Browse Publications Technical Papers 2012-01-1048

Evaporator with Integrated Ejector for Automotive Cabin Cooling 2012-01-1048

The ejector is a fluid pump that recovers expansion energy, which is wasted in the conventional refrigeration cycle decompression process, and converts the recovered expansion energy into pressure energy. In the ejector cycle, the ejector helps to reduce power consumption of the compressor by using the above mentioned pressure-rising effect. Consequently, the ejector system can improve energy efficiency of the refrigeration cycle. In previous work, the ejector cycle was used to reduce power consumption in refrigeration cycles for a cool-box (a beverage cooling inside the vehicle) and refrigerated truck box. Both of these applications used the ejector to achieve refrigerant pressure/temperature below the vehicle cabin temperature. Now, the ejector has been integrated into the vehicle cabin evaporator to reduce power consumption of the refrigeration cycle for vehicle cabin cooling.
The ejector system for passenger vehicle cabin air conditions systems was introduced into the market May, 2009. It consists of an ejector which is integrated into the upper tank of the evaporator and a flow-control valve used to regulate the flow and maintain super heat to the compressor. Having the ejector integrated into the evaporator upper tank means there was no impact to vehicle packaging space from adding the ejector.
The ejector evaporator operation starts with the liquid refrigerant from the condenser (receiver) entering the flow control valve. The slightly expanded refrigerant from the flow control valve is separated into the capillary tube which feeds the down-wind evaporator, and the ejector which feeds into the up-wind evaporator. As explained above, the ejector acts like a pump; in this case pumping refrigerant from the down-wind evaporator to the up-wind evaporator. The downwind evaporator operates at a lower refrigerant pressure/temperature to further cool the air which is exiting from the up-wind evaporator. The air is essentially cooled in two stages. The result is this newly-developed ejector system for vehicle cabin air conditioning can reduce power consumption of the compressor by up to 25% compared to conventional air-conditioning systems. This corresponds to 2.5% improvement in fuel economy; results will vary depending on ambient conditions and vehicle specifications.
Some of the challenges in developing the evaporator with integrated ejector were noise and temperature distribution. To reduce the refrigerant noise level, countermeasures had to be taken to reduce the noise created when the refrigerant exited the capillary tube at a high velocity which would impact the inside wall of the evaporator tank. To solve this, the exit of the capillary tube was increased, which reduced the refrigerant velocity and noise level. Another challenge was temperature distribution of the exit air. Another challenge was using the ejector in wide evaporators. Use in wide evaporators caused a very large temperature distribution which is difficult to countermeasure. This resulted in a new study for the next generation evaporator with integrated ejector.


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