DEVELOPMENT OF STATIC MIXERS FOR MISCIBLE FLUIDS IN LAMINAR FLOW WITH THE USE OF COMPUTATIONAL FLUID DYNAMICS (CFD)

Static mixers with improved performance were developed from CFD simulations in a stepwise approach. The relevant geometric features of simple mixer designs and the corresponding mixing mechanisms-laminar shear, elongational flow, and distributive mixing-were identified first. This information was used to formulate guidelines for the development of new geometries. The solid elements of the static mixer should: (a) provide restrictions to the flow; (b) deflect the flow; (c) be sequentially rotated around the flow direction to provide symmetry; (d) extend from the center of the pipe to the vicinity of the walls to avoid short-circuiting; and (e) distribute and remix the flow. Based on these guidelines, two improved mixer designs were developed: the DS A-I mixer has a good mixing efficiency and an acceptable pressure drop; the Fins 35 degrees mixer is more efficient and compact, but requires a larger pressure drop. Their performance indicates that their use is possible on industrial applications.

The effect of flow arrangement on the pressure drop of plate heat exchangers

For the optimal design of plate heat exchangers (PHEs), an accurate thermal-hydraulic model that takes into account the effect of the flow arrangement on the heat load and pressure drop is necessary. In the present study, the effect of the flow arrangement on the pressure drop of a PHE is investigated. Thirty two different arrangements were experimentally tested using a laboratory scale PHE with flat plates. The experimental data was used for (a) determination of an empirical correlation for the effect of the number of passes and number of flow channels per pass on the pressure drop; (b) validation of a friction factor model through parameter estimation; and (c) comparison with the simulation results obtained with a CFD (computational fluid dynamics) model of the PHE. All three approaches resulted in a good agreement between experimental and predicted values of pressure drop. Moreover, the CFD model is used for evaluating the flow maldistribution in a PHE with two channels Per Pass. (c) 2008 Elsevier Ltd. All rights reserved.

Vortex configuration flow cell based on low temperature cofired ceramics as a compact chemiluminescence microsystern

The integration of optical detection methods in continuous flow microsystems can highly extend their range of application, as long as some negative effects derived from their scaling down can be minimized. Downsizing affects to a greater extent the sensitivity of systems based on absorbance measurements than the sensitivity of those based on emission ones. However, a careful design of the instrumental setup is needed to maintain the analytical features in both cases. In this work, we present the construction and evaluation of a simple miniaturized optical system, which integrates a novel flow cell configuration to carry out chemiluminescence (CL) measurements using a simple photodiode. It consists of a micro-mixer based on a vortex structure, which has been constructed by means of the low-temperature cofired ceramics (LTCC) technology. This mixer not only efficiently promotes the CL reaction due to the generated high turbulence but also allows the detection to be carried out in the same area, avoiding intensity signal losses. As a demonstration, a flow injection system has been designed and optimized for the detection of cobalt(H) in water samples. It shows a linear response between 2 and 20 mu M with a correlation of r > 0.993, a limit of detection of 1.1 mu M, a repeatability of RSD = 12.4 %, and an analysis time of 17 s. These results demonstrate the suitability of the proposal to the determination of compounds involved in CL reactions by means of an easily constructed versatile device based on low-cost instrumentation.

Magnetic suspension of the rotor of a ventricular assist device of mixed flow type

This work presents results of preliminary studies concerning application of magnetic bearing in a ventricular assist device (VAD) being developed by Dante Pazzanese Institute of Cardiology-IDPC (Sao Paulo, Brazil). The VAD-IDPC has a novel architecture that distinguishes from other known VADs. In this, the rotor has a conical geometry with spiral impellers, showing characteristics that are intermediate between a centrifugal VAD and an axial VAD. The effectiveness of this new type of blood pumping principle was showed by tests and by using it in heart surgery for external blood circulation. However, the developed VAD uses a combination of ball bearings and mechanical seals, limiting the life for some 10 h, making impossible its long-term use or its use as an implantable VAD. As a part of development of an implantable VAD, this work aims at the replacement of ball bearings by a magnetic bearing. The most important magnetic bearing principles are studied and the magnetic bearing developed by Escola Politecnica of Sao Paulo University (EPUSP-MB) is elected because of its very simple architecture. Besides presenting the principle of the EPUSP-MB, this work presents one possible alternative for applying the EPUSP-MB in the IDPC-VAD.

