超声清洗过程环境压力对声空化效应的影响*

在不同深度条件下的水下构建物超声清洗中,声空化是重要的源动力之一。为探明水下环境压力对声空化的影响,本文基于数值计算的方法,通过对超声波作用下气泡动力学的研究,讨论了环境压力对空化泡溃灭时的气泡最大半径、释放能量以及溃灭功率等因素的影响。结果表明：空化泡最大半径与环境压力在一定范围内呈近似线性关系;随着环境压力增大,空化泡释放能量和溃灭功率均显著减小,且两者在变化趋势和变化幅度上几乎一致;当环境压力大于声压幅值时,空化泡的最大半径、内部压强、内部温度与释放能量均远低于空化发生在环境压力小于声压幅值时的情形。     

超声空化现象影响因素的实验研究

超声空化在许多不同的学科和工业生产中有着广泛的应用。超声空化的应用与声场的分布及空化的机理密切相关,精准地反映空化场和空化机理是超声空化技术实际应用的关键。该文通过分析采集的声信号和金属箔膜空蚀法对空化区域随液位发生变化的现象进行研究,并利用Matlab对金属箔膜空蚀程度量化。实验发现,超声波会在液面与实验箱体底部形成驻波场。在某一液体温度下,随着液位高度的变化,超声空化现象的出现具有周期性。并且,在同一液位下,当超声功率改变时,空化区域强度分布情况随之改变。小功率时各空化区域空化强度分布均匀,当功率增大到一定时,会出现空化屏蔽现象。该研究为超声清洗设备的改良提供了借鉴,对进一步认识和利用超声空化效应具有重要意义。     

超声波空化作用对ICP光源辐射强度的影响

为了增大电感耦合等离子体辐射强度,降低分析检出限,实验研究了水样品经过超声波空化处理以后样品表面张力和粘度的变化,并探索了空化效应对光谱强度和信背比的影响。实验结果证明,样品溶液的表面张力和黏度随着超声波功率和空化时间的增加均呈现出先减小后增大的变化规律,在功率为50 W、时间为15min时水样品的表面张力和粘度最低。经此条件处理的水样品引入ICP以后,元素Al,Cd,Mn,Ni,Pb和Zn的谱线强度比无空化处理时分别提高了56.73%,57.23%,44.57%,43.20%,39.04%和40.19%,光谱信背比分别提高了61.54%,64.86%,44.95%,52.27%,40.84%和40.85%。可见,空化处理水溶液能够改善ICP发射光谱质量。     

超声波降解有机物溶液的气泡动力学研究

在超声波降解有机物溶液过程中,超声空化产生的高温高压以及空化泡振荡产生的激波在有机物溶液的降解中发挥重要作用.本文通过对超声波作用下气泡动力学的研究,讨论了超声波声压、频率、气泡初始半径等参量对有机物溶液降解效率的影响.研究发现,存在使降解效率极大的声压和频率。在空化稳定的情况下,存在一个使降解效率极大的气泡初始半径,降解效率随着黏滞系数的增大而减小。研究还发现,双频超声作用的空化效果比单频超声作用时强,与双频超声作用下有机物溶液降解率较大这一实验结果一致。      

功率超声珩磨磨削区空化声场的建模与仿真研究

通过建立Φ47功率超声珩磨磨削区流体-结构耦合声场的理论模型,采用ANSYS有限元分析软件对磨削区的空化声场进行了仿真分析,得出磨削区二维、三维空化声场的分布情况和声压幅值,并利用超声波功率测量仪对磨削区的空化声场进行模拟实验测量。结果表明:在谐振频率18.6 kHz下,声场主要集中在油石的中部,二维和三维声场的声压最大值分别为1.39 MPa和1.47 MPa,与实验测得声压最大值1.3 MPa在同一个数量级,为进一步研究功率超声珩磨空化效应提供理论和实验的基础。      

