Numerical modelling and flow analysis of a centrifugal pump running as a turbine: Unsteady flow structures and its effects on the global performance

The purpose of this paper is to investigate the flow patterns in a centrifugal pump when it works as a centripetal turbine, with special interest in the unsteady behavior in order to explain the shape of the performance curves. Also, we focus on the determination of the radial thrust and other mechanical loads over a pump‐designed machine. The pump studied is commercial, with single axial suction and a vaneless spiral volute casing. A numerical study has been carried out in order to obtain more information about the flow into the volute and the impeller. A numerical three‐dimensional unsteady simulation has been developed using a commercial code that solves the URANS set of equations with a standard k–ε turbulence model. The results show the non‐axisymmetric flow developed in the volute, responsible for a significant radial thrust; the interaction between the tongue and the impeller, generating force fluctuations; the velocity and pressure distributions inside the impeller; and the exit flow, characterized with post‐rotation and low‐pressure. These flow results allow us to understand the behavior of the machine by comparing it with the pump mode. Complementarily, an experimental study was conducted to validate the numerical model and characterize the pump‐turbine performance curves at constant head. Fast‐response pressure taps and a three‐hole pneumatic pressure probe were employed to obtain a complete data set of non‐stationary and stationary measurements throughout the centrifugal machine. As a result, loss of efficiency or susceptibility to cavitation, detected numerically, was confirmed experimentally. The study demonstrates that the numerical methodology presented here has shown its reliability and possibilities to predict the unsteady flow and time‐mean characteristics of centrifugal pumps working as turbines. In particular, it is shown that the commercial design of the pump allows a reasonable use of the impeller as a turbine runner, due to the suitable adaptation of the inflow distributions to the volute casing. Moreover, the efficiency for the inverse mode is shown to be as high as achieved for the pumping operational mode. In addition, it is concluded that both axial and radial thrusts are controlled, though important unsteady fluctuations—up to 25%—clocked with the blade passing frequency appear beyond the nominal conditions. In that case, a moderate use of the pump as a turbine is recommended in order to minimize risks of fatigue failure of the bearings. Copyright © 2009 John Wiley & Sons, Ltd.     

Characterization of the polyphenolic fraction of pomegranate samples by comprehensive two-dimensional liquid chromatography coupled to mass spectrometry detection

Abstract

Punica granatum L., commonly known as pomegranate, is an ancient fruit widely consumed all over the world as fresh fruit or juice. In addition, it is extensively used in therapeutic formulas, cosmetics and food seasonings. The fruit is native to Afghanistan, Iran, China and the Indian sub-continent. The pomegranate market has steadily grown, presumably due to the increasing demand of health-conscious consumers for products with potential beneficial effects on human health, due to the synergistic presence of a unique and complex phytochemical composition that enclose anthocyanins, phenolic acids and hydrolysable tannins. Conventionally, for their analysis liquid chromatography is employed even though it can present some drawbacks in terms of resolving power. In this contribution, as a valuable alternative, comprehensive two-dimensional liquid chromatography with “shifted gradients” in the second dimension, was applied for the characterization of three pomegranate samples, leading to the identification of 37 different polyphenolic compounds.     

Polyphenolic compounds with biological activity in guabiroba fruits (Campomanesia xanthocarpa Berg.) by comprehensive two-dimensional liquid chromatography

