7
OPERATING AND MAINTENANCE MANUAL
Chapter 4
- Description
NRC0020-0200 UL
The data in this manual are not binding and may be changed by the manufacturer without notice.
Reproduction of this manual, even partial, is strictly prohibited.
C
HAPTER
4
D
ESCRIPTION
4 . 1
O p e r a t i n g p r i n c i p l e
A refrigerant circuit cools a patented “thermal mass” through which the humid compressed air to be dried flows.
The air cools, resulting in condensation of the water vapor it contains, which is subsequently separated and discharged.
The temperature of the thermal mass is regulated by an electronic controller, which stops the refrigerant compressor when the programmed set-
point is reached.
4 . 2
A i r a n d r e f r i g e r a n t c i r c u i t s
(See attached refrigerant circuit diagrams)
4.2.1 Air circuit
The warm and humid compressed air entering the dryer flows through the air/air exchanger section of the thermal mass.
Here the air is precooled by the cold and dry compressed air leaving the air/refrigerant or evaporator section of the thermal mass.
The precooled air then enters the evaporator section of the thermal mass where it is cooled (in most applications to a temperature of
approximately 3°C/37.4 °F) exchanging heat with the refrigerant fluid and the silica thermal mass.
Heat is exchanged by a process of conduction through the aluminium fins that join the copper tubes through which the compressed air flows, to
the copper tubes in which the refrigerant fluid evaporates.
The aluminium fins exchange heat also with the silica thermal mass keeping it at a temperature of approximately 0°C (32°F).
At this point the compressed air is saturated and conveys with it the condensation produced during the cooling process.
The precooled air then enters a high efficiency condensate separator (demister type with stainless steel mesh) where the condensate is
precipitated and collected on the bottom of the enclosure.
A condensate drain either of the timer controlled or capacitive type, depending on the unit's configuration, opens periodically and drains the
condensate which is expelled by compressed air pressure.
The dry cold air at the outlet of the separator flows for the second time through the air/air section of the thermal mass, where it absorbs the heat
of the warm and humid compressed air entering the dryer and thereby cools the inlet flow.
This air/air exchanger both reduces the amount of energy required to dry a given flow of air and also has the benefit of reducing the relative
humidity thereby avoiding the risk of the formation of condensate at the dryer outlet.
4.2.2 Refrigerant circuit
The high pressure compressed refrigerant gas flows into the condenser.
In the condenser the refrigerant changes from the gaseous to the liquid phase.
•
The condenser is a heat exchanger of the finned core type and it is cooled by an air flow provided by fan.
The condenser is generously sized in such a way that it can function partially also as a liquid receiver.
Downstream from the condenser the refrigerant enters a filter drier and a capillary tube where refrigerant pressure is reduced to lower its boiling
pressure.
The refrigerant then enters the tubes of the evaporator section of the thermal mass, cooling both the compressed air and the thermal mass itself.
The refrigerant at the dryer outlet is now in the form of a cold vapor, which is returned to the compressor to repeat the cycle.
Since the heat provided by the compressed air to cause the refrigerant to evaporate varies significantly because of fluctuations in the compressed
air temperature and flow rate, the dryer is equipped with an electronic system to control the temperature of the thermal mass. This system fulfils
3 important roles:
•
it ensures an almost constant pressurised dew point (approx. +3°C (+37.4°F));
•
it prevents the compressed air temperature from falling below 0°C (32°F) with consequent freezing of the condensate;
•
it ensures that all the refrigerant is evaporated in the evaporator, thus avoiding the risk of any liquid entering the compressor
suction side.
When the load is low or zero, the temperature of the thermal mass tends to fall.
When it reaches 0°C (32°F) the electronic controller stops the compressor.
The compressed air that continues to flow in the evaporator is cooled by the cooling energy stored in the silica.
When the silica temperature starts to rise, the refrigerant compressor is started automatically so that it can cool it down again.
This system offers the benefit of reducing average energy consumption of the dryer in such a way as to make it approximately proportional to
demands.
Summary of Contents for NRC0020-0200 UL
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