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Gamero R.,National University of Engineering of Nicaragua | Martinez J.,KTH Royal Institute of Technology
Chemical Engineering Research and Design | Year: 2012

The effective thermal conductivity of a porous solid containing multicomponent liquid mixtures has been studied. To achieve this, the liquid composition, liquid content and temperature distributions have been measured in a cylindrical sample dried by convection from the open upper side and heated by contact with a hot source at the bottom side. A quasi-steady state reached at high source temperatures permits to calculate the total heat flux from temperatures measured on the surface and the gas stream. The simulations performed and compared with experimental data made it possible to estimate the adjusting geometric parameter of Krischer's model for the effective thermal conductivity. The effective thermal conductivity has been widely studied for two-phase systems, mostly with regard to thermal insulation elements. The calculation of this transport parameter includes the contribution to heat transfer of the evaporation-diffusion-condensation mechanism undergone by the multicomponent mixture. The influence of liquid composition and temperature on the thermal conductivity due to the evaporation-diffusion-condensation mechanism and the effective thermal conductivity is described. The results reveal that in this case the resistance to heat transfer seems to correspond to a parallel arrangement between the phases. © 2012 The Institution of Chemical Engineers. Source


Picado A.,KTH Royal Institute of Technology | Picado A.,National University of Engineering of Nicaragua | Martinez J.,KTH Royal Institute of Technology
Drying Technology | Year: 2012

A mathematical model for the drying of grain in a continuous vibrating fluidized bed dryer was developed. Simple equipment and material models were applied to describe the process. In the plug-flow equipment model, a thin layer of particles moving forward and well mixed in the direction of the gas flow was examined. Mass and heat transfer within a single wet particle was described by effective transport coefficients. Assuming constant effective mass transport coefficient and thermal conductivity, analytical solutions of the mass and energy balances were obtained. The variation in both transport coefficients along the dryer was taken into account by a stepwise application of the analytical solution in space intervals with averaged coefficients from previous locations in the dryer. Calculation results were in fairly good agreement with experimental data from the literature. However, the results depend strongly on relationships used to determine the heat and mass transfer coefficients; because the results from correlations found in the literature vary considerably, the correlations should be adapted to the specific equipment in order to obtain reliable results. © 2012 Copyright Taylor and Francis Group, LLC. Source


Obando P.V.,National University of Engineering of Nicaragua | Mandersson B.,Lund University
Proceedings - 2012 IEEE International Conference on Bioinformatics and Biomedicine Workshops, BIBMW 2012 | Year: 2012

In this work we study in time-frequency domain what has been termed 'tea-kettle' sounds found in audio recordings of arteriovenous fistulas with severe stenosis. These sounds appears as frequency modulated signals (chirps) in the time-frequency plots. We first developed a simple model for generating synthetic bruits containing chirps. Then we performed tracking of the time-varying frequency signals using an Extended Kaiman filter (EKF). Finally we analyzed a data base of recordings from 5 patients suffering from venous stenosis EKF frequency tracker, the results shows the chirps mean frequencies (fundamental) can vary in a rather wide range of frequencies from about 200 Hz to 600 Hz and that up to two harmonics can also be found in the considered cases. © 2012 IEEE. Source


Vasquez P.,National University of Engineering of Nicaragua
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference | Year: 2010

The Empirical Mode Decomposition (EMD) is a method to decompose non linear, non stationary time series into a sum of different modes, named Intrinsical Mode Functions each one having a characteristic frequency. In the present work we used the EMD to investigate the properties of the recorded sounds from the Arteriovenous fistula on hemodialysis patients. Phonoangiographic signals coming from two different vessel conditions, stenotic and non-stenotic, were analyzed by using EMD, the mean energy and mean instantaneous frequency per IMF proved to be good features for classification. Three types of classification schemes were tested on data from the first IMf features achieving good results. Source


Munguia M M.,National University of Engineering of Nicaragua
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference | Year: 2010

In this paper, a feature extraction method based on principal component analysis was developed for classification of the vascular access's condition in hemodialysis patients. The assessment of the method was carried out by discriminating between before and after angioplasty sound recordings as well as before angioplasty and reference recordings. The results showed that when before and after angioplasty recordings were compared by patient, the classification agreed with the result of angioplasty procedure. When all the available before and after angioplasty recordings were compared, it was still possible to discriminate them at a good rate. On the other hand, when the reference recordings substituted the after angioplasty recordings, almost a perfect discrimination was achieved. Source

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