Efficient separation technologies for multi-component liquid streams that eliminate waste and reduce energy consumption are needed. Current technologies suffer from high cost of energy, use of consumables, fouling, and limited separation efficiency of micron-sized particles. We propose a novel platform technology consisting of a large volume flow rate acoustophoretic phase separator based on ultrasonic standing waves. The acoustic resonator is designed to create a high intensity three dimensional ultrasonic standing wave resulting in an acoustic radiation force that is larger than the combined effects of fluid drag and buoyancy, and is therefore able to trap, i.e., hold stationary, the suspended phase. The action of the acoustic forces on the trapped particles results in concentration, agglomeration, and/or coalescence of particles and droplets. Heavier than water particles are separated through enhanced gravitational settling, and lighter particles through enhanced buoyancy. A first prototype consists of a 2 in. by 1 in. flow chamber driven by a single 1 in. by 1 in. transducer at 2 MHz, with flow rates of 30 L/h, and measured oil separation efficiencies in excess of 95%. A second prototype is designed to further scale the system to flow rates of 150 L/h. [Work supported by NSF SBIR 1215021 and NSF PFI:BIC 1237723.]
Cell processing occurs in many technologies such as lab-on-a-chip, biopharmaceutical manufacturing, and food and beverage industry. Centrifuges and filters are used in preprocessing and filtration stages. These technologies are not continuous flow filtration methods, a drawback for automation and miniaturization. Continuous cell filtration using ultrasonic standing waves has been successfully used at limited flow rates [Hawkes and Coakley, Enzyme Microbial Technol. 19, 57–62 (1996)]. Advantages of ultrasonic particle filtration are continuous operation with no mechanical moving parts, no risk of membrane fouling, and no consumables. We present a novel design of an acoustophoretic particle separation system operating at large volume flow rates. The technology operates by creating ultrasonic standing waves that produce an acoustic radiation force on particles which exceeds the drag and gravitational forces thereby trapping the particles. Over time aggregation of trapped particles results in gravitational settling of the agglomerated particles. The system comprises a 1 in. × 1 in. flow section and is powered by a 2 MHz PZT-8 transducer and typically operates at flow rates up to 2 L/H. Concentration reductions in excess of 90% are obtained for yeast suspensions of rehydrated S. cerevisiae in RO-DI water with volume concentrations ranging from 0.5 to 3%. [Work supported by NSF PFI:BIC 1237723.]
Acoustic radiation forces on a particle or droplet in a liquid have been studied mostly for relative simple acoustic fields such as plane traveling waves, or planar standing waves. In this study, a more complicated acoustic field is considered, namely, the acoustic standing wave field generated by a rectangular piezoelectric plate with finite size. The piezo-electric plate is excited in its thickness mode. A three dimensional model of the vibration of the piezo-electric plate has been developed. The plate is loaded by an acoustic standing wave field in a fluid on one side, and is air backed on the other side. The three-dimensional acoustic standing wave field generated by the piezo-electric plate is calculated. The acoustic radiation force on a particle or droplet can then be calculated using a framework such as developed by Gor’kov or Ilinskii and Zabolotskaya. The theoretical calculations are compared with numerical predictions using a two-dimensional model of the piezo-electric plate and resonator. Finally, experimental results were obtained in a resonator with a one inch acoustic path length and driven by a 2 MHz PZT-8 one inch by one inch piezo-electric plate. Experimental results will be compared with theoretical and numerical predictions.
Large scale acoustophoretic separation of particles in a flow field can be accomplished by trapping the particles, i.e., remain in a stationary position, in ultrasonic standing waves. The particles are collected in a column pattern, separated by half a wavelength. Within each nodal plane, the particles are trapped in the minima of the acoustic radiation potential. The axial component of the acoustic radiation force drives the particles to their stable axial position. The radial or lateral component of the acoustic radiation force is the force that traps the particle. It must be larger than the combined effect of fluid drag force, i.e., Stokes drag, and gravitational force. There is a need for a better understanding of the lateral acoustic radiation force in realistic acoustophoretic separation devices. COMSOL Multiphysics® software was used to predict the acoustic field in two and three dimensional models of acoustophoretic separation devices driven by piezoelectric transducers. The resulting acoustic field was then used to calculate the acoustic radiation force acting on a suspended particle in two and three dimensions by applying Gor’kov’s equation. Measurements of trapped particles in standing waves indicate accurate calculations of acoustic field and radiation force. [Work supported by NSF PFI:BIC 1237723.]
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