流动氩气介质阻挡放电特性及振动温度研究

采用双水电极介质阻挡放电装置,在流动氩气中通过改变气隙间距、驱动电源频率和气体流量等研究放电电学特性和振动温度的变化。电学测量结果发现如果固定其他实验条件而只改变某一参数,小气隙间距放电的电流峰值和功率比大气隙间距的高。同样,增大驱动电源频率也能够使放电的电流峰值和功率增加,而增加气体流量使得放电电流峰值和功率减小。最后利用光谱学方法,通过对放电发射光谱中氮分子振动带系的分析,发现振动温度随着放电气隙间距、电源频率和气体流量的变化关系与放电的电流峰值和功率的变化关系基本一致。这些结果对流动气体中大气压介质阻挡放电的应用具有重要意义。     

流体控制方程的超声空化泡动力学模拟*

本文基于流体动力学控制方程和VOF模型,在FLUENT 14.5软件环境下对超声空化泡进行数值模拟。首先研究了超声空化泡一个周期内的形态变化,并且利用空化泡形态变化的最大面积、最小面积、膨胀时间、收缩时间等数值结果分析超声参数对空化效果的影响。同时探究了双频超声作用下空化泡运动的变化,计算结果表明:在其他条件相同的情况下,在1~5MPa范围内,超声声压幅值为3MPa时空化效果最好;当超声频率大于20kHz时,空化效果随着超声频率的增大而降低。对于频率相同的双频超声,较声压幅值为其两倍的单频超声有更好的空化效果;对于频率不同的双频超声,空化效果受到频率差的影响。     

声场中水力空化泡的动力学特性

以水为工作介质,考虑了液体黏性、表面张力、可压缩性及湍流作用等情况,对文丘里管反应器中空化泡在声场作用下的动力学行为特性进行了数值研究.分析了超声波频率、声压及喉径比对空化泡运动特性以及空化泡崩溃时所形成泡温以及压力脉冲的影响.结果表明,超声将水力空化泡运动调制成稳态空化,有利于增强空化效果. 关键词： 超声波 水力空化 湍流 气泡动力学     

可压缩液体中气泡的声空化特性

利用新提出的Gilmore-NASG模型,在考虑液体可压缩效应的边界条件下,研究了可压缩液体中气泡的声空化特性,并与利用原有KM-Vd W模型计算得到的结果进行了比较.结果表明,相比于KM-Vd W模型,由于Gilmore-NASG模型采用新的状态方程来描述气体、液体以及由可压缩性引起的液体密度变化及声速变化,所以用Gilmore-NASG模型得到的空化气泡的压缩比更大、崩溃深度更深、温度和压力峰值更高.随着驱动声压幅值的增大,两种模型给出的结果差别愈加明显,而随着驱动频率的增大,两种模型给出的结果差别逐渐减小.这表明,在充分考虑泡内气体、周围液体在不同温度和压强下共体积的变化所导致的介质可压缩特性下,气泡内的温度和压强可能达到更高值.同时, Gilmore-NASG模型还预测出了气泡壁处液体的密度变化、压力变化、温度变化以及液体中的声速变化.因此, Gilmore-NASG模型在研究高压状态下气泡的空化特性以及周围液体对气泡空化特性的影响方面具有优点.     

降膜蒸发冷却器性能实验台的研制

本文研制的降膜蒸发冷却换热器性能实验台,可针对蒸发式冷却换热器的传热性能进行实验研究。实验台可进行变工况调节,换热量在15～34 kW之间;所需热水水泵的功率为0.37 kW,喷淋水水泵功率为0.15 kW;冷却空气采用变风量控制,风量介于0～2 700 m~3/h;被冷却介质采用软化去离子水,软化水器的供水量≥0.662 m~3/h。实验台可进行蒸发式冷却器冷却介质温度和流量、喷淋密度、迎面风速、环境湿球温度等参数对冷却器传热性能的影响规律研究,可获得优化的运行参数。     

Cavitation dose in an ultrasonic cleaner and its dependence on experimental parameters

The aluminum foil erosion method is widely used in cavitation activity studies of ultrasonic cleaners. However, owing to its limited sensitivity, it is difficult to observe the effects of various experimental parameters on the cavitation activity using this method. In the present work, a higher-sensitivity method for quantifying cavitation activity as a cavitation dose based on passive cavitation detection was presented. The influences of various factors (e.g., insonation duration, driving power, gas content, temperature and cleaning agents) were studied for this system. The results showed that the cavitation dose became unstable over long insonation times, and that the instability was more significant at high power. Generally, the cavitation activity could be enhanced by increasing the power, gas content, and the concentration of a cleaning agent. However, due to the exhaustion of the cavitation gas nuclei, the cavitation activity might tune to saturate of even decrease slightly when some impact parameters (e.g., acoustic driving power, gas content and the concentration of the cleaning agent) are above a certain level of each of these parameters.     

