Ultrasonic Mixing
Ultrasonic aggitation can promote mixing and, even,chemical reactions.
Ultrasonic cavitation is a very effective type of dynamic agitation based on the growth and implosive collapse of bubbles in liquid due to ultrasonic vibrations. Cavitation results from pre-existing weak points in the liquid, such as gas-filled crevices in suspended particulate matter or transient microbubbles from prior cavitation events. As ultrasound passes through a liquid, the expansion cycles exert negative pressure on the liquid, pulling the molecules away from one another. Where the ultrasonic energy is sufficiently intense, the expansion cycle creates cavities in the liquid when the negative pressure exceeds the local tensile strength of the liquid, which varies according to the type and purity of liquid.
Under the proper conditions, these bubbles undergo a violent collapse, generating very high pressures and temperatures. In some fields, such as what is known as sonochemistry, chemical reactions take advantage of these high pressures and temperatures brought on by cavitation. However, the growth and violent collapse of the bubbles themselves provides a desirably rigorous agitation of the liquid. Cavitation that occurs at the interface between the ultrasonically energized liquid and a solid surface is rather asymmetric and generates high speed jets of liquid, further agitating the liquid. This type of cavitation is particularly useful, for example, in facilitating a more complete mixing together of two or more components of a liquid solution.
The waveguide assembly comprises an elongate ultrasonic horn disposed at least in part intermediate the inlet port and the outlet port of the housing and has an outer surface located for contact with liquid flowing within the housing from the inlet port to the outlet port. (RDC 6/25/2010)
Source: Jansen et al from Kimberly-Clark, US Patent 7,703,698 (4/27/2010)
Recent Journal Articles
Dispersion and Exfoliation of Graphene in Rubber by an Ultrasonically-Assisted Latex Mixing and In situ Reduction Process
(590–602)Macromolecular Materials and Engineering 296 #7 (2011)
Zhan et al ofSichuan University, China, prepared NR/GE composites by an ultrasonically-assisted latex mixing and in situ reduction process. Graphene oxide was dispersed in NRL using an ultrasonic field and was then reduced in situ, followed by latex coagulation to obtain the NR/GE masterbatch. The results show that the process produces a much better dispersion and exfoliation of GE in the matrix and contributes to an increase in the tensile strength compared to conventional direct mixing. Compared to pure rubber, the tensile strength and tear strength for NR/(2 wt.-%)GE composites were increased by ≈47 and 50%, respectively. With increasing GE content, the maximum torque, crosslink density, elastic modulus, and thermal conductivity of NR/GE composites were found to increase. (RDC 7/14/2011)