A novel method for optimization of slit Venturi dimensions through CFD simulation and RSM design

This research presents a novel comprehensive method for optimizing the design of cavitating slit Venturi for a given cavitation intensity. This method is applicable to any cavitation number and can be used to provide the Venturi geometry that is suitable for a specific application. In this paper, cavitating Venturi design process is represented in seven steps. As an example, for the cavitation number of 0.2, geometrical and operational parameters of the Venturi were determined using the proposed seven steps. During the design process, the Venturi discharge coefficient was calculated using computational fluid dynamics (CFD) simulations. Furthermore, Venturi parameters such as inlet pressure, throat area, width, length, height and divergence angle, were optimized by the combination of CFD and Response Surface Methodology (RSM). In addition to calculating the mentioned optimum parameters, other hydraulic parameters of Venturi including discharge coefficient, flowrate, throat velocity, cavitation volume and length were also determined. Finally, the proposed design method in this study was verified by conducting sets of laboratory experiments.     

伴随水力空化现象的对流换热数值研究

以水为介质,建立了液体流动的混合物多相流模型及空化模型,运用CFD方法对水平圆管内伴随有水力空化现象的受迫对流换热过程进行了数值研究,详细分析了管道入口压力、入口温度和限流孔与管道直径比等因素对水力空化及对流换热过程的影响规律。数值模拟结果表明,空化现象出现在圆管喉部(限流孔)壁面附近区域;与相同流量下无空化时的传热相比,在发生空化现象的区域,传热壁面被蒸汽所覆盖导致传热急剧恶化,而在远离空化发生区域的下游位置,由于空化的扰流作用使得加热壁面与流体之间的传热得到明显改善。     

Decolourization of Rhodamine B: A swirling jet-induced cavitation combined with NaOCl

A hydrodynamic cavitation reactor (Ecowirl) based on swirling jet-induced cavitation has been used in order to allow the degradation of a waste dye aqueous solution (Rhodamine B, RhB). Cavitation generated by Ecowirl reactor was directly compared with cavitation generated by using multiple hole orifice plates. The effects of operating conditions and parameters such as pressure, pH of dye solution, initial concentration of RhB and geometry of the cavitating devices on the degradation rate of RhB were discussed. In similar operative conditions, higher extents of degradation (ED) were obtained using Ecowirl reactor rather than orifice plate. An increase in the ED from 8.6% to 14.7% was observed moving from hole orifice plates to Ecowirl reactor. Intensification in ED of RhB by using hydrodynamic cavitation in presence of NaOCl as additive has been studied. It was found that the decolourization was most efficient for the combination of hydrodynamic cavitation and chemical oxidation as compared to chemical oxidation and hydrodynamic cavitation alone. The value of ED of 83.4% was reached in 37 min using Ecowirl combined with NaOCl (4.0 mg L⁻¹) as compared to the 100 min needed by only mixing NaOCl at the same concentration. At last, the energetic consumptions of the cavitation devices have been evaluated. Increasing the ED and reducing the treatment time, Ecowirl reactor resulted to be more energy efficient as compared to hole orifice plates, Venturi and other swirling jet-induced cavitation devices, as reported in literature.     

Aerodynamic Focusing Effect in a Rectangular Slit Real Impactor at Different Reynolds Numbers

Numerical investigations were performed to assess the effect of “aerodynamic focusing” achievable by varying the angle of approach in the convergence section of a rectangular slit real impactor, at different Reynolds numbers. Computational Fluid Dynamics (CFD) approach was used as a tool in the study. Simulations were performed on a slit impactor in which the angle of approach in the inlet section was varied from 15° to 75°, at three different Reynolds number values namely 200, 1000, and 2000, to characterize the effect of “aerodynamic focusing”. It is found from the results of the study that the impactor efficiency curve and cut‐point SQRT (Stk)₅₀ value are strong functions of the above parameters. Aerodynamic focusing effect achievable by varying the angle of inlet convergence section is delineated with appropriate particle tracks. Results of the study are expressed as a surface plot of the cut‐point SQRT (Stk)₅₀ value as a function of the Reynolds number and the angle of approach and a correlation relating the parameters is presented.     

