共查询到19条相似文献,搜索用时 125 毫秒
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溶液结晶技术在许多领域有着广泛的应用,其中结晶成核是溶液结晶的关键环节。以无水α-葡萄糖为研究对象,采用双频复合超声(25 k Hz+40 k Hz)强化糖液结晶成核,研究了溶液浓度、超声功率和作用时间对成核速率的影响,对单频和双频作用的晶核形态进行了对比,并采用碘化钾溶液中碘的释放量研究超声空化产额。研究结果表明:在同等条件下,双频复合超声降低了溶液成核的初始浓度,提高了成核速率,同时得到粒度均匀的晶核;双频复合超声的空化产额远高于单频25 k Hz超声和单频40 k Hz超声的空化产额,双频复合超声具有协同作用。双频复合超声强化溶液成核是一种快速、高效、节能的方法。 相似文献
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超声在结晶过程中的应用,近几年引起了国内外学者的广泛兴趣,主要探讨超声对结晶过程中结晶溶液的诱导期、溶液的一次成核、二次成核、晶体的结晶速率以及晶体的形貌和结构的影响.发现超声可以缩短诱导期,加速晶核的生成.提高晶体的结晶速率,改变晶体的形貌.特别是对产品的影响,可以更好地满足人们对产品的要求. 相似文献
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大功率低频超声场的主要特点是有空化产生,这给声场定量测量带来困难,而该类声场的测定是超声清洗、声化学等超声液体处理技术中的基本问题,掌握声场分布和空化强度的信息对于衡量超声系统的性能及其处理效果至关重要。文章综述了迄今用于测量大功率低频超声场的各种方法,将其分为直接测量方法和间接测量方法两大类进行阐述,介绍了每种测量方法的基本原理,并对各自的优缺点进行了对比分析。最后介绍了一些国内外的相关测量设备,结合大功率低频超声场测量领域目前的研究现状,探讨了今后该领域急需解决的问题及其发展方向。 相似文献
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过冷水法动态冰浆制取技术是一种有望实现大规模应用的动态制冰方法,工业上常用施加超声场的方式解除过冷水的过冷态并生成冰浆。本文实验研究了不同超声场对质量分数为3%的氯化钠溶液结晶过冷特性、生成冰晶尺寸及粒径分布的影响。结果表明:一定功率和频率的超声场的引入可快速解除过冷,使溶液在接近超声辐照温度下成核,且高功率、低频率的超声场更有利于成核发生。当功率、频率、辐照温度分别在10.0~40.0 W、28~40 kHz及0~4.0 ℃范围内,最佳超声场设置方案为超声功率40.0 W、频率28 kHz、辐照温度2.0 ℃;超声场的施加可显著减小冰晶尺寸;随着成核后超声辐照时间的延长,冰晶粒径先增大后趋于平缓,超声功率及频率的变化对冰晶粒径尺寸的影响无显著作用。 相似文献
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超声在临床治疗中已得到了广泛应用。近20多年国内外学者围绕超声热疗问题开展了深入研究,对超声热效应的机制已有较清楚的认识[1]。但超声治疗中的非热理象尚未受到足够重视,而这些现象有时可能是治疗的关键,尤其在高强度聚焦超声场中。本文就超声治疗中可能出现的几种主要的非热现象进行了总结。1声流声流源于声吸收。频率在1MHz以上时声流明显[2]。波形失真,声流速度增加。聚焦声场中,声流速度的峰靠近焦点。非聚焦声场中,声流速度沿轴向慢慢地单调增加[3]。脉冲声场中,声流速度随脉冲占空比减小而增加;高脉冲重… 相似文献
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用网篮盛放待清洗工件是最常用的一种清洗方法,影响清洗效果的一个关键因素是清洗槽内的声场分布,而网篮的存在会影响超声清洗槽内声场的分布。从实用的角度研究了清洗网篮对超声清洗槽内声场的影响。在用驻波场理论对清洗槽内声场分布情况进行分析之后.实验上用水听器法和染色法分别测量了放人网格前后超声清洗槽内声场的分布特点。结果表明,当丝径远小于1/4波长时,网格的存在对声场分布的影响很小,只是引起声波传播能量不同程度的衰减。这项研究对使用清洗网篮的超声清洗具有一定的参考价值。 相似文献
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辅助电场下TeO2-Nb2O5-AgCl系统玻璃的核化与析晶机理研究 总被引:8,自引:0,他引:8
在玻璃材料热处理过程中施加辅助电场,如果玻璃相的介电常数小于析出晶相的介电常数,则对玻璃的核化、晶化过程起促进作用;反之则起抑制作用.本文推导了辅助电场与温度场共同作用对玻璃核化、析晶过程的影响机理,研究了辅助电场对TeO2-Nb2O5-AgCl系统玻璃核化与析晶过程的促进作用.结果发现,辅助电场能帮助玻璃在稍低于核化和晶化温度区域的温度下成核和析晶,它可以成为控制玻璃核化和晶化过程的一个“开关”,有可能用以精确控制玻璃中纳米晶体的生长. 相似文献
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Acousto-optic imaging in diffuse media is a dual wave-sensing technique in which an acoustic field interacts with multiply scattered laser light. The acoustic field causes a phase modulation in the optical field emanating from the interaction region, and this phase-modulated optical field carries with it information about the local optomechanical properties of the media. We report on the use of a pulsed ultrasound transducer to modulate the optical field and the use of a photorefractive-crystal-based interferometry system to detect ultrasound-modulated light. The use of short pulses of focused ultrasound allows for a one-dimensional acousto-optic image to be obtained along the transducer axis from a single, time-averaged acousto-optic signal. The axial and lateral resolutions of the system are controlled by the spatial pulse length and width of the ultrasound beam, respectively. In addition, scanning the ultrasound transducer in one dimension yields two-dimensional images of optical inhomogeneities buried in turbid media. 相似文献
