The Experts below are selected from a list of 321 Experts worldwide ranked by ideXlab platform
T Jager - One of the best experts on this subject based on the ideXlab platform.
-
Residence time distribution in kneading Extruders
Journal of Food Engineering, 2000Co-Authors: T Jager, P. Santbulte, D.j. Van ZuilichemAbstract:Abstract The residence time distribution (RTD) of a kneading extruder processing a food material is measured with a lithium tracer. The curve width of the measured RTD curves is comparable with that of co-rotating, twin-screw Extruders. Except for the tail, the extinction curve of the filled part of the extruder can be described reasonably with a cascade of continuously stirred tank reactors (CSTRs). For the integrated form of the extinction curve a model which includes a plug-flow in series to the cascade of CSTRs gives a better fit. In the tail of the logarithmic RTD a divergence can be seen. The use of various RTD models is discussed in relation to the measurement.
-
mixing effects of constituting elements of mixing screws in single and twin screw Extruders
Powder Technology, 1999Co-Authors: D.j. Van Zuilichem, E Kuiper, W Stolp, T JagerAbstract:Abstract In extrusion, mixing of solids and melts has always been problematic, leading to diverse models describing the melting process. It is found that for foods based on cereals, only a few are valid, due to the simultaneous presence of water and high viscous non-Newtonian material. Mixing trials are summarised for single and twin screw Extruders, with particulate solids of different particle sizes like, maize grits, wheat flour, sucrose crystals and glucose syrup. Special mixing-heads for single screw Extruders like, pineapple-heads, and slotted flight sections for counter-rotating twin screw Extruders are investigated. The effects of screw geometry on mixing has been measured using co-rotating twin screw extruder modular elements like: single lead elements, mixing paddles and reversed pitch elements in a translucent model extruder by means of a study of flow phenomena and residence time distribution (RTD) measurements. Mixing effects are reported and their influences on viscous dissipation, residence time, curve spread and stagnancy are explained.
-
Residence time distribution in twin-screw Extruders.
1992Co-Authors: T JagerAbstract:For the twin-screw Extruders used in the food industry at short time high temperature processes the knowledge of their reactor properties is incomplete for mass- and heat flow. Therefore each process change such as: scale-up or product development requires a great number of measurements before an acceptable product quality can be made with a stable process. The number of measurements is considerable by the great number of possible variables in the extrusion process and the interactions between process conditions such as: temperatures, viscous dissipation and distributive mixing. From these constraints the objective of this thesis is expressed as the measurement and characterisation of the mass flow in a twin-screw extruder, possibly without laborious methods. As the direct measurement of these mass flows is quite time consuming, it is chosen to describe the relation between the mass flow and the residence time distribution. This relation is described in a residence time model which translates the axial mass flow in a twin-screw extruder into a residence time distribution. At the start of this project an appropriate measuring method for the average residence time was already available from a collaboration with ITAL. Its accuracy was calculated during this project. The influence of the adjustable variables of the twin-screw extruder on the degree of fill and the shape of the residence time distribution is dependent of the properties of the extruded material as well as of the Extruders geometry. A standard behaviour of the residence time distribution has been found for biopolymers. For non-food applications a considerable number of exceptions can be found in the literature. The mechanisms behind these exceptions are not appointed in the literature. In this work a method is given to search for statistical interesting hypotheses which describe possible relations between the multitude of possible variables in extrusion research. By this method a steam reflux was found in a counter-rotating, twin-screw extruder. The developed residence time distribution model describes the extruder as a machine in which chambers are formed and conveyed by the revolutions of the screws. During there residence in the extruder these chambers lose leakage flows which give a substantial part of the axial mixing. The mixing of these leakage flows and the contents of the chamber is described. The model can be used for co- and counter- rotating, twin-screw Extruders in food and non-food applications. The residence time distribution of the compression zone of a counter-rotating, twin-screw extruder can be simulated with a complete mixing of the leakage flows and chamber content. Incomplete mixing has been used for most of the measurements on a corotating, twin-screw extruder and on the feed zone of a counter- rotating type. In all comparable logarithmical F-curves from the literature a bend was found. This bend can increase the fraction with the longest residence time considerably, while the characteristic variables for the curve width are hardly changed. This phenomenon can be simulated by the developed model with a time dependent change in mixing properties.
D.j. Van Zuilichem - One of the best experts on this subject based on the ideXlab platform.
-
Residence time distribution in kneading Extruders
Journal of Food Engineering, 2000Co-Authors: T Jager, P. Santbulte, D.j. Van ZuilichemAbstract:Abstract The residence time distribution (RTD) of a kneading extruder processing a food material is measured with a lithium tracer. The curve width of the measured RTD curves is comparable with that of co-rotating, twin-screw Extruders. Except for the tail, the extinction curve of the filled part of the extruder can be described reasonably with a cascade of continuously stirred tank reactors (CSTRs). For the integrated form of the extinction curve a model which includes a plug-flow in series to the cascade of CSTRs gives a better fit. In the tail of the logarithmic RTD a divergence can be seen. The use of various RTD models is discussed in relation to the measurement.
