Process Intensification using High Intensity Focussed Ultrasound Techniques

This work programme aims to adapt the High Intensity Focussed Ultrasound (HIFU) methods used in biomedicine for application in industrial process control systems. Analogous with the current research trends in biomedical HIFU, this research programme will aim to create versatile ultrasonic transducer systems for intensification across a wide range of industrial processes associated with the pharmaceutical and food industries, in particular. A non-invasive pressure measurement facility has been established at Strathclyde (GR/N17928/01) and will be used to provide a platform for the development of array based high power ultrasonic systems designed via a finite element (FE) virtual prototyping environment. Here, the FE code will be used in the system design process to identify regions of high intensity which can be considered as offering the highest potential as sites for a cavitating field under HIFU excitation. A number of transducer configurations will be considered, using a combination of FE simulation and experimental evaluation, for application in an industrial HIFU system including: ultrasonic arrays; an array of discrete ultrasonic devices and an integrated monitoring/HIFU transducer. Once the HIFU techniques have been successfully demonstrated in a laboratory scale reactor vessel, the programme will investigate the challenging task of developing these systems into industrial scale process plant instrumentation. This will encompass new reactor vessel designs, in which the ultrasonic transducer configuration is an integral part of the design process; the influence of increased scattering/damping effects in industrial scale reactors; and the application of HIFU techniques to an in-line sampling loop, if appropriate. The key project aim is to investigate strategies which will realise practical industrial HIFU systems which can satisfy the growing industrial demand for process intensification using high power ultrasound.

High power ultrasound is used to enhance reactions and for cleaning purposes across many industries. This project considered new design approaches for both the reactor vessels and ultrasonic transducers to improve efficiency of future high power ultrasound systems.

This work programme has considered the application of ultrasound for pharmaceutical process control in both the low power monitoring and high power intensification regimes. Underpinning this research has been an extensive simulation, characterisation and experimentation programme. Previous EPSRC funding established a non-invasive pressure measurement facility at Strathclyde (GR/N17928/01) and this has been used to provide a platform for the development of high intensity focussed ultrasound (HIFU) ultrasonic systems designed via the finite element (FE) virtual prototyping environment. The FE code, PZFlex, has been used in this system design process, with both multi-transducer vessel reactors and linear array transducer system designs developed. It is observed that the pressure field within a reactor forms a complicated spatial pattern with a strong and highly variable dependence on transducer frequency, material properties of the load medium and vessel geometry. Analysis of the simulation results concluded that a multi-frequency, multi-transducer (MFMT) vessel reactor design can be optimised to produce a consistent cavitating field throughout the load medium. This novel vessel reactor design incorporates 12 ultrasonic transducers operating at three distinct frequencies (27, 40 and 80kHz) and can operate over a wide range of load medium phase velocities (1000m/s - 1500m/s). In addition, linear array transducers have been designed for operation at 210, 270 and 410kHz in standard cylindrical vessels. Moreover, this FE approach has been used to develop a dual frequency ultrasonic monitoring approach which allows the simultaneous acquisition of both the fundamental (linear) and second harmonic (non-linear) frequency responses from a pharmaceutical system.