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  • 1.
    Johansson, Örjan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Pamidi, Taraka Rama Krishna
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Design of high-intensity ultrasound reactor2017In: IEEE International Ultrasonics Symposium, IUS, Piscataway, NJ: IEEE Computer Society, 2017, article id 8092948Conference paper (Refereed)
    Abstract [en]

    Design and optmiziation of ultrasonic reactors are important objectives in sonochemical processing. The recent expansion of the use of ultrasonic reactors in various research projects all faces the problem of scaling up laboratory results for industrial use. A traditional ultrasonic reactor usually has several issues, such as low effectiveness and complex and unstable system performance, which all are unfavorable for efficient sonochemical processing. This study adresses these issues and investigates a new flow type ultrasonic reactor designed to generate transient cavitation as the main source for ultrasound for sonochemical processing. This study proposes the principle of the flow type ultrasonic reactor design to generate transient cavitation. The objective of this work is to design an ultrasonic reactor with a new geometry. The idea is to improve process efficiency based on resonance enhanced ultrasound controlled cavitation

  • 2.
    Johansson, Örjan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Pamidi, Taraka
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Khoshkhoo, Mohammad
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Sustainable and energy efficient leaching of tungsten(W) by ultrasound controlled cavitation2017Report (Other academic)
    Abstract [en]

    The project aims to use ultrasound controlled cavitation to achieve a more energy efficient leaching process. Locally, collapsing cavitation bubbles cause an extremely high pressure, shock waves and high temperature, which provide an opportunity to perform the leaching process at a much lower temperature than in an autoclave (20 bar overpressure and 220 ° C). The results show that the method works, but that a higher static pressure and thus temperatures are necessary to achieve a leaching recovery rate corresponding to today's autoclave technology. Another process parameter of importance is flow control and the initiation of cavitation bubbles that occur through a geometrically optimized nozzle (orifice plate). Numerical and experimental adaptation of the developed reactor with respect to the leaching conditions (Sodium hydroxide and Scheelite concentrate), required more time than expected. Best test results show that an energy supplement with ultrasonic controlled cavitation of 104 kWh / kg increases the leaching recovery by 21%. The leaching reagent temperature 60° C was determined regarding available reference data and was thought to be close to optimum for intensive cavitation in atmospheric pressure. Optimum temperature relates to the leaching reagent, vaporization temperature, density, boiling point, surface tension, and viscosity. Generally, for leaching is that higher temperatures are required to increase the chemical reaction rate (requires overpressure). The modified reactor principle provides stable results and is possible to scale up. Higher cavitation intensity for shorter finishing time and higher recovery rate require advanced flow induction, multiple excitation frequencies adapted to the optimized reactor geometry, as well as optimal process pressure and temperature.

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  • 3.
    Johansson, Örjan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Pamidi, Taraka
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Shankar, Vijay
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Extraction of tungsten from scheelite using hydrodynamic and acoustic cavitation2021In: Ultrasonics sonochemistry, ISSN 1350-4177, E-ISSN 1873-2828, Vol. 71, article id 105408Article in journal (Refereed)
    Abstract [en]

    The primary purpose of this study is to investigate the effects of hydrodynamic and acoustic cavitation (HAC) on the leaching efficiency of tungsten. The aim is to reduce energy use and to improve the recovery rate. The goal is also to carry out a leaching process at a much lower temperature than in an autoclave process that is currently used in the industry. Energy-efficient initiation and collapse of cavitation bubbles require optimization of (i) vibro-acoustic response of the reactor structure, (ii) multiple excitation frequencies adapted to the optimized reactor geometry, and (iii) hydrodynamic cavitation with respect to orifice geometry and flow conditions. The objective is to modify and apply a previously in house developed high power cavitation reactor in order to recover tungsten by leaching of the dissolution of scheelite in sodium hydroxide. In this process, various experimental conditions like dual-frequency excitation, different orifice geometry have been investigated. The numerically optimized reactor concept was excited by two frequencies 23 kHz and 39–43 kHz in various flow conditions. The effects of leaching time, leaching temperature, ultrasonic power and geometry of orifice plates have been studied. The leaching temperature was varied from 40 °C to 80 °C. The concentration of leaching reagent sodium hydroxide (NaOH) was 10 mol/L.The results were compared to conventional chemical leaching. Energy supplement with acoustic cavitation of 130 kWh/kg concentrate resulted in a leaching recovery of tungsten (WO3) of 71.5%, compared to 36.7% obtained in absence of ultrasound. The results confirm that the method developed is energy efficient and gives a recovery rate potentially better than current autoclave technology.

