Thermal effects in the attenuation of ultrasound in dilute suspensions for low values of acoustic radius

Abstract

The importance of thermal effects in contributing to the overall attenuation of ultrasound propagating in suspensions of spherical solids and liquids in a background liquid medium is investigated. At a volume concentration of 0.01 and acoustic radius, ka, value of 0.01, where k is the wave number in the suspending medium, and a is the radius of the suspended (spherical) particles, the relative thermal attenuation has been calculated for seven selected solids suspended in 72 different liquids, and for 71 liquids suspended in water. A generalized approximate curve has been proposed for estimation of the thermal effects. The relative contributions of scattering, viscous effects, particle attenuation, and thermal effects have been calculated for several systems as a function of ka up to ka = 1 at room temperature. It can be seen that results for suspensions in water are unusual due to its unusual thermal properties. Thermal effects are of importance for virtually all systems up to ka ≈ 0.5. Above ka ≈ 1 other mechanisms dominate except for those cases of liquids suspended in liquids where, of all the relevant physical properties, only the thermal ones differ substantially between the two phases.