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首页> 外文期刊>International Journal of Heat and Mass Transfer >Heatline analysis on natural convection for nanofluids confined within square cavities with various thermal boundary conditions
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Heatline analysis on natural convection for nanofluids confined within square cavities with various thermal boundary conditions

机译：不同热边界条件下限制在方腔内的纳米流体自然对流的热线分析

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摘要

Natural convection of nanofluids in presence of hot and cold side walls (case 1) or uniform or non-uni form heating of bottom wall with cold side walls (case 2) have been investigated based on visualization of heat flow via heatfunctions or heatlines. Galerkin finite element method has been employed to solve momentum and energy balance as well as post processing streamfunctions and heatfunctions. Various nanofluids are considered as Copper-Water, TiO_2-Water and Alumina-Water. Enhancement of heat transfer with respect to base fluid (water) has been observed for all ranges of Rayleigh number (Ra). Dom inance of viscous force or buoyancy force are found to play significant roles to characterize the heat trans fer rates and temperature patterns which are also established based on heatlines. In general, convective closed loop heatlines are present even at low Rayleigh number (Ra = 10~3) within base fluid, but all nano fluids exhibit dominant conductive heat transport as the flow is also found to be weak due to dominance of viscous force for case 1. On the other hand, convective heat transport at the core of a circulation cell, typically represented by closed loop heatlines, is more intense for nanofluids compared to base fluid (water) for case 2 at Ra = 10~5. It is also found that heatlines with larger heatfunctions values for nanofl uids coincide with heatlines with smaller heatfunction values for water at walls. Consequently, Nusselt number which is also correlated with heatfunctions show larger values of nanofluids for all ranges of Ra. Average Nusselt numbers show that larger enhancement of heat transfer rates for all nanofluids at Ra = 10~5 and Alumina-Water and Copper-Water exhibit larger enhancement of heat transfer rates.
机译：基于热功能或热线的热流可视化，研究了在冷，热侧壁（情况1）或底壁与冷侧壁的均匀或非均匀加热情况下纳米流体的自然对流（情况2）。 Galerkin有限元方法已用于解决动量和能量平衡以及后处理的流函数和热函数。各种纳米流体被认为是铜-水，TiO_2-水和氧化铝-水。对于瑞利数（Ra）的所有范围，已经观察到相对于基础流体（水）的传热增强。发现粘性力或浮力的主导作用对于表征热传递速率和温度模式也起着重要的作用，这也是基于热线建立的。通常，即使在基础流体中甚至在低瑞利数（Ra = 10〜3）下也存在对流闭环热线，但是所有纳米流体都表现出主导的传导热传递，因为由于粘性力的优势，流动也很弱。案例1。另一方面，在Ra = 10〜5的情况下，与案例2的基础流体（水）相比，纳米流体对循环流体核心的对流传热（通常由闭环热线代表）更为强烈。还发现纳米流体的热功能值较大的热线与壁上水的热功能值较小的热线重合。因此，也与热功能相关的努塞尔数在所有Ra范围内都显示出较大的纳米流体值。平均Nusselt数表明，在Ra = 10〜5时，所有纳米流体的传热速率都有较大的提高，而氧化铝-水和铜-水的传热速率则有较大的提高。

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