大气激光通信用直锥形光纤发射天线

 提出采用直锥形光纤作为大气激光通信的发射天线,将多模光纤输出的部分相干发散光束变换为准平行光束的方案,既能得到发散角很小的部分相干激光光束,又能保证激光器输出能量的完全传输。采用光线追迹法分析了任意光束从锥形光纤小端面输入、大端面输出的发散角。结果表明,当直锥形光纤长度大于某一特定值时,从小端面输入的入射角小于数值孔径角的所有光线理论上都可以变换为出射角度小于光纤半锥角的光线,因此直锥形光纤可以作为部分相干光源的准直透镜,代替传统的凸透镜,用于改善光束的发散角。对远场光斑进行了数值模拟和实验研究,结果显示：直锥形光纤透镜对朗伯光源的准直光束比传统凸透镜的准直光束发散角小,光斑半径小且均匀性好,证明用此方法可以得到低发散、低空间相干性的光斑。     

非线性偏振旋转中偏振控制器方位角的研究

提出一种基于Jones矩阵的非线性偏振旋转锁模光纤激光器数值模型, 对偏振控制器波片方位角的描述具有物理意义清晰的优点. 数值仿真得到均方根宽度为0.28 ps的超短脉冲, 时域对称且振幅稳定. 搭建了非线性偏振旋转锁模光纤激光器, 系统可以自启动, 得到了重复频率为67.35 MHz的锁模脉冲输出. 数值仿真和实验结果都表明偏振控制器两个波片的方位角α₁和α₂都具有周期性, 周期分别为180°和90°. 由于随机双折射的影响, 实验测得的波片方位角调谐范围比数值仿真的结果小, 这一点通过在数值仿真模型中加入随机双折射的作用而得到证明.     

Enhancement of chloroform degradation by the combination of hydrodynamic and acoustic cavitation

The decomposition of chloroform by the combination of hydrodynamic and acoustic cavitation (Hydrodynamic-Acoustic-Cavitation/HAC) has been investigated. The flow rate and the hole diameter of the orifice plate remarkably affect the conversion of chloroform in the combined system. The conversion increases with increasing fluid velocity without any restriction. With a 2.8mm orifice plate the conversion reaches an optimal value. A synergistic effect has been obtained by the hybrid method of acoustic and hydrodynamic cavitation. The total synergistic effect achieves 17% and 73% per pass, respectively. The analysis of the energy efficiencies shows different results. Due to high optimization potential, this hybrid method can be visualized as a new step for wastewater treatment.     

快速实现矩形准直光束的高集光效率LED透镜设计

为了实现LED矩形准直光束,提出一种快速构建高集光效率LED透镜的设计方法。基于分步法、边缘光线定理和几何光学定律,分步设计两个自由曲面轮廓线,快速获取两个自由曲面并构建透镜。结果表明:当LED距透镜内曲面尺寸与LED尺寸的比值为6时,系统的半峰全宽为2.3°×1.15°,集光效率为82.6%,可以有效地实现矩形准直光束。随着比值的增大,透镜的尺寸变大,但是半峰全宽变小,透镜集光效率变高。根据设计参数加工了透镜并对仿真结果进行了实验验证。该方法为实现LED矩形准直光束提供了一种有效途径。     

皮尔斯电子枪非迭代综合法的修正

 对Tiwary非迭代综合法进行了整理分析，根据阴极半锥角大小的不同范围对其计算公式做出了相应修正，使得计算结果与Vaughan迭代综合法的计算结果相吻合，二者之间相差可以实现小于1°；对阳极半径公式也做了合理的修正，使阳极与阴极之间的间隙及电子枪射程的计算精度也与迭代综合法相当。采用非迭代法的修正方法计算精度受阴极半锥角大小的影响大大减小，扩大了其应用范围。     

用于校准能见度仪的标准散射体定标系统中光学系统的设计

为了实现校准能见度仪中标准散射体的快速准确定标,建立了用于校准能见度仪的标准散射体的定标系统.研究了定标系统中全景成像折反光学系统的设计方法.根据抛物面反射镜的光学特性推导出抛物面面型的计算方法.根据定标系统对光学系统的要求,完成全景成像色度计光学系统的设计.对全景成像折反光学系统进行建模仿真并设计实验验证光学系统的设计与仿真结果的正确性.实验结果表明:全景成像折反光学系统的空间检测俯仰角范围为0°~90°,方位角范围为0°~360°,且最小角分辨率为1°,与仿真结果基本一致,满足用于校准能见度仪的标准散射体定标系统中光学系统的设计要求.     

Hydrodynamic cavitation-assisted continuous pre-treatment of sugarcane bagasse for ethanol production: Effects of geometric parameters of the cavitation device

