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Ciudad Juarez, Mexico

Medina-Flores J.M.,Polytechnic University of Guanajuato | Picon-Nunez M.,University of Guanajuato
Chemical Engineering Science

A thermodynamic model for the prediction of the operating performance of back pressure steam turbines with single and multiple extractions is presented. The approach takes the advantage of previous models reported in the literature and incorporates some improvements that allow for the prediction of the shaft work under changes in the operating conditions such as steam flow rate and pressure of each of the extractions. Simulation under changed operating conditions is conducted through the use of expressions that correlate the temperature and enthalpy of the steam as a function of the extraction pressure. The model incorporates the calculation of the isentropic efficiencies of each stage. The validity of the model is demonstrated by comparing the results with those of commercial turbines reported in the open literature. © 2010 Elsevier Ltd. All rights reserved. Source

Picon-Nunez M.,University of Guanajuato | Polley G.T.,University of Guanajuato | Canizalez-Davalos L.,University of Guanajuato | Medina-Flores J.M.,Polytechnic University of Guanajuato

This paper considers the design of cooling systems in the context of piping costs, exchanger costs, pumping costs and its hydraulic and thermal performance. A methodology for designing coolers in the context of both process needs and cooling water system behaviour is introduced. It is recognised that cooling systems need to be flexible. One way of ensuring this is to design a system for the most demanding load and then use bypasses to control performance under reduced load.The hydraulic modelling is based on new formulations of flow resistance for pipes, pipe fittings and equipment items. By using volumetric flow rate rather than velocity as the prime variable it becomes possible to construct hydraulic models for cooling water systems quickly. These calculations then provide predictions of water flows to the individual heat exchangers in the cooling water network. Knowledge of these flows is fundamental to both the design of new coolers and the prediction of the thermal performance of exchangers of known geometry. Previous studies have ignored this aspect of design. © 2011 Elsevier Ltd. Source

Arenas M.C.,National Autonomous University of Mexico | Rodriguez-Nunez L.F.,National Autonomous University of Mexico | Rangel D.,National Autonomous University of Mexico | Martinez-Alvarez O.,Polytechnic University of Guanajuato | And 2 more authors.
Ultrasonics Sonochemistry

In this work, hybrid nanocomposites based on anatase titania:polypyrrole (TiO2:PPy) were directly obtained from a simple, one-step, ultrasonic (UT)-assisted synthesis. The properties of these crystalline nanocomposites were compared with those of others fabricated using cold (Cold)-assisted synthesis without any UT assistance, which required a hydrothermal treatment (HT) to yield crystalline anatase titania in the nanocomposite (TiO 2:PPy) at low temperature (130°C) and in a short time (3 h). The SEM results demonstrated that the UT-assisted synthesis is a feasible method to obtain anatase TiO2:PPy nanocomposites with controlled morphology using low energy. The Fourier transform infrared (FT-IR) bands of the crystalline nanocomposites exhibited a shift with respect to neat components, which was attributed to the strong interaction between the secondary amine groups (N-H) of PPy and the oxygen from TiO2. The acceptable absorption in the visible region (λmax = 670 nm) indicates that these nanocomposites are good candidates for harvesting energy in solar cells. Devices based on these nanocomposites were built to evaluate their electrical properties. An increase in the photocurrent was observed for the devices prepared with the nanocomposites from the UT-assisted synthesis. © 2012 Elsevier B.V. All rights reserved. Source

Portilla-Rivera O.M.,Polytechnic University of Guanajuato | Moldes A.B.,University of Vigo
Journal of Agricultural and Food Chemistry

The results of the present study show that Lactobacillus pentosus can produce extracellular bioemulsifiers by utilizing hemicellulosic sugars from grape marc as a source of carbon. The effectiveness of these bioemulsifiers (LPEM) was studied by preparing kerosene/water (K/W) emulsions in the presence and absence of these emulsifiers. Various parameters such as relative emulsion volume (EV), stabilizing capacity (ES), viscosity, and droplet size of K/W emulsions were measured. The EV values for K/W emulsions stabilized by concentrated LPEM were approximately 74.5% after 72 h of emulsion formation, with ES values of 97%. These values were higher than those obtained with dodecyl sodium sulfate as emulsifier (EV = 62.3% and ES = 87.7%). Additionally, K/W emulsions stabilized by LPEM produced polydisperse emulsions containing droplets of radius between 10 and 40 μm, which were smaller than those obtained for K/W emulsions without LPEM (droplet radius = 60-100 μm). Moreover, the viscosity values of the K/W emulsions without and with LPEM were approximately 236 and 495 cP, respectively. © 2010 American Chemical Society. Source

Arenas M.C.,National Autonomous University of Mexico | Sanchez G.,Autonomous University of Queretaro | Martinez-Alvarez O.,Polytechnic University of Guanajuato | Castano V.M.,National Autonomous University of Mexico
Composites Part B: Engineering

Aqueous suspensions of polyvinyl alcohol-polyaniline (PVA-PAni) nanocomposites were prepared by conventional polymerization of aniline in the presence of a PVA solution mixed with either a surfactant (sodium dodecyl sulfate) or organic acids (poly acrylic acid or 2-acrylamido-2-methyl-1- propanesulfonic acid) used as binary dopants, to improve the solubility of the nanocomposites. Films were prepared by casting at different contents of PAni (1-60 wt.%). The best homogeneous films were obtained from the surfactant nanocomposites with a low threshold percolation, between 3 wt.% and 5 wt.% of PAni, achieving an electrical conductivity about 0.044 S/cm, attractive as an antistatic material in electronics, since also their mechanical properties are adequate. © 2013 Elsevier Ltd. All rights reserved. Source

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