Progress 10/01/99 to 09/30/04
Outputs
It was shown that laser Doppler anemometry (LDA) can be used effectivley to measure velocity distributions in a twin-screw extruders, using model fluids which are optically transparent. We set up and calibrated our LDA system using a Couette flow appraratus. Then we measured velocity distributions in a co-rotating, self-wiping, twin-screw extruder to understand flow field and elucidate the mixing effectiveness of different types of screw elements. A transparent barrel was constructed to access the flow region. Velocity profiles in the translational and nip regions were measured at different screw speeds using heavy corn syrup, a Newtonian fluid, and a mixture of corn syrup and carboxymethylcellulose (CMC) which is a non-Newtonian fluid. Effects of pitch of conveying elements, and the effect of pitch and thickness of individual kneading discs, on the flow field, were investigated. From the measured flow field, the total shear rate distribution and flow number were
calculated. It was found that kneading blocks have substantial leakage flow, which increased with its pitch and rotational speed. Also, the flow number values indicated that there was more dispersive mixing than distributive mixing in the translational region of the kneading section. In the nip region the velocity profiles were significantly different from the translational region. The tangential velocity was maximum in the center of the channel indicating the existence of a pressure flow. Also the magnitude of the backflow or the positive axial velocity was higher than in the translational region for the same screw speed and pitch indicating better mixing. These velocity distributions were compared with those in conveying elements having same pitch. The measurements clearly indicated that the flow field in a kneading block is significantly different than that in a conveying element. The flow field in kneading blocks is characterized by leakage flows between the kneading disks and
dispersion of material.
Impacts
Knowlege of flow characteristics and mixing effectiveness of kneading blocks is essential in the design of screw geometry and selection of screw configurations that are appropriate for a given material that is being extruded. We have been able to show with experimental evidence how the screw geometry and material properties affect mixing in a twin-screw extruder. Through this project we have generated the quantitative information needed for the extruder manufacturers and food processors who use the twin-screw extrusion process to manufacture a variety of food products.
Publications
- 1. L. Yerramilli and M.V. Karwe. Flow field in the translational region of a kneading section of a co-rotating twin-screw extruder. Accepted for publication in Food and Bioproducts Processing, Trans. IChemE (UK), Part C, pp. 5-12, March 2004.
- 2. S. Bakalis and M.V. Karwe. Velocity distributions and volume flow rates in the nip and translational regions of a co-rotating, self-wiping, twin-screw extruder. Journal of Food Engineering, Vol. 51, Issue 4, pp. 273-282, 2002.
- 3. M.V. Karwe. Laser Doppler Anemometry: Powers and Limitations. Proceedings of the Conference on Food Engineering (CoFE), organized by the American Institute of Chemical Engineers, Reno, Nevada, November 4-9, 2001.
- 4. S. Bakalis and M.V. Karwe. Measuring of velocity distributions in the nip region of a co-rotating, twin-screw extruder. Journal of Food and Bioproducts Processing, Transactions of the Institution of Chemical Engineers (U.K.), Vol. 77, Part C, pp. 205-212, September 1999.
- 5. S. Bakalis and M.V. Karwe, Measurement of three-dimensional velocity field in a co-rotating twin-screw extruder, Polymer Engineering and Science, Vol. 38, No. 9, pp. 1549-1558, September 1998.
- 6. S. Bakalis and M.V. Karwe, Measurement of flow field in the translational region of a twin-screw extruder: effect of material behavior, Transport Phenomena in Manufacturing and Materials Processing, Proceedings of the International Mechanical Engineering Congress and Exhibition, Los Angeles, November 1998.
- 7. Kiani, S. Bakalis, and M.V. Karwe, LDA measurements and comparison with numerical modeling of twin-screw extruders, Society of Plastic Engineers, Annual Technical Conference, Vol. I, pp. 12-16, 1998.
- 8. Karwe, M., Bakalis, S., and V. Sernas. 1996. Velocity measurements in the NIP region of a corotating twin-screw extruder using laser Doppler anemometry. Advances in Polymer Technology.
