FLOW PROFILES OF POWER LAW FLUIDS IN SCRAPED SURFACE HEAT EXCHANGER GEOMETRY USING MRI

Scraped surface heat exchangers (SSHE) are prevalent in the food industry to heat/cool viscous fluids and to provide enhanced mixing. This work focused on developing and verifying a theoretical model to characterize the flow patterns in two-dimensional angular flow in an SSHE geometry under isothermal conditions. Experimentally, the model was verified by a noninvasive magnetic resonance imaging (MRI) technique. Good agreement was achieved between the theoretical model and experimental data for a polyalkylene glycol, which behaved as a Newtonian fluid (n = 1), and a 1% CMC solution, a power law fluid with n = 0.77. However, the experimental flow profile tomato puree was characterized by apparent wall slip. The best fit, with respect to the power law model, was a flow behavior index of 0.11. This study provides the framework to quantify the effects of heat transfer on flow profiles in this geometry and the effectiveness of mixing.     

EFFECT of SCREW CONFIGURATION and SPEED ON RTD and EXPANSION of RICE EXTRUDATE

The influence of screw configuration and screw speed on the residence time distribution and product expansion was determined for rice meal processed in a corotating twin screw extruder. Screw speed had strong effect on the E(t)- and F(t)-diagrams, with the mean residence time varying inversely with screw speed from 206 s to 256 s. the F-diagram was modeled by the combination of perfect mixing and plug flow. the P estimates, which express the fraction of material in plug flow, varied inversely with screw speed from 0.41 to 0.55 for the operating conditions in this study. Both screw configuration and screw speed were statistically significant to the expansion ratios of rice extrudate, with the expansion in the height ranging from 2.98 to 4.13.     

Methylcellulose Films to Prevent Lipid Migration in Confectionery Products

Films of methylcellulose ranging in thickness from 0.2 to 1.0 mil (0.0051 to 0.025 mm), and exposed to peanut oil at 30°C and 5 psig pressure differential, allowed less than 1.0 μg linoleic acid equivalents-mil^?1cm^?224 hr^?1 to permeate, provided films were free from imperfections. Examination by scanning electron microscopy verified that many films were imperfect, especially those thinner than 0.2 mil. When films were embedded in chocolate and evaluated by a sensory panel, the 0.2 mil film was detectable, but only slightly objectionable.     

Loading and control policies for a flexible manufacturing system

An experimental investigation of operating strategies for a computer-controlled flexible manufacturing system is reported. The system is a real one, consisting of nine machines, an inspection station and a centralized queueing area—all interconnected by an automatic material-handling mechanism. The operating strategies considered involve policies for loading (allocating operations and tooling to machines) and real-time flow control. A detailed simulation was employed to test alternatives. The results are different from those of classical job shop scheduling studies, showing the dependence of system performance on the loading and control strategies chosen to operate this flexible manufacturing system. Loading and control methods are defined that significantly improve the system's production rate when compared to methods which were previously applied to the system. Finally, some conclusions are presented concerning the control of these automated systems.     

RHEOLOGY OF YOGURT DURING PIPE FLOW AS CHARACTERIZED BY MAGNETIC RESONANCE IMAGING

Flow behavior of yogurt during pipe flow was investigated using a magnetic resonance imaging (MRI) viscometer. The technique utilizes a velocity profile and independent pressure drop measurement to evaluate rheological parameters. The yield stress and slip velocity were obtained directly from the MR images; the Herschel-Bulkley consistency index, K, and the flow behavior index, n, were obtained through curve fitting procedures for product temperatures of 25C and 35C, over a shear rate range of 0.5 - 40 s⁻¹. At 25C, the average value of the yield stress was 14 Pa; the values of K and n were 5.6 Pa sⁿ and 0.36, respectively. As the wall stress increased from 15 to 42 Pa, the slip velocity increased linearly from 13 to 54 mm s⁻¹. At 35C, the average value of the yield stress was 10 Pa; the values of K and n were 1.1 Pa sⁿ and 0.88, respectively. As the wall stress increased from 12 to 31 Pa, the slip velocity increased linearly from 14 to 59 mm s⁻¹. These rheological parameters and slip velocities are relevant to the postfermentation cooling process performed in a continuous heat exchanger.     

