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Effect of fractionation on ejector and system performance in R1234yf/R32 refrigeration system.

Number: 2394

Author(s) : HAIDER M., ELBEL S.

Summary

The fractionation and the composition shift in the zeotropic refrigerant systems adds complexity in their design. Though several studies have shown that the zeotropic refrigerants can improve the system performance of a conventional refrigeration cycle, its impact on an ejector system performance has not been studied systematically. This study numerically investigates two different ejector systems along with a baseline system to understand if the fractionation can improve the performance of system that employs R1234yf/R32 zeotropic mixture as working fluid. The study first introduces the modeling approaches employed to model system components like ejector, heat exchangers, compressor, and separator with fractionation. The performance of the ejector is predicted using the Kornhauser model while considering three different refrigerant mixture compositions at the motive inlet, the suction inlet, and the diffuser exit. The heat exchangers are modeled using harmonic weighted LMTD method, while the variable speed compressor is modeled using ten-coefficient polynomials. For system level investigation, a baseline system model working on a conventional vapor compression cycle is developed in MATLAB. It is assumed that there is no composition shift due to the differential hold up inside the microchannel heat exchangers and the connecting pipes. The first investigated ejector system is working on a standard ejector cycle (SEC) and has a separator in the cycle layout. The fractionation effects that cause high-volatile substance rich composition to move through the high-side and low-volatile substance rich composition to move through the low-side of the cycle, are present in the SEC system due to the separator. The fractionation inside the separator is predicted under uniform pressure and temperature assumption. The second ejector system is working on a condenser outlet split (COS) cycle which employs a receiver. Thus, it is assumed that there are no fractionation effects in the COS system. The study reports that for an ejector as a component, the fractionation improves its performance. The study evaluates the ejector performance with a composition shift at the motive and the suction port for R454B and R454C. It is predicted that the ejector efficiency increases by 7% for an equal composition shift scenario for both the refrigerant mixtures. However, the study also finds that the gain in the ejector performance due to fractionation couldn’t translate into an increase in the system COP for the matched capacity conditions. The SEC system’s COP decreases by -3% with fractionation for the composition with the maximum temperature glide. However, a gain of 45% in the COP is predicted for a hypothetical scenario of no fractionation for the same composition. Similarly, in the COS system with no fractionation effects, a 10% gain in COP is predicted for the mass entrainment ratio that has the highest COP. These numerical calculations are crucial to set the direction of future experimental studies where the ejector cycle architectures that avoid fractionation inside the separator like the COS cycle, should be investigated.

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  • Original title: Effect of fractionation on ejector and system performance in R1234yf/R32 refrigeration system.
  • Record ID : 30030709
  • Languages: English
  • Subject: Technology
  • Source: 2022 Purdue Conferences. 19th International Refrigeration and Air-Conditioning Conference at Purdue.
  • Publication date: 2022

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