Investigation of Convective Heat Transfer to Supercritical Carbon Dioxide with Direct Numerical Simulation
Investigation of Convective Heat Transfer to Supercritical Carbon Dioxide with Direct Numerical Simulation
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DOI：
10.1007/978-3-319-24633-8_21
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发表时间：
2016
期刊：
影响因子：
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通讯作者：
X. Chu;E. Laurien
中科院分区：
文献类型：
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作者：
X. Chu;E. Laurien
对于超临界压力下的流体，不存在从液体到气体的相变。同时，在较窄的温度范围内，流体性质发生了很大的变化。以超临界流体为工质，在加热管内观察到了换热劣化和恢复，这与湍流的再分层和恢复相对应。利用开源软件OpenFOAM开发了压力为8 Mpa的垂直加热圆管内超临界二氧化碳流动的直接数值模拟。数值模拟中考虑了强迫对流和向上、向下混合对流两种情况。详细分析了平均流量和湍流统计量的变化。在强制对流中，由于热膨胀的加速，流动的湍流被减弱，从而导致壁面温度的峰值。浮力对水流的影响更大。在上行流动中，由于浮力的“外部”效应，沿水流方向的平均速度分布变为M型分布。此外，密度变化引起的负浮力产生使雷诺切应力几乎为零，这意味着流动是重新分层的。进一步的下游湍流被恢复。湍流的这种特性被湍流条纹和旋涡结构的可视化所证实。对其流动湍流的观测有助于开发先进的湍流模型，以应用于核能或常规能源发电技术。
For fluids at supercritical pressure, the phase change from liquid to gas does not exist. In the meanwhile, the fluid properties change drastically in a narrow temperature range. With supercritical fluid as working fluid in a heated pipe, heat transfer deterioration and recovery have been observed, which correspond to the turbulent flow relaminarization and recovery. Direct Numerical Simulation (DNS) of supercritical carbon dioxide flow in a heated vertical circular pipe at a pressure of 8 MPa is developed with the open-source code OpenFOAM in the present study. Forced convection cases and mixed convection including upward and downward flow have been considered in the simulation. The change of the mean flow and turbulence statistics has been analysed in detail. In the forced convection, flow turbulence is attenuated due to acceleration from thermal expansion, which leads to a peak of the wall temperature. Buoyancy has a stronger impact to the flow. In the upward flow, the average streamwise velocity distribution turns into an M-shape profile because of the “external” effect of buoyancy. Besides that, negative buoyancy production caused by the density variation reduces the Reynolds shear stress to almost zero, which means that the flow is relaminarized. Further downstream turbulence is recovered. This behaviour of flow turbulence is confirmed by visualization of turbulent streaks and vortex structures. The observation of the flow turbulence of this can help to develop advanced turbulence models for applications in nuclear or conventional energy generation technologies.