The influence of pressure on the acoustic cavitation in saturated CO2-expanded N,N-dimethylformamide

CO₂-expanded organic solvent is a kind of important fluid medium and has broad applications in chemical industry, environmental protection and other fields. Ultrasonic cavitation in gas expanded liquids (GXLs) is conducive to enhancing mass transfer and producing many exciting phenomena. In this paper, the ultrasonic cavitations and streaming in the saturated CO₂-expanded liquid N, N-dimethylformamide (DMF) at 4.2 MPa and 5.2 MPa are observed by a high-speed camera. The cavitation intensity and time trace of pressure pulses are recorded using a PZT hydrophone. The influences of gas–liquid equilibrium pressure and ultrasonic power on the cluster dynamics of transient and stable cavitation are examined. The excess molar enthalpies required for CO₂ dissociation from DMF are calculated by Peng-Robinson equations of state and the change of surface free energy of CO₂-expanded DMF is predicted. The results show that the excess enthalpy of the mixture is one of the key factors to control ultrasonic cavitation at high pressurized conditions, while the surface tension is the key factor for low pressure. As the increase of applied ultrasonic power, the formation and collapsing frequency of bubble clusters increases, and the amplitude and cyclic frequency of pressure pulse are enhanced. The transient cavitation intensity increases as it reaches a maximum value at a certain ultrasonic power and then decreases. The change trends of stable cavitation intensity under different pressures are basically same. It can be concluded from the evidence that ultrasonic cavitation in CO₂-expanded DMF is affected by the combined effect of compression and substitution: compression depresses the nucleation and growth of bubbles, while the high solubility of CO₂ in DMF is conducive to the generation of bubbles in cavitation.     

Sonolytic degradation of endocrine disrupting chemical 4-cumylphenol in water

The sonolytic degradation of endocrine disrupting compound 4-cumylphenol (4-CyP) in aqueous solution was investigated. The influence of operating parameters for sonication process such as 4-CyP initial concentration, frequency, power, pH, temperature and saturating gas was examined. The extent of degradation was inversely proportional to the initial substrate concentration. The rate of 4-CyP degradation was frequency dependent. The degradation rate increased proportionally with increasing ultrasonic power from 20 to 100 W and temperature in the range of 20-50°C. The most favorable degradation pH was acidic media. Destruction in the presence of saturating gas follows the order: argon>air>nitrogen. The 4-CyP degradation was inhibited in the presence of nitrogen gas owing to the free radical scavenging effect in vapor phase within the bubbles of cavitation. The ultrasonic degradation of 4-CyP was clearly promoted in the presence of bromide anions and the promoting effect on degradation increased with increasing bromide concentration. At low 4-CyP concentration (0.05 mg L(-1)), bicarbonate ion drastically enhanced the rate of 4-CyP degradation. Experiments conducted using pure and natural water demonstrated that the sonolytic treatment was more efficient in the natural water compared to pure water.     

Evolution of an 1 MHz ultrasonic cavitation bubble field in a chopped irradiation mode

In this paper the evolution of an ultrasonic cavitation bubble field is studied by means of the void rate, the cavitation noise power and the electric power that feeds the ultrasonic transducer. The ultrasonic irradiation is performed in chopped mode. It is observed two kinds of evolution that differ respectively by a slow (A regime) and a fast (B regime) void rate increase. They correspond to cavitation regimes that are identified as respectively a stable cavitation and an inertial cavitation field. The beginning of the fast increase of the void rate is delayed from the irradiation start and this delay depends on the chopping frequency of the irradiation mode.     

