Flow stratification of supercritical CO2 in a heated horizontal pipe
Flow stratification of supercritical CO2 in a heated horizontal pipe
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DOI：
10.1016/j.supflu.2016.05.003
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发表时间：
2016-10-01
影响因子：
3.9
通讯作者：
Laurien, Eckart
中科院分区：
文献类型：
--
作者：
Chu, Xu;Laurien, Eckart
采用直接数值模拟（DNS）方法研究了超临界CO2在水平管内的传热。一个好的DNS解决了湍流模型带来的不确定性。具有适度低的入口雷诺数（Re-0 = 5400）的小管道直径（D = 1 mm，2 mm）可以与紧凑型热交换器（例如印刷电路热交换器（PCHE））中的通道流进行比较。在我们的模拟中，流入温度To被设定为低于伪临界温度T-pc。在加热条件下，当流体温度升高超过T-pc时，热物理性质迅速变化。在本DNS中，发现壁温T-w在周向方向上是可变的。T-w的大小在顶部比在底部表面高。由于浮力的作用，在管道上部区域形成了低密度的流动分层。波浪线（z）上的流向速度场（U）也被流动分层修改。周壁附近的低速流动首先被加热，并被二次流输送到顶部区域。由于密度高，高速散装流体集中在底部。同时还观察到，湍流动能和径向湍流热通量在上表面附近受到强烈抑制。动量输运和传热的衰减增强了流动分层。进一步的分析表明，在这个位置的湍流产生显着减少。(C)2016爱思唯尔B. V.保留所有权利。
Heat transfer to supercritical CO2 in a horizontal pipe is investigated using direct numerical simulation (DNS). A well resolved DNS eliminates the uncertainty brought by turbulence modeling. The small pipe diameter (D = 1 mm, 2 mm) with a moderately low inlet Reynolds number (Re-0 = 5400) can be compared to the channel flow in a compact heat exchanger, e.g. a printed circuit heat exchanger (PCHE). In our simulation, the inflow temperature To is set to be lower than the pseudo-critical temperature T-pc. The thermo-physical properties change rapidly when the fluid temperature rises across T-pc under heating conditions. In the present DNS, the wall temperature T-w is found to be variable in the circumferential direction. The magnitude of T-w is higher at top than at the bottom surface. As a result of buoyancy, flow stratification with low density in the upper region of pipe is developed. The streamwise velocity field (U) over tilde (z), is also modified by the flow stratification. Low-velocity flow near the circumferential wall is heated firstly and transported to the top region by the secondary flow. High-velocity bulk fluid is concentrated at the bottom as a result of high density. It is also observed that the turbulent kinetic energy and the radial turbulent heat flux are strongly suppressed near the top surface. The attenuated momentum transport and heat transfer enhance the flow stratification. A further analysis shows a significantly decreased turbulence production in this position. (C) 2016 Elsevier B.V. All rights reserved.