| 2. |
- Löfqvist, Torbjörn
(author)
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Ultrasonic measurement technology for characterization of pulp fibre suspensions
- 1999
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Doctoral thesis (other academic/artistic)abstract
- In the papermaking industry, there is a need for sensors to measure the properties of the fibre suspension that determine important parameters in the finished paper. This lack of on-line sensors hampers the development of advanced process control strategies. Ultrasonic measurement techniques might become useful tool for on-line measure of fibre properties. In general, an acoustic wave, propagating through a suspension, inherently carries information about the physical properties of the suspended material. The presented thesis deals with the fundamental physical processes that governs the propagation of ultrasonic waves in dilute suspensions of paper pulp fibres and water. It also presents a simulation tool capable of simulating all components of a pulse-echo, ultrasonic measurement system, including measurement cell and the fluid under investigation. Experiments are performed in a custom-built measurement cell for low intensity, ultrasonic, pulse-echo measurements. It is investigated both theoretically and experimentally how macroscopic, measurable quantities as speed of sound and attenuation of the ultrasonic pulse are affected by fibre mass fraction, fibre geometry and the physical properties of the fibre material. This knowledge could be applied in using ultrasound to evaluate elastic, or other properties, of fibres in a fibre suspension.
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| 3. |
- Löfqvist, Torbjörn
(author)
-
Ultrasonic wave attenuation and phase velocity in a paper-fibre suspension
- 1997
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In: Proceedings. - Piscataway, NJ : IEEE Communications Society. - 0780341538 ; , s. 841-844
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Conference paper (peer-reviewed)abstract
- An ultrasonic pulse-echo technique has been used to investigate whether ultrasonic wave attenuation and phase velocity can be employed to measure fiber mass fraction in a paper fibre suspension. Attenuation and phase velocity has been determined using Fourier transform and cross-correlation techniques. Measurements have been carried out in the frequency range from 250 kHz to 3 MHz. The mass fraction of dispersed fibres varied between 0% to 1.0%. It has been shown that the attenuation varies linearly with fibre mass fraction, and that attenuation is proportional to frequency. Phase velocity is found to correlate weakly with fibre mass fraction, and is also independent of frequency, in the range covered. It is concluded that mass fraction of fibres in a paper fibre suspension can be measured via its attenuation of ultrasonic pulses
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