  • 4.
    Johansson, Örjan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Pamidi, Taraka
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Shankar, Vijay
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Acoustic design principles for energy efficient excitation of a high intensity cavitation zone2019In: Proceedings of theICA 2019 AND EAA EUROREGIO: 23rd International Congress on Acoustics,integrating 4th EAA Euroregio 2019 / [ed] Martin Ochmann, Micchael Vorländer, Janina Fels, Aachen, Germany: RWTH Publications , 2019, p. 948-955Conference paper (Refereed)
    Abstract [en]

    Energy-efficient process intensification is a key aspect for a sustainable industrial production. To improve energy conversion efficiency high intensity cavitation is a promising method, especially in cases where the material to be treated is valuable and on the micro meter scale. Transient collapsing cavitation bubbles gives powerful effects on objects immersed in fluids, like cellulose fibers, mineral particles, enzymes, etc. The cavitation process needs optimization and control, since optimal conditions is multivariate challenge. This study focuses on different design principles to achieve high intensity cavitation in a specific volume in a continuous flow. This study explores some potential design principles to obtain energy efficient process intensification. The objective is to tune several different resonance phenomena to create a powerful excitation of a flowing suspension (two-phase flow and cavitation bubbles). The reactor is excited by sonotrodes, connected to two coupled resonant tube structures, at the critical frequency. Finally cavitation bubbles are initiated by a flow through a venturi nozzle. The acoustically optimised reactor geometry is modelled in Comsol Multiphysics®, and excited by dedicated ultrasound signals at three different frequencies. The effect of the high intensity cavitation is experimentally evaluated by calorimetric method, foil tests and degree of fibrillation on cellulose fibers.

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  • 5.
    Najjarzadeh, Nasim
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Krige, Adolf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Pamidi, Taraka Rama Krishna
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Johansson, Örjan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Enman, Josefine
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Matsakas, Leonidas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Rova, Ulrika
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Christakopoulos, Paul
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Numerical modeling and verification of a sonobioreactor and its application on two model microorganisms2020In: PLOS ONE, E-ISSN 1932-6203, Vol. 15, no 3, article id e0229738Article in journal (Refereed)
    Abstract [en]

    Ultrasound has many uses, such as in medical imaging, monitoring of crystallization, characterization of emulsions and suspensions, and disruption of cell membranes in the food industry. It can also affect microbial cells by promoting or slowing their growth and increasing the production of some metabolites. However, the exact mechanism explaining the effect of ultrasound has not been identified yet. Most equipment employed to study the effect of ultrasound on microorganisms has been designed for other applications and then only slightly modified. This results in limited control over ultrasound frequency and input power, or pressure distribution in the reactor. The present study aimed to obtain a well-defined reactor by simulating the pressure distribution of a sonobioreactor. Specifically, we optimized a sonotrode to match the bottle frequency and compared it to measured results to verify the accuracy of the simulation. The measured pressure distribution spectrum presented the same overall trend as the simulated spectrum. However, the peaks were much less intense, likely due to non-linear events such as the collapse of cavitation bubbles. To test the application of the sonobioreactor in biological systems, two biotechnologically interesting microorganisms were assessed: an electroactive bacterium, Geobacter sulfurreducens, and a lignocellulose-degrading fungus, Fusarium oxysporum. Sonication resulted in increased malate production by Gsulfurreducens, but no major effect on growth. In comparison, morphology and growth of Foxysporum were more sensitive to ultrasound intensity. Despite considerable morphological changes at 4 W input power, the growth rate was not adversely affected; however, at 12 W, growth was nearly halted. The above findings indicate that the novel sonobioreactor provides an effective tool for studying the impact of ultrasound on microorganisms.

