运用液体声学理论研究超临界二氧化碳的声特性

利用液体声学模型，根据美国国家标准局提供的二氧化碳声速、密度、摩尔体积和绝热压缩系数数据，计算了气态、液态和超临界态二氧化碳在不同温度和压力条件下的摩尔声速、摩尔压缩系数及Van der Waals 常数. 分析发现，在较宽的温度和压力范围内，液体中的声学模型能够很好地运用于超临界态二氧化碳的研究. 并在液体声学模型适用范围内，计算了超临界二氧化碳在不同温度及压力状态下的表面张力、粘度、自扩散系数，为超临界流体技术提供了参考数据，并分析了这些参量的变化规律.     

运用液体声学理论研究超临界二氧化碳的声特性

利用液体声学模型,根据美国国家标准局提供的二氧化碳声速、密度、摩尔体积和绝热压缩系数数据,计算了气态、液态和超临界态二氧化碳在不同温度和压力条件下的摩尔声速、摩尔压缩系数及Van der Waals 常数. 分析发现,在较宽的温度和压力范围内,液体中的声学模型能够很好地运用于超临界态二氧化碳的研究. 并在液体声学模型适用范围内,计算了超临界二氧化碳在不同温度及压力状态下的表面张力、粘度、自扩散系数,为超临界流体技术提供了参考数据,并分析了这些参量的变化规律. 关键词： 超临界二氧化碳 声速 摩尔声速 摩尔压缩系数     

Ultrasonic study of nitric acid

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Studies on nano suspensions of silver sol and redispersed nanocrystallite silver in aqueous and alcoholic media

Nanocrystallite silver and silver sol were prepared and characterized by UV-visible spectra, XRD, TEM and HRTEM. The crystallite silver is re-dispersed in two different media, namely, water and alcohol and sonicated before ultrasonic investigation. The silver sol was used as such. Three different models for the propagation of ultrasound through two phase media are compared in these three different types of nano suspensions. Effect of particle size and medium on ultrasonic velocity (U), compressibility (κ) impedance (Z) and viscous relaxation time (τ) is studied. The particle concentration range was 0.2-1 v/v. Density and viscosity of the dispersion and sol are measured at different particle volume fractions. Effective density and ultrasonic velocity are computed by Urick, Kuster and Toksöz and Urick and Ament models and compared with experimental velocities. Values of effective density obtained by using Urick and Urick and Ament equations closely agree with experimental results of density while Urick's equation prediction of velocity is in close agreement with the experimental velocities. This comes as a surprise in view of the large density difference between the medium and suspended particle and suggests the possibility of the balancing effect of the inertial and viscous forces operating in the suspension.     

Ultrasonic and IR study of intermolecular association through hydrogen bonding in ternary liquid mixtures

Complex formation in ternary liquid mixtures of dimethylsulfoxide (DMSO) with phenol and o-cresol in carbontetrachloride has been studied by measuring ultrasonic velocity at 2 MHz, in the concentration range of 0.019-0.162 (in mole fraction of DMSO) at varying temperatures of 20, 30 and 40 degrees C. Using measured values of ultrasonic velocity, other parameters such as adiabatic compressibility, intermolecular free length, molar sound velocity, molar compressibility, specific acoustic impedance and molar volume have been evaluated. These parameters have been utilized to study the solute-solute interactions in these systems. The ultrasonic velocity shows a maxima and adiabatic compressibility a corresponding minima as a function of concentration for these mixtures. The results indicate the occurrence of complex formation between unlike molecules through intermolecular hydrogen bonding between oxygen atom of DMSO molecule and hydrogen atom of phenol and o-cresol molecules. The excess values of adiabatic compressibility and intermolecular free length have also been evaluated. The variation of both these parameters with concentration also indicates the possibility of the complex formation in these systems. Further, to investigate the presence of O-HO bond complexes and the strength of molecular association with concentrations, the infrared spectra of both the systems, DMSO-phenol and DMSO-o-cresol, have been recorded for various concentrations at room temperature (20 degrees C). The results obtained using infrared spectroscopy for both the systems also support the occurrence of complex formation through intermolecular hydrogen bonding in these ternary liquid mixtures.     

