GB621123A - Improvements in air conditioning and cabin pressurising plant for aircraft - Google Patents

Abstract

621,123. Air conditioning. EARL, A. G., and SHAW, J. M. Jan. 7, 1946, No. 544. Class 137] In a pressurizing and air conditioning plant for an aircraft cabin, the pressurizing apparatus comprises an air compressor 1 driven by a motive power unit 2 and is arranged to supply air at two alternative pressures, (viz. at or above the required cabin pressure) or at alternative adjoining ranges of pressure (the minimum in the lower range being substantially cabin pressure), and the air conditioning apparatus includes a humidifier 18 for treating the compressed air or air in the lower pressure range, an expander 11, dehumidifier 16 and heater 17 for treating the overcompressed air or air in the higher pressure range, and a heat exchanger 7 for treating both, and a control and governing means is provided for the plant. In the form shown, the two stage centrifugal compressor 1 is driven by the aircraft engine 2 through a variable speed drive 3, e.g. a multi-speed drive gear box, the drive ratio being selected by a governor 4 according to engine speed and altitude. A master control for the compressor may be incorporated in the variable speed drive. Air is delivered from the compressor to the heat exchanger 7 where it is cooled by fresh air flowing through a duct and having regulating flaps 9 therein. The air then passes through an axial or curved flow turbine expander 11, fixed to the same shaft as the compressor, or through a bypass 13 having a control valve 14, to the duct 12, and then through the rest of the air-conditioning apparatus and a silencer 19 to the cabin 20 via duct 24. In a multiengined aircraft, two identical plants may be used coupled to the same cabin distribution duct, in which case non-return valves 25 are placed in the ducts 24. Air is discharged via duct 28 controlled by a pressure regulating valve 30 and a safety valve 31 is also provided. Some of the air may be recirculated in the cabin by a fan, via duct 37. A humidostat 33 in the duct 24, or, as shown, in the cabin, controls a thermostat 32 at the junction of ducts 12 and 13 having two settings, viz. one at and one below the required cabin temperature corresponding to compressed and overcompressed air respectively. The setting of the thermostat controls the governor 4 to select the right compressor speed, the flaps 9 for the cooler 7, the working of the components 16, 17, 18, and the opening or closing the by-pass valve 14. In a modification, the variable speed drive 3 is a hydraulic torque converter or slipping clutch and the turbine expander 11 is connected to another compressor to form a free-running turbinecompressor unit. Over-compressed air from the compressor 1 is passed from the cooler 7 to this additional compressor, then through another similar cooler to the turbine. The governor 4 is sensitive to intake pressure and temperature and compressor delivery pressure to regulate the flow of fluid to the clutch 3. The valve 14 is adjustable (instead of just opening or shutting) and controlled by the thermostat so that at the high temperature setting as determined by the humidostat the valve moves between a partially and fully open position and at the low setting between a partially and fully closed position. The dehumidifier 16 may be arranged between the expander and the junction of ducts 12 and 13 in which case the thermostat setting only controls the working of components 17 and 18 and the cooler 7. The subsequent mixing of the two air streams from the expander 11 and dehumidifier 16, and from the by-pass 13 respectively, produces part of the necessary heating. The free-running turbine-compressor unit, additional cooler and the dehumidifier 16 may be arranged to be easily removed from the aircraft. The heat of compression may be utilized in the heater 17 or to additionally heat the air. The air may be further humidified at a point in or before the expander 11.