Sonication mechanical vibrations

This technique is used mainly for nonpolar compounds. Typically a small aliquot of soil (10-30 g) is dried by mixing with sodium sulfate prior to extraction. Next, the sample is extracted with a solvent for 10-20 min using a sonicator probe. The choice of solvent depends on the polarity of the parent compound. The ultrasonic power supply converts a 50/60-Hz voltage to high-frequency 20-kHz electric energy that is ultimately converted into mechanical vibrations. The vibrations are intensified by a sonic horn (probe) and thereby disrupt the soil matrix. The residues are released from soil and dissolved in the solvent. 

Ultrasound (sonication) converts AC line voltage to 20-kHz high-frequency electrical energy, which is fed to a converter where, in turn, it is converted to mechanical vibrations. 

The noise sources in control valves include mechanical vibration (usually below 100 dBA) hydrodynamic noise caused by liquid turbulence, cavitation, or flashing (usually below 110 dBA) and aerodynamic noise (can reach 150 dBA). In control valve design, aerodynamic noise can be a major problem. Aerodynamic noise generation, in general, is a function of mass flow rate and the pressure ratio (p /pf) across the valve. The point at which sonic speed is reached in the valve vena contracta is a function of the valve design. 

Ultrasound extraction (sonication) is based on the conversion of AC current at 50/60 Hz into electrical energy at 20 kHz and its transformation in mechanical vibrations. Due to the cavity, microscopical vapor bubbles are formed and, after implosion, they produce strong shockwaves into the sample. For isolating the (semi)volatile organic compounds, the liquid-liquid ultrasound technique is applied to samples such as soils, sediments, coal, etc. The process is also useful for the biological materials destruction (Loconto, 2001). Sonication extraction is faster than Soxhlet extraction (30-60 min per sample) and allows extraction of a large amount of sample with a relatively low cost, but it still uses about as much solvent as Soxhlet extraction, is labor intensive, and filtration is required after extraction. 

Electric energy is converted into mechanical vibrations in modem machinery using the piezoelectric effect. It concerivs the reversible property of special ceramic materials to deliver an electric voltage when affected by external forces. This characteristic is used for the generation of ultrasonic vibrations in such a way that the applied voltage is converted into mechanical vibrations. Modern sonic converters usually contain several piezoceramic disks of lead zirconate titanate restricted by two final masses that are mechanically prestressed by a centric screwing. 

The dynamic elastic modulus is determined by measuring the wave propagation velocity of ultrasonic pulses in the material. It is a nondestructive method, based on the dependence between the elastic modulus and the velocity of the propagation of the sonic or ultrasonic waves (mechanical vibrations). The method is very precise. The apparatus is not complicated, and it is possible to measure the dynamic elastic modulus at high temperatures. It is measured according to the standards ASTM C 1198-01 [53] and ISO 3312 1987 [54], and the elastic modulus of carbon materials is measured according to ASTM standard C747 [55]. 

In addition to the deposition mechanisms themselves, methods for preliminary conditioning of aerosols may be used to increase the effectiveness of the deposition mechanisms subsequently apphed. One such conditioning method consists of imposing on the gas nigh-intensity acoustic vibrations to cause collisions and flocculation of the aerosol particles, producing large particles that can be separated by simple inertial devices such as cyclones. This process, termed sonic (or acoustic) agglomeration, has attained only hmited commercial acceptance. 

ISO 6721-9 1997 Plastics - Determination of dynamic mechanical properties - Part 9 Tensile vibration - Sonic-pulse propagation method ISO 3385 1989 Flexible cellular polymeric materials - Determination of fatigue by constant-load pounding... 

A comparison has been made of the efficiencies of conventional and ultrasonically assisted pollutant extraction procedures using model soil samples (granular pieces of brick) which had been deliberately contaminated with copper oxide at 51 ppm [50]. Analysis of the brick particles after 30 min sonication on a Vibrating Tray [51] revealed an average reduction in copper content to 31 ppm, a reduction of about 40%. Using a conventional mechanically shaken tray for the same time period the residual contamination was 48 ppm representing a reduction of only 6% (Tab. 4.6). 

Horn design is a very important aspect of ultrasonic engineering. The vibrational amplitude of the piezoelectric crystal itself is normally so small that the intensity of sonication attainable by direct coupling of the transducer to the chemical system is not large enough to cause cavitation. The horn acts as an amplifier for the vibration of the transducer and the precise shape of the horn will determine the gain or mechanical amplification of the vibration. It is for this reason that it is sometimes referred to as a... 

The phenomenon sound comes about by periodic pressure waves, which are called acoustic or sonic waves. The term acoustic is sometimes reserved for vibrations that are in the audible range of frequencies, nominally from 20 to 20,000 Flz. Fligher frequencies are referred to as ultra-sonic and lower frequencies as infra-sonic. In the physics of sound and acoustics they play a similar role as the electromagnetic waves in the field of light and optics. Acoustics were unified with mechanics during the development of theoretical mechanics, in the same way as optics were unified with electromagnetism by the famous theory of Maxwell in the nineteenth century. 

The complex mechanical impedance can be obtained by measuring force, velocity, and their phase difference using probes or pickups attached to the transducer at suitable points [144], This method is very convenient with solids [52] (sometimes the most accurate), but not with liquids, although in this case it can be a convenient method of checking the performance of a transducer. The output from an accelerometer or strain-sensitive pickup gives information on resonant frequency and vibrational amplitude. However subsequent correlation with the power transmitted to the sonicated medium is not straightforward. 

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