Comparative physical-chemical characterization of encapsulated lipid-based isotretinoin products assessed by particle size distribution and thermal behavior analyses

Isotretinoin is the drug of choice for the management of severe recalcitrant nodular acne. Nevertheless, some of its physical-chemical properties are still poorly known. Hence, the aim of our study consisted to comparatively evaluate the particle size distribution (PSD) and characterize the thermal behavior of the three encapsulated isotretinoin products in oil suspension (one reference and two generics) commercialized in Brazil. Here, we show that the PSD, estimated by laser diffraction and by polarized light microscopy, differed between the generics and the reference product. However, the thermal behavior of the three products, determined by thermogravimetry (TGA), differential thermal (DTA) analyses and differential scanning calorimetry (DSC), displayed no significant changes and were more thermostable than the isotretinoin standard used as internal control. Thus, our study suggests that PSD analyses in isotretinoin lipid-based formulations should be routinely performed in order to improve their quality and bioavailability. (C) 2010 Elsevier B.V. All rights reserved.

Carbide lime and industrial hydrated lime characterization

This paper focuses on the characterization of carbide lime (CL) - a by-product of acetylene production, composed mainly of calcium hydroxide with minor parts of carbonate - and compares its features to those of ""dry"" hydrated lime (HL) commonly used as a building material. Chemical, thermogravimetric and X-ray diffraction analyses indicated that the limes are similar in chemical and mineralogical compositions. except for the presence of carbon in the waste. Morphological and elemental chemical analyses by SEM and EDS revealed that CL particles differ from HL ones in their morphology and by the presence of carbon formations, Physical characterization included density and BET surface area of the materials. as well as, their particle size distributions in deionized water at diverse time periods. CL underwent agglomeration after approximately 60 min in water, whereas HL progressively became finer with time as determined by laser diffraction. In addition, water retention and squeeze flow tests were used to assess the pastes` fresh properties. (c) 2009 Elsevier B.V. All rights reserved.

Squeeze flow as a tool for developing optimized gypsum plasters

This paper presents a rheological investigation of pure gypsum (PG) and a commercial gypsum-lime-filler plaster (CP) using the modified Vicat apparatus and squeeze flow method. The samples were tested at several different intervals after manual or mechanical mixing. The results confirmed squeeze flow to be more sensitive in determining fresh paste behavior than the modified Vicat apparatus. PG set faster when prepared in mechanical mixer than when manually mixed. Conversely, the CP composition presented longer setting when mixed mechanically. The study also included the analysis of two ready-to-use polymer-based products for leveling and rendering (drywall joint compound - DJC; acrylic putty - AP) measured by squeeze flow and compared to the commercial composition. (C) 2008 Elsevier Ltd. All rights reserved.

Flow rate sprinkler development for site-specific irrigation

Due to the rapid depletion of water resources, water must be used more efficiently in agriculture to maintain current levels of yield in irrigated areas. The efficiency of irrigation systems can be increased by adjusting the amount of water applied to specific conditions of soil and crop, which may vary in a field. Taking into account spatial and temporal variability, it is evident that an equipment capable of providing different irrigation levels is necessary to meet the water requirement of the soil. This work aims to develop and evaluate a flow rate sprinkler to be used in center pivots or linear moving irrigation systems, with potential for utilization in irrigation scheduling. A prototype was developed by duplicating its calibrations, and discharge coefficient adjustment was carried out in the laboratory. To predict the flow rate, a successful model that represented the operation of the flow rate sprinkler was established. The calibration of the flow rate sprinkler prototype showed satisfactory statistical and technical results. Automation of the prototype was achieved by driving a step motor using communication from the parallel port of a microcomputer, which was controlled by a software developed for this purpose. The results were satisfactory and technically feasible.