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  • 6.
    Pamidi, Taraka
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Johansson, Örjan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Shankar, Vijay
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Hydrodynamic and acoustic cavitation effects on properties of cellulose fibers2024In: Chemical Engineering and Processing, ISSN 0255-2701, E-ISSN 1873-3204, Vol. 203, article id 109894Article in journal (Refereed)
    Abstract [en]

    The cellulose pulp refining process is crucial for achieving high-quality paper characteristics. This research aims to enhance energy efficiency while maintaining good fiber quality using hydrodynamic and acoustic cavitation (HAC). Experiments were conducted with an in-house developed flow-through sonicator combined with a novel Venturi nozzle for hydrodynamic cavitation. The Venturi design was determined by analytical modeling and verified by CFD simulation with multi-phase turbulence models to balance cavitation intensity and turbulence against the acoustic cavitation effect. Experimental evaluation of two batches of CTMP fibers, pre-processed in different ways, showed significant improvements in paper strength and fiber properties. The best results for Batch 1 (HC and LC) were obtained with 386 kWh/bdt for AC and 350 kWh/bdt for HC (60 °C, 2 % concentration). The tensile strength index increased by 26 %, and the TEA-index, related to freeness, increased by 55 %. HAC treatment (750 kWh/bdt, 70 °C, 1.5 % concentration) of the less refined Batch2 (HC) yielded results better than the Batch 1 reference. These findings confirm the energy-efficient potential of the sonicator concept compared to traditional industrial processes. The conclusion is that HAC-refining of softwood pulp requires a proper balance between hydrodynamic and acoustic cavitation intensities. Both fiber concentration by weight and temperature are critical for an energy-efficient process.

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  • 7.
    Pamidi, Taraka Rama Krishna
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Process Intensification by Ultrasound Controlled Cavitation2019Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Process industries are cornerstones in today’s industrialized society. They contribute significantly in the manufacturing of various goods and products that are used in our day-to-day life. Our society’s paradigm of consumerism accompanied by a rise in global population drives an ever increasing demand for goods. One of many strategies developed to satisfy these demands and at the same time improve production capabilities is known as process intensification. As an example, this can be accomplished by implementation of devices using the principle of hydrodynamic and acoustic cavitation. High-intensity cavitation in the ultrasonic range can change the physical and chemical properties of a wide range of substances and hence, improve the production rate or quality.

    Despite the generally accepted benefits of hydrodynamic and acoustic cavitation, applications in the process industry are yet limited. The reasons are that the method requires extensive optimization, which depends on multiple process parameters and encounters problem in the implementation on a larger scale. Scalable cavitation reactor concepts for industrial applications need to meet challenges like stability and robustness, energy efficiency and high flow rates. This thesis focuses on the methodology for the design and optimization of a flow through cavitation reactor.

    An ultrasound reactor concept has been developed and tested for two different applications: i) Fibrillation processes typical for paper and pulp industry; ii) Metal leaching of mineral concentrates. Simulations were carried out using a commercially available software for multiphysics modeling which combines acoustics, structural dynamics, fluid dynamics and piezoelectrics. However, the optimization procedure requires extensive experimental work in parallel with multi-physical simulations. In general, the application leads to hydrodynamic initiation of small gas bubbles in the fluid to be excited and collapsed by high-intensity ultrasound. This transient collapse of the cavitation bubbles provides both mechanical and chemical effect on materials.

