LAMINAR FLOW AND HEAT TRANSFER IN BLOCKED ANNULI

Laminar flow and heal transfer in annular passages with axially nonuniform inner tubes are obtained numerically. A characteristic feature of these passages is that the flow separates in the streamwise direction. An axisymmetric coordinate system with an algebraic transformation in the radial direction kas been used. Fully elliptic vorticity-slream function and energy equations in the transformed coordinates are solved using an iterative alternate direction implicit (ADI) method. In an annulus with a smooth blockage, the flow separates immediately downstream of the blockage at Reynolds numbers greater than 100. The main features of the flow are established at a Reynolds number of 1000. The pressure drop is drastic near the maximum constriction. The heat flux is also high in the constricted region. A sharp increase in the heat transfer occurs where the fluid reattaches itself to the wall. The increase in the total pressure drop is about an order of magnitude greater than that in the average Nusselt number.     

Factorial design analysis for dye-sensitized hydrogen generation from water

A factorial design at two levels and four factors has been carried out in order to investigate the potential for hydrogen generation using Eosin Y-sensitized TiO₂/Pt catalyst under visible solar light in presence of triethanolamine (TEOA) as electron donor. The solution pH was found to be a significant parameter, and was maintained at pH 7.0 throughout the investigation. Visible light irradiation time (I-time) showed highest positive effect on hydrogen generation followed by initial Eosin Y concentration (for dye-sensitization) and the TEOA concentration while Pt content (wt %) in TiO₂ showed negative effect toward hydrogen generation. Experimental data were analyzed using both “Pareto analysis” as well as conventional regression analysis techniques. A regression function is proposed that satisfactorily predicts hydrogen generation.     

Photocatalytic reduction of carbonates and formation of some energy rich systems in the presence of Toluidine Blue

Aqueous sodium and potassium carbonates have been photoreduced in the presence of Toluidine Blue solution (which is also the photocatalyst). The photocatalytic formation of formic acid and formaldehyde was measured spectrophotometrically using Nash reagent. The effect of variation of various parameters like pH, amount of photocatalyst (Toluidine Blue concentration), concentration of Na₂CO₃ and K₂CO₃, light intensity, etc., on the yield of photoproducts was also investigated. A tentative mechanism for this reduction has been proposed. Copyright © 2001 John Wiley & Sons, Ltd.     

The fast reaction asymptote of the coalescence-redispersion model

The coalescence-redispersion (CRD) model is examined in the fast chemistry limit for the single bimolecular reaction A+B M R and the series parallel reactions A+B M R;B+R M S occurring in a plug flow reactor with unmixed feed streams. For the single bimolecular reaction it is shown that in this limit the CRD model is asymptotically equivalent to the 3E fast closure as t M 0. For the series parallel reactions the CRD model predictions tend to be bracketed by the 3E slow and fast closure formulations. Representative results are presented for the variance decay of the individual reactants, and it is seen that even in the fast reaction limit where mixing is controlling, the shape of the feed stream PDFs has negligible influence on the progress of the reaction.     

Aging effects of nanoscale ceria in ceria–platinum composite electrodes for direct alcohol electro-oxidation

Nanocrystalline Pt/CeO₂ composite electrodes were fabricated to study the electrochemical oxidation of methanol and ethanol. The performance of the electrodes was tested as the ceria solutions aged over time. It was observed that the performance oscillated with time, suggesting that the catalytic behavior towards alcohol oxidation was greatly dependent on the aging of the particles. These results point to a great dependence of the catalytic effect on the redox state of the ceria particles.     

Parallel and serial heuristics for the minimum set cover problem

We present a theoretical analysis and an experimental evaluation of four serial heuristics and four parallel heuristics for the minimum set cover problem. The serial heuristics trade off run time with the quality of the solution. The parallel heuristics are derived from one of the serial heuristics. These heuristics show considerable speedup when the number of processors is increased. The quality of the solution computed by the heuristics does not degrade with an increase in the number of processors.Research of both authors was supported by NSF Grant No. MIP-8807540.     

