Refrigeration – Air compressor – cooler and expander type
Reexamination Certificate
2000-12-27
2003-02-18
Doerrler, William C. (Department: 3744)
Refrigeration
Air compressor, cooler and expander type
C062S402000
Reexamination Certificate
active
06519969
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an air-conditioning system for preparing pressurized air for the air-conditioning of a space, in particular for the air-conditioning of airplane cabins, and a corresponding process.
2. Prior Art
The fresh air for the air-conditioning of airplane cabins is usually prepared from the air tapped under high pressure and at high temperature from the power unit, referred to as bleed. The air-conditioning systems draw the cooling capacity required for the preparation from the pressure and temperature potential of the precompressed power unit air. The bleed is cooled off during the course of the fresh air preparation process and its pressure drops to the cabin pressure of 1 bar in ground operation or roughly 0.8 bar in flight. During the process of fresh air preparation the air is also dehumidified in order to prevent an icing of individual components of the air-conditioning system and ice crystal formation in the fresh air to be prepared. Dehumidification is necessary primarily in ground operation, however, because in flight, i.e., at high altitudes, the ambient air and thus the tapped power unit air is extremely dry anyway.
With the help of
FIG. 4
, an air-conditioning system is described below of the kind used in today's Airbus and Boeing passenger aircraft, for example the A330/340 and Boe 757/767.
Via a flow control valve FCV, that bleed quantity is drawn from a power unit and fed to the system at 1.5 to 3.5 bar and 150° C. to 230° C. that is needed to supply the cabin with fresh air. In ground operation the bleed is drawn from an auxiliary power unit and fed to the system at roughly 3 bar. The bleed is first guided through a primary heat-exchanger PHX and cooled off to approx. 100° C.
The bleed is then further compressed in a compressor C to approx. 4.5 bar and 160° C. and cooled off again in a main heat-exchanger MHX to approx. 45° C. The high pressure of 4.5 bar is necessary to be able to achieve a high degree of dehumidification in the subsequent water separation circuit. This system is therefore also known as a “high pressure water separation circuit”.
The high pressure water separation circuit comprises a condenser CON as is proposed in EP 0 019 493 A3, and a water extractor WE downstream from the condenser CON. The compressed, cooled bleed is cooled off by roughly T=−15 K in the condenser CON, the condensed water is then extracted in the water extractor WE, and the pressure of the air dehumidified in this way is then expanded in a turbine T to the cabin pressure of roughly 1 bar, while the temperature at the turbine output is roughly −30° C. Before it is mixed as fresh air in a mixing chamber with recycled cabin air, the thus prepared bleed is guided in heat-exchanging manner through the condenser CON of the high pressure water extraction circuit in order to cool the compressed, cooled bleed to down to the temperature necessary for water extraction in the water extractor WE. In this connection, the pressure-relieved, cooled air in the turbine T heats up again by the equivalent of &Dgr;T=+15 K to roughly −15° C.
The air-conditioned air is then mixed with recycled cabin air in a mixing chamber not illustrated. The temperature at the turbine output can be raised by means of a temperature control valve TCV in order to obtain an optimal mixing temperature with the recycled cabin air mixed in. For this purpose, a portion of the bleed precooled in the primary heat-exchanger PHX is diverted and guided back to the prepared airflow behind the turbine T.
In addition to the condenser CON, a reheater REH is provided upstream from the condenser CON in the high pressure water extraction circuit. The compressed, cooled bleed is first guided through the reheater REH before it enters the condenser CON, and subsequently the now dehumidified air is again guided through the reheater REH before it enters the turbine T. In this connection, the reheater REH's task is essentially to heat the dehumidified air by roughly &Dgr;T=5 K and to evaporate residual moisture from the dehumidified air with simultaneous energy regeneration, before the air enters the turbine. This is because residual moisture in the form of fine droplets can destroy the turbine wheel surfaces and the turbine nozzles, since the air in the turbine T almost reaches the speed of sound. A second function of the reheater REH consists in relieving the condenser CON in that the compressed, cooled bleed is cooled by the equivalent of &Dgr;T=−5 K before entering the condenser CON.
The energy generated in the turbine T is used to drive the compressor C on the one hand and a fan F on the other hand. All three wheels, that is, turbine/compressor/fan, are mounted on a shared shaft and form the air cycle machine, also referred to as three-wheel machine. The fan F conveys a cooling airflow diverted from the ambient airflow through a cooling shaft in which the primary heat-exchanger and the main heat-exchanger PHX, MHX are arranged. The fan F must be actively driven by the turbine T in ground operation in particular. The ram air is sufficient to drive the fan in flight; if necessary it can be controlled by an adjustable valve at the cooling shaft entrance.
The entire system is designed for ground operation at an ambient temperature of 38° C. To optimize the efficacy of the heat-exchanging process in the cooling shaft, the water gained in the high pressure water extraction circuit is fed at a temperature of approx. T=25° C. and a pressure of 3.5 bar to the cooling shaft entrance for evaporation there, thereby improving the efficacy of the heat-exchanger.
In the event that the air cycle machine ACM is completely unavailable because, for example, the necessary mass pressurized airflow to fulfill the parameters required for the system to function cannot be attained, a bypass valve BPV is provided in order to circumvent the turbine T. In this case, a check valve CV opens automatically in that an overpressure triggering the check valve CV builds up before the compressor C for lack of drive by the turbine T. The compressor C is circumvented or “short-circuited” by the check valve CV opening. In this condition, the fresh air is immediately fed through the primary and main heat-exchangers PHX, MHX directly to the mixing chamber downstream from the air-conditioning system for mixing with recycled cabin air.
As mentioned in the beginning, ice formation in the prepared fresh air presents a problem. In order to avoid ice formation, an anti-icing valve AIV is provided with which a portion of the air bled from the power unit is immediately diverted and again fed to the prepared airflow behind the turbine T.
A thermodynamically improved variant of this air-conditioning system provides for the air cycle machine ACM to be expanded by a second turbine. In this way, the turbine/compressor/fan three-wheel machine becomes a turbine/turbine/compressor/fan four-wheel machine (see U.S. Pat. No. 5,086,622 to Warner). The second turbine is mounted with the other wheels on a shared shaft in order to feed the energy generated by the turbines back into the air-conditioning system, in the manner of the conventional three-wheel system. The second turbine completes the first turbine in such a way that the pressure of the air dehumidified in the high pressure water extraction circuit is dropped in two steps, in connection with which the condenser of the high pressure water extraction circuit is arranged in heat-exchanging manner with the air conduit between the two turbines.
This saves more energy than the conventional design of the air-conditioning system because the air emerging from the first turbine is comparably warm, preferably above 0° C. to avoid ice, and this air is heated in the condenser CON by &Dgr;T=+15 Kelvin, for example, to a comparably high energy level in such a way that the second turbine can utilize this high energy level to generate energy that is lost with the conventional system. This system
Doerrler William C.
Jacobson & Holman PLLC
Liebherr-Aerospace Lindenberg GmbH
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