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Numerical investigation of heat transfer in parallel channels with water at supercritical pressure

机译：超临界水与水平行通道传热的数值研究

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Thermal phenomena such as heat transfer enhancement, heat transfer deterioration, and flow instability observed at supercritical pressures as a result of fluid property variations have the potential to affect the safety of design and operation of Supercritical Water-cooled Reactor SCWR, and also challenge the capabilities of both heat transfer correlations and Computational Fluid Dynamics CFD physical models. These phenomena observed at supercritical pressures need to be thoroughly investigated.An experimental study was carried out by Xi to investigate flow instability in parallel channels at supercritical pressures under different mass flow rates, pressures, and axial power shapes. Experimental data on flow instability at inlet of the heated channels were obtained but no heat transfer data along the axial length was obtained. This numerical study used 3D numerical tool STAR-CCM+ to investigate heat transfer at supercritical pressures along the axial lengths of the parallel channels with water ahead of experimental data. Homogeneous axial power shape HAPS was adopted and the heating powers adopted in this work were below the experimental threshold heating powers obtained for HAPS by Xi. The results show that the Fluid Centre-line Temperature FCLT increased linearly below and above the PCT region, but flattened at the PCT region for all the system parameters considered. The inlet temperature, heating power, pressure, gravity and mass flow rate have effects on WT (wall temperature) values in the NHT (normal heat transfer), EHT (enhanced heat transfer), DHT (deteriorated heat transfer) and recovery from DHT regions. While variation of all other system parameters in the EHT and PCT regions showed no significant difference in the WT and FCLT values respectively, the WT and FCLT values respectively increased with pressure in these regions. For most of the system parameters considered, the FCLT and WT values obtained in the two channels were nearly the same. The numerical study was not quantitatively compared with experimental data along the axial lengths of the parallel channels, but it was observed that the numerical tool STAR-CCM+ adopted was able to capture the trends for NHT, EHT, DHT and recovery from DHT regions. The heating powers used for the various simulations were below the experimentally observed threshold heating powers, but heat transfer deterioration HTD was observed, confirming the previous finding that HTD could occur before the occurrence of unstable behavior at supercritical pressures. For purposes of comparing the results of numerical simulations with experimental data, the heat transfer data on temperature oscillations obtained at the outlet of the heated channels and instability boundary results obtained at the inlet of the heated channels were compared. The numerical results obtained quite well agree with the experimental data. This work calls for provision of experimental data on heat transfer in parallel channels at supercritical pressures for validation of similar numerical studies.
机译：由于流体性质的变化，在超临界压力下观察到的热现象，如传热增强，传热劣化和流动不稳定性，有可能影响超临界水冷反应堆SCWR的设计和运行安全性，并且也对能力产生挑战。传热相关性和计算流体动力学CFD物理模型。在超临界压力下观察到的这些现象需要彻底研究。Xi进行了一项实验研究，研究了在不同质量流量，压力和轴向功率形状下，超临界压力下平行通道中的流动不稳定性。获得了关于加热通道入口处流动不稳定性的实验数据，但未获得沿轴向长度的传热数据。这项数值研究使用3D数值工具STAR-CCM +来研究超临界压力下水在平行通道轴向上沿水的传热，其结果要超过实验数据。采用均质轴向功率形状HAPS，本研究中采用的加热功率低于Xi为HAPS获得的实验阈值加热功率。结果表明，流体中心线温度FCLT在PCT区域以下和上方线性增加，但对于所有考虑的系统参数，在PCT区域均趋于平坦。入口温度，加热功率，压力，重力和质量流率会影响NHT（正常传热），EHT（增强传热），DHT（恶化的传热）中的WT（壁温）值以及从DHT区域恢复。虽然EHT和PCT区域中所有其他系统参数的变化分别显示WT和FCLT值无显着差异，但WT和FCLT值分别随这些区域中的压力而增加。对于所考虑的大多数系统参数，在两个通道中获得的FCLT和WT值几乎相同。没有将数值研究与沿平行通道轴向长度的实验数据进行定量比较，但是观察到采用的数值工具STAR-CCM +能够捕获NHT，EHT，DHT以及从DHT区域恢复的趋势。用于各种模拟的加热功率低于实验观察到的阈值加热功率，但观察到热传递恶化HTD，这证实了先前的发现，即HTD可能在超临界压力下出现不稳定行为之前发生。为了将数值模拟的结果与实验数据进行比较，比较了在加热通道出口处获得的关于温度振荡的传热数据和在加热通道入口处获得的不稳定性边界结果。获得的数值结果与实验数据非常吻合。这项工作要求提供有关超临界压力下平行通道传热的实验数据，以验证类似的数值研究。

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