For biotechnological conversion of lignocellulosic biomass, a pre-treatment step is required before enzymatic hydrolysis of carbohydrate fractions of the material, which is required to produce fermentable sugars for generation of ethanol or other products in a biorefinery. The most of the reported pre-treatment technologies are in batch operation mode, presenting some disadvantages as dead times in the process. In this context, hydrodynamic cavitation (HC)-assisted alkaline hydrogen peroxide (AHP) pre-treatment in continuous process was proposed for pre-treatment of sugarcane bagasse (SCB). The system was designed with a main reactor containing two devices to generate cavitation by passing liquid medium through orifice plates. For SCB pretreated in continuous process, 52.79, 34.31, 22.13 and 15.81 g of total reducing sugars (TRS) per 100 g of SCB were released in samples pretreated using orifice plates with a number of holes of 24 (d = 0.45 mm), 16 (d = 0.65 mm), 12 (d = 0.8 mm) and 8 (d = 1 mm), respectively. Computational Fluid Dynamics (CFD) tools showed that 0.94 of vapor phase volume fraction and 0.19 of cavitation number were achieved at 31 m/s of throat velocity and upstream pressure of 350,000 Pa. By using pretreated SCB, 28.44 g of ethanol/L (84.31% of yield respect to theoretical value) was produced by immobilized Scheffersomyces stipitis NRRL-Y7124 in a simultaneous hydrolysis and fermentation process at high solid loading (16% S/L). Thus, HC-assisted process was proved as a promising technology for valorization of lignocellulosic biomass.     

基于瑞利-索墨菲积分的大角度激光分束器设计

针对目前激光分束器只能产生小发散角的问题,基于严格的非傍轴近似的衍射积分公式,提出了一种大发散角分束器的设计方法.先对目标光场分布进行坐标和光强修整,再利用改进的GerchbergSaxton迭代算法得到所需分束器的相位分布.分别采用本文设计方法和原有方法设计了发散全角为40°×40°的5×5分束器,仿真和实验结果表明:原有方法设计得到的5×5子光束存在着显著的枕形畸变,并且光强分布不均匀.而本文方法设计得到的子光束呈均匀等间隔排列,并且强度分布更为均匀.     

利用互补天线原理求解孔缝的共振性能

 利用互补天线原理从理论上推导了真空、介质窄缝的共振频率公式,在理想窄缝长度小于5倍波长、辐射角度偏离垂直方向小于30°的情况下,孔缝的共振频率点仍然可以用半波振子的辐射情况来解释,共振点满足孔缝长度等于入射波的半个波长;介质窄缝等效为半个孔缝深度的微带贴片天线,不同介电常数介质填充时的共振频率理论公式推导值和数值模拟值基本一致,相对误差在5%以内。进一步分析了窄缝阵列的耦合性能,结果表明互补天线原理可以很好地应用于分析和求解孔缝的共振性能。     

对皮尔斯电子枪综合法的改进

 在低压缩比、低导流系数情况下，对Vaughan迭代综合法因阴极半锥角初始值取得不合理而失效的原因进行了分析，并对其中的迭代公式进行了合理修正。采用Vaughan迭代综合法和修正后的迭代综合法验算了13支不同性能的电子枪，结果表明：采用修正迭代法，阴极半锥角初始值即使在0°~70°取值，都能得出正确的计算结果。在原来Vaughan法适应的情况下，修正法与原方法的阴极半锥角结果之间差值小于1°；在原来Vaughan法失效的情况下(如低导流系数、低压缩比小于7)，改进后的方法也能得到接近实测值的合理结果。     

Angle extended linear MEMS scanning system for 3D laser vision sensor

Scanning system is often considered as the most important part for 3D laser vision sensor. In this paper, we propose a method for the optical system design of angle extended linear MEMS scanning system, which has features of huge scanning degree, small beam divergence angle and small spot size for 3D laser vision sensor. The principle of design and theoretical formulas are derived strictly. With the help of software ZEMAX, a linear scanning optical system based on MEMS has been designed. Results show that the designed system can extend scanning angle from ±8° to ±26.5° with a divergence angle small than 3.5 mr, and the spot size is reduced for 4.545 times.     

Cavitation based cleaner technologies for biodiesel production and processing of hydrocarbon streams: A perspective on key fundamentals,missing process data and economic feasibility – A review

The present review emphasizes the role of hydrodynamic cavitation (HC) and acoustic cavitation in clean and green technologies for selected fuels (of hydrocarbon origins such as gasoline, naphtha, diesel, heavy oil, and crude oil) processing applications including biodiesel production. Herein, the role of cavitation reactors, their geometrical parameters, physicochemical properties of liquid media, liquid oxidants, catalyst loading, reactive oxygen species, and different types of emulsification and formation of radicals, formation as well as extraction of formed by-products are systematically reviewed. Among all types of HC reactors, vortex diode and single hole orifices revealed more than 95 % desulfurization yield and a 20 % viscosity reduction in heavy oil upgrading, while multi-hole orifice (100 holes) and slit Venturi allowed obtaining the best biodiesel production processes in terms of high (%) yield, low cost of treatment, and short processing time (5 min; 99 % biodiesel; 4.80 USD/m³). On the other hand, the acoustic cavitation devices are likely to be the most effective in biodiesel production based on ultrasonic bath (90 min; 95 %; 6.7 $/m³) and desulfurization treatment based on ultrasonic transducers (15 min; 98.3 % desulfurization; 10.8 $/m³). The implementation of HC-based processes reveals to be the most cost-effective method over acoustic cavitation-based devices. Finally, by reviewing the ongoing applications and development works, the limitations and challenges for further research are addressed emphasizing the cleaner production and guidelines for future scientists to assure obtaining comprehensive data useful for the research community.     

