Air-conditioning system for aircraft

Details Air-conditioning system for aircraft Air-conditioning system for aircraft

2001-07-26

2003-07-22

Tapolcai, William E. (Department: 3744)

Refrigeration

Processes

Reducing pressure on compressed gas

C062S087000, C062S401000

Reexamination Certificate

active

06595010

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to an air-conditioning system for aircraft for conditioning humidity-containing air under excess pressure for air-conditioning an aircraft cabin.
The fresh air for air-conditioning aircraft cabins is conditioned from the air tapped from the engine at high pressure and high temperature, the so-called tap air. The air-conditioning systems utilize the pressure and temperature potential of the engine air for generating the required cooling capacity. The tap air is cooled in the course of the process of conditioning fresh air, is dehumidified and expanded to the cabin pressure of about 1 bar in ground operation and about 0.8 bar in flight operation. When conditioning fresh air, great importance is attached to air dehumidification, in order to prevent an icing of individual components of the air-conditioning system and in particular the formation of ice crystals in the fresh air to be conditioned. However, the necessity of dehumidification chiefly exists in ground operation, because in flight operation, i.e. in large altitudes, the ambient air and thus the tapped engine air is extremely dry in any case.
With reference to
FIG. 1
, an air-conditioning system is described below, as it is known for instance from DE 199 35 918 of the same applicant.
Via a flow control valve
12
, that amount of tap air
10
of about 2 bar and 200° C. is tapped from an engine, which is required for supplying fresh air to the cabin. In ground operation, the tap air is withdrawn from an auxiliary engine with about 3 bar. The tap air is first of all passed over a primary heat exchanger
14
and cooled to about 80° C. The heat exchanger is an air—air heat exchanger, and as cooling medium ambient air
16
is used. In ground operation, the volume flow of the cooling air
16
is adjusted via a fan
18
. In flight operation, the ram air supplied is sufficient as cooling medium, the volume flow being adjustable via a throttle valve. The tap air cooled to about 80° C. is compressed in a first compressor C
1
and proceeding from the same is further compressed in a second compressor C
2
to about 5 bar. In a main heat exchanger
20
, likewise an air—air heat exchanger, this pressurized air coming from the second compressor C
2
is cooled to about 50° C. by means of ambient air
16
. The high pressure of about 5 bar is required for realizing a high degree of dehumidification in the subsequent water separation cycle. Therefore, this so-called aircycle system is also known as “high-pressure water separation cycle”.
The high-pressure water separation cycle comprises a condenser
22
, as it is also proposed for instance in EP 0,019,492 A, and a water separator
24
succeeding the condenser
22
. The compressed, cooled tap air is cooled in the condenser
22
by about 15 K, water being condensed at the same time. The condensed water is then separated in the water separator
24
. The air thus dehumidified is passed over two expansion turbines T
1
and T
2
, the air being expanded to a cabin pressure of about 1 bar. Yet before the tap air emerging from the first turbine is supplied to the second expansion turbine, it is passed in a heat-exchanging manner through the condenser
22
of the high-pressure water separation cycle, in order to cool the compressed, cooled tap air to the temperature necessary for separating water in the water separator
24
. The air expanded and cooled in the expansion turbine T
1
is heated at the same time corresponding to the heat flow transferred in the condenser. In the high-pressure cycle, a heat exchanger
26
preceding the condenser
22
is provided in addition to the condenser
22
. First of all, the compressed, cooled tap air is passed through the heat exchanger
26
, before it enters the condenser
22
, and subsequently the dehumidified air is passed through the heat exchanger
26
, before it enters the expansion turbine T
1
. The main function of the heat exchanger
26
is to heat the dehumidified air and evaporate residual humidity while recovering energy at the same time, before the air enters the turbine T
1
. At the same time, however, the condenser
22
is relieved by the heat exchanger
26
in that before entering the condenser
22
the compressed tap air is additionally precooled by about 5 K.
The conditioned air emerging from the second turbine T
2
at about −10° C. and about ambient pressure is then mixed with recirculated cabin air in a mixing chamber which is not represented.
What is typical for an air-conditioning system as described herein is the fact that the energy recovered in the expansion turbines T
1
and T
2
is utilized for driving on the one hand the compressor C
2
and C
1
, respectively, and on the other hand in addition the fan
18
. In one case, three wheels, i.e. turbine (T
2
)/compressor (C
1
)/fan are arranged on a common shaft and form what is called the aircycle machine ACM, which is also referred to as three-wheel machine. The expansion turbine T
1
together with the compressor C
2
is arranged on a common shaft, but separate from the aforementioned three wheels. Therefore, this combined machine as a whole is also entirely referred to as 2+3-wheel machine.
The total system is designed for ground operation at an ambient temperature of, for instance, 38° C. To optimize the effectiveness of the heat exchanging process in the cooling shaft
17
, the water obtained in the high-pressure water separation cycle with a temperature of about t=30° C. and a pressure of about 5 bar in the cooling shaft is supplied in fine droplets to be evaporated in said cooling shaft, whereby the effectiveness of the heat exchangers
20
and
14
is improved.
By means of a bypass means
28
, the highly pressurized air originating from the main heat exchanger
20
can directly be supplied to the second expansion turbine T
2
, without passing through the water separation cycle. This may be of interest in particular when the tapped air is so dry already that it need no longer be dehumidified. This is the case in particular when flying in large flight altitudes.
With the water separation cycle from the known air-conditioning system described above, a sufficiently dry air can be achieved. It is, however, disadvantageous that the condenser and the preceding heat exchanger for dehumidifying the highly pressurized humid air have a large size. This is true in particular for the heat exchanger, as here only a small temperature gradient &Dgr;T is available for the heat transfer function. In aircraft technology, however, it is the foremost premise to build as small and lightweight as possible.
SUMMARY OF THE INVENTION
It is therefor the object of the present invention to develop an air-conditioning system for aircraft in accordance with
at least one compressor (C
1
, C
2
) for compressing the air (
10
) already supplied under an excess pressure to an even higher pressure,
a first expansion turbine (T
1
) for expanding the air to a lower pressure,
and a second expansion turbine (T
2
) succeeding said first one for the further expansion of the air,
such that the dimension of the entire device is reduced and the weight thereof can be reduced on the whole.
In accordance with the invention, this object is solved proceeding from an air conditioning system above by the combination with the features between the first expansion turbine (T
1
) and the second expansion turbine (T
2
) a droplet coalescing device (
30
) with succeeding water separator (
32
) is disposed.
Conceptually, the solution of the above object is achieved in that the construction of the water separation cycle is changed. Instead of the large-size condenser with preceding heat exchanger a droplet coalescing device is used, behind which a water separator is provided in a manner known per se. This constructional unit used for dehydration is incorporated after the first expansion turbine. In accordance with the invention, the highly pressurized, but still humid air coming from the main heat exchanger is supplied to the first expansion turbine at about 45° C. The still hu

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