Brochure

Parker Hannifin Corporation
Climate & Industrial Controls Group
Cleveland, OH
Catalog CIC-2003-1/US
Filter Dryers
20
FIGURE 1
5
10
15
20
Water capacity, weight %
Molecular Sieve
Activated Alumina
Silica Gel
Water in refrigerant, ppm by weight
TABLE 2
TABLE 3
TABLE 1
Introduction to Dryers Filter Dryers
Figure 1 illustrates the water capacity of different desic-
cants as a percent of weight in an R-12 refrigerant sys-
tem. It can be determined from this that the molecular
sieve desiccant retains the highest amount of moisture.
This type of isotherm represents unimolecular adsorp-
tion. This is due to the strong bond between the
molecular sieve and water. The activated alumina
desiccant retains a fair amount of moisture, as well.
However, the retention isn’t as great as the molecular
sieve. This is indicative of co-adsorption of other materi-
als and the weak hold activated alumina has on water.
Refrigerant and lubricant compatibility is essential
when selecting the correct desiccant. Dryers are often
used on the suction line side of a system to prevent
foreign particles, acids, sludge and moisture from
entering the compressor. Inorganic acid formation is
predominantly found on the suction side and could
cause corrosion and motor burnout. Inorganic acids
(HCI and HF) form from the decomposition of the
refrigerant. This may happen as a result of added heat
and moisture in the system. Inorganic acids formed will
attack the crystalline structure of the molecular sieve
and break it down. Thus, it is important to keep the
fluoride and chloride levels, found on the desiccant, low.
Additionally, if the correct compatible desiccant is used,
the measured levels of the F- and Cl- will remain low.
Incompatible refrigerants and desiccants will promote
decomposition and formation of these inorganic acids.
Table 2 gives a summary of the compatible refrigerant
and molecular sieve.
The formation of these organic and inorganic acids will
cause the water capacity of the desiccant to decrease.
Therefore, it is important to know the compatibility of
the components within a refrigerant system. Table 4 (on
the following page) displays the various refrigerants
and the compatible lubricant.
Desiccants should be strong enough mechanically to
resist breaking up when subjected to system vibrations
and surges. Incompatible combinations of refrigerant,
lubricant and desiccant will have low crush strength
and high attrition values. Crush strength can be defined
as the force required to break the individual beads of
desiccant. Attrition occurs when the desiccant is
shaken or vibrated to yield fine particles.
Hydrolysis of the lubricant will form organic acids.
Organic acids are the carboxylic acids that are the
result of POE lubricants reacting with water in the
system. The water attacks the POE lubricant and
breaks it down into its original components (carboxylic
acid and alcohol). This breakdown of the POE lubricant
will not happen if minimal moisture is present in the
system. The levels of these acids can be reduced by
keeping the moisture level in the system low. Table 3
reveals the acid capacity of two types of desiccants.
In order to properly size a molecular sieve dryer, the
maximum operating temperature should be known. The
dryer should be located in the liquid line between the
outlet of the condenser and the metering device. Typical
water capacity is shown in drops of water per gram of
molecular sieve, based on liquid line temperature, as
shown in Table 1.
75°F 125°F 75°F 125°F 75°F 125°F 75°F 125°F
3.72 3.52 3.40 3.24 3.40 3.24 3.40 3.20
Drops of Water
R-12 R-22 R-502 R-134a
Refrigerant Dessicant
R-12 XH-6, XH-9, XH-11
R-22 XH-6, XH-9, XH-11
R-134a XH-6, XH-9, XH-11
R-401A XH-6, XH-9, XH-11
R-401B XH-6, XH-9, XH-11
R-401C XH-6, XH-9, XH-11
R-402A XH-6, XH-9, XH-11
R-402B XH-6, XH-9, XH-11
R-404A XH-6, XH-9, XH-11
R-407A *XH-6, XH-9*, XH-11
R-407B *XH-6, XH-9*, XH-11
R-407C *XH-6, XH-9*, XH-11
R-410A *XH-6, XH-9*, XH-11
R-502 XH-6, XH-9, XH-11
R-507A XH-6, XH-9, XH-11
* Note: Dessicant may adsorb R-32, causing the water
capacity to be reduced. (Courtesy UOP)
Dessicant
Inorganic
Acid Capacity
(% by wt)
Organic
Acid Capacity
(% by wt)
Molecular Sieve approx 6% 0.80%
Activated Alumina approx 6% 5.50%