Effect of lubricating oil on cooling heat transfer of supercritical carbon dioxide
Effect of lubricating oil on cooling heat transfer of supercritical carbon dioxide
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DOI：
10.1016/j.ijrefrig.2006.09.006
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发表时间：
2007-06
期刊：
影响因子：
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通讯作者：
C. Dang;K. Iino;K. Fukuoka;E. Hihara
中科院分区：
文献类型：
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作者：
C. Dang;K. Iino;K. Fukuoka;E. Hihara
对超临界CO2在夹带PAG型润滑油时的冷却换热系数和压降进行了实验研究。试管内径为1 ~ 6 mm。实验在润滑油浓度从0到5%，压力从8到10 MPa，质量通量从200到1200 kgm-2s-1，热通量从12到24 kWm-2的条件下进行。与无油状态相比，润滑油夹带时，换热系数降低，压降增大。传热系数的最大减少-约75%-发生在伪临界温度附近。油的影响是显着的小管径和大的油浓度。通过目视观察，证实了传热的这种劣化是由于沿试管内壁沿着形成富油层。然而，当油浓度超过3%时，不能确认传热系数的进一步劣化，这意味着在主体区域中与CO2一起沿着流动的油不会影响传热系数并且压力显著下降。对于一个大的管在一个较低的质量通量，没有显着的退化，传热系数，直到油浓度达到1%。这是由于对于大管而言，流型从环状分散流转变为波形流，CO2在测试段的上侧流动，富油层在测试段的下侧。
In this research, the cooling heat transfer coefficient and pressure drop of supercritical CO2with PAG-type lubricating oil entrained were experimentally investigated. The inner diameter of the test tubes ranged from 1 to 6mm. The experiments were conducted at lubricating oil concentrations from 0 to 5%, pressures from 8 to 10MPa, mass fluxes from 200 to 1200kgm−2s−1, and heat fluxes from 12 to 24kWm−2. In comparison to the oil-free condition, when lubricating oil entrainment occurred, the heat transfer coefficient decreased and the pressure drop increased. The maximum reduction in the heat transfer coefficients—about 75%—occurred in the vicinity of the pseudocritical temperature. The influence of oil was significant for a small tube diameter and a large oil concentration. From visual observation, it was confirmed that this degradation in the heat transfer was due to the formation of an oil-rich layer along the inner wall of the test tube. However, when the oil concentration exceeded 3%, no further degradation in the heat transfer coefficient could be confirmed, which implies that the oil flowing along with CO2in the bulk region does not influence the heat transfer coefficient and the pressure drops significantly. For a large tube at a lower mass flux, no significant degradation in the heat transfer coefficient was observed until the oil concentration reached 1%. This is due to the transition of the flow pattern from an annular-dispersed flow to a wavy flow for a large tube, with CO2flowing on the upper side and the oil-rich layer on the lower side of the test section.