A new ultrasonic method to detect chemical additives in branded milk

A new ultrasonic method — thermoacoustic analysis — is reported for the detection of the added chemical preservatives in branded milk. The nature of variation and shift in the thermal response of the acoustic parameters specific acoustic impedance, adiabatic compressibility and Rao’s specific sound velocity for different samples of branded milk as compared to the chemical added pure milk are explained as due to the presence of chemicals in these branded samples.     

On the hydrodynamic sound in polarized Fermi liquids

The velocity of sound for polarized Fermi liquids at frequencies intermediate between the inverse spin relaxation time and the inverse typical relaxation time is found via the kinetic equation. This velocity is not expressed by the static compressibility at a fixed magnetic field but at fixed spin polarization. The measurement of static quantities and this velocity allows one to determine the Landau parameters with l = 0 and the effective masses for the polarized liquid.     

The sound velocity of liquid TeSe mixtures

We have measured the sound velocity of liquid Te₇₀Se₃₀, Te₅₀Se₅₀ and Te₃₀Se₇₀ mixtures and obtained their adiabatic compressibility β_s. There appear prominent maxima in the temperature variations of β_S. It is concluded that the pressure-induced semiconductor-to-metal transition previously observed for liquid Te-Se mixtures is associated with the structural change from Se-like loosely packed to Te-like densely packed structure.     

Ultrasonic velocity in water-ethanol-sucrose mixtures during alcoholic fermentation

During alcoholic fermentation, sucrose and water are transformed into ethanol and carbon dioxide by the action of yeast enzymes. The measurement of the velocity of an ultrasonic pulse travelling through a fermentation tank can be used to characterize the state of the process. In this work, an experimental study of the density and ultrasonic velocity in the ternary mixture (water-ethanol-saccharose) is presented. Experimental results were compared to ideal density and to commonly used expressions of the sound velocity in liquid mixtures (Urick, Natta-Baccaredda and Nomoto). A semiempirical approach was proposed to improve the efficiency of theoretical models when dealing with mixtures of associated liquids.     

Acoustic non-linearity parameter B/A and related molecular properties of binary organic liquid mixtures

Acoustic non-linearity parameter B/A is calculated for binary mixtures using four different methods. The interactions in the liquid mixtures are explained on the basis of excess non-linearity parameter and excess adiabatic compressibility. Sehgal's relations for calculating molecular properties of pure liquids are extended to binary mixtures.     

Compressibility and sound velocity of some liquid rare earths

We report the first measurements of the sound velocity in liquid La, Ce, Pr and Yb and deduce the adiabatic and isothermal compressibilities. The temperature coefficient of the sound velocity in liquid Ce is positive, which we interpret as support for the suggestion that there is increasing delocalization of the 4f electrons in the liquid state.     

Phase transition studies in polymesomorphic compounds (ii): Ultrasonic velocity studies in N-(p-n-hexyloxy benzylidene) p-n-butyl aniline

The variation of ultrasonic velocity in N-(p-n-hexyloxy benzylidene) p-n-butyl aniline with temperature in the isotropic, nematic, S_A S_B and S_G phases is measured. All the phase transitions are of first order. The adiabatic compressibility β _ad , molar sound veclocity or Rao number R_n , and molar compressibility or Wada constant A are computed. Molar sound velocity and molar compressibility of HBBA are compared with the values of other compounds. They are found to be in good agreement with theory.     

The fast-ion transition in FCC silver iodide

An analysis of previously reported data on electrical conductivity, adiabatic temperature change with pressure, and sound velocity confirms that the FCC phase of AgI has a fast-ion type II transition. This results in a steepening of the FCC/α-phase boundary which probably cusps in to a triple point at the α-phase order/disorder transition. Thermal expansion, compressibility and heat capacity are calculated for the FCC phase.     

