ECS & ECLS simulation with Flownex


Environmental Control Systems

Aircraft operate at varying altitudes, thus resulting in changes in ambient pressure and temperature surrounding the aircraft. Environmental Control Systems (ECS) control the temperature, pressure and air flow into the aircraft, which is essentially a pressure vessel and includes the cockpit, cabin and interior compartments. ECS also performs cabin altitude and cabin pressure differential monitoring. Typical transport aircraft ECS comprises various systems performing functions such as bleed air supply, bleed air leak detection, air conditioning and distribution, avionics cooling, cabin pressure control and oxygen supply. The system may also encompass wing anti-ice systems.

In a typical ECS systems, bleed air is bled from a compressor stage in the aircraft engine. The bleed air pressure is controlled with a pressure regulating valve which may include reverse flow protection. Bleed air temperature is controlled via a fan air valve which controls the fan (cold) air flow through the pre-cooler, which is an air-to-air heat exchanger used to cool the bleed air. The bleed air is then conditioned, which involves the regulation of temperature and humidity of the air, and then supplied to the cockpit and the cabin zones at the required mass flow rate. Provision is also made for recirculation of a portion of the cabin air whilst maintaining the required oxygen level and removal of particulate and odours in the re-circulated air by means of filtering systems. A cabin pressure control system regulates the pressure within the cabin by controlling the outflow of air by means of one or more outflow valves and a control system.

Flownex can be used for the design, optimisation and simulation of the ECS. The components making up the ECS can be simulated with Flownex, which allows simulation from basic design to detail design of individual components up to systems level. Flownex’s ability to simulate bleed air from the compressor, through the pressure regulating valve, pre-cooler, air conditioning system including filers and dehumidifier through to cabin pressure control makes it ideally suited for design and optimisation of the complete system. Transient simulation capability allows simulation and design of the system parameters during transient events such as altitude change (change in system inlet pressure and temperature as well as humidity levels) under normal operating conditions as well as for abnormal (accident scenarios) conditions. Flownex has the ability to mix gasses such as air and water vapour, thus allowing the prediction of condensation and icing on components and can also be used for humidity control design to achieve the required humidity levels. The design of control philosophies for complete systems or individual components can be done while control philosophies for existing systems can be improved by means of simulation before hardware is fabricated.

Schematic of a typical transport aircraft ECS

Environmental Control and Life Support Systems

The Environmental Control and Life Support (ECLS) systems aboard a manned spacecraft or space station are responsible for maintaining a liveable environment within a pressurized crew compartment. These subsystems are required to sustain a liveable environment by providing oxygen, drinking water, waste processing, temperature control, ventilation and CO2 removal.

Typically most of these ECLS systems rely on thermo fluid cycles which include pressurized gas containers, filters, heat exchangers, humidifying/dehumidifying equipment, fans, control valves, pumps, storage tanks, piping and ducting as well as control equipment to manage and maintain the required conditions to sustain life.

ECLS system process flow diagram of the International Space Station

Flownex can be used for the design, simulation and optimization of ECLS systems in spacecraft. Flownex has the ability to track the gas concentration of multi gas mixtures in a system, thus enabling the user to determine gas concentrations during transient events. Flownex also has the ability to mix gasses such as air and water vapour, thus allowing the prediction of condensation and icing on components and can also be used for humidity control design to achieve the required humidity levels. Flownex allows the simulation of multiple subsystems with each other consisting of multiple fluids (gas, liquid and two phase fluids) in a single network, thus assisting in the integration design of complete ECLS. Flownex can assist with the design and simulation of insulation systems in order to regulate, control and minimise temperature variations within spacecraft. The Flownex control library can be used to simulate and design control philosophies of the ECLS. The ability to simulate complete systems allows the user to simulate off design and accident conditions to determine subsystem interaction under abnormal conditions.


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