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Löfqvist, Torbjörn
Publications (10 of 40) Show all publications
Johansson, Ö., Pamidi, T. R., Shankar, V. & Löfqvist, T. (2019). Acoustic design principles for energy efficient excitation of a high intensity cavitation zone. In: Martin Ochmann (Ed.), Proceedings of the 23rd International Congress on Acoustics, integrating 4th EAA Euroregio 2019: ICA 2019, 9 - 13 September. Paper presented at 23rd International Congress on Acoustics (pp. 948-955). Aachen, Germany
Open this publication in new window or tab >>Acoustic design principles for energy efficient excitation of a high intensity cavitation zone
2019 (English)In: Proceedings of the 23rd International Congress on Acoustics, integrating 4th EAA Euroregio 2019: ICA 2019, 9 - 13 September / [ed] Martin Ochmann, Aachen, Germany, 2019, p. 948-955Conference paper, Published paper (Other academic)
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.

Place, publisher, year, edition, pages
Aachen, Germany: , 2019
Keywords
Structural acoustics, Ultrasound, Hydrodynamics, Cavitation
National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Acoustics
Identifiers
urn:nbn:se:ltu:diva-76063 (URN)978-3-939296-15-7 (ISBN)
Conference
23rd International Congress on Acoustics
Funder
Swedish Energy Agency
Available from: 2019-09-19 Created: 2019-09-19 Last updated: 2019-10-22
Pamidi, T. R., Johansson, Ö. & Löfqvist, T. (2019). Comparison of Cavitation Effect in Case of Fixed and Free Fibers in an Ultrasound Beaker. In: Martin Ochmann (Ed.), Proceedings of the 23rd International Congress on Acoustics, integrating 4th EAA Euroregio 2019: ICA 2019, 9 - 13 September. Paper presented at 23rd International Congress on Acoustics (pp. 8217-8224). Aachen, Germany
Open this publication in new window or tab >>Comparison of Cavitation Effect in Case of Fixed and Free Fibers in an Ultrasound Beaker
2019 (English)In: Proceedings of the 23rd International Congress on Acoustics, integrating 4th EAA Euroregio 2019: ICA 2019, 9 - 13 September / [ed] Martin Ochmann, Aachen, Germany, 2019, p. 8217-8224Conference paper, Published paper (Other academic)
Abstract [en]

In this study, we investigate the impact of high-intensity ultrasound treatment on the mechanical properties of pulp fibers. The pulp fiber samples are sonicated in an acoustically optimised 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 is 90Watt. 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.

Place, publisher, year, edition, pages
Aachen, Germany: , 2019
Keywords
Ultrasonics, Cavitation, Paper pulp, Cellulose fibers
National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Acoustics
Identifiers
urn:nbn:se:ltu:diva-76050 (URN)978-3-939296-15-7 (ISBN)
Conference
23rd International Congress on Acoustics
Funder
Swedish Energy Agency
Available from: 2019-09-18 Created: 2019-09-18 Last updated: 2019-10-22
Pamidi, T. R., Johansson, Ö., Löfqvist, T. & Shankar, V. (2019). Comparison of Two Different Ultrasound Reactors for the Treatment of Cellulose Fibers. Russian ultrasonics
Open this publication in new window or tab >>Comparison of Two Different Ultrasound Reactors for the Treatment of Cellulose Fibers
2019 (English)In: Russian ultrasonics, ISSN 0048-8828Article in journal (Refereed) Epub ahead of print
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

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
ultrasound reactor, hydrodynamic and acoustic cavitation, cellulose fiber properties
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering Fluid Mechanics and Acoustics
Research subject
Electronic systems; Engineering Acoustics
Identifiers
urn:nbn:se:ltu:diva-76606 (URN)10.1016/j.ultsonch.2019.104841 (DOI)
Available from: 2019-11-04 Created: 2019-11-04 Last updated: 2019-11-04
Pamidi, T. R., Johansson, Ö. & Löfqvist, T. (2018). Comparison of Different Concepts of UltrasoundReactors Using Numerical Simulations. In: : . Paper presented at 16th Meeting of the European Society of Sonochemistry.
Open this publication in new window or tab >>Comparison of Different Concepts of UltrasoundReactors Using Numerical Simulations
2018 (English)Conference paper, Poster (with or without abstract) (Other (popular science, discussion, etc.))
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

