Session: 09-14-01: Fundamentals and Applications of Thermodynamics

Paper Number: 167626

Theoretical Investigation of a Flat Sheet Multistage Vacuum Air Gap Membrane Distillation for Water Desalination 

Water scarcity is a critical global challenge, driven by swift population and industrial expansion. Despite the vast availability of water on Earth, the majority exist in oceans and seas as saline water, while only a small fraction is freshwater, making access to clean water a major concern. As a result, many people struggle with limited freshwater resources. One of the most effective solutions to address this issue is desalination. The desalination process is broadly categorized into two main methods: thermal and membrane-based technologies. Thermal desalination relies on phase change processes, such as distillation, to separate salt from water, while membrane desalination utilizes selective membranes to remove salt and impurities through processes like reverse osmosis (RO). On the other hand membrane distillation (MD) combines both. MD is considered a promising technology for water desalination, as it can achieve nearly 100% salt rejection through allowing water vapor resulting from heated feed water to pass through semi-permeable hydrophobic membrane. This study presents a theoretical analysis of a multistage vacuum-assisted air gap membrane distillation (MSV-AGMD) system for a flat sheet membrane module. The developed module is based on a comprehensive heat and mass transfer analysis.  The system performance is assessed using two key performance metrics: the distillate production rate and the gain output ratio (GOR). The evaluation includes examining various design and operational parameters, including feed and coolant temperatures, flow rate, and gap pressure. Additionally, the study considers different flow arrangements, specifically parallel and series configurations, to assess their impact on system performance and efficiency. The exit coolant stream from the stage is utilized in the heat recovery system, specifically the flashing boxes, to preheat the brine before it enters the membrane modules in the MSV-AGMD system. On the other hand, the study highlights the impact of the number of stages on the overall performance of the system.

The developed V-AGMD mathematical model demonstrates good agreement with results from the literature for a flat sheet membrane. The study shows the significant impact of removing of non-condensable gases in the V-AGMD system, as it enhances the production rate. This effect is particularly pronounced when the gap pressure is maintained at the saturation condition corresponding to the feed temperature which is known as (vacuum air gap). Among all parameters, the inlet feed temperature remains the most influential factor affecting freshwater production in the multistage system. Furthermore, the MSV-AGMD system with a parallel stage configuration yields a higher production rate compared to the series configuration. Overall, the MSV-AGMD system for a flat sheet membrane demonstrates significant advantages over a single MD system, making it a more suitable and efficient solution for water production.

Presenting Author: Dr. Mohamed Antar KFUPM

Presenting Author Biography: Dr. Mohammed Antar is a Professor in Mechanical Engineering at King Fahd University of Petroleum and Minerals. Dr. Antar basic research is related to thermal sciences. His scope is currently focused on water Desalination technologies either conventional or emerging ones. The main objectives is related to effective energy recovery to improve performance of existing conventional systems (MSF and MED) and explore performance improvement of emerging desalination technologies like HDH and Membrane distillation (MD) where high salinity can be used as feed solution. He has developed new courses related to water desalination and a master program of water treatment and Desalination. He has several patents related to water desalination systems and received several teaching and research awards.

Authors:

Dr. Mohamed Antar KFUPM
Ahmed Omera King Fahd University of Petroleum and Minerals