小管径超临界流体传热恶化特性研究

Investigation on Heat Transfer Deterioration Characteristics of Supercritical Fluid in Small Diameter Tube

根据IAPWS公布的IF97临界区比容反推方程重新拟合了超临界区域水的拟临界温度计算公式,进一步提高临界区的水和蒸汽物性计算精度。对水平小管径内超临界水的传热恶化特性进行了实验探究,实验结果表明:当平均流体温度小于拟临界温度时,换热系数出现峰值。平均流体与近壁流体的黏度比达到最大值,换热系数达到峰值;密度比达到最大值,传热恶化已经发生,管内进入拟汽相换热区或发生层流化现象。随着热流密度的增大,换热系数峰值越低;换热系数峰值和传热发生恶化的位置都向低焓值区偏移。

Based on backward equations for IF97-Region 3 published by IAPWS, a fitting formula is proposed to calculate pseudo-critical temperature of supercritical water and steam and the calculation accuracy of the physical properties in Region 3 is approved. A experiment was carried out to analyze the heat transfer deterioration characteristic of supercritical water in small horizontal diameter tube.It results that a heat transfer coefficient peak occurs when the average fluid temperature is lower than the pseudo-critical temperature. When the viscosity ratio of the average fluid to the near-wall fluid reaches the maximum, the heat transfer coefficient peak occurs. When the density ratio reaches the maximum, the heat transfer deterioration characteristic occurs and pseudo-steam heat transfer mechanism or laminarization phenomenon happens at the same time. The higher heat load is, the lower heat transfer coefficient peak is and the heat transfer coefficient peak or deterioration occurs at the lower enthalpy region.