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Optical measurements of liquid film thickness during condensation in a small diameter tube.

Number: 2409

Author(s) : BERTO A., LAVIEILLE P., AZZOLIN M., BORTOLIN S., MISCEVIC M., DEL COL D.

Summary

The measurement of heat transfer coefficient together with liquid film thickness is fundamental to better understand heat transfer mechanisms involved during annular flow condensation. However, the experimental measurement of the liquid film thickness is challenging when considering small diameter channels which have recently been increasingly used by industries. The present work addresses this problem presenting experimental measurements of liquid film thickness and heat transfer coefficients during vertical downflow condensation inside a 3.38 mm inner diameter channel. The test section is composed of two heat exchangers made of copper and connected with a glass tube. Liquid film thickness measurements are performed in the glass window, while the heat transfer coefficient is measured in the two heat transfer sectors. The glass tube has been designed and machined with a special external shape that, as a lens, produces a magnification of the liquid film thickness and allows the use of a chromatic confocal sensor. The liquid film thickness is determined by coupling a shadowgraph technique with the measurements performed by the chromatic confocal sensor. These techniques allow to accurately determine the liquid film thickness without disturbing the two-phase flow. Condensation tests have been run with refrigerant R245fa at 40 °C saturation temperature and mass velocity ranging from 50 kg m−2 s−1 to 150 kg m−2 s−1. The measured values of heat transfer coefficient and liquid film thickness are presented and analyzed together to investigate the effect of waves on the condensation heat transfer.

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Pages: 10 p.

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  • Original title: Optical measurements of liquid film thickness during condensation in a small diameter tube.
  • Record ID : 30030716
  • Languages: English
  • Subject: Technology
  • Source: 2022 Purdue Conferences. 19th International Refrigeration and Air-Conditioning Conference at Purdue.
  • Publication date: 2022

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