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Study on oil behavior at branch of suction line in automotive refrigeration cycle.

Number: 2522

Author(s) : ONISHI T., FUKUTA M., MOTOZAWA M.

Summary

Recent automotive air conditioners need many functions, such as multiple the air conditioning spaces inside the car and cooling the batteries of electric vehicles and the automotive air conditioning system, therefore, are becoming increasingly complex. A certain amount of refrigeration oil is discharged from a compressor and circulates in the system with refrigerant, and the oil behavior in the system also becomes complicated. In a system having two evaporators, there is no problem with oil returning when both evaporators are in operation. However, when one of the evaporators stops, part of the oil flows into a branch pipe in a suction line connected to the unoperated evaporator and the oil accumulates in it. It results in a reduction in oil return to the compressor. Consequently, it may cause the compressor failure. Generally, the branch of pipe from the unoperated evaporator is connected to the top of the suction line with a vertical pipe to prevent the oil from flowing to the unoperated evaporator, but the oil disperses as droplets at the branch by breakup of the oil film and flows into the unoperated evaporator. To establish a design criterion for the pipes in the suction line, the oil behavior at the suction line with branch is necessary to be clarified. In this study, visualization of oil droplets dispersed at the confluence was carried out and the droplet size of dispersal oil and the amount of accumulated oil in the branch pipe were measured by changing the compressor rotational speed from 4000 rpm to 8000 rpm. A visualization section is installed in the suction line which has an inverted U-shape at the branch, and oil behavior was captured by a high-speed camera under each condition. Annular oil film in the suction line and the breakup of the oil film at the branch were observed in the visualization section. The amount of oil flowing beyond the inverted U-tube at the branch in the visualization section of the suction pipe increases with increasing the compressor rotational speed from 4000 rpm to 7000 rpm. However, the amount of oil accumulation decreased at a higher rotational speed then 7000 rpm. It was found that the oil droplet size distribution differed significantly between 7000 rpm and higher compressor rotational speeds. Collision of large oil droplets on the wall of the vertical pipe, and absorption of scattered oil droplets by the oil film on the wall were observed, and this peculiar oil behavior above 7000 rpm resulted in a decrease in the amount of oil accumulation.

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  • Original title: Study on oil behavior at branch of suction line in automotive refrigeration cycle.
  • Record ID : 30033039
  • Languages: English
  • Subject: Technology
  • Source: 2024 Purdue Conferences. 20th International Refrigeration and Air-Conditioning Conference at Purdue.
  • Publication date: 2024/07/17

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