    The developed reactor has a power conversion efficiency of 36% in batch mode and is well suited for a scale-up. In flow-through mode, the cavitation effect improves extensively and provides stable results. Energy efficiency requires hydrodynamic initiation of cavitation bubbles, high acoustic cavitation intensity by multiple excitation frequencies adapted to the optimized reactor geometry, as well as optimal process pressure and temperature with respect to the materials to be treated. The impact of flow conditions and hydrodynamic cavitation is significant and almost doubles the yield at the same ultrasonic power input.

    In the case of fibrillation of cellulose fibers, results obtained indicate that generated cavitation intensity changes the mechanical properties of the fiber wall. In the case of leaching, experiments show that six hours of exposure gave a 57% recovery of tungsten from the scheelite concentrate at 80°C and atmospheric pressure. Future research will focus on different types of excitation signals, extended reactor volume, increased flow rates and use of a higher process temperature. 

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  • 8.
    Pamidi, Taraka Rama Krishna
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Process Intensification through Acoustic and Hydrodynamic Cavitation2021Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Process industries are cornerstones in today’s industrialized world. They contribute significantly to the development of diverse commodities and materials that are used in our daily lives. Process intensification is an approach implemented to boost manufacturing efficiency and capacities in a more sustainable and energy efficient way. The focus of this thesis is to utilize the concept and advantages of hydrodynamic and acoustic cavitation in the ultrasonic range. High-intensity cavitation can improve the physical and chemical properties of a wide range of materials and provides a sustainable alternative for process intensification. Although the use of hydrodynamic and acoustic cavitation techniques have become advantageous, applications in process industry are still limited, as the approach needs thorough refinement based on several process parameters and complications encountered in a large-scale implementation. In order to address challenges such as stability and robustness as well as energy conservation and high flow speeds, scalable reactor designs are essential for industrial applications. 

     This research focuses on the methods to develop and maximize cavitation activity in a flow-through reactor. The application comprises of hydrodynamic activation of tiny gas bubbles in the fluid to be excited and collapsed by high intensity ultrasound. The transient collapse of cavitation bubbles and clouds of bubbles generates high temperatures, extreme pressures and shockwaves in a microscale, leading to both a physical and chemical impact. To achieve an efficient energy transfer and conversion optimization with respect to physical and process related parameters are needed. The optimization of the reactor design requires both experimental and numerical investigations. Numerical simulations have been carried out with the help of a commercially accessible multiphysics simulation software that incorporates acoustics, structural dynamics, fluid dynamics and piezoelectrics. The reactor design methodology is validated by measurements of impedance and acoustic pressure as well as aluminum foil erosion and calorimetric tests. The developed cavitation reactors have been implemented in two case studies: I) Modification of cellulose fiber properties and II) Leaching of metals from mineral concentrates.

     In case study I, the developed method for fibrillation of cellulose fibers enables an energy-efficient change in mechanical properties of the fiber wall. As a consequence of cavitation, fibers are exposed to shear forces and micro-jets, inducing peeling, swelling, delamination and external and internal fibrillation. The parameters of significance are excitation frequency, electrical power, flow characteristics, concentration (viscosity), static pressure and temperature.  The maximum flow rate of the reactor is 80 l/min and power density is 0.45 W/cm3. The developed reactor has a 36 % power conversion efficiency and is well adapted for scale-up. The critical aspect is to balance the contribution of hydrodynamic and acoustic cavitation to the pulp properties. For high temperature chemi–thermomechanical pulp (HT-CTMP) from spruce, the best quality of fiber properties was obtained at 1.5 % concentration and 60° C using an electrical energy supply of 386 kWh/bdt. 

