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Development of MODELICA Libraries for ECS and Thermal management architectures

Periodic Reporting for period 2 - MALET (Development of MODELICA Libraries for ECS and Thermal management architectures)

Reporting period: 2017-09-01 to 2019-02-28

The goal of this project is the development of Modelica libraries (Dymola compatible) to simulate Electrical Environmental Control System (E-ECS) architectures including thermal management perimeter. The efforts have been focused on developing an optimized model to simulate vapour cycle systems (VCS) and liquid loop systems (LCU) at both steady state and transient operational conditions. In addition, an appropriate strategy needs to be adopted to couple the thermal and the electrical environments to achieve an integrated simulation of the complete architecture.

E-ECS architectures include different cooling systems and electrical components which are being modelled within this project. The system/components to be modelled are:

• Vapour cycle systems (VCS), including compressors, reservoirs, valves, heat exchangers, etc.

• Liquid loop systems (LCU), including pipes, pumps, cold plates, heat exchangers, liquid and diphasic coolants, etc.

• Air cycle systems (ACU), including compressors, turbines, air-to-air heat exchangers, fans, sprayers, etc.

• Electrical components, such as power electronics and electrical motors.

A multi-level approach has been considered given the object-oriented nature of Modelica. In general, components are modelled based on their appropriate governing equations (e.g. conservation law of energy, mass and momentum), needed empirical information (e.g. heat transfer correlations), and needed relevant parameters (e.g. compressor efficiencies). However, the modelling will be carried out considering different levels of detail.

System simulations are being performed at both steady state and transient conditions. The computation time will be optimized based on the multi-level approach (i.e. by using simplified component models) but also by implementing/combining different resolution methodologies. The appropriate component level will be chosen according to the needs of the specific development/design phase. In addition, a methodology for coupling the thermal and electrical architectures will be developed in order to simulate a complete E-ECS architecture.
The work has been evolving from the beginning of the project, following the main project plan, while focusing the attention on the critical aspects highlighted by the Topic Manager. VCS (vapour compression cycle) cycle and its two-phase flow nature (centralized in the corresponding heat exchangers, evaporator and condenser) have been identified as the central parts of the project as implying a high non-linear behaviour at component and cycle level. Moreover, this cycle is embedded in the overall ECS system in an intermediate position between liquid and air cycles, taking even more importance its robust resolution in order to achieve the objective of simulation and optimization of the whole ECS including its thermal management perimeter. The developments at VCS level have been also the baseline platform to start the developments on the liquid and air loops.

The evolution of the project has led to the following achievements:

• VCS centrifugal compressor calibration by performance maps.
• VCS tank and valves calibration by LTS parameters.
• VCS air condenser calibration and liquid evaporator fit by look-up tables.
• HEX updated Switching Moving Boundary (SMB) approach model developed.
• CLLCU liquid dry air and liquid moist air heat exchangers calibration.
• HLLCU fit based on CLLCU results.
• ACU compressor, turbine and valves calibration.
• ACU air-air condenser; air-air evaporator and air-air heat exchanger adjustment based on Topic Manager reference data.

• VCS system model development.
• CLLCU and HLLCU system model development.
• ACU system model development.
• Electrical model system and control development.

• VCS + electrical system calibration at both transient and steady state conditions.
• LCU + electrical system calibration including multiple branches on-off control conditions.
• VCS+LCU+electrical system calibration
• VCS+CLLCU and VCS+HLLCU system calibration in a separate manner.
• Complete ECS unit validation test: VCS+LCU+ACU system analysis.
In the latest decades, the preferred solution for large aircraft environmental control systems has been the air cycle machine (ACM) which heats the cabin from compressor air bleeding and cools it via an air cycle. The main advantages of such approach include compactness, lightness, reliability, reduced cost and the fact that it provides a full solution to cooling/heating but also to ventilation and pressurization. The most relevant drawback is related to its relatively low efficiency which is particularly low during ascent/descent and when the aircraft is on ground (ram air flow must be forced with a fan). The later aspect is more significant as the air cycle system is by far the larger energy consumer of all non-propulsive energy aboard.
In most large aircrafts air is bled from the engine compressor and conditioned through the air cycle machine. However, recent developments towards a more electric airplane include an electrically driven air conditioning system. These new architectures will have an increase on both weight and electrical power consumption but the no-bleed engine fuel savings will also increase resulting in an overall energy save.

The development of the optimum E-ECS architecture relies in the use of advanced simulation tools for both the whole system behavior and its components. The MALET simulation tool include the following important aspects: steady state and transient analysis, multi-level approach, integration of thermal and electrical perimeters, combination of multiple loops in order to simulate full complex systems with their most important details.

The present project goal is the development of Modelica libraries including several features that will allow a more flexible, detailed and complete simulation of E-ECS systems. The final product will allow selecting the more suitable E-ECS architecture and to optimize it according to the defined constraints.

The project has a huge potential in terms of Contribution to the European Competitiveness by achieving a significant reduction of fuel consumption and environmental pollution while increasing energy efficiency and aircraft safety, and developing project results with large possibilities of industrial and sector-wide applications.

The Topic Manager is one of the leading companies in the world producing Environmental Control Systems for the aircraft industry. Considering that the use of the more electric aircraft concept is already in the market through the Boeing 787, the implementation of advanced ECS and cooling concepts for the more electric aircraft at the European level is of crucial importance in order to maintain its future competitiveness in the Aeronautics sector against other companies. On the other hand, the development of advanced libraries for the analysis of complex cooling and air treatment systems like those found in the E-ECS will allow the exploitation of these simulation technologies by the Consortium in other sectors, while at the same time giving competitive advantage to those industries as well.
SMB approach: evaporator modes and transitions
Air recirculation cooling system layout