Particle size and concentration of poly(epsilon-caprolactone) and adipate modified starch blend on mineralization in soils with differing textures

The objective of this study was to evaluate the effect of particle size and concentration of poly(F.-caprolactone) and adipate modified starch blend on mineralization in soils with differing textures, comparing it with polyethylene under the same experimental conditions. Two soil types were used: a Kandiudalfic Eutrudox with a clayey texture and an Arenic Hapludult with a sandy texture. The two different plastic specimens were incorporated in the form of plastic films with three increasing particle sizes and six doses, from 0 to 2.5 mg C g(-1) soil. Each plastic dose was incorporated into 200 g of soil placed in a hermetically closed jar at 28 degrees C, and incubated for a 120-day period to determine CO(2) evolution. Once again it was confirmed that polyethylene is almost non-biodegradable, in contrast to PCL/S, which can be defined as a biodegradable material. Soil texture affected the mineralization kinetics of the plastic specimens, with higher values for the clayey soil. No changes in soil microbial biomass-C or -N were observed by adding polyethylene and PCL/S to the soil. Also, no significant differences were observed on seed emergence and development of rice seedlings (Oryza sativa L.) in plastic modified soil. (C) 2009 Elsevier Ltd. All rights reserved.

The relationship of flow cytometry results with classical measures of bacterial counts in raw refrigerated milk

Bulk milk was collected from 100 farms throughout the year and analysed after storage for either 24, 48 or 72 h, using flow cytometry. The total bacterial counts obtained by two methods - flow cytometry and standard plate count were compared and the conversion relationship between them was assessed: the results showed no effect of the age of the samples relationship between these two methods.

Multiphase flow in the vascular system of wood: From microscopic exploration to 3-D Lattice Boltzmann experiments

This paper provides insights into liquid free water dynamics in wood vessels based on Lattice Boltzmann experiments. The anatomy of real wood samples was reconstructed from systematic 3-D analyses of the vessel contours derived from successive microscopic images. This virtual vascular system was then used to supply fluid-solid boundary conditions to a two-phase Lattice Boltzmann scheme and investigate capillary invasion of this hydrophilic porous medium. Behavior of the liquid phase was strongly dependent on anatomical features, especially vessel bifurcations and reconnections. Various parameters were examined in numerical experiments with ideal vessel bifurcations, to clarify our interpretation of these features. (c) 2010 Elsevier Ltd. All rights reserved.

LC-MS-MS determination of ibuprofen, 2-hydroxyibuprofen enantiomers, and carboxyibuprofen stereoisomers for application in biotransformation studies employing endophytic fungi

The purpose of this study was the development and validation of an LC-MS-MS method for simultaneous analysis of ibuprofen (IBP), 2-hydroxyibuprofen (2-OH-IBP) enantiomers, and carboxyibuprofen (COOH-IBP) stereoisomers in fungi culture medium, to investigate the ability of some endophytic fungi to biotransform the chiral drug IBP into its metabolites. Resolution of IBP and the stereoisomers of its main metabolites was achieved by use of a Chiralpak AS-H column (150 x 4.6 mm, 5 mu m particle size), column temperature 8 degrees C, and the mobile phase hexane-isopropanol-trifluoroacetic acid (95: 5: 0.1, v/v) at a flow rate of 1.2 mL min(-1). Post-column infusion with 10 mmol L(-1) ammonium acetate in methanol at a flow rate of 0.3 mL min(-1) was performed to enhance MS detection (positive electrospray ionization). Liquid-liquid extraction was used for sample preparation with hexane-ethyl acetate (1:1, v/v) as extraction solvent. Linearity was obtained in the range 0.1-20 mu g mL(-1) for IBP, 0.05-7.5 mu g mL(-1) for each 2-OH-IBP enantiomer, and 0.025-5.0 mu g mL(-1) for each COOH-IBP stereoisomer (r >= 0.99). The coefficients of variation and relative errors obtained in precision and accuracy studies (within-day and between-day) were below 15%. The stability studies showed that the samples were stable (p > 0.05) during freeze and thaw cycles, short-term exposure to room temperature, storage at -20 degrees C, and biotransformation conditions. Among the six fungi studied, only the strains Nigrospora sphaerica (SS67) and Chaetomium globosum (VR10) biotransformed IBP enantioselectively, with greater formation of the metabolite (+)-(S)-2-OH-IBP. Formation of the COOH-IBP stereoisomers, which involves hydroxylation at C3 and further oxidation to form the carboxyl group, was not observed.

