Heat Transfer Enhancement of Tubes in Various Shapes Potentially Applied to CO2 Heat Exchangers in Refrigeration Systems: Review and Assessment
Heat Transfer Enhancement of Tubes in Various Shapes Potentially Applied to CO2 Heat Exchangers in Refrigeration Systems: Review and Assessment
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DOI：
10.1016/j.ijft.2023.100511
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发表时间：
2023-11
影响因子：
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通讯作者：
Wenguang Li;Sambhaji Kadam;Zhibin Yu
中科院分区：
文献类型：
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作者：
Wenguang Li;Sambhaji Kadam;Zhibin Yu
为了使制冷系统中的二氧化碳（CO2）换热器更高效和紧凑，被动的传热强化方法产生的各种形状的管进行了调查和评估。根据管材的几何特征，将管材分为8类。利用摩擦系数比、努塞尔数比、性能评价标准（PEC）和层流和湍流工况下的强化效率，对每种类型的整体热工水力性能和每种类型中单个管的热工水力性能进行了阐述。引入临界摩擦系数比5，即强化传热管的摩擦系数是光管摩擦系数的5倍，对这些方法进行了评价。对强化传热机理、熵产率分析、第二定律分析和场协同分析进行了探讨。扭曲多边形管、周期性缩放管、螺旋槽管和波纹管的压降大，PEC差。扭曲椭圆管和偏心螺旋管具有较低的压降和较好的PEC性能，是最适合CO2换热器强化传热的被动式换热方式。扭曲椭圆管、扭曲多边形管、周期性缩放管、螺旋波纹管、波形管和偏心螺旋管内的涡的形成、发展和热边界层扰动与强化传热机理有关。对周期性缩放管和扭转椭圆管进行了熵产率分析和场协同分析。在CO2流动条件下，扭曲椭圆管和偏心螺旋管的内外强化传热是值得进一步研究的问题。
To make carbon dioxide (CO2) heat exchangers in refrigeration systems more efficient and compact, passive methods for heat transfer enhancement produced by tubes in various shapes were surveyed and assessed. The tubes were classified into eight types by proposed classification method based on their geometrical features. The overall thermal-hydraulic performance of each type and the thermal-hydraulic performance of individual tubes in each type were elucidated using friction factor ratio, Nusselt number ratio, performance evaluation criteria (PEC) and enhancement efficiency in laminar and turbulent flow regimes. A critical friction factor ratio of 5, i.e. the friction factor of the tube with heat transfer enhancement is five times the factor of the plain tube, was introduced to assess these methods. The mechanism of heat transfer enhancement, entropy generation rate analysis, second law analysis and field synergy analysis were discussed. The twisted polygon tube, periodical convergent-divergent tube, helically corrugated tube and wavy tube suffer from high pressure drop and poor PEC. The twisted elliptical tube and eccentrical helical tube are the most suitable passive methods for enhancing heat transfer in CO2 heat exchangers due to lower pressure drop and better PEC. Vortex formation, development and thermal boundary layer disruption are associated with the mechanism of heat transfer enhancement in the twisted oval tube, twisted polygon tube, periodical convergent-divergent tube, helically corrugated tube, wavy tube and eccentrical helical tube. Entropy production rate analysis and field synergy analysis are applied in the periodical convergent-divergent tube and twisted oval tube. Heat transfer enhancement inside and outside the twisted oval tube and eccentrical helical tube under CO2 flow conditions is worth being studied in the future.