UBC Theses and Dissertations
Design and modeling of a sonochemical reactor using geometry, mode shapes and resonance Dostie, Kristen Amanda
A sonochemical reactor design which addresses deficiencies in current reactor designs is proposed. This design uses a comparatively low power electrostatic transducer because electrostatics are efficient over a wide frequency range and are not limited by their size, shape or placement in a reactor. This allows the creation of a reactor that can match the optimal frequency of a sonochemical process, maximize its sound field using mode shapes and resonance and, with the addition of a tracking system, follow system resonances that change with cavitation. The cylindrical reactor cavity and co-axial cylindrical transducer used in the design focus sound energy at the centre of the reactor, protecting the transducer from cavitation and allowing for analytic modeling of the sound field. A model of the proposed reactor's homogenous sound field was created in mathCAD. The model consists of a transducer model whose stiffness and damping coefficients were derived from a new thermodynamic model and a reactor model given by the reactor's wave equation and boundary conditions. The pressure magnitude generated at the transducer scales the magnitude of the reactor sound field. This allows the transducer pressure to be expressed as a relationship between its input voltage and the reactor mode shapes. A prototype reactor was constructed in order to verify the model experimentally. Data predicted by the model and measured experimentally were collected over a frequency range of 4 to 38 kHz. Ratios of the transducer's calculated electrostatic pressure to the pressure at the centre of the reactor were determined for both data sets. The match between the curves of this pressure ratio versus frequency for the two data sets was very good. Differences in the widths of the curve's frequency peaks were attributed to a smaller than expected air gap in the prototype transducer. Accounting for this produced an excellent match between the curves. Changes to the reactor design that would allow the reactor to achieve cavitation were investigated with the model. Both decreasing the transducer gap space and replacing the air in the gap with a gas of low thermal conductivity and high dielectric strength significantly reduced the voltage required to induce cavitation in the reactor. The model also revealed that the significant effect of the stiffness of small gap space transducers on the magnitude of the reactor's pressure field at low frequencies.
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