FLOW BEHAVIOR of PROCESSED CHEESE MELTS

Flow behavior of processed cheese melts during pipe flow was investigated using a magnetic resonance imaging (MRI) tube viscometer technique. the technique utilized an MR velocity profile and an independent pressure drop measurement to evaluate flow properties. the test fluids were three commercial processed cheese products which were evaluated at a number of volumetric flow rates under melt conditions. MR image analysis was performed using a graphic user interface Matlab program. the three processed cheeses were best characterized as shear thinning power law fluids with flow behavior indices that ranged from 0.28 to 0.40 and consistency indices that ranged from 10 to 79 Pa sⁿ over the shear rate range of 0.1 to 10 s^?1. These flow properties are relevant to the mixing and pumping of these products under melt conditions during manufacture.     

Effect of operating conditions on physical characteristics of extruded rice starch

The effect of screw speed, flow rate, barrel temperature and added moisture on physical characteristics of high moisture extruded rice starch was studied. the product physical characterization was made by measuring density, final moisture content and the maximum load force in a puncture test. Rice flour containing approximately 1.5% protein and 6% moisture was mixed with 55–65% (w/w) water and extruded in a co-rotating twin screw extruder with a slit die. A two level factorial design was used to analyse each parameter. It was found that added moisture was the most important variable affecting the force-deformation curve maxima, with the interaction between added moisture and barrel temperature exhibiting a less significant effect. Added moisture and flow rate each affected density, with the interaction between added moisture and screw speed showing a less significant effect. Temperature and flow rate affected final moisture interactively with added moisture, which was evidently the most important variable.     

MRI METHOD TO EVALUATE INTERNAL STRUCTURAL CHANGES OF TOMATO DURING COMPRESSION

The effects of compression on the structure of red Roma tomato ( Lycopersicon esculentum ) were observed using magnetic resonance imaging (MRI). Images were acquired at six strain levels: 0%, 3%, 6%, 20%, 25% and no load sequentially for each of the replicates. The MR images revealed internal structural changes as the strain level increased; these changes were characterized by three displacement parameters: buckling angle (α), flattening angle (β) and columella position (h_c). The relative change of these parameters as a function of strain was evaluated by analysis of variance (ANOVA), which showed that the difference in the means was significant at the 0.05 level. In the post hoc analysis, structural changes at the low strains of 3% and 6% were different than the structural changes at the higher strains of 20% and 25%. The columella position showed significant recovery after the load was released. In addition to structural changes, the NMR signal intensity changed as a result of the compression. In particular, signal intensity from the columella region and upper radial arm increased with strain level. However, further studies are required to analyze these changes statistically.     

RELATIONSHIP BETWEEN RHEOLOGICAL BEHAVIOR AND BOSTWICK MEASUREMENT DURING MANUFACTURE OF KETCHUP

ABSTRACT

The Bostwick consistometer remains an integral part of assessing the consistency of tomato products. For instance, the consistency of lots of tomato paste are designated at the factory by their Bostwick measurement; tomato ketchup is produced to meet Bostwick ranges given in U.S. Standards for Grades. This work addresses the blending of tomato pastes, at different Bostwick readings, for use in the remanufacture of ketchup. For both blends and ketchup, the Bostwick measurement was correlated to rheological parameters measured by two methods: a single‐point method and rotational viscometry. The correlations between the Bostwick measurement and the viscosity were compared with the theoretical prediction based on gravity current flow. The results illustrate that the relationship between the Bostwick measurement and (K/ρ)^?1/(2n+3) provides a means to predict the Bostwick length from at‐line or in‐line viscosity measurements.

PRACTICAL APPLICATIONS

The results of this work provide a means to predict the Bostwick length from at‐line or in‐line viscosity measurements. Specifically, the quantitative relationships presented in the article allow in‐line process control schemes to improve final product quality.