National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Acoustics
Identifiers
urn:nbn:se:ltu:diva-73782 (URN)
Conference
16th Meeting of the European Society of Sonochemistry
Available from: 2019-04-29 Created: 2019-04-29 Last updated: 2019-09-06
Johansson, Ö., Pamidi, T. R. & Löfqvist, T. (2017). Design of a high-intensity ultrasound reactor. In: : . Paper presented at 2017 IEEE International Ultrasonics Symposium (IUS),Washington, DC, 6-9 Sept. 2017. Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE)
Open this publication in new window or tab >>Design of a high-intensity ultrasound reactor
2017 (English)Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

Design, and optimization of ultrasonic reactors are important objectives in sonochemical processing. The recent expansion of the use of ultrasonic reactors in various research areas all faces the problem of scaling up from laboratory results to industrial purposes. A traditional ultrasonic reactor usually has several issues, such as low effectiveness as well as complex and unstable system performance, which all are unfavorable for efficient sonochemical processing. This study addresses these issues and investigates a new flow type ultrasonic reactor designed to generate transient cavitation as the main source for ultrasound. Some important factors like pressure, material, flow and geometry are considered in the design. Numerical optimization as well as experimental investigations are performed to reach an optimized, energy-efficient and controlled ultrasound cavitation reactor. Results from numerical modeling are used for acoustic optimization of the reactor, which is driven with three transducers mounted radially in the reactor wall with 120° spacing. The final reactor is excited with dual frequencies a total of 9 sonotrodes. The reactor is intended to be used in studies of pre-treatment of cellulose fibers aiming at developing an alternative, energy efficient fibrillation process and for ultrasound leaching of minerals.

Place, publisher, year, edition, pages
Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2017
National Category
Fluid Mechanics and Acoustics Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Acoustics; Industrial Electronics
Identifiers
urn:nbn:se:ltu:diva-66534 (URN)10.1109/ULTSYM.2017.8092948 (DOI)978-1-5386-3383-0 (ISBN)
Conference
2017 IEEE International Ultrasonics Symposium (IUS),Washington, DC, 6-9 Sept. 2017
Available from: 2017-11-09 Created: 2017-11-09 Last updated: 2017-11-24Bibliographically approved
Johansson, Ö., Pamidi, T. R. & Löfqvist, T. (2017). Design of a high-intensity ultrasound reactor. In: IEEE International Ultrasonics Symposium, IUS: . Paper presented at 2017 IEEE International Ultrasonics Symposium (IUS), Washington, DC, 6-9 Sept. 2017. Piscataway, NJ: IEEE Computer Society, Article ID 8091660.
Open this publication in new window or tab >>Design of a high-intensity ultrasound reactor
2017 (English)In: IEEE International Ultrasonics Symposium, IUS, Piscataway, NJ: IEEE Computer Society, 2017, article id 8091660Conference paper, Published paper (Refereed)
Abstract [en]

Design, and optimization of ultrasonic reactors are important objectives in sonochemical processing. The recent expansion of the use of ultrasonic reactors in various research areas all faces the problem of scaling up from laboratory results to industrial purposes. A traditional ultrasonic reactor usually has several issues, such as low effectiveness as well as complex and unstable system performance, which all are unfavorable for efficient sonochemical processing. This study addresses these issues and investigates a new flow type ultrasonic reactor designed to generate transient cavitation as the main source for ultrasound. Some important factors like pressure, material, flow and geometry are considered in the design. Numerical optimization as well as experimental investigations are performed to reach an optimized, energy-efficient and controlled ultrasound cavitation reactor. Results from numerical modeling are used for acoustic optimization of the reactor, which is driven with three transducers mounted radially in the reactor wall with 120° spacing. The final reactor is excited with dual frequencies a total of 9 sonotrodes. The reactor is intended to be used in studies of pre-treatment of cellulose fibers aiming at developing an alternative, energy efficient fibrillation process and for ultrasound leaching of minerals

Place, publisher, year, edition, pages
Piscataway, NJ: IEEE Computer Society, 2017
Series
IEEE International Ultrasonics Symposium, E-ISSN 1948-5719
National Category
Fluid Mechanics and Acoustics Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Acoustics; Industrial Electronics
Identifiers
urn:nbn:se:ltu:diva-66533 (URN)10.1109/ULTSYM.2017.8091660 (DOI)000416948400055 ()2-s2.0-85039413569 (Scopus ID)978-1-5386-3383-0 (ISBN)
Conference
2017 IEEE International Ultrasonics Symposium (IUS), Washington, DC, 6-9 Sept. 2017
Available from: 2017-11-09 Created: 2017-11-09 Last updated: 2018-01-16Bibliographically approved
Johansson, Ö., Löfqvist, T. & Pamidi, T. R. (2017). Design of high-intensity ultrasound reactor. In: IEEE International Ultrasonics Symposium, IUS: . Paper presented at 2017 IEEE International Ultrasonics Symposium (IUS), Washington, DC, 6-9 Sept. 2017. Piscataway, NJ: IEEE Computer Society, Article ID 8092948.
Open this publication in new window or tab >>Design of high-intensity ultrasound reactor
2017 (English)In: IEEE International Ultrasonics Symposium, IUS, Piscataway, NJ: IEEE Computer Society, 2017, article id 8092948Conference paper, Published 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

