Cerezo J.,Institute Ingenieria |
Best R.,National Autonomous University of Mexico |
Romero R.J.,Autonomous University of Mexico State
Applied Thermal Engineering | Year: 2011
There is a continuous research effort being carried out worldwide on the development of absorption cooling systems with the objective of increasing their performance, one important area is the search for more efficient heat exchangers and alternative working fluids that can improve the performance of NH3-H2O and H2O-LiBr that are commonly used in commercial absorption refrigeration machines. In this work the study of a plate heat exchangers used as bubble absorbers with NH3-LiNO3 and NH3-NaSCN as alternative working fluids is carried out. A mathematical model was developed in order to analyze the absorption process in a bubble absorber with NH3-H2O, NH3-LiNO 3 and NH3-NaSCN as working fluids using a plate heat exchanger at refrigeration conditions and low generator temperatures. The results show that NH3-H2O and NH3-NaSCN working fluids obtained higher absorber thermal loads and absorbed vapor mass values than NH3-LiNO3, the lower values for the latter were caused mainly by the high solution viscosity that decreases the efficiency of the absorption process. On the other hand, NH3-LiNO3 obtained the highest COP value from a single effect absorption refrigeration system simulation, however, NH3-NaSCN obtained a higher COP than NH3-H2O; therefore NH3-NaSCN seems to be a good working fluid to be tested in an absorption machine. © 2011 Elsevier Ltd. All rights reserved.
Cruz-Zavala E.,Institute Ingenieria |
Moreno J.A.,Institute Ingenieria |
Fridman L.,National Autonomous University of Mexico
Proceedings of the 2010 11th International Workshop on Variable Structure Systems, VSS 2010 | Year: 2010
In this paper we introduce a modification to the classical Second-Order Sliding Mode Observer (SOSMO), used mainly for mechanical systems, and that consists in adding higher order nonlinear injection terms. Besides the usual finite-time convergence and exactness of the SOSMO, this new algorithm makes the convergence uniform with respect to the initial conditions, that is, the observation error reaches exactly and robustly the origin in a convergence time that is uniformly bounded above for every initial condition. The properties of the Uniform SOSMO (USOSMO) are studied using strong Lyapunov functions. © 2010 IEEE.
Pineda-Porras O.,Los Alamos National Laboratory |
Ordaz M.,Institute Ingenieria
Journal of Pipeline Systems Engineering and Practice | Year: 2010
Though differential ground subsidence (DGS) impacts the seismic response of segmented buried pipelines and increases their vulnerability, there are no fragility formulations that estimate repair rates under such conditions found in the literature. Although physical models that estimate pipeline seismic damage considering other cases of permanent ground subsidence (e.g., faulting, tectonic uplift, liquefaction, and landslides) have been extensively reported, this is not the case for DGS. The refinement of the study of two important phenomena in Mexico City-the 1985 Michoacan earthquake and the sinking of the city due to ground subsidence-has contributed to the analysis of the interrelation of pipeline damage, ground motion intensity, and DGS. From the analysis of the 122 cm (48 in.) diameter pipeline network of the Mexico City water system, fragility formulations for segmented buried pipeline systems for two DGS levels are proposed. The novel parameter PGV2/PGA (composite parameter in terms of peak ground velocity (PGV) and peak ground acceleration has been used as a seismic parameter in these formulations because in previous studies it has shown better correlation to pipeline damage than PGV alone. By comparing the proposed fragility formulations, it is concluded that a change in the DGS level (from low-medium to high) could increase the pipeline repair rates (number of repairs per kilometer) by factors ranging from 1.3 to 2.0, with a higher seismic intensity corresponding to a lower factor. © 2010 ASCE.
