The side stream and different spacers effects on the permeate water flux in forward osmosis process using computational fluid dynamics

Forward osmosis (FO) is a membrane-based process that has an important application in water desalination. However, there are challenges in making this method operational on an industrial scale. This paper investigated a new spacer based on the concept of airfoils and the use of an optimized side stream to increase turbulency and water flux in the FO process. The effect of seven different spacer types and the side stream was investigated using computational fluid dynamics (CFD) and the design of experiment (DOE) techniques. The results showed that when an airfoil spacer was used, the water flux decreased along the membrane with a very slight slope (about 54% less than the base state). Also, the local water flux will increase by about 3%. The optimum side stream had a similar permeable water flux equivalent to the function of nine spacers with the equilateral triangle but with a lower amount of shear stress (1/2) and pressure drop (1/4). Likewise, an average water flux equivalent to an increase of 2.5 was created using a side stream and 3.5 times with an optimum spacer in the inlet flow velocity of the draw solution. A comparison of energy consumption showed that the side stream consumed less energy than the spacers and could improve process costs.