     In case study II, the aim of the investigation was to explore the impact of hydrodynamic and acoustic cavitation (HAC) on the leaching ability of tungsten. The objectives were to minimize leaching time, reduce energy usage and increase the recovery rate. Various experimental conditions such as dual-frequency excitation and various orifice geometries have been explored during this investigation. The reactor was excited by 23 kHz and 39 - 43 kHz frequencies in different flow settings. The effects of leaching time, temperature, acoustic pressure and geometry of the orifice plate have been studied. The leaching temperature varied from 40°C to 80°C. The concentration of sodium hydroxide (NaOH) leaching agent was 10 mol/L. The results has been compared to traditional chemical and laboratory autoclave leaching. The energy enhancement of 130 kWh/kg concentrates acoustic cavitation resulting in a 71.5 % leaching recovery of tungsten (WO3), relative to 36.7 % obtained in the absence of ultrasound. The developed method is found to be energy effective and provides a higher recovery rate than current chemical methods at lower temperature and static pressure.

    Energy efficient process intensification requires hydrodynamic initiation of cavitation bubbles, high acoustic cavitation strength by several excitation frequencies tailored to the reactor's optimized design and optimum process pressure and temperature concerning the materials to be processed. The cavitation effect improves extensively in the flow-through mode and offers stable results. The effect of flow conditions and hydrodynamic cavitation at the same ultrasonic power input is essential and nearly doubles the yield.

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  • 9.
    Pamidi, Taraka Rama Krishna
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Johansson, Örjan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Acoustic optimization of a flow through sonicator for fibrillation of cellulose fibers2022In: Chemical Engineering and Processing, ISSN 0255-2701, E-ISSN 1873-3204, Vol. 181, article id 109154Article in journal (Refereed)
    Abstract [en]

    Fibrillation is identified as the most energy intensive process step in pulp and paper manufacturing and improved energy efficiency is the motivation for development of alternative technologies. The aim of this study is to explore the potential of a new refining concept based on cavitation, focusing on the optimization of acoustic cavitation efficiency of the proposed flow-through sonicator concept. The simulations utilize the linearized wave equation in the frequency domain with an addition of nonlinear attenuation introduced by cavitation bubbles. Verification is made by pressure measurements, calorimetry, and foil tests. The fibrillation capability was validated on chemi-thermo mechanical pulp fibers at low consistencies. Fiber properties was characterized by ultrasonic spectroscopy, fiber analysis and SEM. The objective is to optimize the energy transfer efficiency from electrical input power to acoustic cavitation intensity for efficient fibrillation of cellulose fibers. Results showed changes in fiber dimensions and fiber morphology, however, improvements in tensile strength index, measured and predicted by ultrasonic spectroscopy, was limited to 20 % at an energy level of 804 kWh/bdt. To enhance energy efficiency and paper strength properties, it is suggested to add a hydrodynamic cavitation device prior to the sonicator to initiate cavitation bubbles and to increase turbulence intensity.

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  • 10.
    Pamidi, Taraka Rama Krishna
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Johansson, Örjan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Comparison of Cavitation Effect in Case of Fixed and Free Fibers in an Ultrasound Beaker2019In: Proceedings of the ICA 2019 AND EAA EUROREGIO: 23rd International Congress on Acoustics,integrating 4th EAA Euroregio 2019 / [ed] Martin Ochmann, Micchael Vorländer, Janina Fels, Aachen, Germany: RWTH Publications , 2019, p. 8201-8208Conference paper (Refereed)
    Abstract [en]

    This study investigate the impact of high-intensity ultrasound treatment on the mechanical properties of pulp fibers. The pulp fiber samples are sonicated in an acoustically optimized beaker where high-intensity ultrasound is generated using a tuned sonotrode device. The idea is to create a controlled resonance to efficiently enhance the sound pressure in the beaker. Input power was 90 W. The objective is to define the difference between freely suspended fibers in a beaker compared to keeping fibers in a fixed position. The hypothesis is that fiber treatment at a specific input power will be more efficient in the case when fibers are kept in a high pressure zone. Since the fiber wall is a layered structure, it is likely to delaminate internally which will affect the mechanical properties of the fiber. The effect on fiber properties is verified by measuring the ultrasound attenuation spectra for the treated fibers. The attenuation measurements are based on measurements of a low-intensity ultrasound pulse-echo technique. On a macroscopic scale, changes in the attenuation spectra relates to a change in mechanical properties of the fiber wall, since the suspended fibers more or less retain their diameter and length distributions.