Applications of Genetic Algorithm in Polymer Science and Engineering

In the last several years, genetic algorithm (GA) has gained wide acceptance as a robust optimization algorithm in almost all areas of science and engineering. Polymer science and engineering is no exception. Researchers in this field have devoted considerable attention to the optimization of polymer productionusing objective functions and constraints that lead to products having desired material properties. Multiple-objective functions have been optimized simultaneously. An example is the minimization of the reaction time in a reactor (lower costs) while simultaneously minimizing the concentration of side products (that affect the properties of the product adversely). Several end-point constraints (equality or inequality) may also be present, as, e.g., obtaining polymer of a desired molecular weight. Again, this requirement stems from producing polymer having desired strength. Solving such problems usually result in Pareto sets. A variety of adaptations of GA have been developed to obtain optimal solutions for such complex problems. These adaptations can be used to advantage in other fields too. The applications of GA in areas of polymer science and engineering other than polymerization systems are few and far between, but this field is now maturing, and it is hoped that the future will see several newer applications.     

Effect of substrate adaptation on the microbial fermentation and microbial composition of faecal microbiota of weaning piglets studied in vitro

The in vitro cumulative gas production technique can be used to assess microbial activity of a complex community, in relation to fermentation of a particular energy source. Therefore, in combination with an in vivo study to examine the effects of two different diets for weaning piglets, microbial activities of faeces were compared from animals on the two different diets. The two diets were: CHO diet [containing added fermentable carbohydrates, including sugarbeet pulp (SBP) and wheat starch (WST)], and control diet without any added fermentable carbohydrates. Neither diet contained antibiotics or extra added copper. Twenty‐four piglets were selected from 12 litters (two per litter), weaned at 4 weeks of age (neither creep feeding nor any antibiotic treatment before and during the study), and introduced to one of the two diets. After 9 days on the diet, faecal samples were collected from selected animals, and tested for their activity in terms of gas production kinetics, and end‐products such as volatile fatty acids, ammonia and dry matter disappearance of the two test substrates SBP and WST. The bacterial diversity was also analysed before and after in vitro fermentation using denaturing gradient gel electrophoresis analysis of amplified 16S rRNA genes. There were differences both in kinetics and end‐products of the substrates. More interestingly, significant differences were detected between inocula, although mainly in terms of fermentation kinetics of the two substrates. With the CHO inoculum, SBP was fermented faster than with the control, while this effect was reversed for WST. Significantly higher diversity, as measured by DGGE fingerprint analysis, was detected in the microbial community enrichment on SBP as compared with WST at the end of fermentation. The difference between the kinetics of SBP compared with WST fermentation by faecal microbiota from the CHO diet fed piglets suggests better adaptation to SBP fermentation than to WST fermentation. The WST fermentation was more unexpected, given that a significant amount of starch is known to be fermentable by the small intestinal microbiota. It was concluded that the microbial community composition and activity in the GIT may be changed in response to diet, and that this change can be detected in vitro. Copyright © 2005 Society of Chemical Industry     

Viscoelastic changes and cell opening of reacting polyurethane foams from soy oil

The modulus development of reacting polyurethane foams from modified soy oil (soy polyol) was studied. The reaction and buildup of rheological properties were monitored using vane geometry in a strain‐controlled rheometer. Normal force exerted on the vanes by the expanding foam was measured as a function of time to study the phenomenon of cell opening. The effect of foam ingredients and process parameters on the modulus development was investigated. The morphology of the cured foam was studied using scanning electron microscope (SEM). Experiments were carried out to elucidate the effect of water and addition of petroleum‐based polyol on the modulus development of the reacting foam and the morphology of the cured product. The effect of frequency and thermal history on the modulus development of the reacting foam was also studied. Ozonolysis of soybean oil was carried out to study the effect of adding OH groups on the modulus development during the foaming reaction. Four stages of modulus development, similar to those observed for synthetic polyol (voranol, Aldrich Chemicals) foams, were observed. Increase in water content led to an earlier stiffening of the polymer and a higher modulus. Addition of voranol in soy polyol reduced the liquid foam plateau and significantly reduced the reaction time. Ozonolysis of soy oil led to an earlier phase separation as compared with foams from soy polyol. The temperature at which the foaming reaction takes place dominated the rate of modulus buildup. Higher texture (urea aggregates) and an increase in the cell size were observed with an increase in water content for soy polyol foams. Addition of voranol increased the number of open cells. Polym. Eng. Sci. 44:1977–1986, 2004. © 2004 Society of Plastics Engineers.