This study aimed to evaluate the polyphenolic composition along with the biological activity of guabiroba (Campomanesia xanthocarpa Berg.) fruits using comprehensive two-dimensional liquid chromatography (LC × LC). A simplex centroid design comprising three solvents (methanol, 2% acetic acid, and acetonitrile) was used to optimize the extraction mixture for polyphenols from ripe and unripe guabiroba fruits. A quantitative LC × LC platform was proposed to characterize the guabiroba extracts using a RP-Amide column and a C18 column in the first and second dimensions, respectively. Antidiabetic properties, using in vitro enzyme assay models and in vivo antioxidant activity with the eukaryote model Saccharomyces cerevisiae, was measured. Total phenolics compounds were more efficiently extracted with 2% acetic acid solution and acetonitrile (50:50, v/v). A total of 37 different compounds were identified and quantified using the proposed LC × LC method (linearity ranging from 0.9990 to 0.9994, intra- and interday precision from 0.40 to 10.57% and, accuracy from 81.89 to 108.98%). Significant differences were observed between ripe and unripe guabiroba fruits, especially for the compounds geraldone and methyl galangin isomer. Guabiroba fruits showed significant antidiabetic and antioxidant properties and may be potentially adopted as part of dietary strategies in the management of early stages of type 2 diabetes and associated complications.     

Radioactivity levels in peloids used in main Cuban spas

In this work, an approach for determining both the outer dead layer thickness of the p-type coaxial HPGe detector and the inner dead layer thickness of the n-type coaxial HPGe detector was proposed by using two full energy peak area count ratios of a X-ray and a gamma ray emitted from the same radioisotope of ¹³⁷Cs. Monte Carlo calculations and experimental measurements were conducted to determine these dead layer thicknesses. The results showed that the outer dead layer thickness reached 0.57 ± 0.03 mm on 06 Jan 2017 after nearly 3 years of use for the p-type detector. The inner dead layer thickness reached 1.21 ± 0.24 mm on 01 Aug 2016 after more than 3 years of operation for the n-type detector. Simulation model with the modified dead layer thicknesses was used to estimate full energy peak efficiencies and gamma spectra from seven radioactive sources. The results were in good agreement with the corresponding experimental values in the gamma energy region of interest.     

A comprehensive ESPI based system for combined measurement of shape and deformation of electronic components

This paper describes a very simple and reliable procedure for measuring shape and deformation of electronic components with a single experimental set-up. The procedure is based on two electronic speckle pattern interferometry (ESPI) techniques referred to as conventional ESPI and phase shifting ESPI (PS-ESPI). The present research is motivated by the fact that mismatch in thermal expansion coefficients of the different materials included in electronic packaging (EP) may cause mechanical failures since thermal stresses will change sharply through subsequent loading cycles. ESPI is particularly suitable for measurements on EP since it allows us to perform non–contact testing of non-planar heterogeneous surfaces. It is apparent that gathering detailed topographic information will certainly help us to measure accurately surface deformations of EP along with modeling correctly numerical analysis.As is known, the accuracy of results obtained with ESPI may be significantly improved by phase shifting techniques (PST). Therefore, this paper compares the relative merits of different phase-stepping strategies in order to find which strategy will perform the best for the optical set-up utilized in the experiments. Preliminary investigations on a standard specimen under three-point-bending served to choose properly the optical set-up and phase-stepping procedure which yield the best fringe visibility. Four-phases achieved the best fringe visibility and the minimum number of invalid pixels.These information have been utilized in the experimental campaign on standard and surface mounted technology (SMT) electronic components. ESPI and PS-ESPI have been used for analyzing the transient state and the steady state of devices, respectively. From the experimental results obtained here, it appears possible to measure strains induced by thermal loading cycles. The experimental set-up, based on the Lendeertz's interferometer, proved itself also able to contour specimen surface at a good level of detail. Remarkably, by using the same set-up for deformation and shape measurements we can preserve the pixel by pixel relationship between displacements and surface depth which will hold true if correlation between different exposures is not destroyed.The results obtained in this research justify using PS-ESPI in order to understand better failure mechanisms of electronic components. This fact along with the exact knowledge of object shape may be particularly useful in the different design stages (including FEM modeling and analysis) of electronics for special applications.     