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Progress 01/01/03 to 12/31/03
Outputs
Velocity distributions in a co-rotating, self-wiping, twin-screw extruder were determined using laser Doppler anemometry to understand flow field and elucidate the mixing effectiveness of kneading blocks. Velocity profiles in the translational region were measured at three screw speeds using heavy corn syrup, a Newtonian fluid. Effects of pitch and thickness of individual kneading discs, on the flow field, were investigated. From the measured flow field, the total shear rate distribution and flow number were calculated. It was found that kneading blocks have substantial leakage flow, which increased with its pitch and rotational speed. Also, the flow number values indicated that there was more dispersive mixing than distributive mixing in the translational region of the kneading section. In the nip region the velocity profiles were significantly different from the translational region. The tangential velocity was maximum in the center of the channel indicating the
existence of a pressure flow. Also the magnitude of the backflow or the positive axial velocity was higher than in the translational region for the same screw speed and pitch indicating better mixing. These velocity distributions were compared with those in conveying elements having same pitch. The measurements clearly indicated that the flow field in a kneading block is significantly different than that in a conveying element. The flow field in kneading blocks is characterized by leakage flows between the kneading disks and dispersion of material.
Impacts
Knowlege of flow characteristics and mixing effectiveness of kneading blocks is essential in the design of screw geometry and selection of screw configurations that are appropriate for a given material that is being extruded. Through this project we have generated the quantitative information needed for the extruder manufacturers and food processors who use the twin-screw extrusion process.
Publications
- L. Yerramilli and M.V. Karwe. Flow field in the translational region of a kneading section of a co-rotating twin-screw extruder. Accepted for publication in Food and Bioproducts Processing, Transactions of the Institution of Chemical Engineers (U.K.), March 2004.
- S. Bakalis and M.V. Karwe. Velocity distributions and volume flow rates in the nip and translational regions of a co-rotating, self-wiping, twin-screw extruder. Journal of Food Engineering, Vol. 51, Issue 4, pp. 273-282, 2002.
- L. Yerramilli and M.V. Karwe. Determination of velocity distribution in the kneading section of a co-rotating twin-screw extruder. HEAT AND MASS TRANSFER'2002, Proceedings of the fifth ISHMT-ASME Heat and Mass Transfer Conference and sixteenth National Heat and Mass Transfer Conference, Science City, Kolkata, India, January 3-5, 2002.
- M.V. Karwe. Laser Doppler Anemometry: Powers and Limitations. Proceedings of the Conference on Food Engineering (CoFE), organized by the American Institute of Chemical Engineers, Reno, Nevada, November 4-9, 2001.
- S. Bakalis and M.V. Karwe. Measuring of velocity distributions in the nip region of a co-rotating, twin-screw extruder. Journal of Food and Bioproducts Processing, Transactions of the Institution of Chemical Engineers (U.K.), Vol. 77, Part C, pp. 205-212, September 1999.
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Progress 01/01/02 to 12/31/02
Outputs
Velocity distributions in the kneading section of a co-rotating, self-wiping, twin-screw extruder were determined using laser Doppler anemometry to elucidate the mixing effectiveness of kneading blocks. Velocity profiles in the translational region were measured at three screw speeds using a Newtonian fluid. Effects of pitch and thickness of individual kneading discs were also investigated. The total shear rate distribution and flow number were evaluated. Measured velocity distributions indicated that kneading blocks have substantial back flow, which increased with the pitch and rotational speed of the kneading block. The tangential velocity was maximum in the center of the channel indicating the existence of a pressure flow. Also the magnitude of the backflow was higher than in the translational region for the same screw speed and pitch indicating better mixing. As the channel depth increased it was found that the magnitude of backflow decreased. The distribution of
the total shear rate was nearly the same for both the conveying and kneading block elements of the same pitch. The maximum shear was observed near the barrel and the screw root and minimum at the center of the screw channel. The flow number values indicated that there was more dispersive mixing than distributive mixing in the kneading region.