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The design of crystallization processes depends on a sound knowledge of the underlying kinetics. Due to the competitive market situation, a faster implementation of reliable processes becomes increasingly critical, by considering all involve length and time scales. The objective of this work is to study the crystallization kinetics of α-ammonium chloride with manganese chloride as a habit modifier using in-situ measurement techniques. Experimental data are recorded using a batch laboratory crystallizer equipped with a laser-backscattering device and an ultrasound probe measuring a chord length distribution and supersaturation, respectively. Besides nucleation and growth described in literature, additional kinetic mechanisms could be identified being a dead supersaturation zone as well as agglomeration. α-Ammonium chloride seems to be an ideal model system, due to the various kinetic mechanisms and morphologies that can be studied. In order to gain a deeper understanding of the processes involved a multiscale map for crystallization kinetics from solution is developed based on physical-based equations helping in visualizing preferred length and time scales of a specific kinetic phenomena. 相似文献
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Study on Enhancement in Gibbsite Precipitation of Bayer Process under 33 kHz Ultrasound 总被引:1,自引:0,他引:1
JihuaZHAO QiyuanCHEN 《材料科学技术学报》2003,19(6):607-610
The enhancement of gibbsite precipitation in Bayer process by 33 kHz ultrasound has been studied. From orthomethod experiment, the optimized operating parameters of treatment under 33 kHz ultrasonic cleaner have obtained.Compared with crystallization of Al(OH)3 without treatment of ultrasound, the precipitation time is reduced by 15 h when the precipitation ratio is 45%. From the results of grain size distribution and SEM photographs of gibbsite, it is found that secondary nucleation and agglomeration could be enhanced under 33 kHz ultrasound. The products are same from comparison of X-ray powder diffraction, but the Raman spectrum of sodium aluminate solution under 33 kHz ultrasound is different from that without ultrasound. 相似文献
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Won-Eui Hong 《Thin solid films》2007,515(13):5357-5361
This study revolved around the introduction of a crystallization technology for amorphous silicon film using Joule-heating. As part of this study, an electric field was applied to a conductive layer to induce Joule-heating in order to generate the intense heat needed to carry out the crystallization of amorphous silicon. Polycrystalline silicon was produced via Joule-heating through a solid state transformation under typical processing conditions. Uniformly distributed fine grains were obtained due to enormously high heating rate of this process. Crystallization was accomplished throughout the sample within the range of milliseconds of the heating, thus demonstrating the possibility of a crystallization route for amorphous silicon films at room temperature. 相似文献