Residence Time Distribution of Multiple Particles in Four Configurations of Holding Tubes
15 Nov 2004-
TL;DR: In this paper, the authors investigated the residence time distributions of multiple particles (as affected by process and system parameters) during non-Newtonian tube flow during polystyrene and acrylic particles were used as model food particles.
Abstract: Residence time distributions of multiple particles (as affected by process and system parameters) were investigated during non-Newtonian tube flow. Process parameters included flow rate, particle type, carrier fluid viscosity, and particle concentration. The system parameter of interest was the holding tube configuration. Polystyrene and acrylic particles were used as model food particles. Digital imaging analysis was used to obtain residence time data of particles. A novel type of holding tube (chaotic holding tube) was constructed. Comparisons among the straight, single helical, double helical, and chaotic holding tube were performed in terms residence time distribution (RTD) of particles. In addition, the effect of inclination angle (0 º and 45 º) of the chaotic holding tube was investigated. It was found that the narrowest RTD of particles was obtained in the single helical holding tube. RT std in the chaotic holding tube was greater than that in the single helical holding tube, but lower than those in the straight and double helical holding tubes. The most significant process parameter affecting RTD was flow rate. The effect of flow rate was more pronounced for high density (acrylic) particles. Carrier fluid viscosity, particle type, and particle concentration did not have significant effects on the overall RT std. Trends observed in the chaotic holding tube were similar to those observed in the single helical holding tube. However, there were some cases where use of chaotic holding tube resulted in narrower RTD of particles. Changing the inclination angle from 0 º to 45 º in the chaotic holding tube resulted in wider RTD of both types of particles. Denizli, a small town in the Aegean region of Turkey. In 1993, her family moved to the capital city, Ankara, where she attended high school and college. She graduated from Middle East Technical University in 2002, with a B.S degree in Food Engineering. In the summer of 2002, she was admitted to the graduate school at North Carolina State University where she began her Master of Science degree in the Department of Food Science. She currently works as a research assistant in the same department. iii ACKNOWLEDGEMENTS
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01 Jan 1991
TL;DR: Aseptic processing involves sterilising the product and package separately, and filling under sterile conditions as discussed by the authors, which can provide better product quality compared with canned products, lower transport and storage costs compared with frozen products, and virtually no restriction on package size.
Abstract: Aseptic processing involves sterilising the product and package separately, and filling under sterile conditions. Advantages include better product quality compared with canned products, lower transport and storage costs compared with frozen products, and virtually no restriction on package size. Problems include ensuring adequate heat penetration into the particles to ensure sterility, preventing separation of particles from the carrier liquid, and retention of particle structure and shape. Particulate foods can be sterilised in scraped - surface heat exchangers. Other methods involve heating the particles separately, and combining them during filling. Projects will commence at the International Food Institute of Queensland (IFIQ) on aseptic packaging of a meat and vegetable product, and aseptically packaged mango pieces.
8 citations
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TL;DR: In this paper, it is assumed that the actual secondary motion is replaced by a uniform stream; conditions in the central part of the section mainly determines the motion and the appropriate velocity of the stream can be determined from the relation that has been found experimentally between the rate of flow in a curved pipe and the pressure gradient.
Abstract: In the stream-line motion of fluid in a curved pipe the primary motion along the line of the pipe is accompanied by a secondary motion in the plane of the cross-section. The secondary motion decreases the rate of flow produced by a given pressure gradient and causes an outward movement of the region where the primary motion is greatest. It is difficult to deduce these consequences from the exact equations of motion, but it is easy to do so if it is assumed that the actual secondary motion is replaced by a uniform stream; conditions in the central part of the section mainly determines the motion and here the secondary motion is approximately a uniform stream. The appropriate velocity of the stream can be determined from the relation that has been found experimentally between the rate of flow in a curved pipe and the pressure gradient.
714 citations
"Residence Time Distribution of Mult..." refers background in this paper
...This secondary motion in the radial direction occurs due to a pressure gradient across the tube, which results from the centrifugal force due to the curvature (Dean, 1927, 1928)....
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TL;DR: The Navier-Stokes equations in stream-function/vorticity form were solved numerically by over-relaxation for the case of steady state, fully developed, isothermal, incompressible viscous Newtonian flow within a rigorously treated toroidal geometry as discussed by the authors.
Abstract: The Navier-Stokes equations in stream-function/vorticity form were solved numerically by over-relaxation for the case of steady state, fully developed, isothermal, incompressible viscous Newtonian flow within a rigorously treated toroidal geometry. Solutions were obtained for curvature ratios ranging from 5 to 100 and for Dean numbers as low as I and as high as 1000. The Dean number was demonstrated to be the principal parameter to characterize toroidal flow; however, a second-order dependence upon the curvature ratio above that expressed in the Dean number was observed. Comparisons of the numerically computed axial-velocity profiles were made with experimental data. The cross-sectional pressure distribution was calculated, and a correlation is presented for a diametral pressure drop in terms of the Dean number.
124 citations
"Residence Time Distribution of Mult..." refers methods in this paper
...Austin and Seader (1973) developed a numerical solution to the equations of motion in order to compute the velocity and pressure profiles over a wide range of Dean numbers....
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121 citations
"Residence Time Distribution of Mult..." refers background in this paper
...In addition, frictional energy loss near the wall increases considerably when compared to friction loss in straight pipes (Barua, 1963)....
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...Secondary flow results in shifting of the maximum velocity region towards the outer wall of the tube (Barua, 1963)....
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...In the secondary flow the fluid near the top and the bottom moves inwards whereas the fluid at the center moves outwards (Barua, 1963)....
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...During flow through a curved pipe, a pressure gradient is required to balance the centrifugal force resulting from the curvature of the tube (Barua, 1963)....
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TL;DR: In this paper, a quantitative methodology was developed for evaluating thermal process schedules for low acid foods containing particulates of any shape, using finite element analysis to determine temperature distributions within particulate foods subjected to timevarying boundary conditions.
Abstract: A quantitative methodology was developed for evaluating thermal process schedules for low-acid foods containing particulates of any shape. The methodology uses finite element analysis to determine temperature distributions within particulate foods subjected to timevarying boundary conditions. Simulations were conducted to study the effects of particle size, residence time distributions within heat exchanger and holding tube, and convective heat transfer coefficients. Results indicate that all these factors have significant effects on the thermal process schedule required to achieve commercial sterility. For large particles, simulations indicate that little credit can be given for lethality within the heating section.
106 citations
"Residence Time Distribution of Mult..." refers background or methods in this paper
...Sastry (1986) used a finite element analysis to evaluate thermal process schedules for low-acid particulate foods....
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...Since accurate temperature measurements within freely flowing particles in the heat-hold-cool system is practically impossible, mathematical modeling of heat transfer to the center of the particles is necessary for process design (Sastry, 1986)....
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TL;DR: In this paper, the authors analyzed the effect of chaotic particle paths in steady, laminar flow through a tube and compared the performances of two different coils, one with regular mixing and the other with chaotic mixing.
102 citations
"Residence Time Distribution of Mult..." refers background in this paper
...As a result, chaotic mixing is achieved (Acharya et al., 2001)....
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...Chaotic mixing has been shown to enhance heat transfer in heat exchangers (Chagny et al., 2000; Acharya et al., 2001; Lefevre et al., 2003)....
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...Acharya et al. (2001) numerically analyzed the enhancement of heat transfer in two different coiled tube heat exchangers, one with regular mixing and the other with chaotic mixing....
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