Effect of ultrasonic standing waves on flotation bubbles

Ultrasonic flotation was an effective method to float fine coal. In this study, the effects of the standing waves with different frequencies on ultrasonic flotation were investigated. The dynamic processes of bubble and coal-bubble were revealed by a high-speed camera. The results showed that under the action of Bjerknes force, bubble aggregates were formed within 450 ms and coal bubble aggregates were formed within 20 ms. The bubble aggregates were statistically analyzed by image processing method. The number of aggregates and small bubbles in the ultrasonic field at 100 kHz was greater than those at 80 and 120 kHz. Besides, 100 kHz ultrasonic flotation achieved the highest yields of clean coal (35.89%) and combustible recovery (45.77%). The cavitation bubbles acted as either a “medium” or an “inclusion”, entrapping and entraining the coal particles in the flotation pulp. It promoted the aggregation of bubbles with coal particles, so the flotation efficiency was effectively improved in the presence of ultrasonic standing waves.     

Production of biologically active peptides by hydrolysis of whey protein isolates using hydrodynamic cavitation

Whey protein isolate (WPI) hydrolysates have higher solubility in aqueous phase and enhanced biological properties. Hydrolysis of WPI was optimized using operating pressure (ΔP, bar), number of passes (N), and WPI concentration (C, %) as deciding parameters in hydrodynamic cavitation treatment. The optimum conditions for generation of WPI hydrolysate with full factorial design were 8 bar, 28 passes, and 4.5% WPI concentration yielding 32.69 ± 1.22 mg/mL soluble proteins. WPI hydrolysate showed alterations in binding capacity over WPI. SDS-PAGE and particle size analysis confirmed the hydrolysis of WPI. Spectroscopic, thermal and crystallinity analyses showed typical properties of proteins with slight variations after hydrodynamic cavitation treatment. ABTS, DPPH and FRAP assays of WPI hydrolysate showed 7–66, 9–149, and 0.038–0.272 µmol/mL GAE at 1–10, 0.25–4, and 3–30 mg/mL concentration, respectively. Further, a considerable enhancement in fresh weight, chlorophyll, carotenoids, reducing sugars, total soluble sugars, soluble proteins content and total phenolics content was noticed during in vitro growth of sugarcane in WPI hydrolysate supplemented medium at 50–200 mg/L concentration over the control. The process cost (INR/kg) to hydrolyze WPI was also calculated.     

空泡溃灭及空化噪声研究综述

本文从理论分析,数值计算,试验研究三方面对国内外空泡溃灭,空化噪声研究的最新进展及动态作了一简单的回顾,针对自己做的水翼及轴对称头体空化噪声试验结果,提出了一些尝试性解释。     

周向超声导波在薄壁管道中的传播研究

本文研究了薄壁管道内周向导波的传播及其频散特性，并且通过对比薄壁板与薄壁管道内的导波，找出了一个比较简便研究周向导波的方法。并通过实验验证了周向导波的频散现象以及激励模态与斜探头楔型角的关系，并且认定在管道中可以激励出单一的周向导波模态。     

预压力对超声电机输出特性影响的实验研究

 利用实验方法研究了预压力对行波超声电机摩擦界面输出特性 诸如空载转速、堵转扭矩等等的影响；对实验结果进行了详细的分 析，得出了一些规律性的结论，指出预压力存在一优值范围，可通过 预压力的调节来调整超声电机的输出特性；对现有摩擦驱动模型的仿 真结果进行了验证，提出了对现有模型的改进意见，为行波超声电机 摩擦界面的设计提供了依据.     

A fretting fatigue crack detection feasibility study using shear wave non-destructive inspection

A study was conducted to assess the viability of using ultrasonic shear wave non-destructive inspection (NDI) methods to detect fatigue cracks nucleating in the vicinity of a contact regionin situ. Use of this method is hampered by the presence of electronic and acoustic noise in the laboratory environment and by the contact in the experimental configuration. A previously established fretting fatigue test fixture was selected, in which nominally flat pads are held in contact against a thin, flat specimen and gross sliding between the pad and specimen is eliminated. Experiments were performed with Ti-6Al-4V at 300 Hz andR=0.5 for average clamping stresses of 200 and 620 MPa, and applied fatigue stresses of 330 and 250 MPa. The shear wave response was monitored during each test, and the test was interrupted when changes in the waveform were thought to indicate a crack. Also, the effect of the contact load and the sensitivity of the technique under the contact conditions were assessed. For the lower clamping stress, a sizeable portion of life was spent nucleating cracks, and the propagation life was too short to allow interruption of the tests. At the higher clamping stress, cracks with surface lengths of ∼2.5 mm were detected on, 10 mm wide specimens in tests conducted using the shear wave NDI technique. While the presence of the contact produced changes in the ultrasonic waveform, additional changes occurred as the crack propagated that permitted crack detection. A simple waveform correlation was used post-test to quantify the waveform changes, and thereby validate the viability of this NDI method for use in contact regions. In the configuration used for this study, the shear wave NDI technique was insensitive to small cracks. Some refinements that could dramatically improve crack detection capability are discussed. The original color figures found in this article can be seen in the online verson of this article, or can be obtained from A. Hutson.     

基于行波型超声马达的超声波振动减摩试验研究

提出了行波型超声马达振动减摩的几何模型,采用电磁电机驱动、电磁电机结合一路驻波振动驱动及行波型超声马达驱动3种驱动方式模拟行波型超声马达摩擦驱动特点,借助超声马达摩擦特性模拟试验装置,引入摩擦系数降低率的概念,研究了电机转速、预压力、超声波激励电压和摩擦材料等对定、转子摩擦副摩擦系数的影响.结果表明:在较高相对滑动速度、小预压力及大振幅条件下,超声波振动减摩现象显著.     

脉冲磨料射流中球泡溃灭特性研究及数值分析

从理论上研究了脉冲磨料射流中空化球泡的溃灭特性,建立了脉冲磨料射流中空化球泡的动力学方程,数值计算分析了磨料浓度、磨料粒径、射流振荡频率和幅值以及流场压力对脉冲磨料射流中空泡溃灭过程的影响规律。研究表明,脉冲磨料射流中磨料的存在将增大空泡溃灭历时,从而减弱射流的空蚀破坏能力,其中磨料的粒径、浓度和流场压力影响幅度较大。     

CAVITATION BIFURCATION FOR COMPRESSIBLE ANISOTROPIC HYPERELASTIC MATERIALS

I. INTRODUCTION The cavitation bifurcation problem, sudden formation and growth of voids in solid materials, haslong attracted much attention because of the fundamental role it plays in the local failure and fractureof materials. For hyperelastic materi…     

基于面元法回转体定长局部空泡的绕流计算

基于面元法 ,通过在回转体和空泡壁面放置源汇 ,对回转体定长局部空泡的绕流问题进行计算和分析 ,并讨论了空泡尾部速度过渡闭合模型对绕流计算的影响。计算结果表明 :本文的方法具有快速收敛的特征 ,第 1次叠代和最终收敛时空泡壁面切向速度的误差不超过 5 % ;随着回转体面元总数N的增加 ,局部空泡的空泡数趋于稳定 ;当回转体线型一定时 ,空泡数将随着局部空泡长度的增大而减小