电子膨胀阀掺气超空化降噪优化

空调、冰箱等电器被认为是室内环境的噪声的主要来源,特别是制冷剂的流动产生的噪声.运用掺气超空化理论,对传统电子膨胀阀进行结构优化,通过加装旁通管将蒸发器入口处的制冷引入到电子膨胀阀出口进行掺气,形成超空化现象,提高制冷剂局部压力,有效地抑制两相流中气泡的破裂,对比分析了优化改进后制冷剂的流动状态、局部压力、湍动能及气相体积分数.综合各方面因素发现,改进后制冷剂的流动噪声降低了3.16 dB.说明掺气引起的超空化能够有效地抑制制冷剂的流动噪声,在一定程度上对工程设计具有重要意义.     

掺气条件下水流空化特性的研究

通过对水流的空泡动力学研究,建立了掺气条件下空泡溃灭时所诱导的泡周围水体压力脉冲方程,考虑了不同流速不同掺气浓度对空泡溃灭的影响,揭示了空泡在水体中的溃灭特性,数值模拟了空化数对空泡溃灭的影响规律。结果表明:空化数随着掺气浓度的增加而增加,减弱了空泡溃灭时的空蚀破坏能力,低流速下空化数随掺气浓度增加较大,高流速下空化数增加较小;流速越高,掺气浓度越低,空化数越小,计算结果与试验结果吻合较好。     

掺汽超空化抑制节流喷射噪声研究进展

基于改变出口截面积降低蒸汽压缩式制冷系统中节流喷射噪声的常规方法并不能有效地抑制节流装置突发噪声,根据环泡状流动系统对两相流稳定性的贡献,利用掺汽装置构建超空化系统对抑制节流喷射噪声的前景,系统介绍了空化和超空化抑制噪声的研究进展,提出掺汽降噪在节流喷射系统中的应用技术,利于构建节流阀出口环泡状流动状态,进而抑制制冷装置节流喷射噪声。     

电子膨胀阀失效分析和预防

阐述了多联机电子膨胀阀失效的常见方式。重点研究和探讨了杂质对电子膨胀阀侵蚀的作用机理和危害,并从杂质过滤和逻辑控制等方面讨论了设计预防措施。     

减免空蚀掺气浓度的试验研究

本文在直流式水洞中用先进的量测仪器设备对减免空蚀的最低掺气浓度进行了系统的试验研究。通过对不同掺气浓度、不同配合比混凝土试件的空化空蚀试验,提出减免空蚀最低掺气浓度与高速水流速度的关系,给出不同掺气浓度时空化区的流态,比较了空蚀区掺气与不掺气情形的时均压力,并系统地观察了空化空蚀噪声随掺气量的变化。     

空化区圆柱突体空化特性的研究

通过空泡与空泡运动方程的研究,建立了水流空化区能量守恒方程,理论上对两种不同流速下圆柱突体诱导的空化区中空化特性进行了数值分析.试验在直流式水洞中进行,圆柱突体高为5mm,底部直径为6mm,掺气孔径为5mm.结果表明:同一流速下空泡半径随着掺气浓度的增加而减小;流速越高,掺气浓度越大,空泡半径越小.同一流速下空化数随掺气浓度的增加而增大;低流速下空化数最大值远大于高流速下空化数最大值,试验数据与理论吻合较好.     

电子膨胀阀用爪极步进电机数值优化研究

电子膨胀阀在变频空调系统中能精确调节制冷剂流量,有助于提高空调系统的能效和改善空调环境的热舒适性。研究电子膨胀阀用爪极永磁步进电机有助于提高电子膨胀阀稳定性和可靠性。对电子膨胀阀的电机力矩特性进行数值分析,在保持转子尺寸、通电电流和定转子之间气隙不变的前提下,通过改变爪极形状尺寸,分析了爪极形状参数对电子膨胀阀用爪极式步进电机自定位力矩和保持力矩的影响,认为在满足一定自定位力矩的前提下,保持力矩越大越好,并以此为基础对电机的爪极尺寸进行了优化,认为合理设计爪极尺寸参数,能够使电机的保持力矩和自定位力矩达到最佳,对电子膨胀阀步进电机的研究和设计有借鉴价值。     

关于电子膨胀阀焊接故障的研究及预防

本文验证了电子膨胀阀焊接故障的几种常见原因,针对这些故障提出解决方案,并经过试验验证,提高了电子膨胀阀焊接可靠性。     

电动式电子膨胀阀控制系统的设计

针对温度控制的精确要求,设计了一种基于ATMEGA16单片机和THB6128步进电动机驱动芯片的电子膨胀阀控制系统。温度传感器将温度转换为数字信号输入给单片机,单片机采用PID算法计算出步进电动机要运行的步数,驱动步进电动机控制电子膨胀阀的开度,实现温度的精确控制。实践表明,该控制系统具有控制精度高、价格低廉等优点。     

高速水流空化区和空蚀区掺气特性的试验研究

本文用先进的量测仪器在浙江工业大学水力学实验室直流式水洞中分别对高速水流空化区、空蚀区的掺气特性进行了较为系统的试验研究.实测了空化区掺气前后压力的变化,分析了压力波形的可压缩流特征以及马赫数与压缩比的关系;实测了空蚀区不同掺气浓度的时均压力分布,分析了压力随掺气浓度的变化及背压对空蚀的影响;提出减免空蚀的最低掺气浓度与流速的关系,比较了掺气前后水流的空化数.     

