A Thermodynamic Analysis of Three and Four-Wheel Air Cycle Machines for Aeronautical Applications

Abstract

Air cycle refrigeration is an attractive alternative that has been employed to provide aircraft cabin cooling. The primary function of the cabin air conditioning and pressurization system is to maintain an aircraft environment that will ensure safety and comfort of the passengers and crew during all fly operational conditions and provide adequate avionics cooling. The energy to drive these machines comes from the compressed air bleed from the compressor of the aircraft propulsion turbine. Usually, Air Cycle Machine (ACM) architecture includes mainly two compact air-to-air heat exchangers, a compressor and a expander with one or two expansion stages (called three-wheel or four-wheel configuration, respectively). In this context, this work focuses on a comparative thermodynamic study of three and four-wheels air-conditioning aircraft air cycle machines. This comparison will be performed taking account some design features that affect the ACM performance as: aircraft flight Mach number, cabin altitude, heat exchanger effectiveness and compressed bleed air conditions. Results showed that the second level of expansion from four-wheel air cycle machine increases its thermodynamic efficiency. As the amount of rejected heat in the secondary heat exchanger (SHX) is greater for the 4-wheel architecture, it is possible to have the same cooling effect than the 3-wheel machine but with a more compact SHX. Moreover, the implemented computational tool to solving the air cycle refrigeration mathematical model allows a better understanding of the ACM performance.
Copyright © 2015 Praise Worthy Prize - All rights reserved.