Divergence and aperture angle of conical light guides

Relations derived for the angle of divergence and the aperture of hollow metallic or dielectric cones may not directly be assigned to dielectric core/cladding light guides. The accurate results for the angle of aperture and divergence are stated here under consideration of the total internal reflection at the junction of the core to the surroundings. Furthermore the full angle of the conical element, the geometrical length and the varying diameters, the refractive indices and non-axial ray entrance are considered. All derivations are made by means of geometrical optics for meridional rays.     

基于蚯蚓背孔射流的仿生射流表面减阻性能研究

为了减小流体对固体壁面的阻力, 基于蚯蚓生物学特征, 对蚯蚓背孔射流特性进行分析, 建立仿蚯蚓背孔射流的仿生射流表面计算模型, 采用SST k-ω 湍流模型对仿生射流表面的减阻特性进行数值模拟, 同时对数值模拟结果进行实验验证, 并以此研究了仿蚯蚓背孔射流表面的减阻机理.结果表明, 在一定条件下, 仿蚯蚓背孔射流的仿生射流表面具有较好的减阻效果; 在同一射流方向角下, 随着射流速度的增加, 减阻率逐渐增大; 在同一射流速度下, 随着射流方向角的增加, 减阻率呈先减小后增大的变化趋势; 数值模拟与实验均在射流速度为1 m·s^-1、射流方向角为-30°时达到最大, 分别为8.69%, 7.86%; 射流表面改变了原有光滑壁面的边界层结构, 对壁面边界层进行了有效的控制, 减小了壁面的剪应力, 降低了壁面边界层的速度.     

Extraction of tungsten from scheelite using hydrodynamic and acoustic cavitation

The primary purpose of this study is to investigate the effects of hydrodynamic and acoustic cavitation (HAC) on the leaching efficiency of tungsten. The aim is to reduce energy use and to improve the recovery rate. The goal is also to carry out a leaching process at a much lower temperature than in an autoclave process that is currently used in the industry. Energy-efficient initiation and collapse of cavitation bubbles require optimization of (i) vibro-acoustic response of the reactor structure, (ii) multiple excitation frequencies adapted to the optimized reactor geometry, and (iii) hydrodynamic cavitation with respect to orifice geometry and flow conditions. The objective is to modify and apply a previously in house developed high power cavitation reactor in order to recover tungsten by leaching of the dissolution of scheelite in sodium hydroxide. In this process, various experimental conditions like dual-frequency excitation, different orifice geometry have been investigated. The numerically optimized reactor concept was excited by two frequencies 23 kHz and 39–43 kHz in various flow conditions. The effects of leaching time, leaching temperature, ultrasonic power and geometry of orifice plates have been studied. The leaching temperature was varied from 40 °C to 80 °C. The concentration of leaching reagent sodium hydroxide (NaOH) was 10 mol/L.The results were compared to conventional chemical leaching. Energy supplement with acoustic cavitation of 130 kWh/kg concentrate resulted in a leaching recovery of tungsten (WO₃) of 71.5%, compared to 36.7% obtained in absence of ultrasound. The results confirm that the method developed is energy efficient and gives a recovery rate potentially better than current autoclave technology.     

Flow patterns and heat-transfer characteristics of a top heat mode closed-loop oscillating heat pipe with check valves (THMCLOHP/CV)

The aim of this research was to investigate the flow patterns and heat transfer of a top heat mode closed-loop oscillating heat pipe with check valves (THMCLOHP/CV). In this study, the heat pipe was made of a high-quality glass capillary tube with an inner diameter of 2.4 mm bent into 10 meandering turns. The number of check valves was 2 and the tube was filled with R141b at a filling ratio of 50% of internal volume of the tube. The combined lengths of the evaporator, adiabatic and condenser sections were equal to 50 mm. The pipe was operated at the top heat mode, and the angles of inclination were 20°, 40°, 60°, 80°, and 90°. The heat applied at the evaporator section was controlled at 85°Cto 105°C, and 125°C. The results show that in the evaporator section, bubbles are produced and grow as a result of the continuous nucleate boiling. They coalesced and their volume expanded. Similarly, in the condenser section the vapor plug condensate caused the bubbles to collapse and accumulate as a liquid mass at the lower section of the U-bend tube. A new slug then developed and the bubbles coalesced in an upward flow. Heat flux increased when the evaporator temperature and inclination angle increased causing the average length of the vapor plug to decrease and the average velocity of vapor plug to increase. The maximum heat flux occurred at an evaporator temperature of 125°C and an inclination angle of minus 90°.