共查询到20条相似文献,搜索用时 500 毫秒
1.
利用CFD软件数值研究了颗粒三维有序堆积多孔介质的对流换热问题. 采用颗粒直径分别为14 mm,9.4 mm和7 mm的球形颗粒有序排列构成多孔介质骨架,在多孔骨架的上方有一恒热流密度的铜板. 采用流固耦合的方法研究了槽通道内温度分布和局部对流换热系数的分布以及对流换热的影响因素. 研究结果表明:热渗透的厚度和温度边界层的厚度在流动方向上逐渐增大,并且随流量的增加而减小;当骨架的导热系数比较高时,对流换热随颗粒直径的减小而略有增大;对流换热系数随聚丙烯酰胺溶液浓度的增大而减小,黏性耗散减弱了对流换热.
关键词:
多孔介质
温度场
局部对流换热系数
数值模拟 相似文献
2.
颗粒有序堆积多孔介质对流换热实验研究 总被引:4,自引:0,他引:4
本文采用"瞬态单吹反问题研究方法"对颗粒有序堆积多孔介质内的强制对流换热进行了实验研究。详细研究了颗粒堆积方式变化对多孔介质内对流换热的影响,并对均匀与非均匀颗粒堆积多孔介质内的对流换热特性进行了对比分析。研究表明:通过对颗粒进行合理有序堆积,可以使相应多孔介质内的压降显著降低,其综合换热效率明显提高;通过拟合获得了颗粒有序堆积多孔介质内的宏观流动换热实验关联式,其形式与传统经验公式(Ergun公式和Wakao公式)一致,但部分模型参数值远低于传统经验公式。 相似文献
3.
4.
5.
利用稳态电热拉曼技术测量了碳纳米管纤维对流换热环境下的导热系数. 该方法基于材料拉曼信号与温度之间的关系, 实时探测一维材料在不同电加热(内热源)下的中心点温度, 利用对流环境下的稳态导热模型推导出材料的导热系数, 实现了一维微纳材料热物性的无损化和非接触式测量. 实验发现: 碳纳米管纤维的导热系数远低于单根碳纳米管的导热系数, 但高于碳纳米管堆积床的导热系数. 这表明碳纳米管体材料的热物性主要取决于内部管束的列阵和管束间的接触热阻. 相似文献
6.
7.
我国重载列车广泛采用踏面制动,制动过程中,当车轮温度达到受热极限时,就会造成车轮的疲劳失效。本文通过数值模拟方法,主要研究重载列车在初速度120 km/h时进行紧急制动,车轮各表面温度场和对流换热系数的分布规律。结果表明:在紧急制动中,车轮闸瓦与踏面直接接触的区域温度最高,且在列车制动14 s时该处温度达到最大值478.45 K;在整个制动过程中,车轮踏面的平均温度和对流换热系数都随制动时间呈先增大后减小的趋势;在迎风踏面的上部分和车轮外侧对流换热系数较大,而在迎风踏面下部分和车轮内侧对流换热系数相对较小;到制动结束时,车轮各表面的对流换热系数已基本趋于相同。 相似文献
8.
9.
针对一种返波管常规收集极,实测了电子束在收集极内表面的有效作用面积,以电子能量700 keV、束流7 kA和脉宽50 ns为例,计算了单脉冲时的热功率沉积和平均热流密度。利用通用有限元软件ANSYS,采用脉冲热源加载的方式,在对流换热系数7 000 W/(m2·℃)、水温20 ℃的条件下,得到了收集极10~100 Hz运行时温度历史曲线及温度分布,并比较了不同重复频率下收集极平衡温度与对流换热系数的关系。如果以300 ℃为气体发生显著热脱附的温度阈值,对流换热系数为7000 W/(m2·℃)时,能够满足重复频率50 Hz以下运行,而到100 Hz时,对流换热系数则需增加到104 W/(m2·℃)。根据流体计算公式,给出了不同对流换热系数对应的水流流速。 相似文献
10.
11.
12.
13.
