Person: Fernández Pineda, Cristóbal
Universidad Complutense de Madrid
Faculty / Institute
Now showing 1 - 10 of 14
- PublicationDirect contact membrane distillation of sugar aqueous solutions(Taylor & Francis Inc, 1999) Izquierdo Gil, María Amparo; García Payo, María del Carmen; Fernández Pineda, CristóbalResults are given from direct contact membrane distillation, using tangential flows to the membrane, with sugar aqueous solutions. Several effects on the distillation process are examined: flow rate through the cell, nature of the feed solutions, initial concentrations of the feed solutions, average temperature, and temperature difference. On the basis of enthalpy flux conservation in the different regions, various systems of equations are proposed for the estimation of the interfacial temperatures. Based on the known temperatures of the liquid-vapor interfaces, the experimental distillate fluxes for several sets are fitted to the gas stagnant film diffusion model to obtain the effective diffusion coefficients of the water vapor-air mixture, D-ef, and the results are analyzed.
- PublicationWetting study of hydrophobic membranes via liquid entry pressure measurements with aqueous alcohol solutions(Academic Press Inc Elsevier Science, 2000-10-15) García Payo, María del Carmen; Izquierdo Gil, María Amparo; Fernández Pineda, CristóbalA new concept of liquid entry pressure measurements is applied to study the hydrophobicity of microporous membranes for aqueous alcohol solutions. The effects of alcohol concentration, type of alcohol, and temperature on liquid entry pressure of the membrane have been studied. Two theoretical equations for the determination of membrane pore size have been proposed. The former equation was developed taking into account the deviation from the Laplace-Young equation due to the membrane structure by means of the structure angle. The latter equation was established considering only the range of alcohol concentration in which the dispersion component of liquid surface tension remains practically constant. Hydrophobicity has been expressed in terms of wetting surface tension, gamma (W)(L). Based on these measurements, the maximum concentration before the spontaneous wetting occurs would be predicted.
- PublicationSingle CMOS sensor system for high resolution double volume measurement applied to membrane distillation system(2007) Izquierdo Gil, María Amparo; Lorenz, M. G.; Sánchez Reillo, R.; Fernández Pineda, CristóbalMembrane distillation (MD) [I] is a relatively new process that is being investigated world-wide as a low cost, energy saving alternative to conventional separation processes such as distillation and reverse osmosis (RO). This process offers some advantages compared to other more popular separation processes, such as working at room conditions (pressure and temperature); low-grade, waste and/or alternative energy sources such as solar and geothermal energy may be used; a very high level of rejection with inorganic solutions; small equipment can be employed, etc. The driving force in MD processes is the vapor pressure difference across the membrane. A temperature difference is imposed across the membrane, which results in a vapor pressure difference.The principal problem in this kind of system is the accurate measurement of the recipient volume change, especially at very low flows. A cathetometer, with up to 0,05 min resolution, is the instrument used to take these measurements, but the necessary human intervention makes this instrument not suitable for automated systems. In order to overcome this lack, a high resolution system is proposed, that makes automatic measurements of the volume of both recipients, cold and hot, at a rate of up to 10 times per second.
- PublicationAir gap membrane distillation of sucrose aqueous solutions(Elsevier Science BV, 1999-04-12) García Payo, María del Carmen; Izquierdo Gil, María Amparo; Fernández Pineda, CristóbalIn this paper results obtained with air gap membrane distillation (AGMD) using sucrose aqueous solutions are shown. The role of the relevant process parameters has been investigated experimentally (the flow rate through the cell, the feed initial concentration, the type of membrane, the air gap thickness, etc.). Equations have been proposed to estimate the intermediate temperatures for the air gap configuration. The fluxes given by different gas stagnant film diffusion models showed good agreement with the experimental results over the entire range of temperatures studied. Also a model which accounts for the thermal diffusion phenomenon was used. From the fits of the experimental flux data to the theoretical equations, the diffusion coefficient of the water vapour-air mixture, D-AB, and the thermal diffusion coefficient, K-T (only in the last case), were obtained and the results were analysed. For the D-AB coefficient higher values than the tabulated ones have been obtained, although of the same order of magnitude, and still higher when the thermal diffusion is considered.
- PublicationThermodynamics of a pure substance at the triple point(American Association of Physics Teachers, 2007-12) Velasco Maíllo, Santiago; Fernández Pineda, CristóbalA thermodynamic study of a pure substance at the triple point. is presented. In particular, we show that the mass fractions of the phases coexisting at the triple point obey lever rules in the specific entropy-specific volume diagram, and the relative changes in the mass fractions present in each phase along reversible isochoric and adiabatic processes of a pure substance at the triple point are governed by the relative sizes of the segments of the triple-point line in the pressure-specific volume diagram and in the temperature-specific entropy diagram. Applications to the ordinary triple point of water and to the triple point of Al2SiO5 polymorphs are presented.
- PublicationApplication of thermodynamic extremum principles(American Association of Physics Teachers, 2001-11) Fernández Pineda, Cristóbal; Velasco Maíllo, SantiagoA simple system is used to illustrate the application of different extremum principles in thermodynamics. The system consists of an ideal gas contained in an adiabatically isolated cylinder interacting with a constant-pressure work device through an adiabatic movable piston. A kinetic model is also used to analyze the time evolution of the system toward the final equilibrium state.
- PublicationApplication of Frahn-Venter model to elastic-scattering analysis of alpha-particles(Real Sociedad Española de Química, 1974) Fernández Pineda, Cristóbal; López, M.; Ruiz Bauzá, Carlos
- PublicationA simple example illustrating the application of thermodynamic extremum principles(IOP Publishing Ltd., 2002-09) Velasco Maíllo, Santiago; Fernández Pineda, CristóbalA composite system consisting of two identical ideal gases separated by a movable, frictionless, diathermic piston is used to illustrate the application of different extremum principles in thermodynamics. The time evolution of the system from an initial constrained equilibrium state to the final equilibrium state is analysed by means of a very simple phenomenological model.
- PublicationFlow rate influence on direct contact membrane distillation experiments: Different empirical correlations for Nusselt number(Elsevier Science BV, 2008-08-15) Izquierdo Gil, María Amparo; Fernández Pineda, Cristóbal; Lorenz, M. G.Direct contact membrane distillation (DCMD) experiments using distilled water are reported. Influence on the process of feed and permeate flow rates through the cell has been investigated in a wide flow range, from 2 to 8l/min. Two main effects have been studied, its effect on the heat transfer coefficient and on the effective membrane thickness. An empiric dependence of the membrane thickness with linear velocity through the cell has been included in the equation for mass flux through the membrane obtained from the "Dusty-Gas" model with satisfactory results.