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PhD Defence Gina Alfonso

Gina ALFONSO

Ph.D. defense entitled:Innovative Design in Vacuum Membrane Distillation for Autonomous Seawater Desalination in Remote Regions: Modeling, Parametric Study, and Optimization of an Integrated Solar-Powered Hollow Fiber Module and Full System"

It will take place on November 14th at 09:30 in room 401.

Abstract

The current problem of freshwater scarcity in different regions around the world shows the potential of employing desalination systems powered by solar energy, especially in coastal areas with important solar radiation and seawater access. Membrane Distillation is a simultaneous thermal and membrane process, that permits principally high-water recovery in comparison with reverse osmosis, due to its ability to treat highly concentrated waters, and at the same time to take advantage of renewable thermal energy for its operation.

Challenges such as compacity, adaptation to solar irradiation, management of water and heat hand in both module and full system design must be addressed for its application. The attractive alternative envisioned in this thesis is to directly integrate a non-conventional solar collector in a cylindrical module containing a bundle of hollow fibers (HF). This HF solar collector membrane distillation module (HF-SC-VMD) has numerous potential advantages as compactness, high contact area, low heat loss at the permeate side, and a low operating temperature.

The module design and the pertinent choice of operating conditions of this innovative hybrid system are crucial to improving freshwater production while reducing its electrical energy consumption. Therefore, this study aims to develop and optimize an innovative semi-industrial-scale HF-SC-VMD module and the full system, with the target of supplying fresh water to small communities in remote areas.

In order to achieve this objective, first, a 2D modeling coupling heat and mass transfer in the HF-SC-VMD module was realized, by considering: (a) the energy transfer through the solar collector, seawater, and membrane level, (b) water vaporization and (c) seawater characteristics with the purpose of determining the freshwater production, the longitudinal and radial temperature profiles, and the possible polarization phenomena.

Second, the design of the full system for its autonomous operation was performed by the modeling of the different equipments, and the consideration of water and energy management. The model considers the solar radiation, operating conditions, equipment energy consumption, solar collector material properties, module dimensions, and membrane characteristics to provide the full system characterization, permeate flow rate, and specific electrical energy consumption (SEEC).

A parametric study was realized to comprehend the variables and their impact on the system performances. Subsequently, the model was coupled with an optimization tool (in Python code) in order to maximize the freshwater production and at the same time minimize the SEEC by considering some design parameters (module length, diameter, bundle porosity) for chosen hollow fibers, and operating conditions.

This study allows to determine the appropriate geometry and operational mode of a HF-SC-VMD system for the targeted application, showing the principal variables affecting freshwater production, the importance of studying the full process to reduce the seawater intake and the brine discharge, as well as, reducing the electrical demand of the process. It demonstrates potential operational scenarios, all achieved through a minor SEEC, to yield diverse freshwater production rates.

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