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RISS 인기검색어
- 검색키워드
- 저자 : Mohammad Zoynal Abedin (검색결과 2 건)
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Abedin, Mohammad Zoynal,Tsuji, Toshihiro,Kim, Nae-Hyun Elsevier 2017 The International journal of heat and fluid flow Vol.65 No.-
<P><B>Abstract</B></P> <P>Time-developing direct numerical simulation (DNS) was performed to clarify the higher-order turbulent behaviors in the thermally-driven boundary layers both in air and water along a heated vertical flat plate. The predicted statistics of the heat transfer rates and the higher-order turbulent behaviors such as skewness factors, flatness factors and spatial correlation coefficients of the velocity and temperature fluctuations in the natural-convection boundary layer correspond well with those obtained from experiments for space-developing flows. The numerical results reveal that the turbulent structures of the buoyancy-driven boundary layers are mainly controlled by the fluid motions in the outer region of the boundary layer, and these large-scale structures are strongly connected with the generation of turbulence in the thermally-driven boundary layers, in accordance with the actual observations for space-developing flows. Moreover, to specify the turbulence structures of the boundary layers, the cross-correlation coefficients and the characteristic length scales are examined for the velocity and thermal fields. Consequently, it is found that with a slight increase in freestream velocity, the cross-correlation coefficient for the Reynolds shear stress and turbulent heat flux increases for opposing flow and decreases for aiding flow, and the integral scales for the velocity and temperature fields become larger for opposing flow and smaller for aiding flow compared with those for the pure natural-convection boundary layer.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Temporal DNS is done for thermally-driven boundary layer along a heated vertical flat plate. </LI> <LI> Turbulent structures are mainly controlled by fluid motions in the outer boundary layer. </LI> <LI> Large-scale structures are strongly connected with the generation of turbulence in the boundary layer. </LI> <LI> Cross-correlation coefficient for velocity and temperature fluctuations increases for opposing flow and decreases for aiding flow compared with the natural-convection boundary layer. </LI> <LI> Integral scales for velocity and temperature fields become larger for opposing flow and smaller for aiding flow compared with the natural-convection boundary layer. </LI> </UL> </P>
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Mohammad Zoynal Abedin,NAE-HYUN KIM 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.12
This paper describes the results of accelerated particulate fouling tests performed on three enhanced tubes and a plain tube. The tests were performed using ferric oxide and aluminum oxide as foulant materials. Three enhanced tubes included 25 start, 10 start helically ribbed tubes and a ripple tube. Effects of the water velocity (0.9 to 1.8 m/s) and foulant concentration (750 to 2500 ppm) were investigated. At 750 ppm, the enhanced tubes fouled almost the same as the plain tube for the entire velocity range tested (0.9 to 1.8 m/s). The enhanced tube fouled faster than the plain tube for cases of high concentration combined with low velocities. Of the three enhanced tubes, the 25 start helically ribbed tube fouled faster than the ripple and the 10 start helically ribbed tubes. One thing to be noted is that the fouling concentrations used in the tests are significantly higher than would be expected in commercial heat exchangers. Also, the velocity range investigated is lower than would be expected in heat exchanger operation.
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