(PDF) Fluid Mechanics in Membrane Filtration
Added on 2021-06-15
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Fluid mechanic: effects of variation of pressure and flow rate in RO membrane1Name: Course: Tutor:Date:
Fluid mechanic: effects of variation of pressure and flow rate in RO membrane2Fluid mechanic: effects of variation of pressure and flow rate in RO membraneReverse osmosis (RO) is defined as the process by which a solvent is able to pass through a porous membrane in the direction which is opposite of the natural osmosis (Gupta, 2012). This usually happens when the process is subjected to high hydrostatic pressure than the osmotic pressure. In terms of filtration, RO is the finest level of filtration. Them RO membrane is able to act as the main barrier to all the dissolved salts available, organic molecules and organic molecules, which have higher molecular weight than the approximation of 100 (Khurana and Sen, 2010). The available water molecules on the other hand are able to pass freely through the membrane and therefore able to create a purified product. The rejection rate of the dissolved saltsis usually about 95% and goes to more than 99%. RO has some of major applications such as desalination of sea water, brackish water for drinking, waste water recovery, in food and processing industry, biomedical separations as well as purification of drinking water and industrial water (In Valladares et al., 2017). The principle through which RO happen is when the pure water flows from the dilute saline solution through the membrane to a level of higher concentrated saline solution point (Khurana and Sen, 2010). In the RO situation, the water molecules move from the saline solution to the area where the water concentration is high. Mostly, the RO process is considered a water purification method, which removes ions, molecules and large particles in water through the use of semipermeable membrane. Most of dissolved and suspended particles are removed by the RO process. Reverse osmosis membrane isa critical parameter which helps the functionality of the RO process (Gupta, 2012). As the most reliable, cost effective and energy efficient measure of producing fresh water, RO membrane is acritical element which must be able to function well at all times.
Fluid mechanic: effects of variation of pressure and flow rate in RO membrane3Figure 1: A systematic representation of reverse osmosis diagram (Khurana and Sen, 2010)The RO membrane comes after the pressure feed. This means that the functionality of the membrane will depend and be affected by the changes in pressure from the pump. The pressure system is able to force molecukle4s to the membrane edge (Berge, Gad, Khaled and Rayan, 2009). Therefore the pressure and flow rate will increase and decrease at the same time making them directly related. The reverse osmosis membrane is made up of flat sheet of reverse osmosis membrane. The RO membrane are classified according to different parameters such as flow rate, salt rejection, water feed concentration, temperature, pressure and porosity. These parameters areable to play critical roles in determining the durability of the membrane (Mohammadi, Moghadam & Madaeni , 2002). The RO membrane functionality is able to depend on the balancing on the different parameters. The reverse membrane functionality is affected by different factors. Analysis of the effect when the parameters change is important to help to determine the efficiency of the reverse osmosis (Salls & University of Nevada, Reno, 2017). Flow rate and pressure are some of two key parameters which will be analyzed in this report. Changing the pressure and flow rate is able to lead to different functionality of the Rom membrane. Some of the functionality parameters whichare affected include the salt rejection, recovery rate; permeate concentration (TDS) and also the minerals concentration in permeate (Berge, Gad, Khaled and Rayan, 2009). Pressure change is
Fluid mechanic: effects of variation of pressure and flow rate in RO membrane4able to affect the force which the membrane is able to experience as the molecules are able to move from one point to another. The pressure change is able to change the functionality of the osmotic pressure, which in RO is acting in the negative direction. Flow rate feedThe RO membrane is porous in structure and this means that the flow rate will determine the amount of molecules which are able to pass through the membrane. The porosity is able to determine the amount of water molecules which are able to go across the membrane at any givenmoment. The RO membrane durability is affected by the flow rate. Increasing the flow rate increases the amount of water molecules which are available and fighting to go through the membrane at any given moment (Mohammadi, Moghadam & Madaeni , 2002). Thus the flow rate and pressure at the membrane are directly related. This is because the molecules available are able to provide the pressure change within the membrane edge. The flow rate is affected by the amount of pressure which is inserted to the membrane. Additionally, the pressure pushes the molecules to the membrane and this dictates the amount of stress inserted to the membrane (In Figoli, In Hoinkis, In Altinkaya, & In Bundschuh, 2017). This is able to directly affect the durability of the membrane. Increased flow rate means that many molecules are available to pass through the RO membrane. For the RO membrane to produce water, the pressure provided should be able to exceed the osmotic pressure. First, the osmotic pressure must be understood to depend on two factors which include the concentration of feed water and temperature (Gilau, andSmall, 2008). The osmotic pressure (tt) is the product of feed water concentration C, temperatureof feed water T and ideal gas constant R. tt=C∗R∗T
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