Nirvana Cycling Refrigerated Dryer 75 through 150 scfm
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5
7.1 INTRODUCTION
Ingersoll Rand Nirvana Cycling dryers remove moisture from
compressed air by cooling the air temperature to between 34° and 38°F
(1 and 3°C). This causes vapors to condense into liquid droplets which
can then be easily removed from the air. The major systems of the dryer
which contribute to its operation are the Air System, the Moisture
Removal System, the Refrigeration System, the Thermal Mass
Circulating System and the Controls. The following paragraphs describe
each of the systems in greater detail.
7.2 AIR SYSTEM
The air system consists of the dryer components which are in contact
with the compressed air. Referring to Figure 1 and following the bold “
AIR
7.0 PRINCIPLES OF OPERATION
FLOW
,” hot saturated air from the compressor enters the
precooler/reheater where the air temperature is reduced prior to
entering the chiller by the cool air exiting the air/moisture separator. This
precooling allows for the use of a smaller refrigeration system. The air
then goes into the chiller section where it is further cooled to the desired
dew point by a thermal mass fluid. The temperature of the thermal mass
fluid is maintained by the refrigeration circuit and controls. The air
continues to the separator where moisture is removed, thereby, allowing
the cool, dry air to return back to the precooler/reheater to be heated by
the incoming moist hot air. The air exiting the “reheater” portion of the
dryer should be approximately 15°- 20°F lower than the inlet air
temperature based on standard conditions at full rated flow.
7.3 MOISTURE REMOVAL SYSTEM
Liquid droplets are removed from the air stream in the separator. As the
air and liquid mixture passes through the separator it spins, slows down
and then changes direction. This causes the condensate to fall out of the
air stream and collect in the bottom of the separator. The collected liquid
is removed from the separator by a drain.
7.4 REFRIGERATION SYSTEM
The Refrigeration System consists of all the components which handle
R-404A. This is a hermetically sealed closed-loop system. Referring to
Figure 1 and following the phantom“
REFRIG
(
R
-
404
A
)
FLOW
,” refrigerant is
shown leaving the evaporator section where, in the process of removing
heat, it is changed from a low pressure liquid into a low pressure gas.
This gas enters the suction side of the compressor where it is
compressed into a high pressure gas. The high pressure gas is cooled
in the air cooled condenser section until it becomes a high pressure
liquid. It then goes through a permanent filter dryer that ensures the
refrigeration system is free of contaminants. A small diameter capillary
tube meters the refrigerant for introduction into the evaporator. The
refrigerant pressure is reduced upon entering the evaporator where as
it evaporates, removes heat from the thermal mass fluid.
7.5 THERMAL CIRCULATING SYSTEM
The thermal mass fluid in an Ingersoll Rand Nirvana Cycling dryer is
continuously circulated in a closed pump loop system. Referring to
Figure 1 and following the dashed “
THERMAL FLUID
” line, the heat is
removed from the fluid in the evaporator by the refrigeration system. The
thermal mass reservoir is sized to minimize refrigeration cycles during
reduced air load periods. The thermal mass fluid is pulled from the
bottom of the reservoir and pumped through the chiller, removing heat
from the air and then returned to the evaporator. The pump utilized on
the Ingersoll Rand Nirvana Cycling dryer is a maintenance-free, quiet
cartridge circulator pump similar to those used in residential water
systems. While the refrigeration system cycles on and off based on
loading conditions, the circulating pump runs continuously to maintain
flow through the chiller at all times. Note that when the power switch is
set to the off position, the circulating pump will not operate.
7.6 CONTROLS
The Ingersoll Rand Nirvana Cycling dryer incorporates automatic
controls for proper operation. The thermal mass fluid temperature is
maintained by a thermostat that monitors the temperature and cycles
the refrigeration system in response to varying air flow and temperature.
Upon an increase in the temperature of the thermal mass fluid, the
compressor is cycled on. When the fluid is cooled to its control set point,
the compressor is cycled off. The thermal mass fluid functions as a
thermal storage mass in the Nirvana Cycling dryer.
In addition to the factory set thermostat, a suction pressure gauge is
provided as standard equipment. This gauge monitors the pressure of
the refrigerant gas before it enters the compressor. When the
refrigeration system is running, the suction pressure will pull down to
between 55 to 65 psig, depending upon load and ambient conditions.
After the thermal mass fluid has been cooled and the refrigeration
system is shut off, the system pressure will equalize with a gauge
reading typically between 80 and 150 psig depending on ambient
temperature.
A “High Temp” alarm light is provided to indicate an elevated thermal
mass temperature. The light is controlled by a thermostat that monitors
the thermal mass and closes to energize the light at approximately 50°F.
FLOW DIAGRAM
FIGURE 1