Conductive and viscous sub-layers on forced convection and mechanism of critical heat flux during flow boiling of subcooled water in a circular tube at high liquid Reynolds number
Conductive and viscous sub-layers on forced convection and mechanism of critical heat flux during flow boiling of subcooled water in a circular tube at high liquid Reynolds number
复制标题
DOI：
10.1007/s00231-018-2458-4
复制
发表时间：
2018-08
影响因子：
2.2
通讯作者：
K. Hata;Qiusheng Liu;S. Masuzaki
中科院分区：
文献类型：
--
作者：
K. Hata;Qiusheng Liu;S. Masuzaki
测量了内径为3 mm、加热长度为100 mm的铂圆管的湍流换热、过冷沸腾换热和稳态换热，在较宽的进口过冷度和较宽的流动速度范围内，即RED= 3.01×10~4~1.43×10~5。将稳态一维热传导方程计算的铂圆管内表面温度与作者的湍流换热关联式和K-ε湍流模型的RANS方程(雷诺平均纳维斯托克斯模拟)的数值解进行了比较，得出了从非沸腾段到热膨胀段的导热层厚度，并通过数值分析了强迫对流中导热层和核态沸腾时蒸发所耗散的较薄导热层的厚度。由导电层厚度和受热面表面温度的普朗特数估算了强迫对流中粘性子层的厚度。此外，还根据不同流速下的实测值外推了CHF点处的导电层厚度。CHF的实验值还与作者广泛而精确地预测的过冷水流动沸腾临界热流密度关联式以及其他研究者提出的相应的液体亚层干涸模型的理论值进行了比较。作者的关联式和其他研究人员的理论值可以分别在−13.27%~6.76%和 − 32.51%~13.16%的范围内代表本研究得到的过冷沸腾CHF。根据实验数据，再次证实了在高液体雷诺数下，过冷水在垂直圆管上流动沸腾的临界热流密度的主要机制是什么。在d= 3 mm和L= 100 mm的铂试管上的过冷水沸腾向膜沸腾的转变是由于稳态时的液体亚层干涸模型以及d= 3 mm和L= 66.5 mm的铂试管上的转变，而不是由于非均相自发成核和流体动力不稳定性。
The turbulent heat transfer, the subcooled boiling heat transfer and the steady state CHF for a Pt-circular test tube of a 3 mm inner diameter and a 100 mm heated length are measured with a wide range of inlet subcooling and flow velocity at high liquid Reynolds number, i.e.Red= 3.01×104to 1.43×105. The inner surface temperature of the Pt-circular test tube calculated by the steady one-dimensional heat conduction equation is compared with the values derived from authors’ turbulent heat transfer correlation and with the numerical solutions of the RANS equations (Reynolds Averaged Navier-Stokes Simulation) ofk-εturbulence model for the flow velocities ranging from 4 to 21 m/s. The thicknesses of conductive sub-layer from non-boiling regime to CHF are measured by numerically analyzing the heat transfers with conductive sub-layer on forced convection and with thinner one dissipated by the evaporation on nucleate boiling. The thicknesses of viscous sub-layer on forced convection are estimated from the thicknesses of the conductive sub-layer and Prandtl numbers of the surface temperature on the heated surface. Furthermore, the thicknesses of conductive sub-layer at the CHF point are extrapolated from the measured values at various flow velocities. The experimental values of the CHF are also compared with authors’ widely and precisely predictable correlations of critical heat flux during flow boiling of subcooled water and the corresponding theoretical values of the liquid sub-layer dry-out models suggested by other researchers, respectively. The authors’ correlations and other researchers’ theoretical values can represent the subcooled boiling CHFs obtained in this study within the ranges of −13.27 to 6.76% difference and − 32.51 to 13.16% one, respectively. A suggestion based on the experimental data as to what the dominant mechanism is for critical heat flux during flow boiling of subcooled water on a vertical circular tube is confirmed again at high liquid Reynolds number. The transitions to film boiling at the subcooled water flow boiling on the Pt test tube ofd= 3 mm andL= 100 mm would occur due to the liquid sub-layer dry-out model at the steady-state CHF as well as those on the Pt test tube ofd= 3 mm andL= 66.5 mm, but not due to the heterogeneous spontaneous nucleation and the hydro-dynamic instability.