Jyväskylä, Finland
Jyväskylä, Finland

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Haavisto S.,Spinnova Ltd. | Haavisto S.,VTT Technical Research Center of Finland | Haavisto S.,University of Jyväskylä | Salmela J.,Spinnova Ltd. | And 5 more authors.
Experiments in Fluids | Year: 2015

Pulsed ultrasound Doppler velocimetry and nuclear magnetic resonance imaging are popular non-invasive measurement methods for flows of opaque fluids. The spatial and temporal resolution of these methods, however, is quite limited, and they lack accuracy, especially close to solid boundaries. In this paper, we show that solution to these problems is achieved by using Doppler optical coherence tomography (DOCT). DOCT provides simultaneous information about the fluid structure and velocity with very high spatial and temporal resolution. For benchmarking of the method we use water as the reference fluid. We show how DOCT gives a very good agreement with theory for the velocity profile, skin friction and viscosity directly from the measurement signal. The velocity profile extends from the turbulent region to viscous sublayer, and viscosity of the fluid can be calculated also from a turbulent flow with a good accuracy. Overall, DOCT is seen to be very well suited for providing new insight into boundary-layer flows, rheology and skin friction. © 2015, Springer-Verlag Berlin Heidelberg.

Haavisto S.,Spinnova Ltd. | Salmela J.,Spinnova Ltd. | Jarvinen M.,Academy of Finland Research Fellow | Kankkunen A.,Aalto University | Koponen A.,VTT Technical Research Center of Finland
Tappi Journal | Year: 2015

In this study, we apply ultrasound velocity profiling (UVP) for obtaining velocity data inside black liquor nozzles. We demonstrate the capability of this technique for online measurement of black liquor flow properties and viscosity behavior. The experiments were carried out on an operating recovery boiler where the black liquor from pulping softwood was taken directly from the boiler liquor system and sprayed through a customized splash-plate nozzle. Application: Inline rheology measurement in black liquor nozzles can lead to improved efficiency in the spraying process control. Measurements can also give insight to processes taking place in nozzle flow that have not been possible to measure before.

Haavisto S.,Spinnova Ltd. | Salmela J.,Spinnova Ltd. | Jasberg A.,VTT Technical Research Center of Finland | Saarinen T.,Betulium Ltd. | And 2 more authors.
Tappi Journal | Year: 2015

Fiber suspensions, such as microfibrillated cellulose, are a challenge for conventional rheometers to measure. This is because rheometers have small flow channel dimensions that can restrict flocculation. Often, questionable assumptions are also made about the fluid behavior in the gap. A pipe rheometer and ultrasound velocity profiling-pressure difference (UVP-PD) concept can be used, by which the real flow behavior is used for the rheological analysis of the bulk properties of the suspension. Unfortunately, the resolution of UVP is too low for studying near-wall phenomena, such as the lubrication layer, that are often very important for understanding the rheology and to upscale the results to industrial flows. To address this problem, we have widened the UVP-PD concept with optical coherence tomography measurements. This enables us to measure the bulk and wall-layer behavior simultaneously. Our results demonstrate the benefits of having direct, detailed measurement of the velocity profile inside the rheometer. Application: Velocity profiling in the near-wall region can lead to better understanding of the rheology of complex fluids. This information would be invaluable in flow control and numerical simulations of flows of complex fluids, such as microfibrillated cellulose (MFC).

Koponen A.,VTT Technical Research Center of Finland | Haavisto S.,Spinnova Ltd | Liukkonen J.,Spinnova Ltd | Salmela J.,Spinnova Ltd
Drying Technology | Year: 2016

In this work, a novel experimental filtration device with pressure profiling was used for analyzing water removal from the fiber network in the forming section of a paper machine. The experimental data were used to develop a stratified model for the flow resistance of the developing fiber sheet during the filtration process. The new model was verified with both laboratory- and pilot-scale measurements and excellent agreement was observed between them. It was also observed that there is a strong linear correlation between the maximal attainable solid content of a filtered sheet after the forming section and the instantaneous response to pressure of the flow resistivity of the furnish. © 2016, Copyright © Taylor & Francis Group, LLC.

Shen Y.,VTT Technical Research Center of Finland | Orelma H.,VTT Technical Research Center of Finland | Sneck A.,VTT Technical Research Center of Finland | Kataja K.,VTT Technical Research Center of Finland | And 5 more authors.
Cellulose | Year: 2016

A new process for preparing thin cellulose nanofibril (CNF) filaments (thickness of 16 µm) was investigated by utilizing the dry spinning approach. In the process, CNF hydrogel was extruded through a fine nozzle onto an adhesion controlled capstan (drum) with low friction (slippery surface) at a speed of up to 11 m/s. The utilized capstan enables excellent line speed control when the slippery surface is applied, and prevents drying shrinkage of the spun filaments. The mechanical properties of prepared filaments can be optimized with the stretch ratio, the ratio of the speed of the drum surface, and the CNF jet flow. The developed method allows for manufacturing thin CNF filaments with an elevated spinning rate in a more controlled manner. © 2016 Springer Science+Business Media Dordrecht

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