http://hdl.handle.net/10045/14073 2013-05-24T01:38:03Z http://hdl.handle.net/10045/15257 Título: Visualization by digital holographic interferometry of flux velocity effect in cross-flow reverse osmosis Autor/es: Fernández Sempere, Julio; Ruiz Beviá, Francisco; Salcedo Díaz, Raquel; García Algado, Pedro Resumen: Digital holographic interferometry (DHI) allows interferometric fringe patterns to be obtained, that are indicative of changes in the optical path followed by the light, and are related to changes in the refractive index. In the case of the appearance of the polarization concentration layer during the reverse osmosis process, changes in the concentration distribution, and therefore in the refractive index distribution, can be visualized as an interference fringe pattern. The phenomenon called concentration polarization occurs as filtration proceeds and the solute rejected by the membrane builds up a layer of high concentration near the membrane surface. The formation and development of the concentration polarization layer in the RO process will decrease the effective water filtration driving force and therefore, will decrease the permeate flux. To reduce or control concentration polarization many possible methods have been considered, one of them is the increase of shear at the membrane surface using a greater cross-flow velocity. In this work, DHI has been used to visualize the effect of cross-flow velocity during reverse osmosis of salts. All the experiments were carried out at a constant pressure of 6 bar, using a special module designed with transparent windows to observe the membrane surface. In all experiments a thin film reverse osmosis membrane was used. Two solutes (NaCl and Na2SO4), with different feed concentration (3.5 - 8.5 kg/m3) and different cross-flow velocities (0.002 - 0.017 m/s) (Re = 10 - 77) were used. In every run, the module was filled with the salt solution. The reference state (recorded by a CCD camera) was obtained with the salt solution flowing at the initial cross-flow velocity without pressure. During the reverse osmosis process, different fringe patterns were digitally reconstructed. In all runs, the higher the cross-flow velocity, the lesser the number of interference fringes that appears, showing that the concentration polarization has a minor effect. When higher cross-flow velocities (which reduce the concentration polarization layer) were used, the permeate flux increased. Descripción: Póster presentado en 11th Mediterranean Congress of Chemical Engineering, Barcelona, October 21-24, 2008. 2008-10-01T00:00:00Z http://hdl.handle.net/10045/15256 Título: Digital holographic interferometry experimental setup to study mass transfer processes Autor/es: Fernández Sempere, Julio; Ruiz Beviá, Francisco; Salcedo Díaz, Raquel; García Algado, Pedro Resumen: For many years, holographic interferometry (HI) has been an optical method widely used to study mass transfer processes in liquids and in transparent gels. During an experiment, changes in the refractive index distribution, and therefore in the concentration distribution, are visualized as an interference fringe pattern. In real-time HI, the first step is to obtain the hologram (an image of the object at a certain time, holographically stored), which is usually recorded on a holographic plate by a photographic method. This hologram represents the object at its reference state. The second step is to obtain an interferogram at different times. The interferogram allows changes in the object to be visualized by combining the current object wave with the reference object wave stored in the hologram. A major drawback of classical HI is not so much the cost of the holographic plates but the difficulty in developing the film. Moreover, all interferograms are obtained by comparing the current state of the object with the only hologram taken. Therefore, the temporal states that are compared cannot be freely chosen. These problems were overcome with digital holographic interferometry (DHI) (Marquadt and Richter). Digital holography (DH) is the digital recording and numerical reconstruction of numerous holograms and it offers the possibility of combining the current object wave with reference waves captured at different times. The use of DH has been possible due to the tremendous development in data processing and in opto-electronics. Digital CCD (Charged Coupled Device) cameras, that digitize the hologram, have continuously increased their resolution in the past years and they are now applicable for optical measurements. Adjustments in the classical HI setup previously used to study mass transfer processes have been made to adapt it to the DHI. The main change has been the use of a CCD camera instead of the holographic plates to record the holograms. Furthermore, a MATLAB program has been developed in order to capture and reconstruct the holograms numerically. In this work it was checked that the new DHI technique worked correctly by comparing the new interferograms with those obtained with optical HI in studies about diffusion and polarized reverse osmosis processes. Descripción: Póster presentado en 11th Mediterranean Congress of Chemical Engineering, Barcelona, October 21-24, 2008. 2008-10-01T00:00:00Z http://hdl.handle.net/10045/15255 Título: Diffusion/dilution of desalination discharges into seawater Autor/es: Fernández Sempere, Julio; Ruiz Beviá, Francisco; Salcedo Díaz, Raquel; García Algado, Pedro; García Rodríguez, Miriam Resumen: Holographic interferometry (HI) is an optical technique, by means of which changes in the refractive index can be visualized as interference fringes. The technique has been used to study the behavior of brine discharges from desalination plants into the sea. When the brine discharges in the sea, the diffusion/dilution of the salts in the seawater begins thus causing concentration changes associated to changes in the refractive index. This variation of the refractive index can be visualized as an interference fringe pattern by means of HI. In the present work, the first aim has been to determine the diffusion coefficient of brine in seawater. Diffusion experiments, consisting on slowly introducing brine in spectrophotometric cell containing seawater, have been carried out. When both solutions get in contact, the diffusion of solute starts and interference fringes (interferogram) begin to appear. The diffusion coefficient of brine in sea water has been calculated using these interferograms and a value of 1.27•10-5 cm2/s has been obtained. Dynamic experiments have also been carried out, introducing a flow of brine into a transparent container with seawater. Several characteristics of the brine discharge (flow rate, concentration, depth at which is poured and angle of discharge) have been studied. Using the interferometric fringe patterns obtained, concentration profiles in the container have been calculated. The results obtained show a better diffusion/dilution of the brine when the discharge is not horizontal and a moderate flow rate is used. Descripción: Póster presentado en 7th ANQUE International Congress "Integral water cycle: present and future. A shared Commitment", Oviedo, June 13-16, 2010. 2010-06-01T00:00:00Z