Place, publisher, year, edition, pages
Piscataway, NJ: IEEE Computer Society, 2017
Series
IEEE International Ultrasonics Symposium, ISSN 1948-5719
National Category
Fluid Mechanics and Acoustics Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Acoustics; Industrial Electronics
Identifiers
urn:nbn:se:ltu:diva-67244 (URN)10.1109/ULTSYM.2017.8092948 (DOI)000416948403005 ()2-s2.0-85039437533 (Scopus ID)978-1-5386-3383-0 (ISBN)
Conference
2017 IEEE International Ultrasonics Symposium (IUS), Washington, DC, 6-9 Sept. 2017
Available from: 2018-01-11 Created: 2018-01-11 Last updated: 2018-01-16Bibliographically approved
Hamfelt, J., Gustafsson, J., van Deventer, J., Löfqvist, T., Häggström, F. & Delsing, J. (2016). A passive Barkhausen noise sensor for low-power applications (ed.). In: (Ed.), 2016 IEEE International Instrumentation and Measurement Technology Conference (I2MTC) Proceedings: . Paper presented at International Instrumentation and Measurement Technology Conference : 23/05/2016 - 26/05/2016 (pp. 280-284). Piscataway, NJ: IEEE Communications Society, Article ID 7520374.
Open this publication in new window or tab >>A passive Barkhausen noise sensor for low-power applications
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2016 (English)In: 2016 IEEE International Instrumentation and Measurement Technology Conference (I2MTC) Proceedings, Piscataway, NJ: IEEE Communications Society, 2016, p. 280-284, article id 7520374Conference paper, Published paper (Refereed)
Abstract [en]

This paper proposes a passive Barkhausen noise sensor design suitable for low power applications. The sensor uses a permanent magnet and the relative motion between itself and a measured specimen instead of the conventional method that uses a fixed sensor and an alternating magnetic field. Since this novel design is passive, the sensor is well suited for low power applications and could potentially be used in e.g. A condition monitoring system integrated into a rolling element bearing. Proof of concept testing has been performed showing that the proposed sensor produces similar results as conventional Barkhausen noise sensors when applied to specimens being cyclically loaded until failure in a rotating bending rig. The results imply that material fatigue detection using the Barkhausen noise can be performed with the proposed sensor at a fraction of the energy cost compared to a conventional sensor. This warrants future research into the development of the proposed sensor, its advantages, disadvantages, and functionality

Place, publisher, year, edition, pages
Piscataway, NJ: IEEE Communications Society, 2016
Series
I E E E Instrumentation and Measurement Technology Conference. Proceedings, ISSN 1091-5281
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Industrial Electronics
Identifiers
urn:nbn:se:ltu:diva-27126 (URN)10.1109/I2MTC.2016.7520374 (DOI)000382523600050 ()2-s2.0-84980398147 (Scopus ID)07898908-71e1-408f-9457-00c2f43688d4 (Local ID)9781467392204 (ISBN)07898908-71e1-408f-9457-00c2f43688d4 (Archive number)07898908-71e1-408f-9457-00c2f43688d4 (OAI)
Conference
International Instrumentation and Measurement Technology Conference : 23/05/2016 - 26/05/2016
Note

Validerad; 2016; Nivå 1; 2016-10-11 (andbra)

Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2018-09-06Bibliographically approved
Delsing, J., van Deventer, J., Eliasson, J., Johansson, J., Löfqvist, T. & Sandin, F. (2016). Concepts and Architecture for a Thumb-Sized Smart IoT Ultrasound Measurement System. In: IEEE Ultrasonic Symposium 2016: . Paper presented at IEEE Ultrasonic Symposium, Tours, France, 18-21 Sep 2016. Piscataway, NJ: IEEE conference proceedings
Open this publication in new window or tab >>Concepts and Architecture for a Thumb-Sized Smart IoT Ultrasound Measurement System
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2016 (English)In: IEEE Ultrasonic Symposium 2016, Piscataway, NJ: IEEE conference proceedings, 2016Conference paper, Published paper (Refereed)
Abstract [en]

This paper presents the technology concepts for a “thumb”-sized self-contained ultrasonic IoT measurement sys- tem. An overall architecture is proposed, and key elements are discussed with solutions using existing technology, thus arguing that realization is possible with the current technology.