Arreola-Vargas J.,San Luis Potosí Institute of Scientific Research and Technology |
Celis L.B.,San Luis Potosí Institute of Scientific Research and Technology |
Buitron G.,Institute Ingenieria |
Razo-Flores E.,San Luis Potosí Institute of Scientific Research and Technology |
Alatriste-Mondragon F.,San Luis Potosí Institute of Scientific Research and Technology
International Journal of Hydrogen Energy | Year: 2013
Feasibility of hydrogen production from acid and enzymatic oat straw hydrolysates was evaluated in an anaerobic sequencing batch reactor at 35 °C and constant substrate concentration (5 g chemical oxygen demand/L). In a first experiment, hydrogen production was replaced by methane production. Selective pressures applied in a second experiment successfully prevented methane production. During this experiment, initial feeding with glucose/xylose, as model substrates, promoted biomass granulation. Also, the highest hydrogen molar yield (HMY, 2 mol H2/mol sugar consumed) and hydrogen production rate (HPR, 278 mL H2/L-h) were obtained with these model substrates. Gradual substitution of glucose/xylose by acid hydrolysate led to disaggregation of granules and lower HPR and HMY. When the model substrates were completely substituted by enzymatic hydrolysate, the HMY and HPR were 0.81 mol H 2/mol sugar consumed and 29.6 mL H2/L-h, respectively. Molecular analysis revealed a low bacterial diversity in the stages with high hydrogen production and vice versa. Furthermore, Clostridium pasteurianum was identified as the most abundant species in stages with a high hydrogen production. Despite that feasibility of hydrogen production from hydrolysates was demonstrated, lower performance from hydrolysates than from model substrates was obtained. Copyright © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Verde C.,Institute Ingenieria
European Control Conference, ECC 1999 - Conference Proceedings | Year: 2015
In this paper, it is proposed to estimate the robustness of a closed loop system by a error model which is obtained calculating the difference between the transfer matrix of the closed loop system with nominal and uncertain plant. For the estimation it is assumed an approximated model of the uncertainty in frequency domain. An advantage of this error model is its generality since it allows to consider additive, multiplicative or feedback uncertainty Δ. Additionally, here it is introduced a procedure based on this estimation to select the signals spectrum which must be weighted in the objective function used to synthesize linear controller. This procedure simplifies the task to weight signals in the frequency domain cost to be minimized, which could become a difficult job, specially for MIMO systems. Specifically, considering the standard H∞ optimal control problem, the approach is validated with two design problems. © 1999 EUCA.
Moreno-Andrade I.,Institute Ingenieria |
Buitron G.,Institute Ingenieria
Water, Air, and Soil Pollution | Year: 2012
The biomass characteristics, the process performance, and the microbial community for a sequencing batch reactor (SBR) and a submerged membrane SBR (MSBR) were evaluated. A synthetic wastewater containing only 4-chlorophenol (4CP) was used as the sole source of carbon and energy. Degradation efficiencies of 4CP were higher than 99% for both reactors, and no significant differences on the 4CP degradation rates were observed for the SBR (116.9±0.9 mg 4CP g VSS -1 h -1) as well as for the MSBR (117.3±0.5 mg 4CP g VSS -1 h -1). Despite the similar results obtained for the physicochemical parameters, it was found that the biomass characteristics were different considering the sludge volumetric index, settling velocity, protein content in the mixer liquor, and total suspended solids in the effluent. The settling velocity was three times higher in the SBR than in the MSBR; however, a better quality, considering suspended solids, was observed for the MSBR. The protein concentration in the mixed liquor was higher in the MSBR than in the SBR, generating foaming problems in the MSBR. A similarity analysis was made with the Ochiai-Barkman index. Even though the reactors were inoculated with the same biomass, significant differences in the composition and populations dynamics were observed. © Springer Science+Business Media B.V. 2011.
Azpurua M.,Institute Ingenieria |
dos Ramos K.,Institute Ingenieria
Progress In Electromagnetics Research M | Year: 2010
Several georeferenced measurements of electric field were done in a pilot area of Caracas, Venezuela, to verify that the magnitude of radio frequency electromagnetic fields is below the human exposure limits, recommended by the International Commission on Non-Ionizing Radiation Protection. The collected data were analyzed using geographical information systems, with the objective of using interpolation techniques to estimate the average electromagnetic field magnitude, to obtain a continuous dataset that could be represented over a map of the entire pilot area. This paper reviews the three methods of interpolation used: SPLINE, Inverse Distance Weighting (IDW) and KRIGING. A statistical assessment of the resultant continuous surfaces indicates that there is substantial difference between the estimating ability of the three interpolation methods and IDW performing better overall.
