Bar Psig
How do reverse osmosis membranes work and what affects quality and production?
Osmosis is the flow from a high concentration of water to a low concentration of water. To help understand t...
Bar Psig
How do reverse osmosis membranes work and what affects quality and production?
Osmosis is the flow from a high concentration of water to a low concentration of water. To help understand the flow of water imagine a sealed filled water balloon with a hole in it what happens to the water inside? The water quickly leaves balloon because of the concentration of water inside the balloon is higher than outside which makes the water wants to equalize the concentration of water.
Reverse osmosis is quite the opposite. The flow of water is from a low concentration to a high concentration. Imagine an empty balloon if you’re filling the water balloon with a hose then you are using the water pressure and forcing water against its natural equalization tendencies.
A reverse osmosis (ro) membrane is simply a thin semi-permeable layer that separates two solutions. A ro membrane is a type of physical separation that is capable of separating molecules down to 1/10,000 micron. Since the size of the pores on the membrane is so small, it requires pressure to force water through. Most molecules are too large to pass through a reverse osmosis membrane but small enough for some salts, sugars and water molecules to pass through. Rejection rates of ro membranes average around 96-98% under ideal conditions (250 ppm softened tapwater, 77 °F (25 °C), 50 psig (3.4 bar), and 15% recovery).
TDS levels, temperature, pressure and recovery rates are all things that affect the product water quality of reverse osmosis membrane.
Effect of Pressure
Feed water pressure affects both the product water production and the rejection rates of RO membranes. The increase of feed water pressure directly increases the water production.
Rejection rates also increase when pressure is increased but will plateau.
Effect of Temperature
Temperature has a direct linear effect to production rates. As temperature increase, water production increases almost linearly because of the higher diffusion rates of water through the membrane. Rejection rates are actually lowered when temperature rises. This is due to a higher diffusion rate of salt across the membrane.
Effect of Salt Concentration or TDS
TDS inversely affects the pressure required for reverse osmosis which in turn affects the production rates. If feed water was constant and TDS increases then the production rate decreases because of the osmotic pressure difference.
Osmotic pressure is the pressure and potential energy required to force water to move against its natural direction across a semi-permeable membrane. Every 100 ppm (parts per million) in TDS equals 1 psi (pounds per square inch). The higher the TDS, the more pressure required to force through the membrane.
Effect of Recovery Rates
Recovery rate refers to the amount of product water being produced which is controlled by the flow restriction on the waste line. Most reverse osmosis systems are sized with a sized flow restrictor will have a product to waste ratio of 1 to 4 which is a recovery rate of 25% this is made purposefully as a sales point to produce more product water but lower the rejection rate. For example, the proper size for a 50 GPD membrane is a 15% recovery rate or a 1 to 6.7 ratio. Lowering the recovery rates will increase the rejection rate and improve the quality of water. Raising the recovery rates will cause the quality of the product water to decrease and will affect the required driving pressure needed for reverse osmosis to take effect.
About the Author
Isopure Water carries a wide variety of point of entry filter units ranging from Water softeners, carbon filtration, and iron removal filters as well as point of use drinking water systems for residential, commercial and industrial applications. For more information visit: www.isopourewater.com
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Air Knives and Their Applications
An air knife is an implement that uses compressed air. It is very relevant in industries. The compressed air flows through the inlet of the air knife and into a precise orifice. As this airflow exits the chamber, it passes through a .002” gap that directs the airflow into a perfectly strain line.
Air knives are typically used in manufacturing units to clean and dry products as they move along on a conveyor. The pressurized air curtain formed by such a pneumatic device removes excess oil, dust, and other debris from the products and also helps in cooling them.
Air knives are commonly used in bottling industries to dry bottles and cans after they have been rinsed; used in removing flux and solder paste from electrical products, such as printed circuit boards; and metal scraps and other waste left behind during machining processes. Depending on the application and the industry it is used in, you have a choice of using either an aluminum air knife or a stainless steel (type 303) air knife.
They are cost efficient and deliver large volumes of pressurized and compressed air. A regular air knife delivers a uniform sheet of air at an amplification ratio of, 30:1 and is comparatively less efficient than the advanced version which delivers air at 40:1 ratio, lower noise level, and consumes just 2.9 SCFM @ 80 PSIG. The type of air knife you use depends on the applications.
Air Knife Applications
There are a number of applications for air knives, depending on the industry it is used in.
* Drying – It is practically impossible to hand dry products in large industries. One reason for this is the quantity involved and the other could be the shape of the products. Using air knives for drying is more cost effective and leaves the products completely dried. They are used for drying bottles and cans, PC boards, machined items, and in drying paints, among other uses.
* Cleaning – Cleaning your products through air knives do not ruin the quality of your product. Alternate to using those for cleaning could be using brushes, wiping with a piece of cloth, or a squeegee. These methods could leave marks or scratches on products that are sensitive and delicate. They can also remove debris trapped in places where it cannot be removed mechanically.
* Cooling – They can be efficiently used in processes where you need to keep the products cool. There are many industries where water or other types of coolants cannot be used for cooling, such as in food processing, for products that require dimensional stability, and for extrusion cooling. Metal parts may require to be cooled before they are coated with chemicals or painted. Air knives are a very cost effective and efficient way to do so.
* Anti-Static – Dust is bad for plastic, glass and rubber industries as it sticks to such products. You can effectively deliver an anti-static blanket of air through an air knife fitted with a static bar.
About the Author
For more information about Streamtek Air Knives and Air knives, please visit http://www.streamtek.ca/products.html".
Tags: 1 bar psi, bar psig conversion, psig
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