Water ultrasound with

As any conventional probe, acoustic beam pattern of ultrasound array probes can be characterized either in water tank with reflector tip, hydrophone receiver, or using steel blocks with side-drilled holes or spherical holes, etc. Nevertheless, in case of longitudinal waves probes, we prefer acoustic beam evaluation in water tank because of the great versatility of equipment. Also, the use of an hydrophone receiver, when it is possible, yields a great sensitivity and a large signal to noise ratio. 

Similar spatial distribution of active bubbles has been observed in partially degassed water and in pure water irradiated with pulsed ultrasound [67]. For both the cases, the number of large inactive bubbles is smaller than that in pure water saturated with air under continuous ultrasound, which is similar to the case of a surfactant solution. As a result, enhancement in sonochemical reaction rate (rate of oxidants production) in partially degassed water and in pure water irradiated with pulsed ultrasound has been experimentally observed [70, 71]. With regard to the enhancement by pulsed ultrasound, a residual acoustic field during the pulse-off time is also important [71]. 

Figure 8.43 depicts two typical configurations used to assess the effect of ultrasound on membrane filtration and cleaning. Figure 8.43 a shows a bath configuration where the crossflow cell is immersed in a water bath with ultrasonic transducers attached to the bottom of the bath. Figure 8.43b shows horn configuration where an ultrasonic hom is installed in a conventional cell. 

The high temperatures and pressures produced lead to the formation of free radicals and other compounds thus, the sonication of pure water causes its thermal dissociation into H atoms and OH radicals, the latter forming hydrogen peroxide by recombination [9,11,12]. Table 3.1 shows the main reactions occurring in water irradiated with ultrasounds. If the water contains some salt such as potassium iodide, iodine free radicals are also released in addition to the previous species [4]. 

High-power ultrasound has been used to disrupt cells, disperse aggregates, and modify food texture and crystallization (Knorr et ah, 2004). The ultrasonic wave causes intense localized heating and this generates gas bubbles which cavitate and result in intense pressure and shear (Povey and Mason, 1998). It is the high pressure and shear which cause physical disruption of food components and materials and can change the rate of chemical reactions. Kentish et ah (2008) used a flow-through power ultrasound systems at 20-24 kHz to produce an oil-in-water emulsion with... 

Ultrasound has been successfully employed in conjunction with bactericide for the destruction of microorganisms. In the treatment of raw water, ultrasound enhances chlorination as a method of biological sterilization [36], The results (Figure 6) show survival rates of bacteria in raw water, using a fixed chlorine concentration of 1 ppm, with respect to two parameters chlorine contact time and sonication time. 

Intrinsic losses are related to the molecular-level interaction of ultrasound with the material of the homogeneous phases making up the disperse system. Ultrasonic waves undergo partial attenuation when they propagate through any homogeneous system. For example, in water this attenuation is very low, 20 dB/cm at 100 MHz [33], In disperse... 

Most amino acid based gels are composed of n systems such as phenyl, naphthyl, and dipyridyl groups. For example, the dispersion of particles of the peptide compound 3 in alkanes or the mixture of polar solvents such as water/methanol (with the ratio of 1 4) can undergo a precipitate-gel transition when treated with ultrasound at 20 °C for - min [19]. CP-MAS NMR spectra indicated that the molecules formed nanofibers with jl-sheet structure. Interestingly, the compound can selectively gel alkanes in water/alkane mixtures when exposed to ultrasound without heating at room temperature, which might be more meaningful for potential applications of the gel in industry, for example, in the collection of petroleum from water. 

Conjugate addition of alkyl groups to a-enones with the aid of zinc and ultrasound in a one-step reaction was reported more recently [70]. Here too, the solvent contained water, together with either ethanol or 1- or 2-propanol. A sound absorption maximum was found for this reaction which indicates a maximum three-dimensional structure organisation of the liquid. That such an optimal organisation parallels a maximum in the reaction yield, most probably indicates a strong solvent participation in a determining step [70b]. 

With liquid samples as oils, OL isolation has been realized by two main techniques liquid-liquid extraction (LLE) and solid-phase extraction (SPE) [14, 73]. LLE is based on transfer of the phenolic fraction from VOO to a more hydrophilic phase such as pure methanol or methanol-water mixtures with different alcohol concentrations [42 14]. Ultrasounds can be used as auxiliary energy to accelerate and improve LLE. The main advantages of ultrasound-assisted LLE are shortened extraction time, reduced reagent and sample volume, and improved extraction efficiency [32, 48]. After extraction, cleanup and pre-concentration steps are... 

Based on these results we investigated different methods for the formation of water droplets in the organic phase. The emulsions were generated by extrusion from syringes through capillaries or a thin brass disk with narrow pores in the low micrometer range. In addition, sonication with ultrasound, electrospray and a microemulsion system were analyzed in term of droplet size and stability for the phase transfer process. In all these experiments, we used different techniques to generate water droplets with various sizes and encapsulated compounds. 

Attenuation is also an important factor in air-bome ultrasound. For exampe, attenuation in air at 1 MHz is 1.2 dB/cm, compared with a figure of 0.0022 dB/cm in water [1]. In addition, environmental conditions (temperature, turbulences) can affect the inspection with air-bome... 

Two major sources of ultrasound are employed, namely ultrasonic baths and ultrasonic immersion hom probes [79, 71]- The fonuer consists of fixed-frequency transducers beneath the exterior of the bath unit filled with water in which the electrochemical cell is then fixed. Alternatively, the metal bath is coated and directly employed as electrochemical cell, but m both cases the results strongly depend on the position and design of the set-up. The ultrasonic horn transducer, on the other hand, is a transducer provided with an electrically conducting tip (often Ti6A14V), which is inuuersed in a three-electrode thenuostatted cell to a depth of 1-2 cm directly facing the electrode surface. 

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