用声化学反应器作一简要介绍，以期对我国这方面的工作有所促进．一、液哨式…     

氧化铟锡薄膜的磁感应热声分析

基于优良导体在磁场下的涡流效应理论和固体的热声效应理论,建立了氧化铟锡(ITO)导电薄膜磁-热-声效应的理论模型,推导了导电薄膜热致发声的温度振荡和输出声压表达式。对有基底的ITO导电膜进行了磁场下的热声理论计算和实验测试,结果表明：薄膜的温度振荡值随频率呈上升趋势,与电-热-声模型相比趋势相反;薄膜声压的理论值与实验值在频域内的变化趋势基本吻合,验证了理论模型的正确性。进而,根据磁-热-声的理论模型,分析了线圈相关参数对薄膜声压级的影响,结果表明：薄膜声压级随着线圈匝数的增加而增大,随着薄膜与线圈中心距离的增加而减小,随着线圈半径的增加而减小。文中的研究结果拓展了导电薄膜在扬声器等领域的应用。     

热声制冷机声场中非线性效应

热声制冷的基本原理是热声效应,但热声效应一般只在高声强下发生,随之将产生强烈的非线性效应.本文在自行研制的热声制冷机试验台上,研究了板叠对声场非线性的影响以及非线性对热声系统性能的影响.结果表明,板叠的存在使得声波明显衰减,压比约减小5%,并且各次谐波的幅值和增长速率较无板叠时均有所降低;非线性效应限制了基波的增长,导致了高次谐波产生,且基波和高次谐波的增长均有发展为饱和的趋势.板叠的存在产生明显的声制冷效果,制冷温度随驱动功率增大先增加后减小.在50 W时达到最低温度5.1℃.     

演示用Sondhauss管的研制及理论分析

介绍了演示用 Sondhauss管的结构与制作过程 ,它具有直观、简单、成本低等突出优点 ,是一种比较理想的热声效应演示器件。通过初步实验 ,文中对热声管发声机制进行了理论分析 ,有助于更好地理解热声效应 ,并为进一步研究热声机理奠定了基础     

锅炉声波除灰的声学分析

声波除灰技术是提高锅炉换热效率、保证锅炉安全运行的重要手段之一,早在９０年代初就已经在国内外工业锅炉上推广应用,但是与之相关的多数基本问题目前还没有得到很好的解决,成为制约技术发展和应用的重要障碍［１］。本文采用Ｈｅｌｍｈｏｌｔｚ积分方程数值计算了锅炉换热器管排的声场散射问题,得到了管束表面及管排周围的声场分布特性,针对除灰要求进行了声学分析,对当前声波除灰技术的发展及应用均具有实际意义。     

Realization of enhanced sound-driven CNT-based triboelectric nanogenerator,utilizing sonic array configuration

Triboelectric nanogenerators have been emerged as the most promising mechanical energy harvesters, during last few years. Here, a sonic triboelectric nanogenerator with 7-fold enhanced output power is reported, in which carbon nanotubes are utilized to increase the electrode's effective surface area. To improve the efficiency we have taken advantage of acoustic wave localization in a sonic array. For this purpose, first we have studied an array of periodic acoustic scatterers by simulation. Then, we have designed a 1-D phononic crystal consisting of five steel slabs standing in air medium, which leads to resonance of incident acoustic wave at f = 4.34 kHz. We implemented the design, but replaced the middle scatterer by triboelectric nanogenerator. An enhancement factor of about 4 has been measured for the output voltage of the sonic nanogenerator at f = 4.24 kHz, when it is embedded in the sonic array. Also, power enhancement factor of 7-fold has been achieved (P_out≈4 μW/m²), benefiting from the applied sonic cavity. The measured resonance frequency and enhancement factor are in acceptable agreement with the simulation results. The presented enhanced energy harvesting configuration proposes a compact and low cost structure, which allows parallel energy harvesting, and seems promising for realizing sonic harvesters.     

Compact standing wave thermoacoustic generator for power conversion applications

In the past decade, a variety of thermoacoustic engines (TAEs) were devised to convert thermal energy to acoustic power. In this paper, we optimized the design of a standing wave thermoacoustic generator that can provide high intensity acoustic pressure and convert it into electrical power output using a low cost alternator. Three prototypes of standing wave thermoacoustic generator (TAG) were designed to optimize the overall efficiency. The first prototype of standing wave TAG could produce an acoustic pressure of 0.9 kPa (153 dB) with an input thermal power of 210 W. Further, the maximum heat to electrical conversion efficiency was 0.045% with an input thermal power of 250 W. However, the performance of this system was not fully optimized. The performance of TAE depends upon various parameters including stack position, stack length and resonator length. Hence, a new second prototype of tunable TAG was developed to tune these critical parameters in order to improve the overall efficiency. A compact third prototype of TAG was successfully built with optimized parameters and has been tested. In the improved design, high intensity acoustic pressure of 2.9 kPa (163.5 dB) was observed for the same 210 W input thermal power. The maximum heat to electrical energy conversion efficiency was 0.084% with an input of 250 W which is 87% higher as compared to the first prototype. The major reason for the lower conversion efficiency is due to the low efficiency of the alternator. In future, high efficiency alternator designs can be employed along with careful impedance matching to obtain higher conversion efficiencies. The results described in this paper demonstrate the potential of developing compact portable acoustic power and electricity generators for decentralized power applications.     