Such an ultrasonic IoT measurement system is constrained by its size and available energy, although it requires at least decent computational and communication resources. Because streaming data from such a device is not advisable from an energy viewpoint, there is a need for resource efficient (energy, memory and computational power) data analysis.

An architecture with the following parts as well as some implementation details and performance data are proposed here:

  • Energy supply, battery and super capacitor

  • Transducer excitation achieving almost zero electrical losses

  • Event detection sensor interface

  • Data aggregation using sparse approximation and learned

    feature dictionaries, adapted to resource constrained em-

    bedded systems

  • IoT communication protocols and implementations enabling

    event -based communication and System of Systems integra- tion capabilities

    The optimization of system level performance requires each subsystem to be optimized for the specific measurement situation taking into account the subsystem interdependencies. This can be performed using a combined electrical and acoustical model of the system. Here, the model allowing electronic and acoustic co-simulation using SPICE is an important tool bridging the electronic and acoustic domains. 

Place, publisher, year, edition, pages
Piscataway, NJ: IEEE conference proceedings, 2016
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Industrial Electronics
Identifiers
urn:nbn:se:ltu:diva-59677 (URN)10.1109/ULTSYM.2016.7728708 (DOI)978-1-4799-8182-3 (ISBN)978-1-4673-9897-8 (ISBN)
Conference
IEEE Ultrasonic Symposium, Tours, France, 18-21 Sep 2016
Projects
Arrowhead
Available from: 2016-10-12 Created: 2016-10-12 Last updated: 2018-06-11Bibliographically approved
Aitomäki, Y., Berglund, L., Noël, M., Linder, T., Löfqvist, T. & Oksman, K. (2016). Light scattering in cellulose nanofibre suspensions: Model and experiments (ed.). In: (Ed.), (Ed.), Computers in Chemistry Proceeding from ACS National Meeting San Diego: Proceeding from ACS National Meeting San Diego. Paper presented at American Chemical Society (ACS) National Meeting & Exposition : 13/03/2016 - 17/03/2016 (pp. 122). : American Chemical Society (ACS), Article ID CELL 235.
Open this publication in new window or tab >>Light scattering in cellulose nanofibre suspensions: Model and experiments
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2016 (English)In: Computers in Chemistry Proceeding from ACS National Meeting San Diego: Proceeding from ACS National Meeting San Diego, American Chemical Society (ACS), 2016, p. 122-, article id CELL 235Conference paper, Meeting abstract (Other academic)
Abstract [en]

Here light scattering theory is used to assess the size distribution in a suspension of cellulose as it is fibrillated from micro-scaled to nano-scaled fibres. A model based on Monte carlo simulations of the scattering of photons by different sizes of cellulose fibres was used to predict the UV-IF spectrum of the suspensions. Bleached cellulose hardwood pulp was tested and compared to the visually transparent tempo-oxidised hardwood cellulose nanofibres (CNF) suspension. The theoretical results show that different diameter size classes exhibit very different scattering patterns. These classes could be identified in the experimental results and used to establish the size class dominating the suspension. A comparison to AFM/microscope size distribution was made and the results indicated that using the UV-IF light scattering spectrum maybe more reliable that size distribution measurement using AFM and microscopy on dried CNF samples. The UV-IF spectrum measurement combined with the theoretical prediction can be used even at this initial stage of development of this model to assess the degree of fibrillation when processing CNF.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2016
National Category
Bio Materials Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Wood and Bionanocomposites; Industrial Electronics
Identifiers
urn:nbn:se:ltu:diva-27433 (URN)0e1f8cb1-032d-4e71-956c-b2aca7925036 (Local ID)0e1f8cb1-032d-4e71-956c-b2aca7925036 (Archive number)0e1f8cb1-032d-4e71-956c-b2aca7925036 (OAI)
Conference
American Chemical Society (ACS) National Meeting & Exposition : 13/03/2016 - 17/03/2016
Note
Godkänd; 2016; 20160418 (aitomaki)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2017-11-25Bibliographically approved
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