Abstract： The most popularly used fin types in compact heat exchangers are the serrated fins, wavy fins, louvered fins and plain fins. Amongst these fin types the serrated fins assume lot of importance due to its enh...Abstract： The most popularly used fin types in compact heat exchangers are the serrated fins, wavy fins, louvered fins and plain fins. Amongst these fin types the serrated fins assume lot of importance due to its enhanced thermo-hydraulic performance. Thermo-hydraulic design of CHEs （Compact heat exchangers） is strongly dependent upon the predicted/measured dimensionless performance （Colburnj factor and Fanning friction vs. Reynolds number） of heat transfer surfaces. This paper describes the numerical analysis to study the heat transfer coefficient and friction factor of Serrated fins in water medium. CFD （Computational fluid dynamics） methodology has been used to develop the single phase water heat transfer coefficient and friction factor correlations for serrated fins using ANSYS Fluent 14.5. The results are compared with previous air-cooled models and experimental results of water. The water cooled CFD analysis results shows that the Prandtl number has a large effect on the Nusselt number of the serrated fin geometry. Finally, the generalized correlations are developed for serrated fins taking all geometrical parameters into account. This numerical estimation can reduce the number of tests/experiments to a minimum for similar applications.展开更多
The outside serrated integral-fin tubes fabricated by rolling-plowing-extrusion processing were surface-treated through different processes of annealing in hydrogen atmosphere,electrochemical corrosion or sandblasting...The outside serrated integral-fin tubes fabricated by rolling-plowing-extrusion processing were surface-treated through different processes of annealing in hydrogen atmosphere,electrochemical corrosion or sandblasting.The purpose was to eliminate residual stress,clear secondary micro-fins and enhance heat transfer performance.By comparing the surface characteristics,it is found that the finned tubes treated by electrochemical corrosion have the most glabrous surfaces where the fins are almost perfectly reserved.Clear layer cracks can be observed on the top of the fins.These structures are effective in enhancing heat transfer performance when being applied to flow heat exchange.Therefore,the finned tubes treated by electrochemical corrosion are proper for the tubular exchanger with water coolant.The finned tubes treated by sandblasting have rougher surfaces with layer cracks and micro gaps removed.As these structures are useful to clearing adhesive feculence,the tubes are more suitable for the tubular heat exchanger with oil coolant.展开更多
The microstructure, wettability and chemical composition of the butterfly wing surfaces were investigated by a scanning electron microscope, a contact angle meter and a Fourier transform infrared spectrometer. The mic...The microstructure, wettability and chemical composition of the butterfly wing surfaces were investigated by a scanning electron microscope, a contact angle meter and a Fourier transform infrared spectrometer. The micro/nano structural models for hydrophobicity of the butterfly wing surfaces were established on the basis of the Cassie equation. The hydrophobicity mechanisms were discussed from the perspective of biological coupling. The butterfly wing surfaces are composed of naturally hydrophobic material and possess micro/nano hierarchical structures, including primary structure （micrometric scales）, secondary structure （nano longitudinal ridges and lateral bridges） and tertiary structure （nano stripes）. The wing surfaces exhibit high hydrophobicity （contact angle 138°-157°） and low adhesion （sliding angle 1°-3°）. The micromorphology and self-cleaning performance of the wing surfaces demonstrate remarkable anisotropism. The special complex wettability ascribes to a coupling effect of the material element and the structure element. In microdimension, the smaller the width and the bigger the spacing of the scale, the stronger the hydrophobicity of the wing surfaces. In nano-dimension, the smaller the height and the smaller the width and the bigger the spacing of the longitudinal ridge, the stronger the hydrophobicity of the wing surfaces. This work promotes our understanding of the hydrophobicity mechanism of bio-surfaces and may bring inspiration for biomimetic design and preparation of smart interfacial materials.展开更多
文摘Abstract： The most popularly used fin types in compact heat exchangers are the serrated fins, wavy fins, louvered fins and plain fins. Amongst these fin types the serrated fins assume lot of importance due to its enhanced thermo-hydraulic performance. Thermo-hydraulic design of CHEs （Compact heat exchangers） is strongly dependent upon the predicted/measured dimensionless performance （Colburnj factor and Fanning friction vs. Reynolds number） of heat transfer surfaces. This paper describes the numerical analysis to study the heat transfer coefficient and friction factor of Serrated fins in water medium. CFD （Computational fluid dynamics） methodology has been used to develop the single phase water heat transfer coefficient and friction factor correlations for serrated fins using ANSYS Fluent 14.5. The results are compared with previous air-cooled models and experimental results of water. The water cooled CFD analysis results shows that the Prandtl number has a large effect on the Nusselt number of the serrated fin geometry. Finally, the generalized correlations are developed for serrated fins taking all geometrical parameters into account. This numerical estimation can reduce the number of tests/experiments to a minimum for similar applications.
基金Projects(50675070,50930005) supported by the National Natural Science Foundation of ChinaProject(U0834002) supported by the Natural Science Foundation of Guangdong Province,China
文摘The outside serrated integral-fin tubes fabricated by rolling-plowing-extrusion processing were surface-treated through different processes of annealing in hydrogen atmosphere,electrochemical corrosion or sandblasting.The purpose was to eliminate residual stress,clear secondary micro-fins and enhance heat transfer performance.By comparing the surface characteristics,it is found that the finned tubes treated by electrochemical corrosion have the most glabrous surfaces where the fins are almost perfectly reserved.Clear layer cracks can be observed on the top of the fins.These structures are effective in enhancing heat transfer performance when being applied to flow heat exchange.Therefore,the finned tubes treated by electrochemical corrosion are proper for the tubular exchanger with water coolant.The finned tubes treated by sandblasting have rougher surfaces with layer cracks and micro gaps removed.As these structures are useful to clearing adhesive feculence,the tubes are more suitable for the tubular heat exchanger with oil coolant.
基金supported by the National Natural Science Foundation of China(50875108)the Natural Science Foundation of Jilin Province,China(201115162)the Open Fundof Key Laboratory of Bionic Engineering of Ministry of Education,Jilin University(K201004)
文摘The microstructure, wettability and chemical composition of the butterfly wing surfaces were investigated by a scanning electron microscope, a contact angle meter and a Fourier transform infrared spectrometer. The micro/nano structural models for hydrophobicity of the butterfly wing surfaces were established on the basis of the Cassie equation. The hydrophobicity mechanisms were discussed from the perspective of biological coupling. The butterfly wing surfaces are composed of naturally hydrophobic material and possess micro/nano hierarchical structures, including primary structure （micrometric scales）, secondary structure （nano longitudinal ridges and lateral bridges） and tertiary structure （nano stripes）. The wing surfaces exhibit high hydrophobicity （contact angle 138°-157°） and low adhesion （sliding angle 1°-3°）. The micromorphology and self-cleaning performance of the wing surfaces demonstrate remarkable anisotropism. The special complex wettability ascribes to a coupling effect of the material element and the structure element. In microdimension, the smaller the width and the bigger the spacing of the scale, the stronger the hydrophobicity of the wing surfaces. In nano-dimension, the smaller the height and the smaller the width and the bigger the spacing of the longitudinal ridge, the stronger the hydrophobicity of the wing surfaces. This work promotes our understanding of the hydrophobicity mechanism of bio-surfaces and may bring inspiration for biomimetic design and preparation of smart interfacial materials.