超声珩磨区实际气体的单空泡动力学分析

为进一步揭示功率超声振动的珩磨机理,以珩磨液为工作介质,研究了功率超声珩磨环境中实际气体的单空泡动力学特性。基于Rayleigh-Plesset方程,应用实际气体绝热方程和范德瓦尔斯方程对其进行了修正,建立了功率超声珩磨环境中实际气体的单空泡动力学方程以及实际气体单空泡共振频率方程。并运用4~5阶RungeKutta法模拟了不同超声条件(声压幅值、空泡初始半径、振动频率)对泡壁的运动以及运动速度的影响。结果表明:较高的声压幅值,空泡理论共振半径R'0与初始半径R0的比值为102数量级以及较低的超声频率有利于超声珩磨磨削区空化效应的发生。     

Ultrasonic approach to obtaining partial thermodynamic characteristics of solutions

We describe a method for evaluating the thermodynamic characteristics both of pure liquids and of solutes in solutions using data derived from ultrasonic velocity measurements. The principal possibility of using ultrasound velocity lies in the fact that the velocity of ultrasound is a simple function of the adiabatic compressibility. The problem is formulated as an initial value problem for the parabolic type differential equations in partial derivatives. The validity of the method is demonstrated by calculation of the thermodynamic parameters for water, glycine and alanine in aqueous solutions at infinite dilution.     

A improved incompressible lattice Boltzmann model for time-independent flows

It is well known that the lattice Boltzmann equation method (LBE) can model the incompressible Navier-Stokes (NS) equations in the limit where density goes to a constant. In a LBE simulation, however, the density cannot be constant because pressure is equal to density times the square of sound speed, hence a compressibility error seems inevitable for the LBE to model incompressible flows. This work uses a modified equilibrium distribution and a modified velocity to construct an LBE which models time-independent (steady) incompressible flows with significantly reduced compressibility error. Computational results in 2D cavity flow and in a 2D flow with an exact solution are reported.     

Phase transition studies in N(p-n-pentyloxy benzylidene) p-n-decyl aniline

The temperature dependences of the molar volume, the ultrasonic velocity and the refractive index in N(p-n-pentyloxy benzylidene) p-n-decyl aniline, which exhibits nematic, smectic-A and smectic-B, phases, are presented. The isotropic-nematic and smectic-A-smectic-B phase transitions are found to be of first order while the nematic-smectic-A transition is of second order. The thermal expansion coefficient (a) computed from the molar volume data agrees with a second-order N-S_A transition. The computed adiabatic compressibility β_ad, molar sound velocity (or Rao number R_n ) and molar compressibility (or Wada constant A) are presented.     

Phase transition studies in N-(p-n-pentyloxy benzylidene) p-Toluidine

The variations of molar volume M_v and ultrasonic velocity V with temperature in N(p-n-pentyloxy benzylidene) p-toluidine are presented. The molar volume jump at the nematicisotropic transition suggests it is of first order. The adiabatic compressibility β _ad, molar sound velocity or Rao number R_n , molar compressibility or Wada constant A, the thermal expansion coefficient α, and Van der Waals constant b, are computed. Molar sound velocity and molar compressibility are compared with the values of other members of the homologous series and are found to be in good agreement with Rao's and Wada's observations. The order parameter S_k, at the nematic-isotropic phase transition is 0.441 from our experimental results and the Maier-Saupe table and is found to be in good agreement with the theoretical value.     

除垢超声波传播影响因素的理论研究

从一维平面波理论入手分析了超声波声压分布特性。依据多普勒频移原理,在声场的运动方程,连续性方程,波动方程的基础上,建立一个超声波在流动的液体中传播的控制方程。根据轴对称模型的实际特点,简化了所得方程,并求出解析解。结果表明流动液体可以产生声波的衰减。液体的黏滞性是产生超声波衰减的重要原因。超声波的频率较高,液体的黏滞性对超声波衰减影响明显。依据黏滞力与速度梯度的关系,建立一个超声波在黏滞液体传播的控制方程,并依据边界条件求出解析解,反映了媒质黏滞性对超声波传播尤其是衰减特性的影响。