Sound energy

Sound energy flux p, p. chemical cell reaction ... 

AH materials, even those considered to be sound-reflecting, absorb some small fraction of the sound energy impinging on them. Table 1 provides sound-absorption coefficients for some common building materials. 

Fibrous ndFoa.medMa.teria.ls, Most sound-absorbiag materials are fibrous or porous and are easily penetrated by sound waves. Air particles excited by sound energy move rapidly to and fro within the material and mb against the fibers or porous material. The frictional forces developed dissipate some of the sound energy by converting it iato heat. 

When a sound wave comes in contact with a soHd stmcture, such as a wall between two spaces, some of the sound energy is transmitted from the vibrating air particles into the stmcture causing it to vibrate. The vibrating stmcture, in turn, transmits some of its vibrational energy into the air particles immediately adjacent on the opposite side, thereby radiating sound to the adjacent space. For an incomplete barrier, such as a fence or open-plan office screen, sound also diffracts over the top and around the ends of the barrier. The subject of this section is confined to complete barriers that provide complete physical separation of two adjacent spaces. Procedures for estimating the acoustical performance of partial barriers can be found in References 5 and 7. 

Therefore, when a noise is to be reduced, the sound energy must be con verted into another form of energy, such as kinetic energy of a medium or heat. 

Acoustic insulation A material that has the ability to absorb sound energy. 

Conductive hearing loss Hearing loss that is caused by blockage or other interference in the path by which sound energy is transferred to the inner ear. 

Directivity The characteristic associated with sound energy in the form of waves moving in a straight line from the source. 

Exchange rate The doubling of sound energy for each increase of 3 dB. 

Sound power The rate at which sound energy is produced at the source, given in watts. 

Source of sound energy Transmission pathway Receiver... 

The simplest insulator is a sheet of material placed in the sound-transmission pathways. Sound energy reaches the surface in the form of a pressure wave. Some energy passes into the partition and the rest is reflected. 

Acoustic cavitation based reactors create much higher sound energy/pressure... 

Mass Transport. Cavitation improves mixing but, on a macroscopic scale, it is probably less effective than a high speed stirrer. On a microscopic scale, however, mass transport is improved at solid surfaces in motion as a result of sound energy absorption. This effect is called acoustic streaming and contributes to increasing reaction rates. 

Before we discuss how sound energy can affect chemistry and chemical processing it would be instructive to explore some of the broader applications of the uses of ultrasound in industry [7-9]. Some of these have been in existence for many years and a range of such are shovm in Tab. 1.1. A few of these are explored in more detail in later chapters. 

One of the most important characteristics necessary to completely identify a wave is its intensity, where the intensity is a measure of the sound energy the wave produces. For a sound wave in air, the mass (m) of air moving with an average velocity (v) will have associated with it a kinetic energy of (mv )/2 (joules). In the strictest sense the intensity is the amount of energy carried per second per unit area by the wave. Since the units of energy are joules (J) and a joule per second is a watt (W), then the usual unit of sound intensity (especially in sonochemistry) will be W cm. As we will see later (Eq. 2.13), the maximum intensity (I) of the sound wave is proportional to the square of the amplitude of vibration of the wave (P ). This will have important repercussions in our study of chemical systems. 

If the sound energy passes through unit cross-sectional area (A = 1) with a velocity of c, then the volume swept out in unit time is c (since A = 1), and the energy flowing in unit time is given by E c. Since intensity (I) has been defined as the amount of energy flowing per unit area (A = 1) per unit time (Eq. 2.9)... 

The term sonochemistry is used to describe a subject which uses sound energy to affect chemical processes and the terminology is in keeping with that of the longer established methods such as electrochemistry (the use of electricity to achieve chemical activation). These older technologies require some special attribute of the system being activated in order to produce an effect e. g. the use of microwaves (dipolar species), electrochemistry (conducting medium) and photochemistry (the presence of a chromophore) whereas sonochemistry requires only the presence of a liquid to produce its effects. 

The Sonotech Cello pulse combustion system has the same limitations as a nonpulsating burner attached to a combustion device. Preliminary testing of the Sonotech system showed that in order to prevent slag formation, the temperature of the rotary kiln gas should not exceed 1700°F. The system produces considerable noise, which may be controlled by sound insulation. The Sonotech system uses resonant frequency of the incinerator to create pulsations. In an older incinerator, if the sound energy is not properly applied, the Sonotech system could cause structural problems. 

In the case of sound, the absorption coefficient (which is also called the acoustical absorptivity) is defined as the fraction of the incident sound energy absorbed by a surface or medium. the surface being considered par of an infinite area. 

When a sound wave strikes a material a fraction of its energy is reflected and a fraction is dissipated, or absorbed, by the material. The fraction of sound energy absorbed by a material is designated by its sound-absorption coefficient (oc). The sound-absorption coefficient of a given material is between zero and one if it is zero all the impinging energy is reflected and none absorbed if it is one all the eneigy is absorbed and none reflected. 

A practical consequence of architecture is to permit acoustical performances to large numbers of listeners by enclosing the sound source within walls. This dramatically increases the sound energy to listeners, particularly those far from the source, relative to free field conditions. A measure of the resulting frequency dependent gain of the room can be obtained from the EDR evaluated at time 0. This frequency response can be considered to be an equalization applied by the room, and is often easily perceived. 

In addition to acoustical methods, which take advantage of the fact that gas nuclei (i.e., stable microbubbles) are elastic bodies and thus absorb sound energy (ref. 4,5,9,25,26,31,32,50), another class of methods for detecting these gas microbubbles that has been employed repeatedly is based on their optical behavior. Specifically, most of these optical methods involve detection of these long-lived microbubbles in water from the light scattered by them (ref. 5,26,59,60,127). 

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