Numerical Prediction of Natural Convection in a Vertical Annulus Closed at Top and Opened at Bottom
Numerical Prediction of Natural Convection in a Vertical Annulus Closed at Top and Opened at Bottom
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DOI：
10.1080/01457632.2013.695214
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发表时间：
2013-01
影响因子：
2.3
通讯作者：
S. Lal;V. A. Kumar
中科院分区：
文献类型：
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作者：
S. Lal;V. A. Kumar
对顶部封闭、底部开放的垂直环空中的自然对流流动进行了数值预报。将环空的外圆柱面冷却到较低温度，并将热流体保持在开放端温度以下。内筒和环空顶壁隔热。所用的数值技术是一种二阶精度的有限元/有限体积法。开口处的压力边界条件与迭代格式相结合，用于预测进、流出流区和速度分布。开发的内部程序已经通过求解开口垂直环空的自然对流得到了验证。用流线、等温线、等容度等值线图，以及绝热壁面速度、体积比、努塞尔数和温度的变化，给出了环空内的流动和换热特性。在瑞利数较高时，由于具有典型的流型，环空换热具有明显的空间变化，而在瑞利数较低时，环空内的换热受上游导热的影响。得到了平均努塞尔数和流量与瑞利数(在103~105之间)和百分比间隙比(从2到20之间)之间的函数关系式。
A numerical prediction for natural convection flow in a vertical annulus closed at the top and opened at the bottom is presented. The outer cylindrical surface of the annulus is cooled to a low temperature, and a hot fluid is maintained below the open end temperature. The inner cylinder and the top wall of the annulus are insulated. The numerical technique used is a second-order accurate hybrid finite-element/finite-volume method. A pressure boundary condition at the opening in conjunction with an iterative scheme is employed to predict the regions of inflow and outflow and the velocity distributions. An in-house code developed has been validated by solving the natural convection through an open-ended vertical annulus. The characteristics of flow and heat transfer in the annulus are presented using contour plots of streamlines, isotherms, and isovorticities, and variations of velocity, volume rate of flow, Nusselt number, and temperature of adiabatic wall. Heat transfer through the annulus is subjected to sharp spatial variations due to the typical flow pattern at high values of Rayleigh number and is influenced by upstream conduction at low values of Rayleigh number. Correlations for average Nusselt number and volume rate of flow are obtained as functions of Rayleigh number (in the range of 103 to 105) and percentage gap ratio (from 2 to 20).