共查询到17条相似文献,搜索用时 62 毫秒
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本文以氮气和水为工质,在水平矩形小通道(dh=0.99 mm)中对两相流摩擦压降进行了实验研究.实验是在大气压力下进行的,氮气的折算流速的范围为0.017~33.3 m/s,水的折算流速的范围为0.1~5 m/s.实验对所得的219个数据点进行了分析,并同 L & M 关系式、L&L关系式、均相流模型以及均相流修正模型进行了比较,得出(1)L & M关系式比均相流模型、均相流修正模型以及 L & L 关系式的偏差都小,能更好地预测两相流压降变化.(2) L & M 关系式中的C在不同的流型(流型是由UGS、ULS以及dh决定)具有不同的值,在同一ULS下,C随X(UGS)的变化呈现一定的规律性,在X=7左右,C出现最大值,而此处恰好是块状流最激烈区域.但是C随ULS没有一定的规律性. 相似文献
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分别以0.2%、0.5%、1%质量分数的Al2O3-H2O纳米流体和去离子水为实验工质,在高2mm,宽1mm的矩形微细通道内进行纳米流体与非纳米流体两相沸腾传热和压降对比研究。实验结果表明:增加质量通量对两种工质换热系数影响都较小,但增加热流密度可提高换热系数;在相同工况下,与水基液相比,采用Al2O3-H2O纳米流体换热系数明显增大,且随着纳米流体质量分数的增加而增加,对于该实验换热系数可提高8%~17%;随着纳米颗粒质量分数和质量通量的增加,两相摩擦压降显著增大。 相似文献
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Wang Haiyan Liu Riping Ma Mingzhen Jing Qin Li Gong Sun Liling Wang Wenkui 《中国科学G辑(英文版)》2005,48(2):658-666
Solidification of 0.1–1.0 mm diameter droplets of Fe-66.7 at.%Si alloy was achieved in a 3 m drop tube. The XRD, EDS, and
SEM measurements reveal that all the droplets are composed of the primary phase α and the α+ε eutectic. With decreasing droplet
diameter, the growth mode of the primary phase α changes from faceted to nonfaceted growth and the eutectic changes from needle-like
to anomalous eutectic. In addition, the width of the primary phase α decreases with decreasing droplet size. The different
cooling rates and undercooling levels corresponding to the samples with different sizes are responsible for the morphology
changes. The cooling rates of the samples with different diameters during free fall were calculated and their effects on the
microstructure formation were discussed. This kind of transition is also found inside the same sample, which is due to the
larger cooling rate on the surface than at the center. 相似文献
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WANG Haiyan LIU Riping MA Mingzhen JING Qin LI Gong SUN Liling & WANG Wenkui . Key Laboratory of Metastable Materials Science & Technology Yanshan University Qinhuangdao China . Institute of Physics Chinese Academy of Sciences Beijing China 《中国科学G辑(英文版)》2005,48(6):658-666
Because of their unusual optical, thermoelectric, and magnetic properties, iron sili- cides have attracted considerable attention in recent years. Among them, particular at- tention has been paid to the orthorhombic semiconducting iron disilicide β-FeSi2 due to its direct band gap of about 0.85 eV at room temperature, which makes it a candidate material to be used in optoelectronic devices in near-infrared light sources and detectors. In addition, β-FeSi2 has good physical and chemical sta… 相似文献
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It is widely accepted that the frictional pressure drop is impossible to be negative for pipe flow. However, the negative frictional pressure drops were observed for some cases of two-phase slug and churn flows in pipes, challenging the general sense of thermodynamic irreversibility. In order to solve this puzzling problem, theoretical investigations were performed for the entropy generation in slug and churn flows. It is found that the frictional pressure drop along with a buoyancy-like term contributes to the entropy generation due to mechanical energy loss for steady, incompressible slug and churn flows in vertical and inclined pipes. Experiments were conducted in a vertical pipe with diameter as 0.04 m for slug and churn flows. Most of the experimental data obtained for frictional pressure drop are negative at high gas–liquid ratios from 100 to 10,000. Entropy generation rates were calculated from experimental data. The results show that the buoyancy-like term is positive and responsible for a major part of entropy generation rate while the frictional pressure drop is responsible for a little part of entropy generation rate, because of which the overall entropy generation due to mechanical energy loss is still positive even if the frictional pressure drop is negative in vertical slug and churn flows. It is clear that the negative frictional pressure drops observed in slug and churn flows are not against the thermodynamics irreversibility. 相似文献
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This paper applies techniques of containerless processing, drop tube and glass fluxing, to undercool and solidify Ni77P23 alloys. Different diameter spheres were collected at the bottom of a 52-m long drop tube. Both crystalline and amorphous phase were formed in various size specimens due to the different cooling rate. The variation of partial undercooling with bulk undercooling is calculated for the Ni77P23 alloys. The deep undercooling and rapid solidification behaviour of Ni77P23 melts has been analysed with respect to microstructure formation and transition during fluxing and 52-m drop process of undercooled melts. 相似文献
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研究了空气质量含量在2%~13%,汽油蒸汽和空气的混合气体在水平管内的冷凝换热。并分析了不凝气体质量分数对管内冷凝换热的影响规律。得到Co随Re变化的冷凝换热系数的实验关联式。 相似文献