Performance and energetic analysis of hydrodynamic cavitation and potential integration with existing advanced oxidation processes: A case study for real life greywater treatment

The current work is a “first of a kind” report on the feasibility and efficacy of hydrodynamic cavitation integrated Advanced Oxidation Processes (AOP’s) towards treatment of a real life greywater stream in form of kitchen wastewater. The work has been carried out in a sequential manner starting with geometry optimization of orifice plate (cavitating device) followed by studying the effects of inlet pressure, pH, effluent dilution ratio on degradation of TOC and COD. Under optimized conditions of pH 3, 4 bar pressure, TOC and COD reduction of 18.23 and 25% were obtained using HC for a period of 120 min. To improve the performance of HC, further studies were carried out by integrating H₂O₂ and O₃ with HC. Using 5 g/h optimum dosage of H₂O₂, 87.5% reduction in COD was obtained beyond which it started decreasing. Moreover, integrating O₃ (57.5% reduction in COD) increased the treatment cost. However, a hybrid process (HC + H₂O₂ + O₃) yielded 76.26 and 98.25% reductions in TOC and COD within 60 min. The energetics of all the processes and the treatment costs were studied in detail and it was concluded that combined process of HC + H₂O₂ + O₃ surpassed by far the performances of HC + H₂O₂ and HC + O₃.     

大气激光通信中的多层空间脉冲位置幅度调制

针对现有光空间脉冲位置调制频谱效率低、激光器利用率不高等问题,将分层技术与空间脉冲位置幅度调制相结合,提出了一种适合于大气激光通信的多层空间脉冲位置幅度调制方案.通过额外增加少量几个激光器构成多层结构,并通过脉冲位置幅度调制中的脉冲位置携带比特信息,不同层通过脉冲幅度得到区分.介绍了系统中层映射、空间脉冲位置幅度映射及其逆映射的原理,并推导出该方案的误码率表达式.利用蒙特卡洛仿真方法进一步验证了该方案的正确性,并与传统空间调制系统的性能进行了对比.结果表明:与传统光空间调制系统相比,所提方案提高了系统的频谱效率,且所用激光器数目更少.在传输比特相同的条件下,相对于(32,4,128)-空间脉冲位置调制系统,(9,4,8,2)-多层空间脉冲位置幅度调制系统的频谱效率提高了16倍,当误码率为10-3时,其信噪比改善了约1dB,且所用激光器数目不到前者的1/3.其中,括号中的参数分别表示激光器数目、探测器数目、采用调制方式的阶数及层数,层数为1时忽略.     

Determination of Metronidazole in Tablet Formulations by Differential Pulse Polarography

Abstract

A method for the determination of metronidazole in pharmaceutical tablets is presented. Differential pulse polarography at a static mercury drop electrode is used to observe the reduction of the imidazole. The method is demonstrated to be simple, rapid, linear, reproducible and accurate.     

脉冲调制高压电源高频化改造的仿真分析与实验

对HL-2A 装置原有的高压电源进行了高频化改造，改造后的单元电源采用脉冲步进阶梯调制(PSM)技术，采用24 个不可控整流电源模块与4 个调节电源模块串联输出，通过控制各模块的投入切出，使输出电压范围在0~20kV 可调，模块开关频率最高可以达到20kHz。通过仿真和实验测试结果表明，该电源运行参数可以达到20kV/200A，开关频率最高达到了20kHz，能够满足系统的实验需求。     

Surface functionalization by nanosecond-laser texturing for controlling hydrodynamic cavitation dynamics

The interaction between liquid flow and solid boundary can result in cavitation formation when the local pressure drops below vaporization threshold. The cavitation dynamics does not depend only on basic geometry, but also on surface roughness, chemistry and wettability. From application point of view, controlling cavitation in fluid flows by surface functionalization is of great importance to avoid the unwanted effects of hydrodynamic cavitation (erosion, noise and vibrations). However, it could be also used for intensification of various physical and chemical processes. In this work, the surfaces of 10-mm stainless steel cylinders are laser textured in order to demonstrate how hydrodynamic cavitation behavior can be controlled by surface modification. The surface properties are modified by using a nanosecond (10–28 ns) fiber laser (wavelength of 1060 nm). In such a way, surfaces with different topographies and wettability were produced and tested in a cavitation tunnel at different cavitation numbers (1.0–2.6). Cavitation characteristics behind functionalized cylindrical surfaces were monitored simultaneously by high-speed visualization (20,000 fps) and high frequency pressure transducers. The results clearly show that cavitation characteristics differ significantly between different micro-structured surfaces. On some surfaces incipient cavitation is delayed and cavitation extent decreased in comparison with the reference – a highly polished cylinder. It is also shown that the increased surface wettability (i.e., hydrophilicity) delays the incipient cavitation.     

Physical and chemical characterization of shock-induced cavitation

A strong impact on a water surface induces a shock wave propagation with a significant pressure variation leading to cavitation bubble formation. A new shock induced cavitation reactor described in this work was characterized by physical and chemical techniques. Water hammer model verification with Joukowsky approach allowed to determine the wave speed propagation and gas fraction in water submitted to shock. These values were used for frequency analysis and compared with direct bubble visualization in order to estimate the influence of the experimental parameters on the shock-induced cavitation. Thereby, the shock wave contains a broad spectrum as decomposed into frequencies. This multi-frequency nature induces heterogeneous bubbles with calculated radii of 0.01 to 3.5 mm and observed radii of 0.01 to 2.8 mm depending on experimental conditions (initial pressure, impact height, gas atmosphere). For the first time, the formation of hydroxyl radicals was proven under impact-induced cavitation. The concentration of radicals increases with increasing number of successive impacts, reaching ca. 1.3 µmol.L⁻¹ after 500 impacts in the presence of 20% O₂-Ar as saturating gas. Radical generation seems to be relatively independent of the impact height but strongly depend on the type of gas saturating water, being substantially lower in the presence of air. Moreover, radical generation increases when decreasing the initial pressure and depends on the frequency at which water is impacted by the piston. Nevertheless, yield of OH radicals during shock-induced cavitation remains much lower than that produced by power ultrasound.     

