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Effect of thermo-physical properties on wall superheat at onset of nucleate boiling.

Number: 2539

Author(s) : AKAI S., SUGIMOTO K., ASANO H.

Summary

For further improvement of COP and reduction of refrigerant charge, the use of compact heat exchangers using aluminum multiport tubes are spreading. Multiport tubes have non-circular mini-channels with a hydraulic diameter of less than 1.0 mm, which results in a thicker liquid film at the corners due to surface tension when used as an evaporator. Nucleate boiling at the channel corners would play an important role in evaporative heat transfer. In this study, we proposed to stir the thick liquid by nucleate boiling to improve the heat transfer performance. The method would be effective for zeotropic refrigerant mixture. As the first step, a pool boiling experimental setup had been constructed to measure the wall superheat required for the onset of nucleate boiling (ONB), and the measurement validity was verified. R134a and R1234yf were used as the refrigerant. The heat transfer surface was a smooth circular surface with a diameter of 10 mm. The surface was polished with #400 sandpaper to simulate a surface of general industrial products. Heat flux was gradually increased under saturated condition to measure the wall superheat at the ONB. As a result, the wall superheat at the ONB was higher for R1234yf than R134a and was higher with the lower saturation temperature. The maximum wall superheat degree was 35.5 K for R1234yf at a saturation temperature of 5°C in precise measurements where the heat flux gradually increased to maintain steady state conditions.

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Pages: 9 p.

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  • Original title: Effect of thermo-physical properties on wall superheat at onset of nucleate boiling.
  • Record ID : 30033034
  • 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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