Impacts
The results of this investigation will be beneficial to those who design screw configuration for twin-screw extruders in food, pharmaceutical, and plastics industries. They will be able to select kneading blocks to achieve a certain level of mixing.
Publications
- S. Bakalis and M.V. Karwe, "Velocity distributions and volume flow rates in the nip and translational regions of a co-rotating, self-wiping, twin-screw extruder," Journal of Food Engineering, Vol. 51, Issue 4, pp. 273-282, 2002.
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Progress 01/01/01 to 12/31/01
Outputs
Co-rotating twin-screw extruders are used to make a variety of food products. The characteristic section of co-rotating twin screw extruder is the kneading section where intense mixing and shearing of the ingredients occurs. The width and the stagger angle of these kneading elements determine the amount of backflow that is generated which in turn determine the nature of mixing, i.e., dispersive or distributive. Kneading blocks generate high and low-shear regions, which enhance mixing effectiveness of the extruder. The objective of this research was to determine the velocity distribution in the kneading sections of a co-rotating, self-wiping, twin screw extruder so as to quantify the mixing effectiveness of kneading blocks. An extruder with Plexiglas barrel was used to carry out velocity measurements. A laser Doppler anemometry system was used to measure two components of the instantaneous velocity vector at a point in the screw channel. Using this data the velocity
profiles were generated. Velocity profiles in the translational region were measured at different screw speeds using a Newtonian and non-Newtonian fluid. These velocity profiles were compared with those in a forward conveying element of the same pitch. Effect of pitch and thickness of individual kneading disc was also investigated. Near the screw root, axial and tangential velocity distributions were similar to those in a conveying element of the same pitch. However, near the barrel the axial and tangential velocity showed steeper gradients and more back flow. Near the barrel, the velocity distributions were different at different axial locations. The results indicated that in kneading blocks, average the residence time of a food particle would be more due to back flow and more mixing will occur. The geometry of kneading block significantly affects the amount of mixing that occurs.
Impacts
The results of this research will benefit equipment manufacturers and food processors using twin-screw extrusion technology to make a variety of food products.
Publications
- M.V. Karwe, 'Laser Doppler Anemometry: Powers and Limitations,' Proceedings of the Conference on Food Engineering (CoFE), organized by the American Institute of Chemical Engineers, Reno, Nevada, November 4-9, 2001.
- L. Yerramilli and M.V. Karwe, 'Determination of velocity distribution in the kneading section of a co-rotating twin-screw extruder,' HEAT AND MASS TRANSFER'2002, Proceedings of the fifth ISHMT-ASME Heat and Mass Transfer Conference and sixteenth National Heat and Mass Transfer Conference, Science City, Kolkata, India, January 3-5, 2002.
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Progress 01/01/99 to 12/31/99
Outputs
The research is in its early stage. The exprimental apparatus has been redesigned and reassembled to allow increased torque on the screws of a table-top twin-screw extruder with Plexiglas barrel. Some measurements of velocity distribution in kneading blocks have been carried out using laser Doppler anemometry. The data is still being collected. Initial results indicate that the flow field in a kneading block could be chaotic. Flow reversal between the adjacent kneading paddles was noticed and the magnitude of reverse flow was as much as the forward flow.
Impacts
Kneading blocks form an important part of a twin-screw extruder because they are responsible for effective mixing and shearing of the material going through a twin-screw extruder. Our preliminary measurements have indicated that flow in a kneading block is quite different than in a conveying element. Increased residence time and reverse flow was seen in the kneading elements which will affect the product quality. Our measurements will provide key data for validation of mathematical models.