Convective heat transfer coefficients were measured experimentally for a tube immersed vertically in a circulating fluidized bed. Circulating fluidized beds operate in the dilute transport regime of two-phase (solid/gas) flow. The dominant mechanism for heat transfer to surfaces is particle-induced convection. In this study, experiments were carried out in a circulating fluidized bed of15 cm diameter and 11 m height. An instrumented tube of 9.5 mm diameter and 1.3 m length was placed vertically at the centeriine of the fluidized bed to measure convective heat transfer coefficients at several different elevations in the bed. Three types of particles, with mean diameters ranging from 68 to 2S1 urn, were used in the experiments at superficial gas velocities in the range of 1.3 to 8.2 m/s. Results showed that the convective heat transfer coefficients with solid/gas two-phase circulation were two to three times greater than those for single-phase gas convection at the same velocity. For a given gas velocity, the coefficients increased with increasing solid mass flux, but decreased with elevation. It was demonstrated that the heat transfer coefficients for the immersed tube and for the bed wall could be correlated with different functional dependence on the two-phase suspension density. 相似文献
14.
圆管层流脉冲流动对流换热数值分析 总被引:3,自引:0,他引:3
对等热流和等壁温边界条件下圆管内层流脉冲流动对流换热问题进行了数值模拟。在等热流边界条件下的数值计算结果与理论解吻合很好。计算结果表明:在等热流和等壁温边界下脉冲流动可引起速度、温度以及努塞尔数随时间波动,振幅越大,脉冲频率越小,波动越大。但它们的时均值均等于在相同雷诺数下稳态流动的值,脉冲流动不能强化换热。 相似文献
15.
Microfin arrays with fin heights of 100 and 200 μm are fabricated, and natural convection around microfin arrays on a vertical surface is experimentally investigated. Microfins are fabricated by DRIE in a bulk silicon wafer. The array spacing investigated ranges from 30–360 μm, and the temperature difference between the wall temperature of the microfin array and the ambient temperature varies from 20–80 K. For comparison, minifin arrays with a fin height of 1 mm are also tested. The heat loss through the backside of the arrays was avoided by a symmetric design of fin arrays on the vertical surface. The convective heat transfer coefficients are measured and compared with the existing heat transfer correlation for the microfin arrays. It turns out that the heat transfer correlation for macrofin arrays is inadequate for the accurate estimation of the heat transfer rate in microscale systems. In addition, microfin and minifin arrays are also tested on a horizontal surface to examine the orientation effect at small scales. 相似文献
16.
Forced convection heat transfer from a helically coiled heat exchanger embedded in a packed bed of spherical glass particles was investigated experimentally. With dry air at ambient pressure and temperature as a flowing fluid, the effect of particle size, helically coiled heat exchanger diameter, and position was studied for a wide range of Reynolds numbers. It was found that the particle diameter, the helically coiled heat exchanger diameter and position, and the air velocity are of great influence on the convective heat transfer between the helically coiled heat exchanger and air. Results indicated that the heat transfer coefficient increased with increasing the air velocity, increasing helically coiled heat exchanger diameter, and decreasing the particle size. The highest heat transfer coefficients were obtained with the packed-bed particle size of 16 mm and heat exchanger coil diameter of 9.525 mm (1/4 inch) at a Reynolds number range of 1,536 to 4,134 for all used coil positions in the conducted tests. A dimensionless correlation was proposed for Nusselt number as a function of Reynolds number, particle size, coil size, and coil position. 相似文献
17.
带内热源多孔介质中的受迫对流换热 总被引:11,自引:0,他引:11
本文利用扩展型达西流动方程,采用考虑相际传热的能量方程,通过对体平均化原始变量方程的无量纲分析,用Rep,H/dp和ks/kf三个无量纲参数分析了通道内具有内热源多孔介质固定床的冷却过程,讨论内热源对骨架与流体热平衡的影响,对数值计算的结果进行了对比分析. 相似文献
18.
19.
在无扰动、随机式扰动以及正弦式扰动下,通过对竖直恒温面处状态Ra为1.328×10^9、Pr为6.24的自然对流进行模拟,探索了热边界层的不稳定性和共振强化自然对流换热。结果表明:(1)竖直自然对流边界层上游位置的随机式扰动对热边界层的影响主要体现在稳定阶段;(2)该状态下的竖直自然对流边界层的特征频率为15 067,且相比于无扰动状态,频率为15 067的正弦式扰动能在竖直恒温面处提高5.15%的换热量;(3)在竖直自然对流边界层上游位置加入特征频率的正弦式扰动,竖直恒温面处的局部努塞尔数Nu均出现明显波动,且波动随着边界层高度的增加而增大。 相似文献