OPTIMIZATION METHODS FOR SOLVING NON-LINEAR EQUATIONS IN VISCOELASTIC FLOW PROBLEMS

Numerical simulation of complex flows of viscoelastic fluids requires the use of efficient algorithms for solving the non-linear governing equations. In this paper, optimization algorithms, associated to a non-linear least squares methods are considered. The governing equations are written in the context of stream-tube analysis. This method is particularly adapted to handle memory-integral constitutive equations and permits calculation of flows by considering elementary sub-domains in a mapped computational domain where the transformed streamlines are parallel and straight. The procedure used to solve the equations is the Trust Region optimization algorithm, which satisfies a global convergence property. Using an integral codeformational equation, various tests involving the influence of parameters of the algorithms are applied to different flow geometries and underline the robustness and efficiency of the Trust Region algorithm.     

Performance of Single and Multi-stage Spouted Bed Drying Systems

ABSTRACT

A mathematical model is developed to predict the performance of single-stage and multi-stage drying systems using spouted beds. The model uses unsteady state analysis for batch operation to simulate the steady state operation of a continuously fed spouted bed. A parametric study is carried out to study the effect of the following parameters on the performance of a single-stage grain drying system: air flow rate per unit mass of the grain in the bed, ambient air temperature and humidity, initial and target moisture contents, the residence time in the bed, and the effectiveness of the heat exchanger to recover the thermal energy in the exhaust air. The parametric study is also extended to investigate the effect of these parameters (except ambient air temperature and humidity) on the performance of the multi-stage system. In addition, the number of stages is also included in the latter study. The results are presented in terms of charts which may be adopted for the design of such systems.     

EFFECTS OF GLUCOSE OXIDASE, HEMICELLULASE AND ASCORBIC ACID ON DOUGH AND BREAD QUALITY

ABSTRACT

In this study, glucose oxidase alone or its combinations with hemicellulase or ascorbic acid were used in bread making. Glucose oxidase alone mainly decreased dough extensibility. It produced stiffer and less extensible dough. Combinations of glucose oxidase–hemicellulase presented lower extensibility and were more resistant to extension than glucose oxidase alone. When glucose oxidase–ascorbic acid combinations were used, the softening degree significantly decreased, regardless when added the lowest glucose oxidase in combination with ascorbic acid. Glucose oxidase–ascorbic acid combinations significantly modified dough resistance. The glucose oxidase alone significantly increased specific loaf volume. The Dallman value of loaves made with glucose oxidase alone was found higher than for control. The most dramatic effect of additives on specific loaf volume was observed when glucose oxidase–hemicellulase combinations were added. This effect has been ascribed to redistribution of water from the hemicellulose to gluten, which would render the gluten more extensible. Specific loaf volume showed a significant enhancement when glucose oxidase–ascorbic acid combinations were added, but this effect was not as good as glucose oxidase–hemicellulase. The effects of glucose oxidase and its combinations with ascorbic acid and hemicellulase on dough rheology and bread quality are highly dependent on the amount of enzyme and the original wheat flour quality.

PRACTICAL APPLICATION

In practice, appropriate combinations of glucose oxidase with hemicellulase can be used as improvers in bread making, depending on their combination levels. This study will show the way to new research about glucose oxidase, ascorbic acid and hemicellulose.

     

Chemical Changes After Irradiation and Post-Irradiation Storage in Tilapia and Spanish Mackerel

Influence of gamma irradiation (1.5–10 kGy) and post-irradiation storage up to 20 days at 2 ± 2°C on some chemical criteria of tilapia and Spanish mackerel were studied. Total volatile basic nitrogen formation was lower in irradiated fish than in the unirradiated. Irradiation also caused a larger increase in thiobarbituric acid values which continued gradually during storage. Some fatty acids decreased by irradiation treatments at all doses. Thiamin loss was more severe at higher doses (≥4.5 kGy), whereas riboflavin was not affected. Alpha and gamma tocopherols of tilapia and alpha, beta, gamma, and delta tocopherols, in Spanish mackerel, decreased with increased dose and continued to decrease during 20-day post-irradiation storage.     

The viability of three probiotic organisms grown with yoghurt starter cultures during storage for 21 days at 4°C

This study investigated the viability of probiotic ( Lactobacillus acidophilus LA5, Lactobacillus rhamnosus LBA and Bifidobacterium animalis subsp . lactis BL-04) in milk fermented with Lactobacillus delbrueckii subsp . bulgaricus LB340 and Streptococcus thermophilus TAO (yoghurt – Y). Each probiotic strain was grown separately in co-culture with Y and in blends of different combinations. Blends affected fermentation time(s), pH and firmness during storage at 4°C. The product made with Y plus B. animalis subsp . lactis and L. rhamnosus had counts of viable cells at the end of shelf life that met the minimum required to achieve probiotic effect. However, L. acidophilus and L. delbrueckii subsp . bulgaricus were inhibited.     

Improvement in tensile properties of PVC–montmorillonite nanocomposites through controlled uniaxial stretching

In this paper we present the results exhibiting an improvement in the tensile properties of polyvinyl chloride (PVC)?Cmontmorillonite nanocomposites through uniaxial stretching. The clay was dispersed in PVC matrix with the help of dodecylamine. PVC?Cmontmorillonite nanocomposites films containing varying amounts of clay (0?C5%) were produced through solution elution technique. The films were stretched uniaxially at a constant temperature of 80?°C in three different steps using controlled loads. X-ray diffraction and stress?Cstrain curves were obtained for both unstretched and stretched films in order to determine the improvement in various properties. The controlled uniaxial stretching of films close to the softening temperature of PVC has resulted in enhancement in the degree of crystallinity in the nanocomposites. This improvement in the structural order has also imparted increase in tensile strength and Young??s modulus of the nanocomposite films.