Carina Rodrigues

24 Aug 2012

Carina P. Rodrigues completed her MSc in Biomedical Engineering at Instituto Superior Técnico, Technical University of Lisbon in 2007. In 2008, she joined Prof. Norberta de Pinho’s group of Membrane Separation and Processes, as an investigator. Under the supervision of Prof. Vítor Geraldes, she focused her investigation in analysing the flow structure and mass-transfer in spacer-filled membrane channels with relevance for spiral-wound modules used in biomedical and water purification applications. In 2010, she was granted a PhD scholarship to continue her work. Using techniques as Holographic Interferometry, Limit Current Technique and CFD simulations, the combination between them is essential to predict, programme and validate new experiments using new spacer configurations and membrane configurations, a work in progress.


Holographic Interferometry Visualization and CFD Simulation of the Concentration Boundary Layer Developed in NF Spiral-Wound Modules Feed Channels

In recent years, simulation methods based in CFD-techniques have been widely developed for the study of the polarization layer formed in the membranes separation processes [1]. However, these models are not usually accompanied by a comparison with experimental data. Holographic Interferometry (Fig 1) is a technique that allows measuring the changes in the concentration of a solution, which can be seen as a series of interference fringes. Therefore, the formation of the polarization layer, which involves a change in the concentration of the solution, may be seen as an interference fringe pattern.

In this paper, the experimental study of the polarization layer has been carried out using a cell that has been used in a previous work [2]. The cell has been slightly modified to adapt it to the technique of holographic interferometry. Basically, two windows have been placed in the cell to allow the laser beam crossing the solution, and a new support for the nanofiltration membrane was introduced. The fluid in the cell flows through a narrow rectangular channel with and without ribs, which act as the typical spacers of spiral-wound modules. The ribbed piece is interchangeable, so the distance between the ribs can be modified to study its effect on the polarization layer.

Besides using different ribbed pieces or none (open channel), the study of the formation of the polarization layer at steady state will be carried out using different working conditions. Different cross flow velocities (Reynolds between 1 and 40, based on channel height) and a variable pressure between 5 and 8 bar were used. Different fluid solutions were used, namely aqueous solutions of potassium sulphate, sucrose and glucose, all with concentrations of 2 and 4 g/l.

The solute concentration profiles obtained were adjusted using a data interpolation method [3, 4] to determine the influence of light diffraction and posteriorly compared with those obtained by CFD simulation of the system investigated. As predicted, it is necessary to correct the solute concentration profiles taking into account diffraction to obtain the numerical predicted profiles.

[1]        G.A. Fimbres-Weihs, D.E. Wiley (2010) Review of 3D CFD modeling of flow and mass transfer in narrow spacer-filled channels in membrane modules , Chemical Engineering and Processing: Process Intensification, 49 (7), , 759-781

[2]        C. Rodrigues, M. N. de Pinho, V. A. Semião, V. Geraldes (2012) Mass-transfer entrance effects in narrow rectangular channels with ribbed walls or mesh-type spacers, Chemical Engineering Science, 78 , 38-45.

[3]        Anurag Sharma, D. Vizia Kumar, and A. K. Ghatak (1982) Tracing rays through graded-index media: a new method, Appl. Optics, 21 (6),  984-987

[4]      K. W. Beach, R. H. Muller, and C. W. Tobias (1973) Light-deflection effects in the interferometry of onedimensional refractive-index fields, J. Optic. Soc Amer. 63(5) 559-566.