利用液氮冷能的小型天然气液化流程

为了简化小型天然气液化流程中的制冷装置,增加产品的收益率,设计了一种利用液氮冷能且带精馏的天然气液化流程,在得到液化天然气(LNG)的同时得到液化石油气(LPG)。采用HYSYS软件对流程进行模拟,选取P-R方程计算天然气气液相平衡特性,以生产单位质量的LNG耗功最小为目标函数进行优化,得到了关键节点参数,主要分析了塔内工作状况和换热器管路的热负荷分布情况。结果表明:塔的操作压力对产品纯度影响很大,换热器过大的温差和负荷造成了主要的火用损失,LNG回收率大于90%。     

Theoretical model of ice nucleation induced by acoustic cavitation. Part 1: Pressure and temperature profiles around a single bubble

This paper deals with the inertial cavitation of a single gas bubble in a liquid submitted to an ultrasonic wave. The aim was to calculate accurately the pressure and temperature at the bubble wall and in the liquid adjacent to the wall just before and just after the collapse. Two different approaches were proposed for modeling the heat transfer between the ambient liquid and the gas: the simplified approach (A) with liquid acting as perfect heat sink, the rigorous approach (B) with liquid acting as a normal heat conducting medium. The time profiles of the bubble radius, gas temperature, interface temperature and pressure corresponding to the above models were compared and important differences were observed excepted for the bubble size. The exact pressure and temperature distributions in the liquid corresponding to the second model (B) were also presented. These profiles are necessary for the prediction of any physical phenomena occurring around the cavitation bubble, with possible applications to sono-crystallization.     

变温热源布雷顿循环的功率密度优化

计入工质与高、低温侧换热器的热阻损失及压气机和涡轮机中的不可逆压缩和膨胀损失,用有限时间热力学方法,导出了恒温热源条件下不可逆布雷顿循环功率密度与压比间的解析式,借助于数值计算,研究了高、低温侧换热器的热导率分配和工质与热源间的热容率匹配对最大功率密度的影响。     

The efficiency of ultrasonic oscillations transfer into the load

The results of ultrasonic action to the substances have been presented. It is examined, the correlation between the electrical parameters of ultrasonic equipment and acoustic performances of the ultrasonic field in treating the medium, the efficiency of ultrasonic technological facility, and the peculiarities of oscillations introduced into the load under cavitation development. The correlation between the acoustic powers of oscillations securing the needed level of cavitation and desired technological effect, and the electrical parameters of the ultrasonic facility, first of all, the power, is established. The peculiarities of cavitation development in liquids with different physical-chemical properties (including the molten low-melting metals) have been studied, and the acoustic power of oscillations introduced into the load under input variation of electric power to the generator has been also estimated.     

Study on removing calcium carbonate plug from near wellbore by high-power ultrasonic treatment

In this paper, the effects of ultrasonic wave on the removal of inorganic scaling and plugging in cores and the influence of the key wave field parameters, process parameters and core physical parameters on the plugging removal efficiency are systematically studied. The main dynamic mechanism of ultrasonic plugging removal is also systematically analyzed. Results show that the transducer frequency, transducer power, ultrasonic treatment time and initial permeability of core have great influence on the effect of ultrasonic scale removal. When the cumulative treatment time of ultrasonic wave exceeds 60 min, the recovery rate of core permeability tends to be stable. Best effect can be achieved when processing for 80–120 min cumulatively; the plugging removal effect is improved with the increase of ultrasonic transducer power and ultrasonic frequency, but the effect of plugging removal is not obvious with the further increasing of them. In addition, it is proved that the effect of removing calcium carbonate plug from near wellbore by hydrochloric acid solution is slightly better than that by ultrasonic treatment alone. Finally, the micro dynamic mechanism of removing inorganic scale plug by high-power ultrasonic treatment is discussed in view of ultrasonic inorganic scale body crushing, ultrasonic cavitation, ultrasonic friction, ultrasonic peristaltic transport operation and ultrasonic fracture-making and permeability-increasing effect.