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  • 11.
    Pamidi, Taraka Rama Krishna
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Johansson, Örjan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Comparison of Different Concepts of UltrasoundReactors Using Numerical Simulations2018Conference paper (Other academic)
    Abstract [en]

    Sonochemical reactors are used for process intensification based on efficientenergy transfer due to ultrasound in order to cause transient cavitation in the medium.Ultrasonic reactors are extensively used for numerous applications due to their differentfeatures. The process of ultrasound cavitation can be defined as generation, growth andviolent collapse of microbubbles under ultrasonic irradiation which can release a highamount of energy in a small volume. The released energy causes a sudden increase intemperature and pressure which thereby can lead to extensive process intensification. Thepresent work deals with the evaluation of two different configurations of ultrasound reactorsusing both numerical modeling and experimental verification. The evaluation is based onprediction of the pressure distribution, verified by foil tests and with calorimetric method.The two reactors were developed to be used for the treatment of cellulose fibers to improveenergy efficiency in the fibrillation process. The goal is to optimize cavitation intensityand minimize the coupling loss factors. The development and evaluation of these two reactorconcepts aim to improve the design methodology for a scalable flow through reactor conceptwith high yield and energy efficiency

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  • 12.
    Pamidi, Taraka Rama Krishna
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Johansson, Örjan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Energy Efficient Fibrillation of Cellulose Fibers using an Ultrasound Reactor2019Conference paper (Refereed)
    Abstract [en]

    The pulp and paper industry is in continuous need for energy-efficient production processes. Therefore, there is a focus in reducing electrical energy use in the production of paper.  The most energy demanding processes are related to fibrillation, which in some cases use up to 80% of required electrical power, with a net efficiency of 1%. The presented work focus on ultrasound controlled cavitation in concentrating the processing energy to provide an energy efficient development of cellulose fibers. The objectives are to develop a scalable cavitation reactor to obtain energy-efficient fibrillation of cellulose fibers aiming at reducing the energy use by 50%. Our goal is to develop a methodology based on multiphysic simulation for the design of an alternative refiner based on ultrasound cavitation. The reactor concept is of a flow through type where cavitation bubbles are initiated in the fiber suspension by the pressure release when the pulp flow through a venturi nozzle. The induced cavitation bubbles are collapsed by high intensity ultrasound at resonant frequencies. The collapsing bubbles and their associated shock waves modify the fiber wall properties which enables fibrillation.  Energy efficient fibrillation of cellulose fibers is therefore possible to achieve through an optimized combination of hydrodynamic and ultrasonic controlled cavitation. Initial results shows a positive effect on fiber quality. However, further optimization of process parameters like temperature and static pressure is required.

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  • 13.
    Pamidi, Taraka Rama Krishna
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Johansson, Örjan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Experimental and Numerical Optimization for Energy Efficient Treatment of Cellulose Fibers by Acoustic CavitationManuscript (preprint) (Other academic)
    Abstract [en]

    In the case of pulp refining, there is a need for high quality pulp in the paper industry.  Pulp refining is a viable method for enhancing pulp consistency by modifying the properties of the fiber wall. Mechanical refining is the most energy intensive process in paper manufacturing. In order to reduce the energy use for a more sustainable process, the development of alternative refining methods are of importance. Ultrasound cavitation has proved to be an energy efficient refining process but so far it is limited to smaller volume and batch process. The developed ultrasonic refiner is a capable of handling greater fiber volume in a continuous flow process and easy to scale up. This method could therefore be an alternative and effective way of processing fibers to minimize energy usage. In this study, both numerical simulations and experiments are combined and analysed to design a scaled-up, flow-through ultrasound reactor.  The implemented model is based on the linearized wave equation in the frequency domain with appropriate addition of nonlinear attenuation by cavitation bubbles. The influence of ultrasound cavitation was experimentally verified by characterization of the modification of soft wood cellulose fibers (CTMP) properties.  Results shows that the proposed method using ultrasound cavitation can modify the fiber bulk properties at low energies per 804 kWh/bdt. However, there was no significant change in fiber strength properties as per ISO 1924-3.

