Ultrasound attenuation dependence on air compression or expansion processes


Jakevicius, L. and Demcenko, A. and Mardosaite, R. (2010) Ultrasound attenuation dependence on air compression or expansion processes. Ultragarsas, 65 (1). pp. 42-46. ISSN 1392-2114

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Abstract:In this work variation of ultrasonic attenuation coefficient is analyzed in terms of air compression or expansion processes. In
closed spaces changing air volume, the ultrasound attenuation coefficient depends on thermodynamic processes which occur
during the air volume change. Two limiting cases are possible: 1) if the change of air volume is very slow or intensive heat
exchange occurs between the system and surrounding environments, so the system stays in a thermodynamic equilibrium;
therefore an isothermal process occurs; 2) if the change of air volume is very fast or the working environment has a good thermal
insulation, so the heat exchange between the system and the surrounding environment does not occur. In this case an adiabatic
process is presented. The attenuation coefficient of ultrasound varies very differently depending on the process (isothermal or
adiabatic) that occurs during the change of air volume. In particular, these differences occur when measurements are carried out in
a frequency range above 500 kHz during air compression. Initial relative air humidity has high influence on the ultrasonic signals
attenuation. Carrying out ultrasonic measurements in such systems, due to reliability of the measurements it is necessary to
evaluate thermodynamic process and ultrasound attenuation variation during the process. Oversaturated water vapour may occur
during the measurement process, therefore the measurement conditions become more complicated.
Keywords: attenuation of acoustic signals in air, relative humidity, isothermal process, adiabatic process
Item Type:Article
Engineering Technology (CTW)
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Link to this item:http://purl.utwente.nl/publications/74546
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