Separación de disoluciones acuosas de azúcares mediante membranas porosas hidrófobas y gradientes de temperatura

Tesis de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Física Aplicada I, leída el 22-10-1997En este trabajo se han diseñado, construido y puesto a punto dos tipos de dispositivos experimentales, que nos permiten, los dos, medir los flujos en destilación en membranas con las modalidades de contacto directo y con "gap" de aire. Se ha estudiado la influencia de diversos factores en el proceso de destilación en membranas, unos que intervienen positivamente y otros que lo hacen negativamente. Entre los primeros se pueden mencionar: la velocidad de paso a través de la célula, la temperatura media, la diferencia de temperaturas, el tamaño de poro; y entre los últimos se pueden citar: la concentración inicial de la disolución alimento, y para el caso con "gap" de aire, la longitud de poro, el espesor del "gap" y la apertura a la atmósfera de lo tubos superiores en la zona de la placa fría. Se han propuesto diferentes modelos, que generalizan los que aparecen en la literatura, para el cálculo de la polarización de temperaturas, tanto para el sistema en contacto directo como para el sistema con "gap" de aire. Se han interpretado algunos resultados experimentales, en los casos de contacto directo y de "gap" de aire, mediante el modelo de difusión en película estancada. Se han probado otros modelos más complicados que no ofrecían mejora respecto a éste.Depto. de Estructura de la Materia, Física Térmica y ElectrónicaFac. de Ciencias FísicasTRUEpu

Estimation of the temperature of a radiating body by measuring the stationary temperatures of a thermometer placed at different distances

This paper presents a novel method for determining the temperature of a radiating body. The experimental method requires only very common instrumentation. It is based on the measurement of the stationary temperature of an object placed at different distances from the body and on the application of the energy balance equation in a stationary state. The method allows one to obtain the temperature of an inaccessible radiating body when radiation measurements are not available. The method has been applied to the determination of the filament temperature of incandescent lamps of different powers

Electro-Osmotic Behavior of Polymeric Cation-Exchange Membranes in Ethanol-Water Solutions

The aim of this work is to apply linear non-equilibrium thermodynamics to study the electrokinetic properties of three cation-exchange membranes of different structures in ethanol-water electrolyte solutions. To this end, liquid uptake and electro-osmotic permeability were estimated with potassium chloride ethanol-water solutions with different ethanol proportions as solvent. Current-voltage curves were also measured for each membrane system to estimate the energy dissipation due to the Joule effect. Considering the Onsager reciprocity relations, the streaming potential coefficient was discussed in terms of ethanol content of the solutions and the membrane structure. The results showed that more porous heterogeneous membrane presented lower values of liquid uptake and streaming potential coefficient with increasing ethanol content. Denser homogeneous membrane showed higher values for both, solvent uptake and streaming coefficient for intermediate content of ethanol

The Correlation between the Water Content and Electrolyte Permeability of Cation-Exchange Membranes

The salt permeability through three commercial cation-exchange membranes with different morphologies is investigated in aqueous NaCl solutions. Ion-exchange membranes (IEMs) find application in different processes such as electrodialysis, reverse osmosis, diffusion dialysis, membrane electrolysis, membrane fuel cells and ion exchange bioreactors. The aim of this paper is the experimental determination of the electrolyte permeability in the following membranes: MK-40 membrane, Nafion N324 membrane and Nafion 117 membrane. The latter is selected as being a reference membrane. The effect of an increase in the NaCl concentration in the solutions on membranes transport properties is analyzed. With regard to membranes sorption, a decrease in the water content was observed when the external electrolyte concentration is increased. Concerning permeation through the membranes, the salt permeability increased with concentration for the Nafion 117 membrane and remained nearly constant for the other two membranes. A close relation between the degree of liquid sorption by the membranes and the electrolyte permeability was observed

Estimation of the through-plane thermal conductivity of polymeric ion-exchange membranes using finite element technique

The aim of this study is to calculate the through-plane thermal conductivity of commercial polymeric ion-exchange membranes. Different membranes were considered to study the influence of membrane properties on the thermal conductivity values. In particular we focused on reinforcement, ion exchange capacity and membrane density and thickness. For this purpose, we use a simple experimental setup and a numerical simulation to estimate the thermal conductivity from the experimental temperature profiles. Once the system is calibrated, the model includes as the only unknown parameter the membrane thermal conductivity. To validate the method, the thermal conductivity of the well-known Nafion membranes has been determined, a very good agreement was achieved in context from reliable literature values. The study also provides the thermal conductivity of other polymeric ion-exchange membranes with great potential in diverse applications under non-isothermal conditions. The calculated thermal conductivity for the different ion-exchange membranes is in the range from 0.04 Wm(-1) K-1 to 0.42 Wm(-1) K-1. The results show that the reinforcement leads to lower values of thermal conductivity whereas a higher density or heterogenous structure leads to higher thermal conductivity values. The approach presented here, combining experimental and simulation techniques, may provide a basis for confirming the effect of the polymeric ion-exchange membrane properties on the thermal conductivity and may shed light on the best choice for the electrolyte of membrane-based applications performance under non-isothermal conditions. Published by Elsevier Ltd

Actualización e internacionalización del catálogo "OSCAR" de experiencias de Física General

En convocatorias anteriores de la convocatorias de Proyectos de Innovación Docente de l UCM, la última de ellas correspondiente a 2014, desarrollamos un Catálogo de experiencias de cátedra para la docencia de Física General, OSCAR. En esta edición los hemos ampliado con nuevas experiencias. Asimismo se ha desarrollado un programa de visitas de colegios a la Facultad de Ciencias Físicas de la UCM

Desarrollo de material docente para la ejecución de prácticas de laboratorio virtuales mediante la creación de medios audiovisuales

Se han desarrollado 4 videos audiovisuales ene español y en inglés, de 4 prácticas experimentales del Laboratorio de Física II de Termodinámica, del Grado de Física de la UCM