Paez E.,Institute Ingenieria |
Tremola C.,Institute Ingenieria |
Azpiirua M.A.,Institute Ingenieria
Progress In Electromagnetics Research B | Year: 2011
Throughout the performance of a RF immunity test according IEC 61000-4-3 there are several factors that should be taken into account to ensure the quality and to estimate the uncertainty associated to the results. One phenomenon that should be considered to calculate uncertainty is the disturbing effect produced by the EUT over the electric field generated within the calibrated uniform field area; nevertheless the mentioned effect is not easily quantifiable because the measuring process using additional antennas or field probes inside the semianechoic chamber could also alter the electric field distribution. An experimental method for quantifying the mentioned uncertainty contribution is presented. The method is based upon the fact that antenna-EUT coupling and reflection effects could be measured through changes in the input impedance of the field generation antenna. A validation procedure for the proposed method is also described. Hence, a relationship between the reflection coefficient at the antenna input port and the electric field strength is derived. The uncertainty contribution is calculated through the maximum relative change in the E-field intensity magnitude for the frequency range of 80-1000 MHz, considering the worst case for several EUT positions.
Azpurua M.,Institute Ingenieria |
Tremola C.,Institute Ingenieria |
Paez E.,Institute Ingenieria
Progress In Electromagnetics Research B | Year: 2011
The rigorous uncertainty estimation in Electromagnetic Compatibility (EMC) testing is a complex task that has been addressed through a simpli-ed approach that typically assumes that all the contributions are uncorrelated and symmetric, and combine them in a linear or linearized model using the error propagation law. These assumptions may affect the reliability of test results, and therefore, it is advisable to use alternative methods, such as Monte Carlo Method (MCM), for the calculation and validation of measurement uncertainty. This paper presents the results of the estimation of uncertainty for some of the most common EMC tests, such as: the measurement of radiated and conducted emissions according to CISPR 22 and radiated (IEC 61000-4-3) and conducted (IEC 61000-4-6) immunity, using both the conventional techniques of the Guide to the Expression of Uncertainty in Measurement (GUM) and the Monte Carlo Method. The results show no significant differences between the uncertainty estimated using the aforementioned methods, and it was observed that the GUM uncertainty framework slightly overestimates the overall uncertainty for the cases evaluated here. Although the GUM Uncertainty Framework proves to be adequate for the particular EMC tests that were considered, generally the Monte Carlo Method has features that avoid the assumptions and the limitations of the GUM Uncertainty Framework.
Azpurua M.A.,Institute Ingenieria
Progress In Electromagnetics Research B | Year: 2012
This paper proposes a simple semi-analytical method for designing coil-systems for homogeneous magnetostatic field generation. The homogeneity of the magnetic field and the average magnitude of the magnetic flux density inside of the volume of interest are the objective functions chosen for the selection of the coil-system geometry (size and location), number of coils and the number of turns of each winding. The spatial distribution of the magnetostatic field is estimated superposing the magnetic induction numerically computed from the analytical expression of the magnetic field generated by each coil, obtained using the Biot-Savart's law and the current filament method. The homogeneous magnetic field is synthesized using an iterative algorithm based on TABU search with geometric constraints, which varies the design parameters of the windings to meet the requirements. The number of turns of each coil and gauge of wire used for the windings is adjusted automatically in order to achieve the target average magnitude of the magnetic induction under the constraints imposed by power consumption. This method was used to design a coil arrangement that can generate up to 10 mT within a volume 0.5 m×0.5 m×1 m with 99% of spatial homogeneity, with square loops of length less than or equal to 1.5 m, and with a power dissipated by Joule effect less than or equal to 1 W per coil. The synthesized magnetic field distribution was validated using Finite Element Method simulation, showing a good correspondence between the objective values and the simulated fields. This method is an alternative to design magnetic field exposure systems over large volumes such as those used in bioelectromagnetics applications.