A sonic crystal diode implementation with a triangular scatterer matrix

This paper investigates a nonreciprocal sound transmission effect provided by a triangular lattice two-dimensional sonic crystal made of rods in a triangular cross-section. This sonic crystal (SC) device works as a frequency selective acoustic diode operating at a frequency of 8950 Hz. The scatterer matrix of the sonic crystal diode prototype was composed of triangular shaped wood rods that break the symmetry of the spatial inversion and provide nonreciprocal wave transmission with a contrast rate of 89% in experiments. This acoustic diode device can provide a high contrast, narrow band, one-way sound transmission for acoustic wave control applications.     

Applications of antireflection coatings in sonic crystal-based acoustic devices

The unwanted reflection seriously baffles the practical applications of sonic crystals, such as for various acoustic lenses designed by utilizing the in-band properties of sonic crystals. Herein we introduce the concept of the antireflection coating into the sonic crystal-based devices. The efficiency of such accessorial structures is demonstrated well by an originally high reflection system. Promising perspectives can be anticipated in extending the antireflection coating layers into more general acoustic applications through a flexible design process.     

The radiative and thermodynamic processes in DBD driven XeBr and KrBr exciplex lamps

The radiative and thermodynamic parameters of a dielectric barrier discharge XeBr and KrBr excilamp were studied. The power expended in heating the gas mixture and the excilamp bulb was determined by measuring the fast and slow components of a pressure jump. The power consumed by the exilamp was estimated using oscillograms of voltage and current pulses. The maximum UV power and efficiency of a XeBr excilamp were 3.8 W and 7.5%, respectively. For the same conditions the maximum UV power and efficiency of a KrBr excilamp were 1.6 W and 3%, respectively. Analysis of the experimental results shows that at low mixture pressures most of the discharge power is expended in heating the gas and at the elevated pressure the most of the discharge power goes into the generation of acoustic waves and heating of the excilamp bulb walls through electron and ion bombardment. The concept proposed earlier for the energy balance in DBD lamps as thermodynamic systems was verified.     

Optoacoustic analysis of the laser-cleaning process

Laser cleaning is an optodynamic process in which the optically induced removal of a liquid or a solid contaminant from a substrate is accompanied by a optoacoustic wave in the surrounding air. In our experiments we used both dry and steam laser-cleaning techniques for various samples. Optoacoustic wave, produced by the abrupt heating and detachment of the contaminants, was observed with a probe-beam deflection technique. We determined two characteristic parameters of the optoacoustic wave: the amplitude and the time-of-flight of the acoustic signal. With an analysis of these waves we also determined possible generating mechanisms. The decrease of the amplitude and the velocity of propagation, which approaches sonic speed, of the consecutive waves indicate that the dynamics during the laser-cleaning process is progressively weakened. The cleaning process is over when both the parameters reach a constant value, so with measuring optoacoustic waves the progress of the cleaning process could be observed on-line.     

Ultrasound induced cleaning of polymeric nanofiltration membranes

Cleaning of the flat sheet nanofiltration membranes, using backflushing, chemical cleaning, and ultrasonication operated individually as well as in combination with chemicals, has been studied in the present work. Identical hydrophilic polyamide membranes were fouled individually using an aqueous solution containing a single dye, an aqueous solution containing a mixture of dyes, and a synthetically prepared petroleum refinery effluent. Effect of different parameters such as the concentration of cleaning solution, contact time, frequency, and power of ultrasound on the efficacy of membrane cleaning has been studied. Optimal cleaning was achieved under sonication conditions of frequency of 24 kHz and power dissipation of 135 W. It was demonstrated that application of sonication under optimum conditions without chemical agents, gave about 85% water flux recovery. In the case of combined chemical and ultrasonic treatment, it was clearly observed that the use of chemical agent increased the efficacy of ultrasonic cleaning. The hybrid method recovered the initial water flux to almost 90% based on the use of 1.0 M aqueous NaOH and 4 min of sonication. Overall, the use of aqueous NaOH in combination with sonication showed a better efficiency for cleaning than the individual processes thus demonstrating a new avenue for membrane cleaning.     

Study and optimization of the ultrasound-enhanced cleaning of an ultrafiltration ceramic membrane through a combined experimental–statistical approach

Membrane fouling is one of the main drawbacks of ultrafiltration technology during the treatment of dye-containing effluents. Therefore, the optimization of the membrane cleaning procedure is essential to improve the overall efficiency. In this work, a study of the factors affecting the ultrasound-assisted cleaning of an ultrafiltration ceramic membrane fouled by dye particles was carried out. The effect of transmembrane pressure (0.5, 1.5, 2.5 bar), cross-flow velocity (1, 2, 3 m s⁻¹), ultrasound power level (40%, 70%, 100%) and ultrasound frequency mode (37, 80 kHz and mixed wave) on the cleaning efficiency was evaluated. The lowest frequency showed better results, although the best cleaning performance was obtained using the mixed wave mode.A Box–Behnken Design was used to find the optimal conditions for the cleaning procedure through a response surface study. The optimal operating conditions leading to the maximum cleaning efficiency predicted (32.19%) were found to be 1.1 bar, 3 m s⁻¹ and 100% of power level.Finally, the optimized response was compared to the efficiency of a chemical cleaning with NaOH solution, with and without the use of ultrasound. By using NaOH, cleaning efficiency nearly triples, and it improves up to 25% by adding ultrasound.