Activated alumina is derived out of aluminum hydroxide, and an extremely porous substance is formed through dehydroxylating. This type of material can have a broad area on the surface of over 200 square meters. The compound is basically utilized for the purposes of absorbing water from out of the air, namely as a desiccant, fluoride, selenium, arsenic, and sapphire found in most drinking water. Being made up of aluminum oxide and related substances, which are also found in rubies and sapphires is what gives all types of gems their many colors. In addition, it carries an extremely high surface-area-to-weight breakdown. Basically, it contains a lot of tiny pores that resemble tunnels running throughout them.

Desiccant dryers function through the process of adsorption. Basically, the water found in the small passages bonds to the activated alumina, while the air passes through them. Water molecules are imbedded, and as the air courses through the filter, the air is then dried. It may be interesting to note that the process can be reversed, and if the process reaches 200 degrees Celsius, it will then release the stored water in a process known as regeneration. There is always water present in air, and the way in which to measure the amount is through the dew point.

Desiccant dryers have in most cases two cylinders that contain desiccant, which is connected to a system of valves. Basically, when the initial cylinder becomes saturated, the flow of air is then transferred to a cylinder that contains the dried desiccant. The major types include silica gel, alumina, and calcium sulfate. Many kinds of dryers have desiccant applications that are regenerative, even though there are manual desiccant dryers as well. Typically, the most expensive kind of desiccant dryers will run a bit of dried and compressed air through a cylinder, at which point, moisture is extracted.

The best compromise might be to utilize air that comes from outside the dryer, and then the air is heated and given to the water-saturated desiccant in order to dry properly. Another option might be the heated purge, which uses far less air than the other varieties, and in this case, the air is carried away while passing through the desiccant.