Numerical simulations of stable cavitation bubble generation and primary Bjerknes forces in a three-dimensional nonlinear phased array focused ultrasound field

We present a model developed for studying the generation of stable cavitation bubbles and their motion in a three-dimensional volume of liquid with axial symmetry under the effect of finite-amplitude phased array focused ultrasound. The density of bubbles per unit volume is determined by a nonlinear law which is a threshold-dependent function of the negative acoustic pressure reached in the liquid, in which nuclei are initially distributed. The nonlinear mutual interaction of ultrasound and bubble oscillations is modeled by a nonlinear coupled differential system formed by the wave and a Rayleigh-Plesset equations, for which both the pressure and the bubble oscillation variables are unknown. The system, which accounts for nonlinearity, dispersion, and attenuation due to the bubbles, is solved by numerical approximations. The nonlinear acoustic pressure field is then used to evaluate the primary Bjerknes force field and to predict the subsequent motion of bubbles. In order to illustrate the procedure, a medium-high and a low ultrasonic frequency configurations are assumed. Simulation results show where bubbles are generated, the nonlinear effects they have on ultrasound, and where they are relocated. Despite many physical restrictions and thanks to its particularities (two nonlinear coupled fields, bubble generation, bubble motion), the numerical model used in this work gives results that show qualitative coherence with data observed experimentally in the framework of stable cavitation and suggest their usefulness in some application contexts.     

超声换能器对线性调频信号脉冲压缩性能的影响分析*

该文研究了不同编码带宽下超声换能器对编码信号脉冲压缩后信噪比与轴向分辨率的影响关系。将脉冲压缩后的时域峰值转化为频域积分的形式，得到考虑换能器影响的脉冲压缩信噪比公式。以线性调频信号为例，仿真与实验结果表明，编码激励相对于方波激励的信噪比增益随编码带宽的减小而增大，因为受换能器带宽限制，编码激励的轴向分辨率随编码带宽的增大先减小后趋于稳定。该研究为编码激励方法更有效地应用于超声检测的背景中提供了参考。     

Clove essential oil emulsion-filled cellulose nanofiber hydrogel produced by high-intensity ultrasound technology for tissue engineering applications

High-intensity ultrasound (HIUS) was used to produce emulsion-filled cellulose nanofiber (CNF) hydrogel using clove essential oil (0.1, 0.5 and 1.0 wt%) as dispersed phase towards tissue engineering applications. The novel encapsulating systems obtained using HIUS specific energy at the levels of 0.10, 0.17, and 0.24 kJ/g were characterized by oil entrapment efficiency, microstructure, water retention value, color parameters, and viscoelastic properties. Freeze-dried emulsion-filled CNF hydrogels were characterized by porosity and swelling capacity. In addition, human gingival fibroblast cell cytocompatibility tests were performed to evaluate their potential applications as tissue engineering scaffold. The clove essential oil content strongly affected the oil entrapment efficiency, water retention value, color difference and whiteness of the prepared emulsion-filled CNF hydrogel. And, the HIUS energy only affected the yellowness of the emulsion-filled CNF hydrogel. Via HIUS processing, the CNF hydrogel successfully acted as a continuous phase in the emulsion-filled gel system with maximum oil entrapment efficiency of 34% when 0.5 wt% clove essential oil was added to the system. The encapsulating systems had predominantly gel-like property with maximum elastic modulus of 411 Pa. Furthermore, the emulsion-filled CNF hydrogels with the addition of clove essential oil up to 0.5 wt% indicated good cell viability rates (74–101%) to human gingival fibroblast cells. The newly developed clove essential oil emulsion-filled CNF hydrogel shows desirable cytocompatibility characteristics and can be considered as an alternative scaffold for tissue engineering applications.     

Temperature and aging dependence of strain‐induced crystallization and cavitation in highly crosslinked and filled natural rubber

We have investigated the structural changes occurring in highly crosslinked and carbon‐black filled natural rubber under uniaxial extension by small‐ and wide‐angle X‐ray scattering using synchrotron radiation. The experiments focused on strain‐induced crystallization (SIC) and nanocavitation and were carried out on a model series of materials as a function of temperature and aging conditions. We find that for all materials both SIC and cavitation decrease markedly with temperature and aging. However, the presence of carbon black filler shifts the ceiling temperature where SIC is observed to at least 120°C, presumably by a nucleating effect, maintaining the high strength of the elastomers. Interestingly, although in pure elastomers, the cavitation strength decreases with temperature, we find that in these filled elastomers the critical stress for the onset of cavitation increases significantly with temperature strongly suggesting that cavitation is due to the local confinement between fillers and supporting the idea of a glassy layer near the filler. Aging for 10 days at 110°C in oxygen‐free conditions decreases both SIC and cavitation and reduces the strength of the elastomer at high temperature. This is attributed to the formation of sulfur side chains hindering the crystallization. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 780–793