What Is a Defoamer?
Defoamers are devices used to remove gas (bubbles) from liquids. They are used in the production process of various products, ranging from low-viscosity liquids such as water and chemical solutions to high-viscosity liquids such as resins and oils.
Defoamers are available in various forms depending on the liquid used and the uses of the product. In addition to vacuum (decompression), pressurization, and centrifugal force, defoamers using ultrasonic waves and gas-permeable membranes are also available.
By removing air bubbles from liquids, the strength, properties, and surface characteristics of products can be made uniform, thereby improving product yield and quality.
Uses of Defoamers
Vacuum defoamers are most commonly used to defoam by reducing pressure. Because bubbles can be expelled into decompressed air over time, even in liquids of high viscosity, vacuum defoamers are used to defoam silicone rubber and various resins. Sometimes, additives called defoamers are used in combination to help break up the foam film that has reached the surface of the liquid.
Pressurized de-aerators use pressure to compress bubbles temporarily to a very small size. When the pressure is released, the bubbles return to their original size, so they are used for materials such as thermosetting resins and glues for adhesive tapes, where the size of the bubbles is fixed when the product is made.
Principle of Defoamers
Vacuum defoamers use a vacuum pump to depressurize a sealed container containing a sample, causing the bubbles in the liquid to expand. The expanded bubbles float to the surface of the liquid due to buoyancy. Then, they are discharged into the depressurized air as the liquid film on the surface is destroyed over time. Although this method is useful for liquids with high viscosity, it is important to note that decompression may cause the liquid to boil at room temperature. The rapid decompression causes the temperature of the gas to drop due to Boyle-Charles’ law, and the higher the clay content of the liquid, the longer it takes to defoam the sample.
Centrifugal defoamers utilize the principle of separation of liquid and gas with density difference due to the centrifugal force generated when the container containing the sample rotates on its axis and revolves on its axis. Depending on the model, centrifugal deaerators can generate acceleration 100 times greater than the acceleration of gravity.
Vacuum defoamers and centrifugal defoamers are sometimes used together. In this case, the centrifugal force separates the bubbles, whose density has greatly decreased due to expansion caused by decompression, from the liquid, resulting in a more powerful defoaming action.