ABSTRACT

The analysis and evaluation of transient heat transfer are essential to predict stability and safety of helium gas cooling fusion blanket due to plasma disruption. In this study, transient turbulent heat transfer characteristics of helium gas flowing in a narrow tube were experimentally investigated by using a forced convection gas loop. A narrow tube with an inner diameter of 1.8 mm was employed as test heater and heated exponentially increasing with time under various e-folding time of heat generation rate (0.04–15 s), flow velocities (101–248 m/s), inlet gas temperatures (293–313 K), and pressures (298–502 kPa). The experimental results showed that the heat transfer process can be separated into transient-state heat transfer and quasi-steady-state one at the e-folding time of near 1.5 s. The dependence of quasi-steady-state heat transfer on gas pressure and flow velocity was significant, but the transient-state one was less dependent on gas pressure and flow velocity. The influence of inlet gas temperature on the heat transfer coefficient was not obvious under both transient and quasi-steady conditions. A semi-empirical correlation of the relationship between transient-state and steady-state heat transfer was developed based on substantial experimental data by employing a nondimensional parameter of Fourier number.

摘要

瞬态传热的分析和评估对于预测由于等离子体破坏导致的氦气冷却聚变层的稳定性和安全性至关重要。在这项研究中，通过使用强制对流气体回路，实验研究了在窄管中流动的氦气的瞬态湍流传热特性。采用内径为 1.8 mm 的窄管作为测试加热器，在发热速率（0.04-15 s）、流速（101-248 m/s）、入口气体温度 (293–313 K) 和压力 (298–502 kPa)。实验结果表明，在电子折叠时间接近1.5 s时，传热过程可以分为瞬态传热和准稳态传热。准稳态传热对气体压力和流速的依赖性很大，而瞬态传热对气体压力和流速的依赖性较小。在瞬态和准稳态条件下，进气温度对传热系数的影响并不明显。基于大量实验数据，采用傅里叶数的无量纲参数，建立了瞬态和稳态传热之间关系的半经验相关性。