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结合螺旋管圈和垂直管圈的特点,阐述了变压运行下超临界压力及超超临界压力直流锅炉水冷壁产生水动力不稳定和传热恶化的原因及其解决问题的方法.介绍了近几年在国产机组中出现的螺旋管圈水冷壁的结构,其基本型式是螺旋管圈与垂直管圈相结合,并分析了该结构型式的技术特点.认为采用螺旋管圈水冷壁可提高水动力稳定性、抗燃烧干扰能力和运行可靠性,能抑制传热恶化,尤其是内螺纹管的变压运行技术性能较优越,因此,螺旋管圈水冷壁必将成为超临界压力及超超临界压力直流锅炉水冷壁的主要结构型式. 相似文献
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Chiranjeeva Rao Seela B. Ravisankar 《Energy Sources, Part A: Recovery, Utilization, and Environmental Effects》2018,40(21):2564-2571
This work investigates the suspension duration of the nanosized multiwalled carbon nanotubes (MWCNT) and aluminum oxide (Al2O3) in B20, B50 and B70 blends of Jatropha Methyl ester. The MWCNT and aluminum oxide (Al2O3) are added to the fuel blends in the proportions of 50 and 100 pmm separately by ultra sonication. The prepared fuel samples are characterized, and turbidity analysis was done to find the stability rate of nano-additives. The outcomes reveal the maximum stability rate for MWCNT and Al2O3 as 83.3% and 87.03%, respectively, with 50ppm in B20 over a period of eighteen days. A considerable drop in suspension was observed with the 100 ppm MWCNT and Al2O3 biodiesel blends. 相似文献
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Ahmed Waheed Mustafa 《亚洲传热研究》2019,48(2):624-643
The heat transfer density rate from a row of rhombic tubes cooled by forced convection is maximized based on constructal design. A row of parallel rhombic tubes are placed in a fixed volume, the horizontal axis of the tubes is kept constant while the vertical axis of the tubes and the spacing between the tubes are changed to facilitate the heat flow from the tubes to the coolant. The tubes are kept at constant temperature and the incoming free‐stream flow is induced by constant pressure drop. For steady, two‐dimensional, incompressible, and laminar forced convection, the governing equations are solved numerically by finite volume method with SIMPLE algorithm. The dimensionless pressure drop (Bejan number, Be) ranging from 10 3 to 10 5, the range of the vertical axis of the tube is 0.2 ≤ B ≤ 2, and the working fluid is air ( Pr = 0.71). The results show that the optimal spacing decreases and the maximum heat transfer density increases as the Bejan number increases for all vertical axes of the tube. Bejan number and the bluntness of the tube have a significant effect of the flow structure (separation and vortex formation) around the tubes at the optimal spacings. 相似文献
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The density of heat transfer rate from a vertical array of flat tubes in cross flow is maximized under fixed pressure drop using constructal design. With the constructal design, the tube arrangement is found such that the heat currents from the tubes to the coolant flow easily. The constraint in the present constructal design is the volume where the tubes are arranged inside it. The two degrees of freedom available inside the volume are the tube‐to‐tube spacing and the length of the flat part of the tubes (tube flatness). The tubes are heated with constant surface temperature. The equations of continuity, momentums, and energy for steady, two‐dimensional, and laminar forced convection are solved by means of a finite‐volume method. The ranges of the present study are Bejan number (dimensionless pressure drop) (103 ≤ Be ≤ 105) and tube flatness (dimensionless length of the tube flat part) (0 ≤ F ≤ 0.8). The coolant used is air with Prandtl number (Pr = 0.72). The results reveal that the maximum heat transfer density decreases when the tube flatness decreases at constant Bejan number. At constant tube flatness, the heat transfer density increases as the dimensionless pressure drop (Bejan number) increases. Also, the optimal tube‐to‐tube spacing is constant, irrespective of the tube flatness at constant Bejan number. 相似文献
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