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Observation of CO2 transcritical expansion process.

Author(s) : FUKUTA M., HIGASIYAMA M., YANAGISAWA T., et al.

Summary

An expander is used to improve cycle performance of a CO2 transcritical refrigeration cycle. An expansion process occurring in the expander operated under typical condition goes from supercritical to subcritical. When the process goes into the two-phase region through a saturated gas line on a p-h diagram, the liquid phase will appear in the gas phase in an expansion chamber, while the gas phase will appear in the liquid phase with the process passing across a saturated liquid line. In general, that kind of transition occurs under non-equilibrium condition. Therefore, the expansion process is complicated and still not clear. In this study, the expansion process in a vane type expander is examined at first. Then, the expansion process is investigated in detail by a simple piston-cylinder expander having a glass window. It is shown that a pressure change under the trans-critical expansion process has an inflection point and it appears with a certain time delay in comparison with an ideal case when the inlet temperature is low. However, no change of appearance inside the expansion chamber is observed even at the inflection point and it takes relatively long time to become a complete two-phase condition. Further study will be done to make clear a flash inception phenomenon and to examine the influence of expansion speed, existence of oil and surface roughness of an inside wall on the transcritical expansion process.

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Details

  • Original title: Observation of CO2 transcritical expansion process.
  • Record ID : 2009-1440
  • Languages: English
  • Source: 2008 Purdue Conferences. 19th International Compressor Engineering Conference at Purdue & 12th International Refrigeration and Air-Conditioning Conference at Purdue [CD-ROM].
  • Publication date: 2008/07/14

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