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Internal heat exchanger performance quantification and comparison testing methods including exploration of the effects of location of measurements and oil in circulation.

Number: pap. 2453

Author(s) : MUSSER A., HRNJAK P., ELBEL S.

Summary

The Internal Heat Exchanger (IHX) is well known for its potential to improve the performance of air conditioning systems. The adoption of alternative, more environmentally friendly, refrigerants such as R744 has brought elevated attention to IHX development due to relatively large performance increases from IHX usage compared to conventional refrigerants. Many alternative refrigerants exhibit performance shortfalls thus furthering the need for system enhancements such as IHX introduction. In addition, the increasing need for even small incremental improvements in systems using conventional refrigerants, and EPA credits for such improvements, has driven the expanded development and implementation of IHXs. The focus of this paper is the evaluation of test methods commonly used for quantification and comparison of the performance of internal heat exchangers and the effects of location of measurements and oil in circulation rates on the measurement accuracy and actual IHX performance. Typical IHX performance measurements yield the heat exchanger capacity, effectiveness, and the refrigerant pressure drop across each side of the heat exchanger. Existing test standards vary widely on the required test conditions, allowable oil in circulation rates, and instrumentation locations. The goal of comparison testing is, of course, to accurately quantify performance while also achieving repeatable results which allow for a fair and useful comparison between IHXs. Test conditions and temperature measurement location can have a large effect on both the accuracy and repeatability of measurements. Conditions close to the saturation dome, i.e. low subcooling or superheat, can make it difficult to accurately determine and control the state point while high superheat presents an unrealistic operating condition which can limit the impact of the IHX. Thermal stratification across the cross section of the IHX tubes can also lead to measurement inconsistency depending on the temperature probe placement. Oil in circulation rates directly factor into the heat exchanger capacity calculations but also can affect the actual heat exchanged. This paper will discuss these effects and their implications on standard development and test facility design.

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Pages: 7

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Details

  • Original title: Internal heat exchanger performance quantification and comparison testing methods including exploration of the effects of location of measurements and oil in circulation.
  • Record ID : 30018874
  • Languages: English
  • Source: 2016 Purdue Conferences. 16th International Refrigeration and Air-Conditioning Conference at Purdue.
  • Publication date: 2016/07/11

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