Influence of compressor oil contained in the CO2 refrigerant on evaporative heat transfer and its visualization

Name: Keeni, Jyoji

Organization : Mie University. Graduate School of Engineering

Name: Hatano, Atsuki

Organization : Mie University. Faculty of Engineering

Name: Wai, Thiri Shoon

Organization : Mie University. Graduate School of Engineering

Name: Maruyama, Naoki

Organization : Mie University. Graduate School of Engineering

Email : maruyama.naoki@mie-u.ac.jp

Name: Hirota, Masafumi

Organization : Aichi Institute of Technology. Faculty of Engineering

LCSH: Carbon dioxide

LCSH: Refrigerants

LCSH: Heat -- Transmission

LCSH: Visualization

LCSH: Lubricating oils

Abstract: Natural refrigerants with minimal impact on global warming are gaining attention for use in low-temperature refrigeration systems. Among these, CO₂ is particularly suitable due to its non-toxic properties and ability to cool to -35 °C. However, a challenge arises when compressor oil mixes with the refrigerant, causing a reduction in the heat transfer coefficient. This study aims to evaluate the effect of varying compressor oil concentrations on the heat transfer performance of CO₂ refrigerant in the evaporator of a CO₂ refrigerator, using flow visualization techniques. The evaporator used in this experiment simulated horizontal flow, with a tube diameter of 4.5 mm and a channel length of 300 mm, divided into 10 sections. A high-speed camera was introduced to visualize and analyze the behavior of the compressor oil within the CO₂ refrigerant. The experimental conditions reflected practical equipment settings, with a CO₂ refrigerant evaporation temperature of approximately -35 °C, a mass flux of 120 kg/(m²∙s), and compressor oil concentrations ranging from 0 to 10 wt%. The results showed that at 10 wt% oil concentration, the heat transfer coefficient of the CO₂ refrigerant was approximately 2 kW/(m²∙K), representing a reduction of up to 75% compared to CO₂ refrigerant without oil. Furthermore, the heat transfer coefficient at 10.1 wt% oil concentration was about half that of the 2.6 wt% concentration. This demonstrates that even small amounts of compressor oil significantly reduce the heat transfer coefficient. The difference in oil thickness became clearly visible through the visualization method as the oil concentration increased. This increase in oil thickness raised the thermal resistance, resulting in a decline in the heat transfer coefficient with higher compressor oil concentrations

King Mongkut's University of Technology North Bangkok. Central Library

Address: BANGKOK

Email: library@kmutnb.ac.th

Created: 2024

Modified: 2025-08-19

Issued: 2025-08-19

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BibliograpyCitation : In Thai Society of Mechanical Engineers (TSME) and Kasetsart University (KU). The 14th TSME International Conference on Mechanical Engineering (TSME-ICoME14 2024) (TSF0009). Chonburi : Kasetsart University Sriracha Campus, 2024

eng

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