Elucidation of Antioxidant Compounds in Moroccan Chamaerops humilis L. Fruits by GC–MS and HPLC–MS Techniques

The aim of this study was to characterize the phytochemical content as well as the antioxidant ability of the Moroccan species Chamaerops humilis L. Besides crude ethanolic extract, two extracts obtained by sonication using two solvents with increased polarity, namely ethyl acetate (EtOAc) and methanol-water (MeOH-H₂O) 80:20 (v/v), were investigated by both spectroscopy and chromatography methods. Between the two extracts, the MeOH-H₂O one showed the highest total polyphenolic content equal to 32.7 ± 0.1 mg GAE/g DM with respect to the EtOAc extract (3.6 ± 0.5 mg GAE/g DM). Concerning the antioxidant activity of the two extracts, the EtOAc one yielded the highest value (1.9 ± 0.1 mg/mL) with respect to MeOH-H2O (0.4 ± 0.1 mg/mL). The C. humilis n-hexane fraction, analyzed by GC–MS, exhibited 69 compounds belonging to different chemical classes, with n-Hexadecanoic acid as a major compound (21.75%), whereas the polyphenolic profile, elucidated by HPLC–PDA/MS, led to the identification of a total of sixteen and thirteen different compounds in both EtOAc (major component: ferulic acid: 104.7 ± 2.52 µg/g) and MeOH-H₂O extracts (major component: chlorogenic acid: 45.4 ± 1.59 µg/g), respectively. The attained results clearly highlight the potential of C. humilis as an important source of bioactive components, making it a valuable candidate to be advantageously added to the daily diet. Furthermore, this study provides the scientific basis for the exploitation of the Doum in the food, pharmaceutical and nutraceutical industries.     

Wikipedia mining of hidden links between political leaders

We describe a new method of reduced Google matrix which allows to establish direct andhidden links between a subset of nodes of a large directed network. This approach usesparallels with quantum scattering theory, developed for processes in nuclear andmesoscopic physics and quantum chaos. The method is applied to the Wikipedia networks indifferent language editions analyzing several groups of political leaders of USA, UK,Germany, France, Russia and G20. We demonstrate that this approach allows to recoverreliably direct and hidden links among political leaders. We argue that the reduced Googlematrix method can form the mathematical basis for studies in social and political sciencesanalyzing Leader-Members eXchange (LMX).     

On the multiple crystallization behavior of PTFE in PMMA/PTFE nanocomposites from core–shell nanoparticles

The peculiar thermal behavior of four PTFE/PMMA (Polymethylmethacrylate) core–shell nanoparticle samples, marked DV2M1, DV2M2, DV2M4, and DV2M6, was studied by combined differential scanning calorimetry and thermogravimetric analysis. The melting process of the PTFE in the various samples, subjected to annealing and thermal treatments, does not change. In contrast, a complex fractionated crystallization‐type behavior for the PTFE component was observed. The nanocomposite produced by the PMMA shell fluidification features a perfect dispersion of the nanometric PTFE cores. In these conditions, only one crystallization exotherm at very high undercooling is observed, possibly deriving from the homogeneous nucleation mechanism. In contrast, when high temperature thermal treatments cause the decomposition with partial loss of the PMMA shell and allows some cores to get in contact and merge, a crystallization process structured into several components is observed. This behavior indicates that different nucleation mechanisms are active, possibly involving the participation of distinct types of active nuclei with distinct crystallization efficiencies. Finally, when the PMMA shell amount is substantially reduced by the thermal degradation, only the expected crystallization process at moderate undercooling (310 °C) is observed, corresponding to the bulk crystallization induced by the most efficient heterogeneous nuclei. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 548–554, 2010     

An original nitrate sensor based on silver nanoparticles electrodeposited on a gold electrode

The electroreduction of nitrate in synthetic seawater was investigated by cyclic voltammetry (CV) at a bare gold electrode modified by electrodeposited silver nanoparticles (AgNPs). The AgNPs were generated by chronoamperometry using a charge, Q, lower than the theoretical one corresponding to a silver monolayer. In these conditions, a linear range for nitrate determination is obtained from 10·10^-6 mol L^-1 to 10·10^-3 mol L^-1. Such a low limit of detection was achieved due to the combination of two chemical reactions coupled with electron transfer.