Publications
- No publications reported this period
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Progress 01/01/98 to 12/31/98
Outputs
The axial and tangential velocity profiles in the screw channel of a co-rotating twin-screw extruder were measured using laser Doppler anemometer in a Newtonian and a pseudoplastic materials. The velocity distributions were measured in the screw channels of a 14 mm pitch screw element. For the low pressure gradient encountered in our experiments the measured velocity distributions did not seem to depend on the rheological properties of the flowing fluids. The predictions from a simplified model seemed to agree reasonably well with the experimental data. Velocity measurements were also carried out in the nip region of a 28 mm pitch screw element at a screw speeds of 120 rpm. The velocity distributions in the intermesh of the two screws were very different from those measured in the translation region, indicating the distinct character of the nip region. Much higher velocity values (0.08 m/s) for the axial velocity component were measured in the nip region, when
compared to those measured in the translational (0.02 m/s). Transfer flow towards the hopper was also detected. Our focus for the next six months would be on calculating the shear rate distribution and mixing intensities from the measured flow field.
Impacts
(N/A)
Publications
- S. Bakalis and M.V. Karwe, "Measurement of three-dimensional velocity field in a co-rotating twin-screw extruder," Polymer Engineering and Science, Vol. 38, No. 9, pp. 1549-1558, September 1998.
- S. Bakalis and M.V. Karwe, "Measurement of flow field in the translational region of a twin-screw extruder: effect of material behavior," Transport Phenomena in Manufacturing and Materials Processing, Proceedings of the International Mechanical Engineering Congress and Exhibition, Los Angeles, November 1998.
- Kiani, S. Bakalis, and M.V. Karwe, "LDA measurements and comparison with numerical modeling of twin-screw extruders," Society of Plastic Engineers, Annual Technical Conference, Vol. I, pp. 12-16, 1998.
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Progress 01/01/97 to 12/31/97
Outputs
Velocity measurements were carried out from the top and side of the plexiglas zone mounted on the ZSK-30 twin screw extruder. This allowed measurement of all three components of velocity vector. Measurements indicated that the magnitude of the total velocity.
Impacts
(N/A)
Publications
- No publications reported this period
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Progress 01/01/96 to 12/30/96
Outputs
Velocity measurement experiments were carried out on the ZSK-30 twin screw extruder. An optical window mounted in the vent port of the extruder, was used for visualizing and accessing the flow in the screw channels. Using laser Doppler anemometer (LDA), two components of velocity were measured in 14mm and 28mm pitch forward conveying screw elements for corn syrup at three different screw speeds of 30, 60 and 90 rev/min. It was found that for forward conveying screw elements, the flow field was affected by the pitch of the screw element, however, the average shear rate was not significantly affected. The screw speed affected the magnitudes of velocity but the velocity distrbution was not significantly affected. The transfer flow through the clearances was detected and was found to be towards the hopper due to rising pressure towards the die. In the nip, of the foward conveying elements most of the flow was towards the die indicating of a forward jog to the flow. An
Excel program based on Visual Basic was written to generate contours for isovelocity lines and to calculate shear rate distribtuion in the screw channels.
Impacts
(N/A)
Publications
- Karwe, M., Bakalis, S., and V. Sernas. 1996. Velocity measurements in the NIP region of a corotating twin-screw extruder using laser Doppler anemometry. Advances in Polymer TEchnology.
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Progress 01/01/95 to 12/30/95
Outputs
A laser Droppler anemoneter system was set up to make velocity measurements in aCouette flow apparatus and a twin-screw extruder. The experimental results from the Couette flow apparatus agreed very well with the theoretical results. Next the velocity measurements inside the screw channels of a corotating, self-wiping twin-screw extruder were carried out. The tangential and axial velocity components, in the translational and the intermeshing regions of a ZSK-30 twin screw extruder were measured. The velocity measurements were carried out suing heavy corn syrup at different screw speeds and for two different screw elements. It was found that screw speed does not have a significant effect on the shape of the velocity profiles. Velocity profiels in the tangential region were substnatially affected by the pitch of the screw element. A screw element of smaller pitch resulted in wider range of velocity values than those from a larger pitch element. This impies that by using
screw elements of smaller pitch higher shear rates can be applied to the material. Velocity field in the nip region of the exruder was found to be very different than that in the translational region. Measured velocity profiles indicated leakage flows between the two screws.
Impacts
(N/A)
Publications
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