关于电子膨胀阀误动作故障的研究

电子膨胀阀作为空调制冷的关键零部件,其故障对产品性能有重大影响,生产过程及售后反馈的误动作是电子膨胀阀常见故障,本文结合实际生产制造工艺的经验分析电子膨胀阀误动作失效故障、失效机理和预防措施。     

基于小波收缩的心音降噪最优化分析

基于小波收缩技术提出一种最优化降噪方案用于去除心音信号噪声。依据频带相似匹配原则,分析心音信号频率特征和Haar、Daubechies、Symlets和Coiflets正交小波的特性,基于分析结果选取了Coif5小波并确定最优小波包进行分解重构。另外,提出一种光滑连续的自适应弹性阈值函数,能够克服硬阈值函数间断点问题,并基于4种阈值规则定量评价了其在不同信噪比下的降噪效果。仿真结果表明,当信噪比小于50 d B时,本优化方案配合启发式阈值规则能保留充足的心音细节信息,同时有效去除噪音。     

Fan noise reduction of household refrigerator

The authors describe the method of reducing the fan noise, especially the impeller noise, of a household refrigerator. The fan in the refrigerator tested is a propeller fan, and the fan unit consists of an impeller, which has four blades, a rear board, which covers the evaporator, and a front board, which has a number of openings. The flow through the openings freezes food in the freezer. By measuring the internal flow with a laser Doppler velocimeter, it was made clear that the flow through the impeller was not symmetrical to the axis. The unsymmetrical flow seems to be caused by the restrictions of flow passages, and it might produce the impeller noise. The search for the sound source by the sound intensity method indicated that the noise was radiated through the openings of the front board. Guiders were installed on the rear board in the fan unit to guide the flow away from the openings. As a result, the impeller noise was reduced, whereas the flow was kept almost the same     

Analysis and reduction of radiated EMI noise from converter systems

It is well known that high dv/dt rates on switching devices are the source of EMI noise. This paper describes a mechanism and reduction methods of radiated EMI noise on IGBTs. The radiated EMI noise is generated by oscillating current flowing through the IGBT's output capacity and the snubber circuit, which we call equivalent circuit of radiated EMI noise. The oscillating current of the equivalent circuit is forced to flow by high dv/dt rates of IGBT switching operation. Radiated EMI noise can be analyzed by frequency evolution of oscillating current. The results of this analysis show the relationship of high‐frequency impedance of the equivalent circuit to radiated EMI noise, as well as the behavior of the IGBT's switching voltage waveform. In addition, it is indicated that using a di/dt control gate drive circuit is effective as a means for reducing radiated EMI noise. It is clarified that the standard for industrial equipment of CISPR can be satisfied by using the proposed gate drive circuit. The effects of the method have been verified by experimental and simulational results. © 1999 Scripta Technica, Electr Eng Jpn, 130(1): 106–117, 2000     

大通量净水机降噪技术研究及应用

当前大通量(≥800 G)反渗透(RO)净水机为了满足用户需求,尽可能减少用户接水的等待时间,采用较大的出水流量.但与此同时,会导致净水机噪音比较大,严重影响用户的使用体验.净水机噪音主要来源于水泵本身产生的噪音,水泵振动引起的壳体共振,管路中水流冲击引起的湍振等.通过对以上三个主要的噪音源采用新型的降噪方案,并结合仿真模拟、计算和实验分析,在不影响净水机流量的情况下,低成本实现整机噪音的较大程度降低.     

Mode-field expansion and reduction in dispersive fibers by localheat treatments

A novel method is proposed to make the mode-field expander and reducer using dispersive fibers which are fabricated from optical glasses with different transformation temperatures and index reductions caused by rapid cooling. The dispersive fibers are heated locally at low or high temperatures, and the index difference is decreased or increased at the heated part. The mode-field is confined weakly or strongly in the core owing to the reduced or raised index difference, and is expanded or reduced partially     

心电信号降噪及R波提取技术研究

心电信号中R波的准确定位是其他波形定位的基础,在心电信号特征波形的研究中处于首要位置。本文根据R波在整个心电波形中幅值最为明显的特点,提出了一种基于小波理论提取R波的方法。首先选择合适的方法去除心电信号中的噪声,其次对去噪后的心电信号做5层小波分解得到各阶近似信号与细节信号,再次将得到的第3、4阶细节信号叠加,将叠加信号的均值作为搜索的阈值,并确定搜索起点,最后将搜索起点的横坐标映射至纯净的心电信号中,并使用逐点比对幅值的方式向后搜索,直至找到R波。使用MIT-BIH数据库中的数据进行多次实验验证,实验结果表明此算法能够准确的定位R波,检验的准确率为99.65%,召回率为99.86%。     

空间自适应有源消声系统研究

本文提出一种采用模型参考自适应状态观测器实现空间有源消声控制的方案。计算机仿真及硬件实验表明,该系统跟踪速度快,消声效果显著,并且结构简单,工作稳定可靠,具有良好的应用前景。     

The origin and reduction of acoustic noise in doubly salientvariable-reluctance motors

An experimental study of the acoustic noise emitted from an inverter-driven doubly salient variable-reluctance motor (VRM) is presented. A list of possible noise sources is given. Through a series of experiments, all but one source is eliminated as being important, and the remaining source is shown to be dominant. The dominant noise source is the ovalizing deformation of the stator due to its radial magnetic attraction to the rotor. The emitted noise is particularly strong when the frequency of deformation coincides with that of a natural mechanical resonance of the stator. Several methods of reducing acoustic noise emission are studied. One successful method is the introduction of dither into the control of the motor in order to spread the spectrum of noise excitation and reduce its coupling to the mechanical resonance of the stator