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An important design objective for an automotive air-conditioning system is ensuring sufficient oil return to the compressor. Maintaining proper lubrication of the compressor extends compressor life and thus minimizes warranty and consumer replacement costs. An automotive air-conditioning test stand capable of monitoring transient system parameters was utilized. Real-time oil concentration data were obtained using an optical, oil-concentration sensor installed in the liquid line. The mass flow rate of the refrigerant-oil mixture and the evaporator superheat were varied with an electronic expansion valve. Steady-state oil concentration data are presented for both saturated and superheated evaporator exit conditions. Experimental oil concentration data taken during system startup and quasi-steady compressor-clutch-cycling conditions are also presented. Steady-state results show that oil return rate is maximized by maintaining a two-phase condition at the evaporator exit.

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.