How To Choose A Desiccant For A Filter-dryer?

If you are going to buy a filter-drier for your air conditioner system, you have to opt from various choices of desiccants that are used in it. Choice of desiccant for a filter dryer depends on various factors. Desiccants are mainly of two types- Molecular sieve and activated alumina.

Molecular sieve is a material with pores. The pores are of same sizes. The diameter of these pores is very small and bigger molecules cannot get inside. Zeolite is often a popular choice for making molecular sieve.

Activated alumina is made by dehydroxylating aluminium hydroxide it in a way that produces a highly porous material; it is commonly used to keep things dry by absorbing water.

The factors that are important in choosing a desiccant are

• Water capacity
• refrigerant and lubricant compatibility
• acid capacity
• physical strength

Water capacity implies the amount of moisture that a descant can hold. The more it can soak in and hold the lower will be the moisture level in the refrigeration system. A molecular sieve is often the best choice when it comes to water capacity. This is on account of the strong bond that water makes with molecular sieve.

Refrigerant and lubricant compatibility is also an important factor. Reaction of refrigerant with incompatible lubricant can lead to formation of acid. It will attack the crystalline structure of the molecular sieve as well as surfaces of the system and break them down. Organics acids can be formed due to breakdown of the lubricant in the presence of an incompatible desiccant and water can accumulate and jam the system’s expansion device.

Acid capacity is the capacity to remove acids. Activated alumina is more effective in removing the various acids when it is used in the suction line of the system. It should be avoided in in the liquid line of a system. This is because there is a strong chance of hydrolysis reaction between the lubricating oil and water to occur which will form organic acids.

The desiccant should also be strong. It should be able to withstand system vibrations and surges. The beads of desiccant often brush against each other they are violently shaken or vibrated, breaking down to granular particles.

Zeolite is choice for an ideal desiccant. It is s activated alumina, silica gel, calcium chloride, and calcium oxide. They are available in nature as well as can be manufactured artificially. They are able to soak, and hold moisture through capillary action.

HVAC technicians often recommend adding alcohol-based additives in refrigeration systems. This is because alcohol does not let moisture to freeze and thereby affect the metering device. However, adding alcoholic additives is not recommended. As modern desiccants, such as zeolite are prone to absorb these additives to an even greater degree than moisture. They will release certain amount of moisture into the system that they had absorbed to soak in these additives.



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