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Dryer module: air treatment and cooling system of the dryer
After the air is compressed by the compressor and partially cooled by the radiator the compressed air is filtered by a pre-filter
5 where part of the water, oil and contaminants is removed. Then, the compressed air passes through the air dryer, which re-
moves the humidity of the air by means of a cooling system, that is, the humidity is removed by the cooling of the compressed
air in a heat exchanger, seeing that the water produced in this process is eliminated through a separator and drain with time
control.
The cooling process of the compressed air is done in two steps:
- First the pre-cooling takes place in a heat exchanger between the hot and humid air that is getting in and the dry and cold that
is coming out.
- The second step is through the exchange between humid air and cooling fluid. The thermal exchange occurs up to close to
the evaporation temperature of the cooling fluid. With the temperature low, the excessive humidity present in the compressed
air condenses because the dew point or water condensation temperature is reached. Inside the heat exchanger itself the air,
already dry and cold, is reheated by thermal contact with the humid and hot air that is getting in. This exchange allows a pre-
-cooling of the air that gets into the dryer and a slight heating of the dry compressed air that returns to the consumption system.
The cooling system of the Air Dryer - SRS has a hermetic compressor, which aspirates the cooling fluid in the gas phase from
the evaporator, where the thermal exchange between the humid air and the cooling fluid occurs. The evaporator absorbs the
heat of the compressed air, condensing the water vapor contained in the air. While passing by the hermetic compressor, the
cooling fluid is compressed raising pressure and temperature. Then, it enters the condenser, which features a fan responsible
for the circulation of the cooling air between the tubes and fins that cool down the cooling fluid. After cooled down, it passes
by the expansion device, located at the beginning of the evaporator, lowering the pressure and temperature of the cooling fluid,
restarting the cycle.
Drop of thermal load
When the reduction of the flow and/or temperature of the compressed air in the inlet of the Air Dryer, there is a tendency of the
pressures and temperature of the cooling system to decrease, which may cause the condensate to freeze before it is drained.
In order to solve this problem, the Air Dryers - SRS feature a hot air bypass system. When there are situations that may cause
the freezing of the condensate inside the heat exchanger, the bypass system is activated diverting part of the hot cooling fluid to
the evaporator, preventing the freezing of the condensate and the clogging of the passage of compressed air. The hot air bypass
valve controls the amount of cooling fluid that will return to the low pressure circuit, preventing its excess.
If the temperature drops below -1°C, the dryer will shut down in order to prevent its freezing.
Low temperature in the discharge of the compressor for refrigeration
In case the ambient temperature is excessively low, there is a tendency of reduction of the discharge pressure in the compres-
sor, jeopardizing the activation of the bypass system and of the expansion device. Besides, too low condensing temperatures
hinder the return of the oil that is in the refrigeration circuit to the hermetic compressor. The resource used to avoid this problem
is a pressure switch that shuts down the fan of the condenser when the high pressure of the refrigeration system drops below
normal.
Safety pressure switch
The dryer has a pressure switch installed in the refrigeration system that shuts down the dryer in case of an increase in pres-
sure out of the normal conditions of the system.
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