  • 14.
    Pamidi, Taraka Rama Krishna
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Johansson, Örjan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Löfqvist, Torbjörn
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Shankar, Vijay
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Comparison of two different ultrasound reactors for the treatment of cellulose fibers2020In: Ultrasonics sonochemistry, ISSN 1350-4177, E-ISSN 1873-2828, Vol. 62, article id 104841Article in journal (Refereed)
    Abstract [en]

    The pulp and paper industry is in continuous need for energy-efficient production processes. In the refining process of mechanical pulp, fibrillation is one of the essential unit operations that count for up to 80% of the total energy use. This initial study explores the potential and development of new type of scalable ultrasound reactor for energy efficient mechanical pulping. The developed reactor is of continuous flow type and based on both hydrodynamic and acoustic cavitation in order to modify the mechanical properties of cellulose fibers. A comparison of the prototype tube reactor is made with a batch reactor type where the ultrasonic horn is inserted in the fluid. The pulp samples were sonicated by high-intensity ultrasound, using tuned sonotrodes enhancing the sound pressure and cavitation intensity by a controlled resonance in the contained fluid. The resonant frequency of the batch reactor is 20.8 kHz and for the tube reactor it is 22.8 kHz. The power conversion efficiency for the beaker setup is 25% and 36% in case of the tube reactor in stationary mode. The objective is to verify the benefit of resonance enhanced cavitation intensity when avoiding the effect of Bjerkenes forces. The setup used enables to keep the fibers in the pressure antinodes of the contained fluid. In case of the continuous flow reactor the effect of hydrodynamic cavitation is also induced. The intensity of the ultrasound in both reactors was found to be high enough to produce cavitation in the fluid suspension to enhance the fiber wall treatment. Results show that the mechanical properties of the fibers were changed by the sonification in all tests. The continuous flow type was approximately 50% more efficient than the beaker. The effect of keeping fibers in the antinode of the resonant mode shape of the irradiation frequency was also significant. The effect on fiber properties for the tested mass fraction was determined by a low-intensity ultrasound pulse-echo based measurement method, and by a standard pulp analyzer.

  • 15.
    Shankar, Vijay
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Lundberg, Anton
    Chalmers University of Technology Gothenburg, Sweden.
    Frenander, Kristian
    ÅF Industry AB Gothenburg, Sweden.
    Ingelsten, Simon
    ÅF Industry AB Gothenburg, Sweden.
    Landström, Lars
    Chalmers University of Technology Gothenburg, Sweden.
    Pamidi, Taraka
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Johansson, Örjan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Flow Induced Venturi Cavitation to Improve Energy Efficiency in Pulp Production2018In: Journal of Fluid Flow, Heat and Mass Transfer (JFFHMT), ISSN 2368-6111, Vol. 5, p. 10-17Article in journal (Refereed)
    Abstract [en]

    In order to lower the energy consumption of the fibrillation stage for the pulp and paper industry, a new technology need to be innovated and developed. This paper presents an innovative new design of a venturi nozzle as a concept for refining pulp using hydrodynamic cavitation. The conditions created by cavitation bubbles collapsing near paper fibres are similar to the conditions in conventional refiners used in the pulp and paper industry. The cavitation created in the venturi implodes on the surface of the cellulose fibres, increasing the fibrillation and processing the fibres further. Cavitation is hard to control and can cause high mechanical wear, therefore an optimization study of the venturi nozzle is performed using Computational Fluid Dynamics (CFD) and state-of-the-art optimization techniques. Finally, the optimal venturi shape is investigated in a series of detailed numerical simulations, using a Bingham fibre model to include the effect pulp fibres has on the flow. The investigation shows that cavitation bubbles start to form at an outlet pressure of 1.87 bar, for an inlet pressure of 3.00 bar. The intensity of the bubble collapse depends on the surrounding pressure and this outlet pressure therefore enables a powerful treatment of the pulp fibres. In conclusion, the venturi concept is plausible and seems promising at this stage. More research, in particular physical experiments, is however required before a conclusive verdict can be given.

