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This paper presents a dynamic model of a transcritical air-conditioning system, specifically suited for multivariable controller design. The physically-based model retains sufficient detail to accurately predict system dynamic response while also being simple enough to be of value in determining appropriate control strategies. The control focus would be quasi-steady transitions between operating states by modulating flow rates of both air and refrigerant to meet changing constraints on capacity, efficiency, noise, etc. The model structure is highly modular, accommodating various system configurations and component types. The modeling results are programmed as a library of components for use in Simulink, a graphical programming package.

An experimental methodology and test facility has been developed to perform measurements of internal sound pressure radiated from expansion devices in refrigerant. The experimental test facility is designed to help attenuate reflected sound waves and minimize both vibrations to the test section and other flow disturbances. Measurements are made using microphones mounted flush to the inner wall of the refrigerant tube and the two-microphone technique is used to account for unattenuated reflections. Results show that expansion noise is related to system operating conditions. When vapor flow is present, the far field expansion noise is significant white noise over the audible frequency range. Downstream screens were found to significantly reduce the noise generated. Also, internal sound pressure attenuation with distance has been measured and the results agree closely with theoretical predictions for visco-thermal attenuation.

Reductions of noise in vehicle passenger compartments in recent years have made some previously undetectable noises audible. Expansion devices used in automobile air conditioning systems are known producers of noise. The fact that these devices are mounted very close to the passengers increases the problems associated with the reduction of this noise. The understanding of the propagation mechanisms from the noise generated in the refrigerant by the expansion device, through the tube and evaporator walls, and finally to the outside air is important. This paper will focus on how noise from expansion devices is transmitted through tube walls downstream of the expansion valve.