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| ©2004 |
| Earthship USA, Inc. |
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| What is Air Cycle? |
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Air
is by nature the safest and cheapest refrigerant.
Environmental concerns about ozone depletion,
global warming and increasingly stringent
legislation have made it an extremely attractive
technology in the refrigeration application.
The
use of air as a refrigerant is based on the
principle that when a gas expands adiabatically
from a given temperature, its final temperature
at the new pressure is much lower. The resulting
cold gas, in this case air, can then be used
as a refrigerant, either directly in an open
system, or indirectly by means of a heat exchanger
in a closed system. The efficiency of such
systems is limited to a great extent by the
efficiencies of compression and expansion,
as well as those of the heat exchangers employed.
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In
the early days when air cycle was explored, slow
speed reciprocating compressors and expanders were
used. The poor efficiency and reliability of such
machinery were major factors in the replacement
of such systems with vapor compression equipment
using freon. However,
the development of rotary compressors and expanders
greatly improved the isentropic efficiency and reliability
of the air cycle. Advances in turbine technology,
together with the development of air bearings and
ceramic component offer further efficiency improvement.
Combining this with newly available compact heat
exchangers with greatly improved heat transfer characteristics
make this a logical alternative to existing halocarbon/ammonia
based refrigeration technologies and liquid nitrogen
systems. |
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Air
cycle systems have specific advantages that apply
to all potential applications:
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- The
working fluid (air) is free, environmentally
benign, totally safe and non-toxic.
- Air
cycle equipment is extremely reliable, thereby
reducing maintenance costs and system down-time.
- The
performance of an air cycle unit does not deteriorate
as much as that of a vapor-compression unit
when operating away from its design point.
- When
operating in a refrigeration cycle, an air cycle
unit can also produce heat at a useful temperature
more...
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Click here
for more on History and Potentials of Air Cycle
System
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