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Modeling a vapor compression cycle : report internship Aeronamic

Goossens, M. (2015) Modeling a vapor compression cycle : report internship Aeronamic.

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Abstract:Problem area: The assignment was given by Aeronamic - Aircraft Subsystems, Almelo. In the near future, Aeronamic is going to deliver scroll compressors for the Airbus A350. These compressors have to be tested with the use of a test rig of a Vapor Compression Cycle. However, Aeronamic received some conflicted measurement data of the test installation of the Vapor Compression Cycle, which at that moment was placed in the USA. It was useful for Aeronamic to have a theoretical model of the cycle for a better understanding of the Vapor Compression Cycle. The assignment was to make a computer simulation model of the Vapor Compression Cycle. With the simulation model, it may be possible to explain the inexplicable measurement data from the test rig and come up with solutions by for example changing controller settings. Finally, in the future it may also be possible to use the model as an appliance to make it easier to build test rigs for testing other types of scroll compressors. Discussion of work: First, a theoretical analysis of a scroll compressor is made. The geometry of the scroll compressor is obtained from a point cloud from the original CAD-model and is transformed into analytical functions. With the use of these analytical functions some thermodynamic quantities (such as pressure and temperature) are calculated in all of the compression chambers. Also the influence of two types of leakage are investigated. Finally pressure ratios from the inlet to the outlet of the compressor are calculated. Secondly, the working principle of the the test rig of the VCC is explained. A description of the coolant medium phases is given. The entire VCC is also displayed in a Mollier diagram. Also, the different types of used control valves are explained. All these valves are electronically controlled by a step motor. A simulation model is made with xCos, which is a toolbox of the free software Scilab. However, some limitations and errors were found in xCos and it appears not to be a good program for such a complex model as the VCC. A user manual for the xCos simulation model was at that moment already made and can be found in the report. Through consultation with some employees of Aeronamic, Aeronamic decided to buy licenses of Matlab with the toolbox Simulink. A entire description of the Simulink simulation model is given. Finally, a comparison between the test rig test results and the Simulink simulation results is made. Conclusions: Most important conclusion is that the Simulink simulation results show many similarities with the test rig test results. However, during the start-up phase of the compressor there are differences. Reason for this is that there are no mass flows present in the system, which means that the used energy and mass balances in the model are not applicable. The Simulink simulation model is flexible in terms of changing input values and changing the simulation time. Important to note is that the Simulink simulation model simulates approximately 15 times faster than the real test rig. Also changing PID-settings and characteristics of valves (such as position limits and step rate values) is very easy.
Item Type:Internship Report (Master)
Aeronamic B.V., the Netherlands
Faculty:ET: Engineering Technology
Subject:52 mechanical engineering
Programme:Mechanical Engineering MSc (60439)
Keywords:Vapor Compression Cycle, scroll compressors, motorized control valves
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