Filter dryer in refrigeration system has two functions: one adsorption system debris such as water and acid; Second, provide filtering function.

Various technical factors need to be considered in the selection of filter dryer for special purposes, including: system type, size of connecting pipe, water content (moisture content), system flow, filtration capacity, material (copper or steel) and safe working pressure. It is necessary to evaluate each factor to ensure that an economical filter dryer is selected.

ParkerHannifin developed the filter dryer based on the existing technology and years of practical experience. These filters were tested strictly in accordance with ASHRAE631 standards and ARI710 standards for flow capacity and moisture absorption, and the obtained data were made into the capacity table of liquid flow filter dryer (based on ARI standard working conditions). Can be used as a comparison filter dryer. Of course, there are other factors to consider for different forms of equipment.

Absorbs moisture and prevents acid production

For the filter dryer, the ability to adsorb moisture from the refrigeration system is a very important function. Moisture in the system can come from many sources, such as: residual air caused by improper evacuation, system leakage, motor coil, etc. Another important source is improper operation of ester lubricants, which have strong moisture absorption. Or rather, they're happy to soak up the moisture. Ester lubricants absorb more moisture from the environment and are more difficult to separate than previously used mineral oils. Moisture can cause ice jams in the system and corrode metal parts in the system. The moisture in the system also reacts with ester lubricants to generate organic acids.

To prevent the formation of organic acids, moisture in the system must be minimized. The desiccant in the filter dryer accomplishes this process. Molecular sieve activated alumina and silica gel are the three most commonly used desiccant.

Molecular sieve is a crystalline sodium aluminosilicate (synthetic zeolite), it has a cubic crystal mechanism, so it can be selectively adsorbed according to the size and polarity of the molecule. Molecules with crystalline structures vary in size. This allows some molecules to be adsorbed, such as water; It also allows the passage of a large number of other molecules, such as refrigerants, lubricants and acids. The surface of the desiccant is covered with cations, which act as magnets for polar molecules such as water, which can be tightly adsorbed. The water molecules are separated from the lubricating oil, greatly reducing the likelihood of hydrolysis of the fatty lubricating oil.

Activated alumina is composed of aluminum oxide (A1O) and is not a very good crystalline material. Alumina and silica gel are shown in various forms

Various pore sizes and none of them showed selectivity based on molecular size. In addition to using their surfaces to adsorb water, they can also adsorb large amounts of refrigerants, lubricants, and acid molecules due to the size of their diverse pores. After both water and oil are adsorbed into the pores of the alumina, the alumina also provides the opportunity for hydrolysis of the POE oil.

Silica gel is composed of silica (SiO) bound polymerization of an amorphous molecular structure of the material, the gel like structure of the desiccant heralds

A weak bond between water and a desiccant. Silica gel is an old form of desiccant that is not used much in today's filter dryers.

Choose desiccant material

There are many thorny problems in choosing the most suitable desiccant material required. Water content, compatibility of refrigerant and lubricating oil, self-performance and acid content are all important characteristic parameters. These important characteristics need to be considered when selecting dryers.

Dryers are often placed on the liquid line before the refrigerant passes through the expansion valve to absorb moisture and some solid impurities. Acid content, both organic and inorganic, is not particularly high on liquid lines, but some are present, so the dryer must be able to absorb them. However, even if the dryer is able to pull most of the moisture out of the system, acidity will remain low. To achieve this purpose, the dryer needs to have a sufficient moisture absorption capacity. Moisture content refers to the amount of water that can be absorbed by the dryer when the water and moisture in the refrigeration system remain at a low level.