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  • 16.
    Shankar, Vijay
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Lundberg, Anton
    Chalmers University of Technology, Gothenburg, Sweden.
    Frenander, Kristian
    Chalmers University of Technology, Gothenburg, Sweden.
    Landström, Lars
    Chalmers University of Technology, Gothenburg, Sweden.
    Pamidi, Taraka
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Johansson, Örjan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    An Automatic Method for Optimizing Venturi Shape in Cavitation Flows2017In: Proceedings of the 4th International Conference of Fluid Flow, Heat and Mass Transfer (FFHMT'17), Avestia Publishing, 2017, p. 160-1-160-8, article id 160Conference paper (Refereed)
    Abstract [en]

    In order to lower the energy consumption of the fibrillation stage for the pulp and paper industry, a new technology need to be innovated and developed. The current research work deals with a new innovative concept based on creating cavitation in the pulp flow. A venturi nozzle is designed and optimized, where hydrodynamic cavitation is achieved by the so called Venturi effect. This paper focuses on the development of an automatic method for venturi shape optimization. The process of cavitation is hard to control and can cause high mechanical wear, therefore an optimization study of the venturi shape is performed with two main objectives. Firstly, to achieve cavitation that is sustained for as long as possible downstream and secondly to avoid cavitation at the walls. The developed method is a type of two-level optimization based on neural networks and evolutionary optimization. A number of simulations are executed and the optimization is then performed on a solver approximation instead of the real solver, which considerably reduces computation time. The obtained results show the optimal venturi configuration and the relative importance of each shape parameter. The optimal configuration is a clear improvement of the baseline configuration and an improvement also compared to all of the tested samples, thereby validating the optimization method.

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    fulltext
  • 17.
    Shankar, Vijay
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Lundberg, Anton
    VOLVO AB, Gropegårdsgatan 2, 417 15 Göteborg, Sweden.
    Pamidi, Taraka
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Landström, Lars-Olof
    ÅF Industry AB, Grafiska vägen 2, 401 51 Göteborg, Sweden.
    Johansson, Örjan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    CFD Analysis of Turbulent Fibre Suspension Flow2020In: Fluids, E-ISSN 2311-5521, Vol. 5, no 4, article id 175Article in journal (Refereed)
    Abstract [en]

    A new model for turbulent fibre suspension flow is proposed by introducing a model for the fibre orientation distribution function (ODF). The coupling between suspended fibres and the fluid momentum is then introduced through the second and fourth order fibre orientation tensors, respectively. From the modelled ODF, a method to construct explicit expressions for the components of the orientation tensors as functions of the flow field is derived. The implementation of the method provides a fibre model that includes the anisotropic detail of the stresses introduced due to presence of the fibres, while being significantly cheaper than solving the transport of the ODF and computing the orientation tensors from numerical integration in each iteration. The model was validated and trimmed using experimental data from flow over a backwards facing step. The model was then further validated with experimental data from a turbulent fibre suspension channel flow. Simulations were also carried out using a Bingham viscoplastic fluid model for comparison. The ODF model and the Bingham model performed reasonably well for the turbulent flow areas, and the latter model showed to be slightly better given the parameter settings tested in the present study. The ODF model may have good potential, but more rigorous study is needed to fully evaluate the model.

  • 18. Vijigiri, Vipul
    et al.
    Pamidi, Taraka Rama Krishna
    Ultrasound induced cavitation and resonance amplification using adaptive feedback Control System2014Independent thesis Advanced level (degree of Master (Two Years)), 10 credits / 15 HE creditsStudent thesis
1 - 18 of 18
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