Ultra-Fast Gradient LC Method for Omeprazole Analysis Using a Monolithic Column: Assay Development, Validation, and Application to the Quality Control of Omeprazole Enteric-Coated Pellets

A method was optimized for the analysis of omeprazole (OMZ) by ultra-high speed LC with diode array detection using a monolithic Chromolith Fast Gradient RP 18 endcapped column (50 x 2.0 mm id). The analyses were performed at 30 degrees C using a mobile phase consisting of 0.15% (v/v) trifluoroacetic acid (TFA) in water (solvent A) and 0.15% (v/v) TFA in acetonitrile (solvent B) under a linear gradient of 5 to 90% B in 1 min at a flow rate of 1.0 mL/min and detection at 220 nm. Under these conditions, OMZ retention time was approximately 0.74 min. Validation parameters, such as selectivity, linearity, precision, accuracy, and robustness, showed results within the acceptable criteria. The method developed was successfully applied to OMZ enteric-coated pellets, showing that this assay can be used in the pharmaceutical industry for routine QC analysis. Moreover, the analytical conditions established allow for the simultaneous analysis of OMZ metabolites, 5-hydroxyomeprazole and omeprazole sulfone, in the same run, showing that this method can be extended to other matrixes with adequate procedures for sample preparation.

Development and Validation of a Simple Method for Routine Analysis of Ractopamine Hydrochloride in Raw Material and Feed Additives by HPLC

A simple method was optimized and validated for determination of ractopamine hydrochloride (RAC) in raw material and feed additives by HPLC for use in quality control in veterinary industries. The best-optimized conditions were a C8 column (250 x 4.6 mm id, 5.0 mu m particle size) at room temperature with acetonitrile-100 mM sodium acetate buffer (pH 5.0; 75 + 25, v/v) mobile phase at a flow rate of 1.0 mL/min and UV detection at 275 nm. With these conditions, the retention time of RAC was around 5.2 min, and standard curves were linear in the concentration range of 160-240 mu g/mL (correlation coefficient >= 0.999). Validation parameters, such as selectivity, linearity, limit of detection (ranged from 1.60 to 2.05 mu g/mL), limit of quantification (ranged from 4.26 to 6.84 mu g/mL), precision (relative standard deviation <= 1.87%), accuracy (ranged from 96.97 to 100.54%), and robustness, gave results within acceptable ranges. Therefore, the developed method can be successfully applied for the routine quality control analysis of raw material and feed additives.

Retention of the Enzymatic Activity and Product Properties During Spray Drying of Pineapple Stem Extract in Presence of Maltodextrin

The aim of this work was to investigate the effects of drying parameters on the retention of the enzymatic activity and on the physical properties of spray-dried pineapple stem extract. A Box and Behnken experimental design was used to investigate the effects of the processing parameters on the product properties. The parameters studied were the inlet temperature of drying gas (Tgi), the feed flow rate of the pineapple extract relative to evaporative capacity of the system (Ws /Wmax), and the concentration of maltodextrin added to the extract (MD). Significant effects of the processing parameters on the retention of the proteolytic activity of the powdered extract were observed. High processing temperatures lead to a product with a smaller moisture content, particle size, and lower agglomerating tendency. A product with insignificant losses of the proteolytic activity ( 10%) and low moisture content (less than 6.5%) is obtained at selected conditions.