三叶孔板换热器壳程流动及传热数值模拟

Numerical simulation on shell side fluid flow and heat transfer in heat exchanger with trefoil-baffles

三叶孔板换热器是一种新型纵流换热器,广泛应用于核电装备领域。针对目前使用较多的壳程'单元流道'模型的局限性,建立了三叶孔板换热器壳程整体模型,包括进出口接管。采用商用软件FLUENT14.0及RNG k-ε湍流模型对壳程流体流动与传热进行了数值研究,分析了三叶孔板换热器壳程流动与传热特性。结果表明:流经第一块支撑板后,流体已充分发展,并且随着壳程结构周期性变化,传热与压降也呈现周期性变化。在支撑板附近,流体流速变大,形成射流,并且由于支撑板阻挡,在支撑板前面和尾部产生二次流,能有效冲刷管壁,减薄流动边界层,起到强化传热作用。

Heat exchangers with trefoil-baffle are a new type heat transfer device and are widely used in nuclear power system due to their special advantages, with the fluid flowing longitudinally on the shell side. In this study, to avoid the limitation of unit duct model, a whole model for the heat exchanger with trefoil-baffles is established including inlet and outlet nozzles. Based on the RNG k-e model, numerical simulation shell side fluid flow and heat transfer are conducted by using commercial CFD software FLUENT14.0. Characteristics of fluid flow and heat transfer performance on the shell side are analyzed. The results show that the fluid is fully developed after the first trefoil-baffle and the heat transfer coefficient and pressure drop vary periodically along the shell side. Fluid velocity increases gradually and the jet flow forms in the region near baffles. The secondary flow is also produced on two sides of baffles when the fluid flows through the trefoil-baffle. The jet flow and secondary flow can decrease the thickness of boundary layer and enhance the heat transfer.