In the past decade, water desalination using forward osmosis (FO) started getting considerable attention from researchers. This work aims to develop a computational fluid dynamics model for water desalination using FO systems that include the effect of operating temperatures. There are a few experimental and computational studies available in the literature that discuss the effect of temperature on the flux performance of FO modules. Water desalination using FO relies on the existence of an osmotic pressure difference across a semipermeable membrane. The osmotic pressure difference is caused by the concentration difference between the feed and the draw solutions. To increase the osmotic pressure difference across the membrane, the draw solution is heated to a higher temperature than the feed solution. In return, the water flux permeation increases. The computational domain consists of a section from a flat sheet membrane module. The separation module will have no spacers present. The flow inside the porous membrane will not be resolved, and the membrane will be considered as a functional surface only. The hydrodynamics inside the flow channels is characterized by solving the Navier-Stokes equations. The effect of the temperature distribution inside the flow channels is examined by solving the energy equation. The only solute considered in the feed solution is salt. Therefore, the feed solution is taken as NaCl solution with different concentration values. The draw solution is also taken as NaCl solution; however, the concentration is higher compared to the feed solution. Therefore, the transport of the solute concentration within the membrane module is characterized by utilizing a suitable mass transport equation. Also, with the existence of the temperature difference across the membrane, conduction heat transport will be modeled. The draw solution temperature will tend to decrease along with the membrane module, while the temperature of the feed solution will increase. Furthermore, heat transfer will occur due to the flux permeation from the feed to the draw, causing a further decrease in the draw temperature. The CFD model will couple the effect of the hydrodynamics, solute and temperature distribution inside the flow channels. The effect of solute and water permeation through the membrane and the heat transfer will be modeled using proper boundary conditions along the membrane surface. The model will consider a variable pure water permeability as a function of concentration and temperature. The solute permeation coefficient will be taken as a direct function of concentration. The porous layer of the membrane is characterized by the membrane structural parameter. The effect of the porous support layer could be eliminated from the CFD model, and only the effect of the membrane active layer is considered. However, when the porous layer effect is included, the effect of temperature could be considered by letting the solute diffusion coefficient varies with temperature. The proposed study will rely only on CFD simulations, and the model will be validated using published experimental work.


The Effect of Working Temperature on the Performance of Water Desalination Using Forward Osmosis: A CFD Study

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

IMECE2020 - Virtual Conference

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.