-
mixing effects of constituting elements of mixing screws in single and twin screw Extruders
Powder Technology, 1999Co-Authors: D.j. Van Zuilichem, E Kuiper, W Stolp, T JagerAbstract:Abstract In extrusion, mixing of solids and melts has always been problematic, leading to diverse models describing the melting process. It is found that for foods based on cereals, only a few are valid, due to the simultaneous presence of water and high viscous non-Newtonian material. Mixing trials are summarised for single and twin screw Extruders, with particulate solids of different particle sizes like, maize grits, wheat flour, sucrose crystals and glucose syrup. Special mixing-heads for single screw Extruders like, pineapple-heads, and slotted flight sections for counter-rotating twin screw Extruders are investigated. The effects of screw geometry on mixing has been measured using co-rotating twin screw extruder modular elements like: single lead elements, mixing paddles and reversed pitch elements in a translucent model extruder by means of a study of flow phenomena and residence time distribution (RTD) measurements. Mixing effects are reported and their influences on viscous dissipation, residence time, curve spread and stagnancy are explained.
M F Cerqueira - One of the best experts on this subject based on the ideXlab platform.
-
on line monitoring of the residence time distribution along a kneading block of a twin screw extruder
Polymer Testing, 2004Co-Authors: O S Carneiro, J A Covas, J A Ferreira, M F CerqueiraAbstract:An on-line Residence Time Distribution (RTD) measuring set-up that enables the characterisation of twin screw Extruders at short axial increments is presented. It uses the light emission of a fluorescent tracer (perylene) to generate concentration versus time curves, which are then used to determine the usual RTD parameters, delay time, mean residence time and variance. The system is initially mounted on a rectangular die coupled to a single screw extruder, on-line and off-line measurements being directly contrasted. Then, the optical probe is positioned at several points along the axis of a modular co-rotating twin screw extruder, on-line and off-line data being again compared. Having gained confidence in the measuring technique, an experimental unit utilizing a transparent barrel is used to characterize the evolution of RTD along a kneading block of a twin screw extruder.
Kathryn L Mccarthy - One of the best experts on this subject based on the ideXlab platform.
-
flow fields in straight and tapered screw Extruders using magnetic resonance imaging
Journal of Food Engineering, 1995Co-Authors: Cynthia K Agemura, Robert J Kauten, Kathryn L MccarthyAbstract:Abstract Improving the fundamental knowledge of fluid transport in extrusion is essential for the improved control and design of extruder systems. In particular, velocity profiles give valuable insight into residence time distributions and shear history which control final product characteristics. Due to the complicated geometry of Extruders, mathematical models to predict flow behavior have been based on simplifying assumptions. Experimental verification of theory has proved to be a challenge due to the difficulty in obtaining complete flow profiles. This paper demonstrates the use of MRI to study flow in extruder geometries. Images of the velocity profile in both a straight screw and a tapered screw extruder have been generated using this non-invasive technique. Good agreement exists between experimental and theoretical velocity profiles for open and closed discharge for both straight and tapered screws.
Milford A Hanna - One of the best experts on this subject based on the ideXlab platform.
-
phosphorus binding to starch during extrusion in both single and twin screw Extruders with and without a mixing element
Journal of Food Engineering, 2003Co-Authors: Mustafa Şeker, Hasan Sadikoglu, Murat Ozdemir, Milford A HannaAbstract:The effect of a mixing element in single- and twin-screw Extruders on the amount of phosphorus incorporated into starch was investigated for chemical modification of starch that has applications in the food and paper industries. Starch was mixed with sodium hydroxide and sodium trimetaphosphate and then the mixture was extruded. Screw speeds, which result in approximately the same residence time in both single- and twin-screw Extruders with and without a mixing element, were determined. Screw speeds of 220 rpm in a single-screw extruder with a mixing element, 180 rpm in a single-screw extruder without a mixing element, and 160 rpm in a twin-screw extruder with and without a mixing element resulted in similar residence times. The presence of a mixing element did not have an effect on vessel dispersion number and flow pattern in the single-screw extruder but it affected vessel dispersion number and changed the flow pattern in the twin-screw extruder. The amount of phosphorus bound to starch did not increase with the mixing element in single- and twin-screw Extruders for a constant mean residence time.
-
starch stearic acid complex development within single and twin screw Extruders
Journal of Food Science, 1996Co-Authors: Sandeep Bhatnagar, Milford A HannaAbstract:Corn starch was extruded with 4% stearic acid in Brabender single screw and twin screw laboratory Extruders. The screws were cooled and removed and samples were collected from locations along the screws. In the single screw extruder, starch gelatinization as determined by DSC and polarized light microscopy started in the compression zone and was completed in the metering zone. Starch-stearic acid complex formation as determined by iodine binding capacity and X-ray diffraction started at the same point as gelatinization and increased to a maximum near the tip of the screw. In the twin screw extruder, starch gelatinization and starch-stearic acid complex formation started at a distance of seven screw diameters and continued from there to the die end.
