521 / 2018-12-31 23:07:05

Numerical investigation on flow and heat transfer of liquid in micropillars at low Reynolds number (低雷诺数下液体在微柱群中流动与传热的数值研究)

minichannel; micropillar groups; numerical simulation; heat transfer enhancement (小通道；微柱群；数值模拟；强化传热)

全体主题 > 数值模拟、建模与CFD

Micropillars in minichannels can increase the heating area and produce turbulence, which can enhance heat transfer, but they also produce flow resistance to the fluid. The existence of the micropillars may result in more complex flow and heat transfer characteristics in the channels. How to select the optimal structure of micropillars to achieve the best heat transfer performance at the minimum pressure drop is the focus of the investigation.
The flow and heat transfer of water are studied in the range from 25 to 150 Reynolds number in the micropillar groups. A three-dimensional incompressible numerical model is employed, which the upper surface is a heating surface, and the micropillar groups are interpolated, the lower and both sides are adiabatic walls, as shown in Figure 1. The method of numerical simulation investigates the temperature, the velocity distributions and the flow heat transfer characteristics at different Reynolds numbers in micropillar groups with different geometrical parameters, including micropillars diameters d (0.1, 0.25 and 0.5mm), micropillars height h (0.25, 0.5 and 0.75mm), ratios of pitch to micropillars diameter s/d (1.2, 1.5 and 3) and the arrangement (in-line and staggered), simultaneously they compare with no micropillars channel. It was found that the Nusselt number increased with the increase of Reynolds number. The heat transfer of channel with micropillar groups increased obviously, but the pressure loss was also larger than that without micropillars. Meanwhile, the Nusselt number varied with the diameter, the height, the pitch and the arrangement of micropillar groups, then we need to select the optimum size according to the comprehensive consideration.
小通道内的微柱可以增大受热面积同时产生扰流，起到强化传热的作用，但也会对流体产生流动阻力，微柱的存在可能导致通道内更为复杂的流动和传热特性。如何选出最优微柱结构，使通道在最小的压降下达到最佳的换热性能是研究的重点。
本文研究了雷诺数在25～150范围内，水在微柱群中的流动与传热情况。采用三维不可压缩数值模型，上壁面为加热壁面，且内插微柱群，下壁面和两侧为绝热壁面，如图1所示。利用数值模拟研究了不同几何参数，包括微柱直径d（0.1mm、0.25mm、0.5mm）,高度h（0.25mm、0.5mm、0.75mm），间距与直径比s/d（1.2、1.5、3），以及排列方式（直排、错排）在低雷诺数下的温度、速度分布及流动传热特性，同时与无微柱通道作对比。结果表明，努塞尔数随着雷诺数的增大而增强；与无微柱群相比，有微柱群通道传热性能明显增加，但压降也会增大；努塞尔数随着微柱直径、高度、间距及排列方式的改变有着不同的规律，并综合考虑选择最佳尺寸。